EP1955353A2 - Ion sources, systems and methods - Google Patents
Ion sources, systems and methodsInfo
- Publication number
- EP1955353A2 EP1955353A2 EP06837664A EP06837664A EP1955353A2 EP 1955353 A2 EP1955353 A2 EP 1955353A2 EP 06837664 A EP06837664 A EP 06837664A EP 06837664 A EP06837664 A EP 06837664A EP 1955353 A2 EP1955353 A2 EP 1955353A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- sample
- ion beam
- ion
- tip
- less
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
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Classifications
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- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/26—Bombardment with radiation
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
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- H01J2237/3175—Lithography
- H01J2237/31752—Lithography using particular beams or near-field effects, e.g. STM-like techniques
- H01J2237/31755—Lithography using particular beams or near-field effects, e.g. STM-like techniques using ion beams
Definitions
- Ions can be formed using, for example, a liquid metal ion source or a gas field ion source.
- ions formed by an ion source can be used to determine certain properties of a sample that is exposed to the ions, or to modify the sample.
- ions formed by an ion source can be used to determine certain characteristics of the ion source itself.
- the invention features an ion microscope having a damage test value of 25 nm or less.
- the invention features a system that includes a gas field ion source with an electrically conductive tip with an average full cone angle of from 15° to 45°.
- the invention features a system that includes a gas field ion source capable of interacting with a gas to generate an ion beam that can interact with a sample to cause primary neutral particles to leave the sample.
- the system also includes at least one detector configured so that, during use, the at least one detector can detect at least some of the primary neutral particles.
- the system further includes an electronic processor electrically connected to the at least one detector so that, during use, the electronic processor can process information based on the detected primary neutral particles to determine information about the sample.
- the invention features a system that includes a gas field ion source capable of interacting with a gas to generate an ion beam having a spot size with a dimension of 10 nm or less on a surface of a sample.
- the system also includes ion optics configured to direct the ion beam toward the surface of the sample, the ion optics having at least one adjustable setting.
- the adjustable setting of the ion optics are at a first setting
- the ion beam interacts with a first location of the sample.
- the adjustable setting of the ion optics are at a second setting
- the ion beam interacts with a second location of the sample.
- the first setting of the ion optics is different from the second setting of the ion optics, and the first location of the sample is different from the second location of the sample.
- the invention features a method that includes generating an ion beam by interacting a gas with a gas field ion source, and interacting the ion beam with a sample to cause secondary neutral particles to leave the sample.
- the method also includes detecting at least some of the secondary neutral particles or particles derived from the secondary neutral particles.
- the invention features a method that includes generating an ion beam by interacting a gas with a gas field ion source, and interacting the ion beam with a sample to cause particles to leave the sample.
- the method also includes detecting at least some of the particles, and determining crystalline information about the sample based on the detected particles.
- Embodiments may include one or more of the following advantages.
- an ion source e.g., a gas field ion source
- a gas field ion source can provide a relatively small spot size on the surface of a sample.
- An ion microscope e.g., a gas field ion microscope using such an ion source can, for example, obtain an image of a sample with relatively high resolution.
- an ion source e.g., a gas field ion source
- a relatively high brightness for a given ion current e.g., a relatively low etendue
- An ion microscope e.g., a gas field ion microscope using such an ion source can, for example, take a good quality image of a sample with relatively little damage to the sample.
- FIG. 1 is a schematic diagram of an ion microscope system.
- FIG. 3 is a schematic representation of an enlarged side view of an embodiment of a tip apex.
- FIG. 7 is a schematic representation of an enlarged side view of the W(111) tip of
- FIG. 1 IA is a perspective view of an embodiment of a support assembly for a tip.
- FIG. 18 is a schematic diagram of an Everhart-Thornley detector.
- FIG. 19 is a cross-sectional view of a portion of a gas field ion microscope system including a microchannel plate detector.
- FIG. 2OC is a plot of average measured secondary electron total abundance as a function of ion beam position for the sample of FIGS. 2OA and 2OB.
- FIG. 22 is a schematic diagram of a portion of a gas field ion microscope including a flood gun.
- FIG. 29 is a schematic diagram of an embodiment of a vibration-decoupled sample manipulator.
- FIG. 33 is a schematic diagram of a filtering system that includes a dispersionless sequence of electric and magnetic fields for separating neutral atoms, singly-charged ions, and doubly-charged ions in a particle beam.
- FIG. 35A, 35D and 35G are schematic diagrams showing respective embodiments of helium ion scattering patterns from a surface using different detectors to detect the scattered helium ions.
- FIG. 35C, 35F and 351 are plots of the relative abundance of scattered helium ions detected by the detectors in FIGS. 35A, 35D and 35G, respectively.
- FIG. 40 is a field ion microscope image of an electrically conductive tip having a trimer as the terminal shelf at its apex.
- FIG. 41 is a scanning field ion microscope image of an electrically conductive tip having a trimer as the terminal shelf at its apex.
- FIG. 53 is an image of a sample taken with a helium ion microscope configured to detect secondary electrons.
- FIG. 54 is an image of a sample taken with a helium ion microscope configured to detect secondary electrons.
- FIG. 56 is a schematic representation of a support for a tip.
- FIG. 59A is an image of a sample taken with a helium ion microscope configured to detect secondary electrons.
- FIG. 68 is an image of a sample taken with a helium ion microscope configured to detect helium ions and neutral helium atoms.
- FIG. 7OA is an image of a sample taken with a helium ion microscope configured to detect helium ions and neutral helium atoms.
- FIG. 76 is an expanded view of a portion of the image of FIG. 75.
- FIG. 77 is a plot of image intensity as a function of pixel position for a line scan through the image of FIG. 76.
- gas source 110 can supply one or more gases in addition to the noble gas(es).
- gases in addition to the noble gas(es).
- an example of such a gas is nitrogen.
- each atoms in the atomic shelves near tip apex 187 can have a corresponding ionization disk 148.
- An ionization disk 148 is a region of space in which a neutral He atom, venturing thereinto, has a high probability of undergoing ionization. Typically, ionization of a neutral He atom occurs via electron tunneling from the neutral He atom to a tip apex atom. Ionization disks 148 therefore represent spatial regions in which He ions are generated, and from which the He ions emerge.
- ion optics 130 are configured to direct ion beam 192 onto surface 181 of sample 180. As described in more detail below, ion optics 130 can, for example, focus, collimate, deflect, accelerate, and/or decelerate ions in beam 192. Ion optics 130 can also allow only a portion of the ions in ion beam 192 to pass through ion optics 130.
- ion optics 130 include a variety of electrostatic and other ion optical elements that are configured as desired. By manipulating the electric field strengths of one or more components (e.g., electrostatic deflectors) in ion optics 130, He ion beam 192 can be scanned across surface 181 of sample 180.
- ion optics 130 can include two deflectors that deflect ion beam 192 in two orthogonal directions. The deflectors can have varying electric field strengths such that ion beam 192 is rastered across a region of surface 181. When ion beam 192 impinges on sample 180, a variety of different types of particles 194 can be produced.
- multiple detectors are used, and some of the multiple detectors are configured to measure different types of particles.
- the detectors are configured to provide different information about the same type of particle (e.g., energy of a particle, angular distribution of a given particle, total abundance of a given particle).
- combinations of such detector arrangements can be used.
- the information measured by the detectors is used to determine information about sample 180.
- Exemplary information about sample 180 includes topographical information about surface 181, material constituent information (of surface 181 and/or of a sub-surface region of sample 180), crystalline orientation information of sample 180, voltage contrast information about (and therefore electrical properties of) surface 181, voltage contrast information about a sub-surface region of sample 180, optical properties of sample 180, and/or magnetic properties of sample 180.
- this information is determined by obtaining one or more images of sample 180. By rastering ion beam 192 across surface 181, pixel-by-pixel information about sample 180 can be obtained in discrete steps.
- Detectors 150 and/or 160 can be configured to detect one or more different types of particles 194 at each pixel.
- FIG. 5 shows a schematic diagram of a He ion microscope system 200.
- tip 186 can be formed of any appropriate electrically conductive material.
- tip 186 can be formed of a single crystal material, such as a single crystal metal.
- a particular single crystal orientation of the terminal shelf of atoms of tip apex 187 is aligned with a longitudinal axis of tip 186 to within 3° or less (e.g., within 2° or less, within 1° or less).
- apex 187 of tip 186 can terminate in an atomic shelf having a certain number of atoms (e.g., 20 atoms or less, 15 atoms or less, 10 atoms or less, nine atoms or less, six atoms or less, three atoms or less).
- this trimer surface is advantageous (in terms of its ease of formation, re-formation and stability) because the surface energy of the W(111) crystal face favorably supports a terminal shelf formed by three W atoms arranged in an equilateral triangle to form a trimer.
- the trimer atoms 302 are supported by a second shelf of W atoms 304.
- the degree to which tip 300 is asymmetrically formed along longitudinal axis 308 can be quantified using parameters such as, for example, an average full cone angle and an average cone direction. These parameters are determined as follows.
- FIG. 8 is a schematic representation of such an image.
- Tip 300 includes an apex point 310 and a second point 312, both located on longitudinal axis 308, with point 312 spaced one ⁇ m from apex point 310 along longitudinal axis 308.
- An imaginary line 314 extends perpendicular to axis 308 and through point 312 in the plane of FIG. 8. Line 314 intersects the profile of tip 300 at points 316 and 318.
- the left cone angle ⁇ i is the angle between the tangent to the profile of tip 300 at point 316 and line 320 (an imaginary line through point 316 and extending parallel to axis 308).
- the average full cone angle is determined by measuring the full cone angle for eight different side views of tip 300 (each corresponding to a successive rotation of tip 300 by 45° about axis 308 with respect to the previous side view of tip 300), and then calculating the average of the eight full cone angles thus determined, resulting in the average full cone angle.
- arcing may occur during use of the tip (e.g., when tip 300 is used to produce ion beam 192), and generation of He ions via the interaction He atoms with tip atoms other than those on the terminal shelf of the tip may occur due to large electric fields in the vicinity of tip 300.
- Tip 300 can also be characterized by its radius of curvature, which can be determined as follows.
- FIG. 9 shows a schematic side view of tip 300. In practice, this side view is obtained using a SEM. On either side of longitudinal axis 308, the slope of the profile of tip 300 is measured. Points 324 and 326 are points on the surface of tip 300 nearest to apex 310 where the slope of the profile of tip 300 (indicated by tangent lines 328 and 330, respectively) has a value of 1 and -1, respectively (e.g., 45° lines of inclination). The distance, measured perpendicular to axis 308 and in the plane of FIG.
- R 1 ⁇ -T 1
- R r the right radius
- the average radius of curvature is determined by measuring the radius of curvature for eight different side views of tip 300 (each corresponding to a successive rotation of tip 300 about axis 308 by 45° with respect to the previous side view), and then calculating the average of the eight radii of curvature, resulting in the average radius of curvature.
- the average radius of curvature of tip 300 is from 40 nm to 200 nm (e.g., from 50 nm to 190 nm, from 60 nm to 180 nm, from 70 nm to 170 nm, from 80 nm to 160 nm).
- the standard deviation of the eight radius of curvature measurements is 40% or less (e.g., 30% or less, 20% or less, 10% or less) of the average radius of curvature.
- FIG. 10 is a flow chart for a process 400 of making a W(111) tip having a terminal atomic shelf that is a trimer.
- a single crystal W(111) precursor wire is attached to a support assembly.
- the W(111) precursor wire has a diameter of 3 mm or less (e.g., 2 mm or less, 1 mm or less), and/or 0.2 mm or more (e.g., 0.3 mm or more, 0.5 mm or more).
- the W(111) precursor wire has a diameter of from 0.2 mm to 0.5 mm (e.g., from 0.3 mm to 0.4 mm, 0.25 mm).
- Suitable precursor wires can be obtained, for example, from FEI Beam Technology (Hillsboro, OR).
- the tip precursor can be in a form that is different from a wire.
- the tip precursor can be formed of an electrically conductive material that has a protrusion that terminates in a crystalline structure.
- the terminus of the protrusion can be a single crystal structure, for example, and can be formed of W(111), or formed of another material in a similar or different crystal orientation.
- FIGS. HA and 1 IB show perspective and bottom views, respectively, of an embodiment of a support assembly 520.
- Support assembly 520 includes support posts 522a and 522b connected to a support base 524.
- Posts 522a and 522b are connected to heater wires 526a and 526b, and a length of a W(111) precursor wire 528 is connected to heater wires 526a and 526b (e.g., via welding).
- Posts 522a and 522b can be connected to auxiliary devices such as, for example, electric current sources (e.g., power supplies) to permit control of the temperature of W(111) precursor wire 528.
- electric current sources e.g., power supplies
- Base 524 provides mechanical support for assembly 520 and is generally formed of one or more materials that can withstand temperature cycling, and that act as electrical insulators.
- base 524 is formed from electrically insulating materials such as glass and/or rigid polymers and/or ceramic.
- Posts 522a and 522b are generally formed of one or more electrically conducting materials.
- the material used to form posts 522a and 522b is chosen so that posts 522a and 522b and base 524 have a similar coefficient of thermal expansion, and so that posts 522a and 522b remain fixed in position relative to base 524 during temperature cycling of precursor wire 528.
- posts 522a and 522b are formed from an alloy that includes iron, nickel and cobalt.
- An example of a commercially available material from which posts 522a and 522b can be formed is KOVARTM.
- precursor wire 528 can be held in position by a support assembly that applies a compressive force to the wire.
- FIG. 12 shows an exemplary support assembly 550 including a Vogel mount to secure precursor wire 528. Suitable Vogel mounts are available commercially from AP Tech (McMinnville, OR), for example.
- Support assembly 550 includes a support base 556 and mounting arms 552 attached to base 556. To secure precursor wire 528, arms 552 are pried apart and spacers (e.g., formed of pyrolytic carbon) 554 are inserted into the space between the arms.
- spacers e.g., formed of pyrolytic carbon
- spacers 554 are oriented so that the higher resistivity direction of spacers 554 is approximately parallel to the direction of compressive force applied by arms 552 (e.g., approximately parallel to arrows 558 and 560). When current is introduced into arms 552, spacers 554 generate heat due to their high resistivity.
- other corrosive agents can be added to the etching solution in place of, or in addition to, NaOH.
- corrosive agents include KOH (including molten KOH), HCl, H 3 PO 4 , H 2 SO 4 , KCN, and/or molten NaNO 3 .
- Corrosive agents in the etching solution may be selected based on their ability to corrode a precursor wire formed of a specific type of material. For example, an agent such as NaOH can be used to corrode wires formed of W. For wires formed of a different material such as Ir, other corrosive agents can be used in the etching solution.
- the etching solution can include a relatively small amount of surfactant.
- surfactant can assist in promoting symmetric etching of precursor wire 528.
- Suitable surfactants for this purpose include materials such as PhotoFlo 200, available from Eastman Kodak
- pulses of varying duration and/or amplitude can be applied to the etching solution to cause erosion of precursor wire 528 in the region of the wire that contacts the solution.
- a portion of the end of precursor wire 528 drops off into the etching solution, and the newly exposed, etched region of precursor wire 528 is processed further in subsequent steps.
- a suitable etching regimen includes an initial application of approximately 100 AC pulses of amplitude 5 V, each pulse having a duration of approximately 580 ms. Thereafter, a series of approximately 60 pulses are applied, with each pulse having a duration of approximately 325 ms and an amplitude of 5 V. Then, pulses having a duration of 35 ms and an amplitude of 5 V are applied until a portion of the end of wire 528 drops off into the etching solution.
- the first pulse can be from 1 V to 10 V (e.g., from 3 V to IV, 5 V) with a duration of from 20 ms to 50 ms (e.g., from 30 ms to 40 ms, 35 ms)
- the second pulse can be from 1 V to 10 V (e.g., from 3 V to 7V, 5V) with a duration of from 10 ms to 25 ms (e.g., from 15 ms to 20 ms, 17 ms).
- This process generally involves imaging the tip (e.g., using FIM or SFIM) and shaping the tip (e.g., using field evaporation).
- step 408 includes installing the support assembly in a FIM and evacuating the FIM.
- the tip of wire 528 is cooled (e.g., to liquid nitrogen
- Heat can be applied to the tip using a variety of devices such as a resistive heating device (e.g., a filament heater), a radiative heating device, an inductive heating device, or an electron beam. From 15 seconds to 45 seconds (e.g., from 25 seconds to 35 seconds, 30 seconds) after the first appearance of light from the tip, both the applied potential and the heating device are turned off, yielding wire 528 with a trimer as its terminal atomic shelf.
- a resistive heating device e.g., a filament heater
- a radiative heating device e.g., an inductive heating device
- an electron beam e.g., from 15 seconds to 35 seconds, 30 seconds
- a flat sample with a relatively high secondary electron yield can be positioned where sample 180 is normally positioned, and the secondary electrons generated by the interaction of the He ions with the flat sample are detected because the intensity of the secondary electrons detected will generally scale with the intensity of the He ions incident on the flat sample.
- system 200 can be operated in SFIM mode during the process of imaging/shaping the wire tip apex, hi such embodiments, the process is as described in the preceding paragraphs, except that alignment deflectors 220 and 222 are used to raster the ion beam across the surface of aperture 224 to generate a field emission pattern of the apex of the wire tip. Portions of the ion beam which pass through aperture 224 can optionally be focused by second lens 226, or remain unfocused. In SFIM mode, an image of the wire tip is acquired pixel-by-pixel, and each measured pixel intensity corresponds to a portion of ion beam permitted to pass through aperture 224.
- the pixel intensities together can be used to represent the field emission pattern of the tip as an image or, more generally, as a plurality of electrical signals.
- the field emission pattern can then be used to assess various properties of the tip to determine its suitability for use in a gas field ion microscope.
- the detector In SFIM mode, the detector can be located and of the type as described in the preceding paragraphs.
- the detector can be a spatially integrating detector such as a photomultiplier tube or a photodiode.
- the procedures described above can generally be used to sharpen a W tip for the first time, and can also be used for re-sharpening of a W tip within an ion microscope system. Such re-sharpening can be performed in system 200 even if the initial process for sharpening the W tip was performed in a FIM other than system 200. Re-sharpening can generally be performed in the same manner as the initial sharpening, or the re-sharpening techniques can be different from the original sharpening technique. In some
- microscope system 200 can be configured to operate in FIM and/or SFIM mode, as described above. Based upon one or more images of the tip, the re-sharpening process can be initiated or postponed. In certain embodiments, other criteria can be used to determined when to initiate re-sharpening. For example, if the measured ion current from the tip falls below an established threshold value after a period of operation, re-sharpening can be initiated.
- the tip can be field evaporated to remove atoms near the tip apex.
- microscope system 200 can be configured to operate in FIM and/or SFIM mode, as discussed above, and the potential applied to the tip can be carefully adjusted to produce controlled field evaporation of tip atoms.
- a field emission image of the tip can be obtained in FIM or SFIM mode by a detector (e.g., a phosphor-coupled photon detector, or a secondary electron detector configured to measured secondary electron emission from a flat sample) and monitored to determine when to halt the field evaporation process.
- a detector e.g., a phosphor-coupled photon detector, or a secondary electron detector configured to measured secondary electron emission from a flat sample
- the tip can be re- sharpened.
- He gas is pumped out of microscope system 200 until the background He pressure is less than approximately 10 "7 Torr.
- a negative electrical potential is applied to the tip to operate microscope system 200 in electron mode, and the tip is sharpened via heating as described previously.
- a sharpening gas such as oxygen is introduced into microscope system 200, and the tip is heated in the presence of oxygen for a selected time, as described previously.
- the pressure of oxygen gas in the FIM chamber can be 10 "7 Torr or more (e.g., 10 "6 Torr or more, 10 "5 Torr or more, 10 “4 Torr or more), and/or 1 Torr or less (e.g., 10 "1 Torr or less, 10 "2 Torr or less, 10 "3 Torr or less).
- the pressure of oxygen gas in the FIM chamber can be from 10 "8 Torr to 10 "2 Torr (e.g., from 10 "7 Torr to 10 "3 Torr, from 10 "6 Torr to 10 "4 Torr).
- trimer as the terminal atomic shelf during tip sharpening.
- gases and materials can also be used to promote formation of a trimer as the terminal atomic shelf during tip sharpening.
- materials such as palladium, platinum, gold, and/or iridium can be vapor deposited onto the surface of a rounded tip prior to re-sharpening. It is believed that these materials may promote more reliable trimer formation at the apex of the tip.
- one or more additional gases may be present during tip sharpening.
- nitrogen gas may be present. Without wishing to be bound by theory, it is believed that nitrogen gas may assist in etching the tip to provide a more rounded structure with a terminal atomic shelf that is a trimer; such a structure is believed to be more stable than a less-rounded, trimer-terminated tip.
- the nitrogen gas is introduced simultaneously with the oxygen gas.
- the pressure of nitrogen gas in the FIM chamber can be 10 "8 Torr or more (e.g., 10 " Torr or more), and/or 10 " Torr or less (e.g., 10 Torr). In certain embodiments, the pressure of nitrogen gas in the FIM chamber can be from 10 "5 Torr to 10 "8 Torr (e.g., from 10 "6 Torr to 10 "7 Torr).
- the positive electrical potential applied to the sharpened tip is increased so that controlled field evaporation of the tip occurs.
- the tip apex reassumes a rounded shape.
- the rounded tip produces an emission pattern that is similar to the emission pattern of the tip after the initial field evaporation step.
- the rounded tip is again sharpened in electron mode to produce a terminal atomic shelf that is a trimer (e.g., using the procedure described above).
- one or more trimers can be removed from the sharpened tip using field evaporation techniques.
- the apex 187 of tip 186 is aligned within system 200.
- microscope system 200 is evacuated using one or more vacuum pumps, and then heat is applied to tip 187 to remove, for example, oxides, condensates, and/or any other impurities that may have adhered to the tip surface.
- tip 186 is heated to a temperature of 900 K or more (e.g., 1000 K or more, 1100 K or more) for a duration of 10 s or more (e.g., 30 s or more, 60 s or more). Heating may also assist in re-faceting tip 186, in the event that the tip shape is compromised by the presence of impurities.
- tip 186 With tip 186 glowing radiatively as a result of the applied heat, the tip is then roughly aligned with the longitudinal axis of ion optics 130 by observing light from tip 186 propagating along the longitudinal axis (e.g., by inserting a reflective element such as a mirror and directing a portion of the light to a detector such as a CCD camera).
- the position and/or orientation of tip 186 can be changed by adjusting tip manipulator 208 to direct the light from tip 186 through ion optics 130.
- microscope system 200 is configured to operate in FIM or SFIM mode by reducing the background pressure in vacuum housings 202 and 204, cooling tip 186 (e.g., to approximately liquid nitrogen temperature), and introducing a stream of He gas atoms into a region in the vicinity of tip 186 via gas source 110.
- An image of the field emission pattern of He ions from tip 186 is measured by a suitably configured detector and based upon this image, tip manipulator 208 is used to align the field emission pattern with a longitudinal axis of ion optics 130, so that the field emission pattern of tip 186 is centered upon the longitudinal axis.
- a centering test can be performed by changing the electrical potential applied to first lens 216 while observing the induced modulation of the field emission pattern of tip 186. If the size of the field emission pattern observed by the detector changes due to the variation of the electrical ⁇ potential applied to lens 216, but the position of the center of the pattern does not change, then tip 186 is aligned with a longitudinal axis of first lens 216. Conversely, if the center position of the field emission pattern of tip 186 changes in response to the variation of the potential applied to first lens 216, then tip 186 is not centered on the longitudinal axis of first lens 216. Adjustments of the orientation and position of tip 186 via tip manipulator 208 can be repeated iteratively until tip 186 is sufficiently well aligned with the longitudinal axis of first lens 216. Typically, this centering test is performed without aperture 224 in position.
- the adjustment of the potentials applied to deflectors 220 and 222 ensures that aperture 224 prevents 50% or more (e.g., 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 98% or more) of the He ions in ion beam 192 generated by the interaction of He gas atoms with the other two trimer atoms from reaching surface 181 of sample 180.
- the He ion beam that passes through aperture 224 and exits ion optics 130 includes He atoms that were ionized primarily in the vicinity of only one of the three trimer atoms at the apex of tip 186.
- the potential applied to tip 186 is 5 kV or more (e.g., 10 kV or more, 15 kV or more, 20 kV or more), hi certain embodiments, the potential applied to tip 186 is 35 kV or less (e.g., 30 kV or less, 25 kV or less). For example, in some embodiments, the potential applied to tip 186 is from 5 kV to 35 kV (e.g., from 10 kV to 30 kV, from 15 kV to 25 kV).
- the He gas pressure is 10 "8 Torr or more (e.g., 10 "7 Torr or more, 10 “6 Torr or more, 10 “5 Torr or more).
- the He gas pressure in microscope system 200 is 10 "1 Torr or less (e.g., 10 "2 Torr or less, 10 "3 Torr or less, 10 "4 Torr or less).
- the He gas pressure in microscope system 200 is from 10 "7 Torr to 10 "1 Torr (e.g., from 10 "6 Torr to 10 "2 Torr, from 10 "5 Torr to 10 "3 Torr).
- tip 186 can be periodically monitored by operating microscope system 200 in FIM or SFIM mode, as discussed above. If the trimer structure remains intact at tip apex 187, then tip 186 can continue to be used to provide ion beam 192 to microscope system 200. However, under certain circumstances, FIM or SFIM imaging of tip 186 may reveal that the trimer structure is no longer intact on tip apex 187. In this case, tip 186 can first be field evaporated to round the tip and remove the damaged trimer structure, and then re- sharpened in situ (e.g., without removing tip 186 from microscope system 200) using a process as described above.
- a detector can be introduced as described for FIM imaging, and aperture 224 can be maintained in position.
- Alignment deflectors 220 and 222 can be used to raster the ion emission pattern of tip 186 across aperture 224 to acquire an image of tip 186 in pixel-by-pixel fashion. Acquisition of one or more images of tip 186 can be automated by electronic control system 170, which can control placement of apertures, movement of samples and detectors, and electrical potentials applied to tip 186 and to alignment deflectors 220 and 222.
- Extractor 190 includes an opening 191.
- the shape of extractor 190 and of opening 191 can be selected as desired. Typically, these features are chosen to ensure that He ions are efficiently and reliably directed into ion optics 130.
- extractor 190 has a thickness t e measured in the z direction, an opening 191 of width a measured in the x-direction, and is positioned a distance e measured in the z-direction from apex 187 of tip 186.
- Extractor 190 can generally be biased either positively or negatively with respect to tip 186.
- the electrical potential applied to extractor 190 is -10 kV or more (e.g., -5 kV or more, 0 kV or more), and/or 20 kV or less (e.g., 15 kV or less, 10 kV or less) with respect to tip 186.
- Suppressor 188 can be used, for example, to alter the electric field distribution in the vicinity of tip 186 by adjusting the potential applied to suppressor 188. Together with extractor 190, suppressor 188 can be used to control the trajectory of He ions produced at tip 186.
- Suppressor 188 has an opening of width k measured in the x-direction, a thickness t s measured in the z-direction, and is positioned at a distance s, measured in the z-direction, from the apex of tip 186.
- k is three ⁇ m or more (e.g., four ⁇ m or more, five ⁇ m or more) and/or eight ⁇ m or less (e.g., seven ⁇ m or less, six ⁇ m or less).
- t s is 500 ⁇ m or more (e.g., 1 mm or more, 2 mm or more), and/or 15 mm or less (e.g., 10 mm or less, 8 mm or less, 6 mm or less, 5 mm or less, 4 mm or less). In some embodiments, s is 5 mm or less (e.g., 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less).
- suppressor 188 is positioned further along in the +z-direction than tip 186.
- tip 186 is positioned further along in the +z-direction than suppressor 188, so that tip 186 extends through suppressor 188 in the +z-direction.
- the distance p can be 1 mm or more (e.g., 5 mm or more, 10 mm or more), and/or 100 mm or less (e.g., 70 mm or less, 50 mm or less, 30 mm or less, 20 mm or less).
- Changing the position of point C can change the size of ion beam 192 in the x- and/or y- directions at the position of aperture 224, which can selectively control the fraction of ions in ion beam 192 that pass through aperture 224.
- cross-over point C can, in some embodiments, be positioned further in the +z-direction than aperture 224.
- Deflectors 220 and 222 can each deflect He ion beam 192 in both x- and y- directions.
- the electrical potentials applied to the electrodes of deflectors 220 and 222 can be adjusted to ensure that a portion of ion beam 192 passes through both aperture 224 and second lens 226.
- the potentials applied to deflectors 220 and 222 are adjusted to achieve a particular alignment condition, and then the potentials remain static while microscope system 200 is in operation. Alignment of ion beam 192 through aperture 224 is assessed by observing ion beam 192 using a suitable detector configured, for example, to image aperture 224.
- Deflectors 220 and/or 222 can also be adjusted so that the portion of ion beam 192 that passes through aperture 224 is aligned with a longitudinal axis of second lens 226.
- the electrical potential applied to second lens 226 can be varied (commonly referred to as wobbling) and the results observed on the imaging detector. If, as a result of the changing potential applied to second lens 226, the image of ion beam 192 changes in size but not in position, then ion beam 192 is aligned through second lens 226. If the position of the center of ion beam 192 changes as a result of the changing potential, then ion beam 192 is not aligned with second lens 226. hi this case, the potentials applied to deflectors 222 and/or 220 can be further adjusted and the wobble test repeated, in iterative fashion, until alignment is achieved.
- openings 225a-225g and 229a-229e have diameters that can be chosen as desired.
- the diameter of any of the openings can be five ⁇ m or more (e.g., 10 ⁇ m or more, 25 ⁇ m or more, 50 ⁇ m or more) and/or 200 ⁇ m or less (e.g., 150 ⁇ m or less, 100 ⁇ m or less).
- the diameters of openings 225a-225g and/or 229a-229e can be from five ⁇ m to 200 ⁇ m (e.g., five ⁇ m to 150 ⁇ m, five ⁇ m to 100 ⁇ m).
- devices other than an aperture can be used to permit only a portion of the ions in ion beam 192 to pass through ion optics 130 and impinge on the surface of sample 180.
- two perpendicular slits can be positioned in series along the flight path of the ion beam.
- the eight electrodes of an octupolar astigmatism corrector are divided into two groups of four electrodes, with a first controller configured to adjust the voltages of four of the electrodes (e.g., the first group of four electrodes, positively biased with respect to tip 186) and a second controller that adjusts the voltages of the other four electrodes (e.g., the second group of four electrodes, negatively biased with respect to tip 186). Electrodes from the first and second electrode groups are arranged in alternating fashion to form the segments of the octupole, where adjacent segments have bias voltages of opposite signs. This arrangement of electrodes forms a cusp field which focuses ion beams propagating along a longitudinal axis of the octupole, and de-focuses off-axis ion beams.
- ion optics 130 include scanning deflectors 219 and 221. Scanning deflectors 219 and 221 are typically positioned between astigmatism corrector 218 and second lens 226, although in general, other arrangements of scanning deflectors 219 and 221 within ion optics 130 are also possible.
- the relatively large distance h also permits a variety of detectors and other devices to be positioned in close proximity to the region of incidence of ion beam 192 on surface 181, and can allow for detection of particles leaving the sample over a relatively large range of solid angles. Typically, this permits detection of stronger signals and detection of multiple different types of signals (e.g., using different types of detectors).
- second lens 226 is shaped as a right-angled cone with a cone half-angle of 10° or more (e.g., 15° or more, 20° or more, 25° or more) and/or 50° or less (e.g., 45° or less, 40° or less. 35° or less).
- the cone half-angle of second lens 226 is from 10° to 50° (e.g., from 15° to 45°, from 20° to 40°).
- one or more additional electrodes can be positioned along the path of ion beam 192 in ion optics 130.
- Additional electrodes can be positioned after second lens 226, for example, or can be introduced between existing elements.
- the additional elements can be biased either positively or negatively with respect to tip 186 to perform functions such as increasing or decreasing the energy of the ions in ion beam 192 within ion optics 130 and/or to change the trajectories of the ions.
- one or more accelerating electrodes can be positioned in the vicinity of sample 180 to change the energy with which the ions in ion beam 192 are incident on sample 180.
- the ion optics include a first lens, a second lens, an aperture between the first and second lenses, no electrodes, and the ion optics are designed so that the first lens can reduce the divergence of the ion beam (e.g., such that the ion beam is substantially aligned with the longitudinal axis of the ion optics system), the aperture can block a portion of the ion beam from passing therethrough, and the second lens can help focus the ion beam to a relatively small spot size on the surface of the sample.
- the first lens can reduce the divergence of the ion beam (e.g., such that the ion beam is substantially aligned with the longitudinal axis of the ion optics system)
- the aperture can block a portion of the ion beam from passing therethrough
- the second lens can help focus the ion beam to a relatively small spot size on the surface of the sample.
- the ion beam can include approximately equal numbers of ions generated via the interaction of gas atoms with each of the atoms at the apex of tip 186.
- the ion beam can include approximately equal numbers of ions generated via the interaction of gas atoms with each of the atoms at the apex of tip 186.
- Tip manipulator 208 is configured to permit both translation of tip 186 in the x-y plane, and tilting of tip 186 with respect to axis 132 of ion optics 130.
- FIG. 17 is a cross- sectional view of a portion of microscope system 200 including tip 186, support assembly 520 and an embodiment of a tip manipulator.
- Tip manipulator 208 includes a shaft 502, a dome 504, a shoulder 510 and a translator 514.
- Translator 514 is connected to shaft 502, which is dimensioned to fit through an opening 516 in shoulder 510.
- Shaft 502 is further connected to base 508, which in turn is connected to assembly 520.
- Shoulder 510 is in a fixed position relative to dome 504 by static factional forces between surfaces 512 and 513, and translator 514 is in a fixed position relative to shoulder 510 by static factional forces between surfaces 518 and 519.
- Tip manipulator 208 also provides for tilting of tip 186 with respect to axis 132 of ion optics 130.
- a high pressure gas is introduced into inlet 505.
- the high pressure gas introduced into inlet 505 can be a gas such as room air, for example.
- the gas can be introduced at a pressure of 50 pounds per square inch (psi) or more (e.g., 75 psi or more, 100 psi or more, 125 psi or more).
- psi pounds per square inch
- the gas can be introduced at a pressure of 50 pounds per square inch (psi) or more (e.g., 75 psi or more, 100 psi or more, 125 psi or more).
- psi pounds per square inch
- 75 psi or more e.g., 75 psi or more, 100 psi or more, 125 psi or more
- the applied force lessens (but does not reduce to zero) the frictional force between surfaces 512 and 513.
- Shoulder 510 can then be re-positioned with respect to dome 504 by applying a lateral force to translate shoulder 510 in a direction indicated by arrows 506. Translation of shoulder 510 corresponds to relative movement along the curved surface of dome
- tip manipulator 208 is configured so that the center of the radius of curvature, R, of dome 504 coincides with the position of the apex of tip 186. As a result, when tip 186 is tilted to change the angle between axes 132 and 207, translation of tip 186 in the x-y plane does not occur. As a result, tip manipulator 208 can be used to align the trajectories of ions generated via the interaction of gas atoms with one of the tip atoms with the longitudinal axis of first lens 216 without causing translation of tip 186 with respect to the axis of first lens 216.
- microscope system 200 includes a sample manipulator 140 for supporting and positioning sample 180.
- sample manipulator 140 can translate sample 180 in each of the X-, y-, and z-directions.
- sample manipulator 140 can also rotate sample 180 in the x-y plane in response to control signals. Further, in certain embodiments
- sample manipulator 140 can tilt sample 180 out of the x-y plane in response to suitable control signals. Each of these degrees of freedom can be independently adjusted to achieve a suitable orientation of sample 180 with respect to ion beam 192.
- a negative potential bias of -200 V or more e.g., -150 V or more, -100 V or more, -50 V or more, -40 V or more, - 30 V or more, -20 V or more, -10 V or more, -5 V or more
- the potential applied to manipulator 140 can be chosen as desired according to the particular material under study, the He ion current, and exposure time of the sample.
- Detectors 150 and 160 are depicted schematically in FIG. 5, with detector 150 positioned to detect particles from surface 181 of sample 180 (the surface on which the ion beam impinges), and detector 160 positioned to detect particles from surface 183 of sample 180.
- detector 150 positioned to detect particles from surface 181 of sample 180 (the surface on which the ion beam impinges)
- detector 160 positioned to detect particles from surface 183 of sample 180.
- a wide variety of different detectors can be employed in microscope system 200 to detect different particles, and a microscope system 200 can ' typically include any desired number of detectors.
- the configuration of the various detector(s) can be selected in accordance with particles to be measured and the
- a spectrally resolved detector may be used. Such detectors are capable of detecting particles of different energy and/or wavelength, and resolving the particles based on the energy and/or wavelength of each detected particles. In certain embodiments, a spectrally resolved detector includes componentry capable of directing particles to different regions of the detector based on the energy and/or wavelength of the particle.
- FIG. 18 shows a schematic diagram of an ET detector 600 that includes a particle selector 601, a conversion material 602, a support 604, a photon detector 606, and voltage sources 607 and 608.
- Particle selector 601 is formed of an electrically conductive material.
- particle selector 601 can be a metal grid or mesh with a metal fill-factor of less than approximately 30% (e.g., less than 25%, less than 20%, less than 10%, less than 5%). Because the grid is predominantly open space, particles impinging on the grid can pass through relatively unobstructed.
- particle selector 601 can be formed from any open electrode structure that includes a passage for particles to pass through.
- Particle selector 601 can be formed from one or more electrodes, and potentials applied to the one or more electrodes can generally be selected as desired according to the type of particles being measured.
- Conversion material 602 is formed of a material that, upon interaction with a charged particle (e.g., an ion, an electron) can form a photon.
- exemplary materials include phosphor materials and/or scintillator materials (e.g., crystalline materials, such as yttrium-aluminum-garnet (YAG) and yttrium-aluminum-phosphate (YAP).
- Support 604 is formed of a material that is relatively transparent to photons formed by conversion material 602.
- sample 180 can also be biased (with respect to the common external ground) to assist in delivering particles from sample 180 to detector 600.
- the ET detector when used to measure secondary electrons from sample 180, the sample can be negatively biased relative to the common external ground. Applying a negative potential bias to manipulator 140 may be particularly useful, for example, when detecting secondary electrons generated in a high aspect ratio (e.g., deep) hole or via in the sample.
- the negative potential bias relative to the common external ground can assist in accelerating electrons out of the hole or via and away from the sample, making detection of the electrons easier. In the absence of the negative bias, many of the secondary electrons might instead re-enter the sample at points along the hole or via walls, never escaping the hole or via to be detected.
- Sample 180 can be positively biased, for example, when the ET detector is used to measure ions from the sample.
- the magnitude of the electrical potential applied to bias the sample can be 5 V or more (e.g., 10 V or more, 15 V or more, 20 V or more, 30 V or more, 50 V or more, 100 V or more).
- Charged particles 610 e.g., electrons or ions
- Charged particles 610 from sample 180 are attracted to particle selector 601, pass through particle selector 601, and are accelerated toward conversion material 602.
- Charged particles 610 then collide with conversion material 602, generating photons 612.
- Photons 612 pass through support 604 and are detected by photon detector 606.
- an ET detector can also be used to detect neutral particles because, in general, particles impinging on conversion material 602 do not have to be charged to generate photons 612.
- primary atoms from sample 180, impinging on conversion material 602 can generate photons 612 for detection by photon detector 606.
- Photon detector 606 can be, for example, a photomultiplier tube (PMT), a diode, a diode array, or a CCD camera.
- An ET detector can be located at any position relative to sample 180 to detect neutral or charged particles.
- an ET detector is positioned adjacent to second lens 226 of ion optics 130.
- an ET detector can also be positioned such that it is tilted downward slightly towards sample 180 (e.g., in a similar configuration as that depicted for detector 150 in FIG. 5).
- an ET detector can be positioned in the vicinity of surface 183 of sample 180. Such a configuration may be desirable, for example, when seeking to measure secondary electrons from sample 180 that emerge from surface 183 (e.g., after being transmitted through sample 180).
- the ET detector can have a configuration that is similar to the configuration of detector 160 in FIG. 5.
- the filters can, for example, block photons of undesired wavelengths (e.g., by absorbing photons of undesired wavelengths, by reflecting photons of undesired wavelengths, by diverting photons of undesired wavelengths).
- the optical elements can provide spectral resolution (e.g., to measure the spectrum of photons generated by sample 180) by dispersing different wavelengths spatially (e.g., diffractive elements such as one or more gratings, and/or refractive elements such as one or more prisms, and/or one or more spectrometer systems that provide wavelength-resolved detection of photons).
- the photon detector can include polarization manipulating elements such as waveplates and/or polarizers. These polarization manipulating elements can be configured to permit photons having only a selected polarization state to reach the PMT, for example, allowing polarization-selective detection of the photon signal emerging from sample 180 (e.g., to assist in determining crystalline orientation information for sample 180).
- the photon detector can also include optical elements such as mirrors, lenses, beamsplitters, and other elements for re-directing and manipulating incident photons (e.g., to increase the solid angle of the photons that are detected).
- photons are scattered in particular directions according to selection rules for optical processes occurring in sample 180, and angle-resolved measurement of the photon yield from sample 180 can provide, for example, material constituent information about sample 180.
- MicroChannel plates amplify an incoming particle signal and convert the incoming signal to an outgoing electron signal.
- microchannel plate-based detectors can also include a conversion material, a screen, and a photon detector (see discussion above).
- microchannel plates are affixed directly to elements of ion optics 130.
- FIG. 19 shows a cross-sectional view of a microchannel plate detector 620 mounted directly to second lens 226.
- Second lens 226 has a conical shape, with a flat lower surface 622.
- Detector 620 is mounted directly to surface 622.
- ions, secondary electrons, and/or neutral atoms from sample 180 can be detected by microchaniiel plate detector 620.
- Detector 620 registers a current that is proportional to the detected particle flux, which can be conveyed to electronic control system 170.
- a conversion plate can be used to detect ions (e.g., scattered ions, secondary ions) from sample 180 or neutral particles (e.g., primary neutral He atoms) from sample 180.
- ions e.g., scattered ions, secondary ions
- neutral particles e.g., primary neutral He atoms
- a conversion plate can be formed from a thin foil material that, when struck by an incident ion or atom, has a high secondary electron yield.
- An example of such a material is platinum.
- the secondary electron yield produces an abundance of secondary electrons that are readily detected, for example, by an appropriate electron detector configured, for example, as detectors 150 and/or 160 (FIGS. 1 and 5).
- channeltron detector can be located in a position similar to that depicted for detector 150 and/or detector 160 in FIGS. 1 and 5.
- a channeltron detector is located in a position similar to the position of detector 150 and/or the position of detector 160 as depicted in FIGS. 1 and 5.
- Phosphor-based detectors which include a thin layer of a phosphor material deposited atop a transparent substrate, and a photon detector such as a CCD camera, a PMT, or one or more diodes, can be used to detect electrons, ions and/or neutral particles from sample 180. Particles strike the phosphor layer, inducing emission of photons from the phosphor which are detected by the photon detector. Phosphor-based detectors can be arranged in positions similar to those of detector 150 and/or detector 160 as depicted in FIGS. 1 and 5, depending upon the type of particle that is measured (see discussion above).
- Solid state detectors can be used to detect secondary electrons, ions, and/or neutral atoms from sample 180.
- a solid state detector can be constructed from a sensor formed of a material such as silicon, or a doped silicon material. When incident particles strike the sensor, electron-hole pairs are created in the sensor material, producing a current that can be detected by electronic control system 170. The number of electron-hole pairs generated by an incident particle, and therefore the corresponding magnitude of the current produced, depends in part upon the particle's energy.
- a solid state detector can be particularly useful for energy measurements of particles, which can be especially advantageous when detecting high energy particles (e.g., scattered He ions and neutral He atoms) from sample 180.
- scintillator-based detectors include a scintillator material that generates photons in response to being struck by an incident particle (electron, ion, or neutral atom).
- Suitable scintillator materials include, for example, YAG and YAP.
- the photon yield in scintillator-based detectors depends on the energy of the incident particles.
- a scintillator detector can be particularly useful for energy measurements of particles, which can be especially advantageous when detecting high energy particles (e.g., scattered He ions and neutral He atoms) from sample 180.
- Electrostatic prism detectors in which an electric and/or magnetic field is used to deflect incident ions, where the amount of deflection depends on the energy of the ions, can be used to spatially separate ions with different energies.
- Magnetic prism detectors may also be used to spatially separate ions based on the energy of the ions. Any of the suitable detectors discussed above (e.g., microchannel plates, channeltrons, and others) can then be used to detect the deflected ions.
- Quadrupole detectors can also be used to analyze energies of ions from sample 180.
- a radio-frequency (RF) field within the quadrupole ensures that ions having a chosen mass and energy propagate along a straight, undeflected trajectory within the quadrupole. Ions with a different mass and/or energy propagate along a curved trajectory within the quadrupole. From the deflected position of ions within the quadrupole analyzer, energies of the ions can be determined.
- RF radio-frequency
- ion energy can be determined by placing a positively biased particle selector (e.g., a screen or mesh of electrically conductive material, or a cylindrical metal tube or ring) along the flight path of the ions and in front of the detector.
- the magnitude of the electrical potential applied to particle selector 601 can initially be very high (e.g., a value certain to prevent ions from sample 180 from passing therethrough), and the magnitude of the electrical potential can be reduced while using an appropriate detector (see discussion above) to detect the ions.
- the current of ions that reach the detector as a function of the magnitude of the potential bias on the particle selector can be used to determine information about the energy of the ions.
- detectors and detection schemes can be implemented to measure energies of electrons (e.g., secondary electrons) from sample 180.
- Prism detectors in which an electric and/or magnetic field is used to deflect incident electrons, and where the amount of deflection depends on the energy of the electrons, can be used to spatially separate electrons with different energies. Any of the suitable detectors discussed above can then be used to detect the deflected electrons.
- the detectors disclosed above can also be configured to measure time-of- flight information for secondary electrons, ions, and neutral atoms.
- ion beam 192 is operated in pulsed mode. Ion beam 192 can be pulsed, for example, by rapidly changing the electrical potential applied to one or both of deflectors 220 and 222. By increasing these potentials, for example, ion beam 192 can be diverted from its usual path in ion optics 130 such that ion beam 192 is temporarily blocked by aperture 224. If the potentials of deflectors 220 and 222 are then returned to their normal values for a short time before being increased again, a pulse of He ions can be delivered to sample 180. '
- angle-dependent scattering information can be obtained using the detectors disclosed above.
- a detector is affixed to a mount (e.g., a swivel mount) that permits movement of the detector throughout a range of solid angles about sample 180.
- a mount e.g., a swivel mount
- abundance and/or energy measurements of particles are recorded.
- the detector is sequentially re-positioned at different solid angles and the measurements are repeated to determine the angular dependence of the measured quantities.
- a limiting aperture such as a pinhole can be placed in front of the detector in the path of the scattered particles to further restrict the range of angles over which measurement of particles from sample 180 occurs.
- Ion beam 192 can have a relatively small spot size on surface 181 of sample 180.
- the spot size of ion beam 192 on surface 181 of sample 180 can have a dimension of 10 nm or less (e.g., nine nm or less, eight nm or less, seven nm or less, six nm or less, five nm or less, four nm or less, three nm or less, two nm or less, one nm or less).
- Measurement samples that include gold islands deposited on carbon, suitable for the resolution measurements described herein, are available commercially from Structure Probe Inc. (West Chester, PA), for example.
- the ion microscope is operated such that it moves ion beam 192 linearly across a portion of the gold island, as well as the portions of the carbon surface on one side of the gold island (arrow 1730).
- the intensity of secondary electrons is measured as a function of the location of the ion beam (FIG. 20C).
- Asymptotic lines 1740 and 1750 are calculated (or drawn) corresponding to the average total abundance values for the carbon and gold, and vertical lines 1760 and 1770 are calculated (or drawn) corresponding to the locations where the total abundance is 25% and 75%, respectively, of the abundance difference between asymptotic lines 1740 and 1750.
- the spot size of ion microscope 200 is the distance between lines 1760 and 1770.
- the current of ion beam 192 at surface 181 of sample 180 is one nA or less (e.g., 100 pA or less, 50 pA or less), and/or 0.1 fA or more (e.g., one fA or more, 10 fA or more, 50 f A or more, 100 fA or more, one pA or more, 10 pA or more).
- the current of ion beam 192 at surface 181 of sample 180 is from 0.1 fA to one nA (e.g., from 10 fA to 100 pA, from 100 fA to 50 pA).
- ion beam 192 has an energy spread at surface 181 of sample 180 of five eV or less (e.g., four eV or less, three eV or less, two eV or less, one eV or less, 0.5 eV or less). In some embodiments, ion beam 192 has an energy spread at surface 181 of sample 180 of 0.1 eV or more (e.g., 0.2 eV or more, 0.3 eV or more, 0.4 eV or more). For example, ion beam 192 can have an energy spread at surface 181 of sample 180 of from 0.1 eV to five eV (e.g., from 0.1 eV to three eV, from 0.1 eV to one eV).
- Ion beam 192 can have a relatively high brightness at surface 181 of sample 180.
- ion beam 192 can have abrightness of IxIO 9 A/cm 2 sr (e.g., IxIO 10 A/cm 2 sr or more, IxIO 11 A/cm 2 sr or more) at surface 181 of sample 180.
- the brightness can be increased by increasing the gas pressure adjacent to tip 186 and/or decreasing the temperature of tip 186.
- the brightness of an ion beam is measured as follows.
- the FWHM of the distribution of ion trajectories in ion beam 192 - in a region of space between extractor 190 and first lens 216 where the net electric field is relatively small and the ion trajectories are nearly straight lines - is determined in both the x- and y-directions.
- a total of 100 ion trajectories that fall within the FWHM width in both the x- and y-directions are chosen at random from the distribution of ion trajectories in ion beam 192.
- Each of the 100 ion trajectories is nearly a straight line, and is projected back toward tip apex 187.
- the spatial extent of the trajectories at a particular point z t along the z-axis is assessed by constructing, in a plane Z t parallel to the x-y plane and passing through point z t , the smallest-diameter circle that encloses all of the points of intersection of the back-propagated trajectories with the plane Z t .
- the diameter of the smallest-diameter circle is d s .
- d s will be smaller and for points z t closer to sample 180, d s will be larger.
- d s will be a minimum value d 0 .
- the spatial extent of the trajectories in a plane parallel to the x-y plane will be a minimum.
- the diameter d 0 of the minimum-diameter circle at point Z 0 is referred to as the virtual source size of microscope system 200.
- the divergence and beam current of ion beam 192 in the FWHM region of ion beam 192 between extractor 190 and first lens 216, as discussed above, are measured.
- brightness is calculated as beam current divided by the product of the virtual source size and the solid divergence angle of ion beam 192.
- Ion beam 192 can have a relatively high reduced brightness at surface 181 of sample 180.
- ion beam 192 can have a reduced brightness of 5x10 8 A/m 2 srV or more (e.g., IxIO 9 A/cm 2 srV or more, IxIO 10 A/cm 2 srV or more) at surface 181 of sample 180.
- the reduced brightness of an ion beam is the brightness of the ion beam divided by the average energy of the ions in the ion beam at the position where the beam current is measured
- Ion beam 192 can have a relatively low reduced etendue at a distal end 193 of extractor 190.
- ion beam 192 can have a reduced etendue of 1x10 '16 cm 2 sr or less (e.g., 1x10 " cm sr or less, 1x10 " cm sr or less, 1x10 " cm sr or less) at distal end 193 of extractor 190.
- Reduced etendue of an ion beam is the mathematical product of the etendue of the ion beam and the ratio of the average energy-to-charge of ions in the ion beam at the position where the beam current is measured.
- Ion beam 192 is then translated linearly along the diameter of the gold island and the focused spot size, S f , of the ion beam is measured, as described above.
- the convergence angle ⁇ can then be determined trigonometrically from the measurements of the focused and defocused spot sizes, along with the translation distance, as
- the convergence half angle of ion microscope 200 is ⁇ /2.
- the He ion source (tip 186, extractor 190 and optionally suppressor 188) is capable of continuously interacting with gas atoms to generate an ion beam for a time period of one week or more (e.g., two weeks or more, one month or more, two months or more) without removing tip 186 from the system.
- the current of ion beam 192 at surface 181 of sample 180 varies by 10% or less (e.g., 5% or less, 1 % or less) per minute.
- the gas field ion source (tip 186, extractor 190 and optionally suppressor 188) is capable of interacting with gas atoms to generate an ion beam for a time period of one week or more (e.g., two weeks or more, one month or more, two months or more) with a total interruption time of 10 hours or less (e.g., five hours or less, two hours or less, one or less).
- the gas field ion source may interact with gas atoms to generate the ion beam continuously for the entire time period (corresponding to a total interruption time of zero hours), but this is not necessary.
- Such time periods correspond to an interruption time.
- interruption times may occur one time or more than one time (e.g., two times, three, times, four times, five times, six times, seven times, eight times, nine times, 10 times).
- the interruptions may be due, for example, to scheduled maintenance, unexpected maintenance, and/or down time between shifts (e.g., overnight down time).
- the total of the interruption times is the total interruption time. As an example, if during the time period there are three interruption times, each of one hour, then the total interruption time is three hours.
- the total interruption time is three hours.
- the current of ion beam 192 at surface 181 of sample 180 varies by 10% or less (e.g., 5% or less, 1% or less) per minute.
- the resolution of an ion beam refers to the size of the smallest feature that can be reliably measured from images obtained using the ion microscope.
- a size of a feature is reliably measured if it can be determined to within an error of 10% or less of the actual size of the feature, and with a standard deviation in the measured size of less than 5% of the actual size of the feature, from ten images of the feature obtained under similar conditions.
- Ion microscope 200 can be used to take a good quality image in a relatively short period of time.
- ion microscope 200 can have a quality factor of 0.25 or more (e.g., 0.5 or more, 0.75 or more, one or more, 1.5 or more, two or more).
- the quality factor is determined as follows.
- the sample is imaged pixel-by-pixel by sub-dividing the surface of the sample into an x-y array of 512 pixels by 512 pixels.
- the dwell time per pixel is 100 ns during the measurement.
- the total abundance of secondary electrons from the sample is measured as a function of the position of the ion beam on the surface of the sample.
- an average pixel intensity G 1 is determined, along with a standard deviation SD 1 from the distribution of Si pixel intensities.
- an average pixel intensity G 2 is determined, along with a standard deviation SD 2 from the distribution of Cu pixel intensities.
- the quality factor is calculated according to the equation
- Surface 181 of sample 180 can undergo relatively little damage when exposed to ion beam 192.
- surface 181 of sample 180 can have a value of 25 nm or less (e.g., 20 nm or less, 15 nm or less, 10 nm or less, five nm or less) according to the damage test.
- the damage test is performed as follows. An atomically flat5 silicon (99.99% purity) sample with a four square ⁇ m field of view is imaged for 120 seconds while rastering the ion beam across the surface of the sample pixel-by-pixel using an ion beam current at the sample of 10 pA and a spot size of the ion beam at the sample of 10 nm or less.
- the four square ⁇ m field of view is broken into a 512 pixel by 512 pixel array for rastering purposes.
- the value of the damage test corresponds to the maximum0 distance of etching into the imaged portion of the silicon sample resulting from performing the damage test.
- Ion microscope 200 can have a relatively large depth of focus.
- the depth of focus of ion microscope 200 can be five nm or more (e.g., 10 nm or more, lOOnm or more, one ⁇ m or more), and/or 200 ⁇ m or less (e.g., 100 ⁇ m or5 less, 10 ⁇ m or less).
- the depth of focus of ion microscope 200 can be from 200 ⁇ m to five nm (e.g., from 500 ⁇ m to five nm, from one mm to five nm).
- the depth of focus of an ion beam is measured in the following manner.
- a gas field ion microscope e.g., He ion microscope
- a gas field ion microscope can be used to distinguish elements in a sample having very close atomic numbers (Z values) using, for example, secondary electron yield, scattered ion abundance, and/or angle- and energy-resolved scattered ion detection.
- the gas field ion microscope can be used to distinguish elements having atomic numbers (Z values) that differ only by one.
- the gas field ion microscope can be used to distinguish elements having masses that differ by one atomic mass unit or less (e.g., 0.9 atomic mass unit or less, 0.8 atomic mass unit or less, 0.7 atomic mass unit or less, 0.6 atomic mass unit or less, 0.5 atomic mass unit or less, 0.4 atomic mass unit or less, 0.3 atomic mass unit or less, 0.2 atomic mass unit or less, 0.1 atomic mass unit or less).
- a sample may have domains formed of materials (e.g., alloys) having different average masses.
- the gas field ion microscope can, for example, be used to distinguish domains of material having masses that differ only by one atomic mass unit or less (e.g., 0.9 atomic mass unit or less, 0.8 atomic mass unit or less, 0.7 atomic mass unit or less, 0.6 atomic mass unit or less, 0.5 atomic mass unit or less, 0.4 atomic mass unit or less, 0.3 atomic mass unit or less, 0.2 atomic mass unit or less, 0.1 atomic mass unit or less).
- one atomic mass unit or less e.g., 0.9 atomic mass unit or less, 0.8 atomic mass unit or less, 0.7 atomic mass unit or less, 0.6 atomic mass unit or less, 0.5 atomic mass unit or less, 0.4 atomic mass unit or less, 0.3 atomic mass unit or less, 0.2 atomic mass unit or less, 0.1 atomic mass unit or less.
- a more focused delivery of He gas to tip 206 can increase the efficiency of He gas utilization within microscope system 200.
- un-ionized He gas atoms can enter ion optics 130, which can increase the width of the distribution of energies of the ions in ion beam 192.
- low energy un-ionized He gas atoms can participate in charge exchange interactions with high energy He ions, which can also increase the width of the energy distribution of ions in ion beam 192.
- a gas delivery system can be designed to provide gas
- FIG. 21 is a schematic diagram of a portion of a gas field ion microscope that includes gas source 110 and a vacuum pump 734.
- Gas source 110 includes a delivery tube 730 of length q and diameter n terminating in a delivery nozzle 736, and vacuum pump 734 includes an inlet port 732.
- Nozzle 736 is positioned at a distance g from apex 187 of tip 186, and inlet port 732 is positioned at a distance 1 from apex 187 of tip 186.
- g can be 10 mm or less (e.g., 9 mm or less, 8 mm or less, 7 mm or less).
- g is 3 mm or more (e.g., 4 mm or more, 5 mm or more, 6 mm or more).
- g can be from 3 mm to 10 mm (e.g., from 4 mm to 9 mm, from 5 mm to 8 mm).
- 1 can be 100 mm or less (e.g., 90 mm or less, 80 mm or less, 70 mm or less, 60 mm or less, 50 mm or less).
- 1 is 10 mm or more (e.g., 20 mm or more, 30 mm or more, 40 mm or more).
- 1 can be from 10 mm to 100 mm (e.g., from 30 mm to 100 mm, from 40 mm to 80 mm).
- the local pressure of He gas at the position of apex 187 of tip 186 is 10 "5 Torr or more (e.g., 10 "4 Torr or more, 10 "3 Torr or more, 10 "2 Torr or more, 10 "1 Torr or more, 1 Torr or more).
- the overall pressure of He gas in microscope system can be reduced relative to systems that employ background
- the distance 1 and the cross-sectional area of inlet port 732 are selected so that vacuum pump 734 captures un-ionized He atoms within a particular solid angle region of microscope system 200.
- the solid angle subtended by inlet port 732 is 5° or more (e.g., 10° or more, 15° or more, 20° or more, 30° or more, 40° or more).
- the ratio of the length q of delivery tube 730 to the diameter n of tube 730 can be selected to control the distribution of trajectories of He gas atoms delivered to tip 186.
- the ratio q/n can be 3 or more (e.g., 4 or more, 5 or more, 6 or more) and/or 10 or less (e.g., 9 or less, 8 or less, 7 or less). In certain embodiments, the ratio q/n can be between 3 and 10 (e.g., between 3 and 9, between 4 and 9, between 4 and 8, between 5 and 8, between 5 and 7).
- the gas delivery system can include more than one delivery tube and nozzle.
- the gas delivery system can include two or more (e.g., three or more, four or more, five or more, six or more) gas delivery tubes.
- Each of the multiple gas delivery tubes can be positioned to deliver He gas, in a relatively directed fashion, to tip 186.
- the local pressure of He gas at the position of apex 187 of tip 186 can be increased even further.
- One or more vacuum pumps can be used to remove un-ionized He gas from microscope system 200.
- gas delivery tube 730 can be incorporated into another component of the system.
- gas delivery tube 730 can be formed by one or more passageways (e.g., two or more passageways, four or more passageways, six or more passageways) for gas delivery in extractor 190 and/or suppressor 188.
- one or more passageways (e.g., two or more passageways, four or more passageways, six or more passageways) for gas delivery can be provided in posts which support tip 186 (e.g., posts 522a/b and 552).
- extractor 190 can include four passageways for gas delivery to tip 186.
- the passageways can be equally spaced and arranged radially along a circumference of extractor 190 so that the opening of each passageway directly faces tip 186.
- the length- to-diameter ratios of each of the passageways can be the same, or different.
- a number of advantages can be realized by incorporating gas delivery tubes into other elements of microscope system 200. For example, using a metal tube 730 placed close to tip 186 for gas delivery can perturb electric fields in the vicinity of tip 186.
- positive charging of the surface of the sample can cause inaccurate ion beam rastering. Deflection and deceleration of the incident ion beam as a result of the electric field created by positive charges at the surface of the sample can reduce the energy of the incident ions, and change their trajectories in difficult-to-predict fashion.
- the surface of the sample can act as an electrostatic mirror for He ions, deflecting He ions away from the surface of the sample before the He ions reach the surface of the sample.
- FIG. 22 shows a portion of a gas field ion microscope that includes a flood gun 840 configured to deliver an electron beam 842 to surface 181 of sample 180 while He ion beam 192 is incident on surface 181.
- the electron flux on surface 181 can, in general, be controlled so that surface charging effects are counterbalanced by electron beam 842 to the extent desired.
- the depth m and thickness r, as well as the density of electrons in layer 846, can be controlled by the energy of the electrons in electron beam 842, the angle of incidence of the electrons in electron beam 842 with respect to surface 181, and the total dosage of electrons delivered to sample 180.
- the average energy of the electrons in electron beam 842 when incident on surface 181, is adjustable.
- the average energy of the electrons can be 500 eV or more (e.g., 1 keV or more, 2 keV or more), and/or 20 keV or less (e.g., 15 keV or less, 10 keV or less).
- the average energy of the electrons in electron beam 842 when incident on surface 181, can be from 500 eV to 20 keV (e.g., from 1 keV to 15 keV, from 2 keV to 10 keV).
- the total current of electrons delivered to sample 180 is 10 pA or more (e.g., 100 pA or more, 1 nA or more, 10 nA or more), and/or 100 ⁇ A or less (e.g., 10 ⁇ A or less, 1 ⁇ A or less, 500 nA or less, 100 nA or less).
- the total current of electrons delivered to sample 180 can be from 10 pA to 1 ⁇ A (e.g., from 100 pA to 100 nA, from 1 nA to 10 nA).
- m is 10 nm or more (e.g., 25 nm or more, 50 run or more, 75 nm or more, 100 nm or more), and/or 500 nm or less (e.g., 400 nm or less, 300 nm or less, 200 nm).
- m can be from 10 nm to 500 nm (e.g., from 25 nm to 500 nm, from 50 nm to 500 nm, from 75 nm to 400 nm, from 100 nm to 400 nm).
- multiple flood guns can be used.
- different flood guns can be used to expose different portions of surface 181 of sample 180 to electrons.
- each flood gun can be used to expose the same portion of surface 181 to electrons.
- different flood guns can be operated at different times.
- one or more flood guns can be used to expose surface 181 to electrons before surface 181 is exposed to He ions (e.g., to form a subsurface charge layer), while one or more different flood guns can be used to expose surface 181 to electrons while surface 181 is also being exposed to He ions.
- all the flood guns can be used to expose surface 181 to electrons before surface 181 is exposed to He ions (e.g., to form a sub-surface charge layer), whereas in certain embodiments all the flood guns can be used to expose surface 181 to electrons while surface 181 is also being exposed to He ions.
- Other combinations may also be used.
- collector electrodes can be used to neutralize charging at surface 181 while surface 181 is being exposed to He ions.
- Other combinations are also possible.
- flood gun 840 can be configured to deliver a very low energy beam of electrons 842 to sample 180.
- electrons in beam 842 can have an average energy of about 50 eV or less.
- the low energy electrons have low landing energies, and this limits the amount of negative charge that can accumulate on surface 181.
- the average electron energy in electron beam 842 is 50 eV, once sample 180 charges to a potential of -50 V relative to the common ground, electrons from flood gun 840 will no longer land on the surface of the sample.
- the energy of the low energy electrons from flood gun 840 the maximum accumulated negative charge on surface 181 of sample 180 can be controlled.
- This method can be used to image non-conducting materials without depositing a layer of conductive material on top of the non-conducting material to prevent charging of the nonconducting material.
- An example of this method is shown in FIG. 25.
- Ion beam 192 is incident on surface 181 of sample 180, which is a dielectric material with relatively low electrical conductivity (e.g., sample 180 is not metallic).
- Sample 180 is supported by sample manipulator 140, which is biased at an electrical potential of -600 V relative to the common external ground of microscope system 200. The electrical potential applied to manipulator 140 creates an electric field at surface 181 of sample 180.
- flood gun 840 can be configured to deliver electrons to sample 180 which have a negative landing energy - that is, in the absence of positive charge on the sample surface, electrons that do not land at all on surface 181.
- sample 180 -acquires surface charge due to incident He ions
- electrons from flood gun 840 begin to land on surface 181, neutralizing the positive charge.
- surface 181 of sample 180 is maintained in an approximately uncharged state.
- a conversion surface can be used to generate secondary electrons, which can then be used to neutralize positive charges that accumulate at surface 181 of sample 180.
- a conversion surface formed of a material with a high secondary electron yield e.g., platinum
- High energy He ions and/or neutral atoms, leaving sample 180, can strike the conversion surface, generating secondary electrons.
- the generated secondary electrons experience attractive forces due to accumulated positive surface charge on sample 180.
- the secondary electrons land on the sample surface, neutralizing the positive charges and reducing the electric field due to surface charge. Consequently, secondary electrons are attracted more strongly to surface 181 of sample 180 when there is a greater accumulation of surface positive charge. This provides a self-regulating mechanism for reducing surface charging.
- a conversion plate can be mounted directly to an element of ion optics 130 to provide secondary electrons for surface charge neutralization of sample 180.
- a conversion plate 845 is attached to a surface of second lens 226. Electrons 842 from flood gun 840 are directed to be incident on the conversion plate, which is formed from a material with a high secondary electron yield. He ion beam 192 is incident on surface 181 of sample 180 and, over time, positive charge accumulates on surface 181 in the region where ion beam 192 is incident. Secondary electrons 847, generated from conversion plate 845, are attracted to surface regions with excess positive charge and land on these regions, neutralizing excess positive charge. Once the excess surface charge is eliminated, further secondary electrons do not land on surface 181. As a result, surface 181 can be maintained in a quasi-neutral state.
- flood gun 840 can be configured for either continuous or intermittent operation. In particular, during intermittent operation, flood gun 840 can be turned on and off at a desired rate. For example, in some embodiments, flood gun 840 can be turned on and off to provide charge neutralization of sample 180 at a pixel exposure rate. Ion beam 192 can be rastered across the surface of sample 180 in discrete steps to expose successive portions of the sample surface. After each portion is exposed, flood gun 840 can be used to neutralize surface charge in the exposed region. This corresponds to charge
- flood gun 840 can be used to perform neutralization at a line scan rate (e.g., after an entire line of discrete portions of sample 180 have been exposed to ion beam 192), and/or at a frame rate (e.g., after an entire two-dimensional area of discrete portions of sample 180 have been exposed to ion beam 192).
- FIGS. 27 A and 27B An example of the use of an embedded layer of negative charge is shown schematically in FIGS. 27 A and 27B.
- ion beam 192 is incident on surface 181 of sample 180.
- a plurality of secondary electrons 2012 are generated within the first few nanometers of sample 180.
- many of the secondary electrons escape as free electrons 2014, which can be detected by a suitably configured detector.
- incident He ions implant within sample 180, forming a positively-charged layer 2010 within sample 180.
- secondary electrons 2012 are increasingly attracted toward layer 2010, and fewer and fewer secondary electrons 2012 escape sample 180 as free electrons 2014.
- imaging of sample 180 via detection of secondary electrons can become increasingly difficult.
- FIG. 27B A solution to this problem is shown in FIG. 27B.
- flood gun 840 (not shown) is used to embed a layer of negative charge 2016 (e.g., electrons) within sample 180.
- the embedded layer of negative charge is similar to layer 846 in FIG. 23.
- layer 2016, secondary electrons 2012 generated in sample 180 are accelerated away from sample 180, resulting in an increase in the number of generated secondary electrons 2014 that escape sample 180, and therefore enhancing the detected secondary electron signal from the sample, hi effect, layer 2016 acts as an electrostatic mirror for secondary electrons, enhancing their detectability.
- flood gun 840 can be used to implant electrons in a sample prior to the analysis of the sample, and/or flood gun 840 can be used to implant electrons in a sample while imaging the sample.
- the sample may be exposed to electrons from flood gun 840 at intervals (e.g., regular intervals). This can, for example, assist in maintaining a relatively consistent level of charging.
- the sample may be exposed to electrons from flood gun 840 at time periods corresponding to a dwell time per pixel (e.g., 100 ns).
- sample manipulator 140 can be configured to decouple sample 180 from other parts of system 200, thereby reducing the impact of external mechanical disturbances.
- FIG. 28 shows a vibration-decoupled sample manipulator 140 that includes a guiding needle 906 supported by an actuator 908, with needle 906 and actuator 908 each located within a stage 904.
- a support disk 902 is positioned atop stage 904, and a friction spider 900, which supports sample 180, is placed atop disk 902.
- actuator 908 receives a suitable signal from electronic control system 170 and actuates guiding needle 906. Guiding needle 906 nudges sample 180 and/or spider 900, causing translation in the x-y plane, in response to signals from actuator 908.
- a width j of guiding needle 906 at its apex is typically chosen to be slightly smaller than a diameter b of aperture 910 in spider 900.
- j can be 1 mm
- b can be 1.1 mm.
- spider 900 and disk 902 are selected such that the static frictional force between disk 902 and spider 900 is large, but can be overcome by the force applied by actuator 908 to sample 180 through guiding needle 906.
- Guiding needle 906 is formed of a mechanically compliant material that can deform under an applied stress to reduce transmission of vibrations to sample 180, but is stiff enough to transmit to sample 180 the force applied by actuator 908.
- guiding needle 906 can have a substantially rectangular cross-sectional shape.
- a rectangular cross-sectional shape may assist in ensuring that rotation of sample 180 and/or of spider 900 does not occur as spider 900 is translated in the x- and/or y-directions by guiding needle 906.
- the materials used to form spider 900 and/or disk 902 can be selected so that an even higher static frictional force between these elements is present.
- spider 900 and disk 902 can be magnetically coupled to increase the frictional force between these elements. Magnetic field coupling can be carefully implemented to ensure that the magnetic field is localized and does not disturb sample 180 or impinging ion beam 192.
- Assembly 1510 may be connected to an ion microscope such that tip 186 is pointed towards aperture 1524 on sample stage 1514.
- Body 1511 may be formed from suitable rigid materials such as hardened steel, stainless steel, phosphor bronze, and titanium. Body 1511 may be sized and shaped to suit the particular needs of the application. As an example, the size and shape of body 1511 may be chosen for use with the microscope systems disclosed herein.
- a sample may be introduced to assembly 1510 through opening 1512.
- Sample stage 1514 is supported by arms 1518 connected to body 1511 along adjustable connectors 1522.
- Adjustable connectors 1522 allow for vertical movement of arms 1518. Arms 1518 and sample stage 1514 can be moved in a vertical direction and locked in a specific position.
- Connectors 1522 can be pneumatic or vacuum controlled such that arms 1518 and stage 1514 can be tightly locked in a desired vertical position.
- Connectors 1522 can Optionally include other types of connectors.
- Sample stage 1514 is connected to arms 1518 using grip 1520.
- Arm 1518 can have a shaft extending inwards such that grip 1520 of sample stage 1514 can clasp the shaft.
- Grip 1520 can be pneumatically or vacuum operated such that stage 1514 can be tilted.
- Grip 1520 can be controlled such that stage 1514 is tilted to a desired position. In some embodiments, after a desired position has been reached, grip 520 can be tightened such that sample stage 1514 is tightly locked in the desired tilted position.
- Sample stage 1514 further includes surface disk 1516 having an opening 1524.
- a sample may be placed on disk 1516 and a sample position control system can be introduced through opening 1524 to move the sample on the plane of disk 1516.
- disk 1516 can be rotated about its center to rotate and move the sample located on the surface of the disk as desired.
- Disk 1516 may be formed from suitable rigid materials including ceramic, glass and polymers.
- FIG. 30 depicts a sample holder assembly for a microscope system.
- the sample holder assembly of FIG. 30 is similar to the sample holder assembly of FIG. 29 with a spider 1600 placed on a surface of disk 1516.
- Spider 1600 can have legs to allow it to be positioned on top of opening 1524.
- spider 1600 can have an opening on a portion of the surface.
- Spider 1600 can be formed from suitable rigid materials including ceramic, glass and polymers.
- sample manipulator 140 can transmit tilt angle information for sample 180 to electronic control system 170.
- tilt angle information can be entered manually by a system operator via a user interface.
- Electronic control system 170 can determine, based upon the orientation of sample 180, a set of voltage corrections to apply to second lens 226 to dynamically change the focal length of lens 226 as ion beam 192 is scanned over the surface of tilted sample 180.
- the lateral dimensions of the inclined sample are distorted due to the projection of the tilted sample on a plane surface and due to the difference in distance to the ion optics 130.
- lateral dimensions of inclined sample surfaces may appear shorter that they actually are due to the orientation of sample 180 with respect to ion beam 192.
- Another example is the keystone distortion of the image. The effect is that a rectangular feature is distorted so that the image of the rectangle appears to be keystone in its shape.
- the electronic control system 170 can get the information about the tilt angle for sample 180 in the same way as described above.
- Electronic control system 170 can determine, based upon the tilt of sample 180, adjustments of the scan amplitude to apply to scanning deflectors 219 and 221 to adapt the ion beam deflection as ion beam 192 is scanned over the surface of tilted sample 180 for an undistorted imaging of the surface of tilted sample 180.
- these two distortion effects can be corrected by digital manipulation of the distorted image.
- Doubly-charged He ions e.g., He 2+
- gas field ion source 120 can also be produced in gas field ion source 120, either via double-ionization of He atoms in the vicinity of tip 186, or by collisions between He ions.
- the focusing properties of doubly-charged He ions are different from singly-charged ions, and doubly-charged ions present in ion beam 192 can lead to larger spot sizes on sample 180 and other undesirable effects.
- One approach to reducing the population of neutral particles in ion beam 192 involves reducing the probability that neutral particles will make their way into the ion beam. Such an approach can involve, for example, using directed gas delivery to tip 186 (see discussion above) to reduce the overall presence of un-ionized He gas atoms in microscope system 200.
- FIG. 31 shows ion optics 130 in which deflector 220 is offset from longitudinal axis 132 of ion optics 130, and in which an additional deflector 223 is disposed.
- He ion beam 192 includes He ions 192a and He atoms 192b.
- the electrical potential applied to deflector 223 is adjusted to cause deflection of He ions 192a in the x-direction. He atoms 192b are unaffected by deflector 223, and are therefore undeflected. He atoms 192b are subsequently intercepted by collector 1016, which prevents He atoms 192b from passing through aperture 224.
- the electrical potentials applied to deflectors 220 and 222 are also adjusted so that the trajectories of He ions 192a are re-aligned with longitudinal axis 132, and a portion of He ions 192a pass through aperture 224 and are incident on surface 181 of sample 180 as ion beam 192.
- Other techniques may also be used to remove neutral particles from an ion beam.
- such techniques involve deflecting the ions in the ion beam using electric and/or magnetic field(s), without deflecting the neutral particles.
- combinations of electric and magnetic fields can be used to compensate for energy dependent spatial separation of ions resulting from ion deflection in ion optics 130.
- various asymmetric ion column geometries e.g., bent ion columns
- the neutral atoms are therefore spatially separated from He + ions, providing a neutral atom beam 192b which is intercepted by collector 1016b.
- He 2+ ions are deflected to an even greater extent than He + ions, spatially separating singly- and doubly-charged ions, and providing an ion beam 192c OfHe 2+ ions.
- the He 2+ ion beam 192c is intercepted by collector 1016c.
- ion beam 192a which emerges from ion optics 130 includes substantially only He + ions.
- FIG. 33 shows another embodiment of an ion optical system for separating He atoms, He + ions, and He 2+ ions.
- the ion optical system shown in FIG. 33 includes a dispersionless sequence of electric and magnetic fields which are used to isolate He atoms, He ions, and He ions from one another, and which do not contribute prism-like effects to the particle beams.
- the ion optical system includes a series of three deflectors 223 a, 223b, and 223c, which are configured to deflect and direct He + ions through ion optics 130 so that ion beam 192a, which includes substantially only He + ions, emerges from ion optics 130.
- Neutral atom beams 192b are undeflected and are intercepted at positions following each deflector by collectors 1016b. Doubly-charged He ions are deflected even further than He + ions, and multiple He 2+ beams 192c are intercepted by collectors 1016c. As a result, He atoms, He + ions, and He 2+ ions are spatially separated from one another, and the He + ions are directed toward sample 180 as ion beam 192, while the undesired beam constituents are blocked in ion optics 130.
- the use of magnetic fields can lead to spatial separation of the trajectories of ions in ion beam 192 which have the same charge, but which correspond to different isotopes of the gas introduced by gas source 110.
- gases such as He, which have a dominant naturally occurring isotope (e.g., greater than 90% relative abundance)
- separation effects due to magnetic fields are typically small.
- an isotope separator e.g., a block used to prevent undesired isotopes from traversing the length of ion optics 130
- a collector 1016 that is used to block neutral atoms or doubly-charged ions can also be used to block unwanted isotopes in ion beam 192.
- a secondary electron is an electron that is emitted from a sample species and that has an energy of less that 50 eV.
- secondary electrons are emitted from the sample surface at a range of angles and energies.
- the information of most interest is usually the total abundance of secondary electrons (as opposed to energy-resolved secondary electron information, or angle-resolved secondary electron information) because, as explained below, the total abundance of the secondary electrons is what can provide information regarding the sample surface.
- Secondary electrons can be detected using one or more appropriate detectors capable of detecting electrons (see discussion above regarding types of detectors). If multiple detectors are used, the detectors may all be the same type of detector, or different types of detectors may be used, and may generally be configured as desired.
- the detectors can be configured to detect secondary electrons leaving surface 181 of sample 180 (the surface on which the ion beam impinges), surface 183 of sample 180 (the surface on the opposite side from where the ion beam impinges) or both (see discussion above regarding configurations of detectors).
- detecting the total abundance of secondary electrons can provide information regarding the topography of a sample.
- the secondary electron total abundance at a given location on a surface generally depends upon the slope of the surface relative to the ion beam at that point. In general, the secondary electron total abundance is higher where the slope of the surface relative to the ion beam is higher (i.e., where the angle of incidence of the ion beam as measured from the surface normal is larger).
- the change in the total abundance of secondary electrons as a function of the location of the ion beam on the surface of the sample can be correlated to a change in the slope of the surface, providing information regarding the topography of the surface of the sample.
- detecting the total abundance of secondary electrons can yield material constituent information (e.g., elemental information, chemical environment information) about a sample.
- the information is predominantly related to the surface of the sample.
- each element or material in a given chemical environment will have a particular inherent secondary electron yield.
- the secondary electron total abundance at a given location on a surface generally depends on the material present at that location. Therefore, the change in the total abundance of secondary electrons as a function of the location of the ion beam on the surface of the sample, can be correlated to a change in the element(s) and/or material(s) present at the surface of the sample, providing material constituent information about the surface of the sample.
- specific materials in a sample can be identified based on quantitative measurements of secondary electron yields from the sample.
- materials such as Al, Si, Ti, Fe, Ni, Pt, and Au have known secondary electron yields when exposed to a He ion beam under controlled conditions.
- An ion microscope e.g., a gas field ion microscope
- secondary electron yields for various materials are shown in Table I. The yields were measured at normal incidence of the He ion beam, and at an average ion energy of 21 keV.
- the yields shown in Table I are typically scaled by a multiplicative factor that corresponds to the secant of the angle of incidence of the ion beam on the surface of the sample.
- Other experimental conditions are described in the corresponding Example noted below.
- detecting the total abundance of secondary electrons can yield voltage contrast information, which in turn, can provide information regarding the electrical conductivity properties and/or the electrical potential of an element and/or a material at the surface of a sample.
- the secondary electron total abundance at a given location on the surface of a sample usually depends on the electrical properties of the material present at the surface of the sample. In general, less electrically conducting materials will tend to become positively charged over time while being exposed to an ion beam over time, whereas more electrically conducting materials will have less of a tendency to become positively charged over time while being exposed to an ion beam.
- the secondary electron total abundance at a given location of the surface of a sample will tend to decrease over time for a material that is less electrically conducting (due to more surface charging resulting in fewer secondary electrons escaping the sample), while the secondary electron total abundance at a given location of the surface of the sample that is more electrically conducting will tend to undergo less reduction in secondary electron total abundance over time (due to less surface charging).
- the change in the total abundance of secondary electrons as a function of the ion beam location at the sample surface can be correlated to the electrical conductivity of the material at that location, providing voltage contrast information about the surface of the sample.
- Sub-surface voltage contrast effects can be provided by He ions which become embedded within sub-surface regions of the sample. As described in connection with FIGS. 27A and 27B, sub-surface He ions can prevent secondary electrons generated in the sample from escaping the sample surface. Thus, contrast in secondary electron images of the sample can be due to sub-surface charging of the sample by incident He ions.
- voltage contrast measurements can be used to determine whether portions of electrical devices and/or circuits are at different potentials when exposed to the ion beam due to the presence or absence of electrical connections between the portions, and therefore whether the devices and/or circuits are operating correctly or not.
- detecting the total abundance of secondary electrons can provide crystalline information about a sample.
- the total abundance of secondary electrons can vary depending on whether the ion beam is aligned with the crystal structure of the sample (e.g., aligned parallel to one of the unit vectors describing the crystal lattice) or not. If the ion beam is aligned with the crystal structure of the sample, the probability that ions in the ion beam can generally penetrate into a given distance into the sample without undergoing a collision with a sample atom (commonly referred to as channeling) is relatively high, resulting in a lower total abundance of secondary electrons.
- Such regions can, for example, have the same crystal orientation, and the size of the regions can provide grain size and/or crystal size information (e.g., in a polycrystalline sample that includes multiple, oriented crystal domains), and/or can provide information regarding strained regions of sample .(whether amorphous or crystalline) because the magnitude of the secondary electron total abundance for a material of a given chemical composition (e.g., elemental composition, material composition) can depend on the strain of the material.
- a material of a given chemical composition e.g., elemental composition, material composition
- detecting the total abundance of secondary electrons can provide magnetic information about a sample.
- the total abundance of secondary electrons can depend on the magnitude of a magnetic field adjacent the sample surface.
- the magnetic field adjacent to the sample surface varies due to magnetic domains within the sample that produce local magnetic fields at the sample surface.
- a static magnetic field is applied by an external magnetic field source, and magnetic domains within the sample produce local magnetic fields at the surface of the sample that introduce variations in the applied external magnetic field. In either case, variations in the local magnetic field at the surface of the sample can, for example, change the trajectories of secondary electrons ejected from the sample.
- the change in secondary electron trajectories can correspond to an increase in the total abundance of secondary electrons when the trajectories of the secondary electrons are changed so that more secondary electrons are directed toward the detector(s), or the change in secondary electron trajectories can correspond to a decrease in the total abundance of secondary electrons when the trajectories of the secondary electrons are changed so that more secondary electrons are directed away from the detector(s).
- the contrast that appears in a secondary electron image of the sample may be due to two or more of the mechanisms discussed above.
- secondary electron images of certain samples can include contrast that is due in part to topographic variations in the sample surface, material constituent variations in the sample surface, voltage contrast variations in the sample surface, crystalline variations in the sample surface, and/or magnetic variations in the sample surface. Accordingly, it can be advantageous to combine information gained from measuring the secondary electron total abundance with information gained from measuring other types of particles to
- Secondary electron imaging techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Secondary electron imaging techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. More generally, secondary electron imaging techniques can be used for a wide range of ion beam testing applications of semiconductor articles. Optionally, this approach can similarly be used for purposes of mask repair.
- sample class for which secondary electron imaging techniques can be used is metals and alloys.
- images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- sample class where secondary electron imaging techniques can be used is read/write structures for data storage.
- Additional examples of classes of materials for which secondary electron imaging techniques can be used are biological materials and pharmaceutical materials.
- Imaging samples using secondary electrons generated by exposure to a He ion beam can provide a number of advantages relative to secondary electron imaging via other techniques, such as SEM.
- the spot size of the He ion beam on the sample can be smaller than the spot size of an electron beam from a SEM.
- the region of the sample that is exposed to the He ion beam is more carefully controlled than the exposed region in a SEM.
- He ions are heavier than electrons, scattering events do not disperse He ions as readily within the sample as electrons are dispersed by scattering.
- He ions incident on the surface of a sample can interact with the sample in a smaller interaction volume than electrons in a SEM.
- secondary electrons detected in a gas field ion microscope e.g., a He ion microscope
- the secondary electrons which are generated by the He ion beam can correspond to a more localized interrogation of the surface of the sample (e.g., with less lateral averaging of material properties) than the secondary electrons generated in a SEM.
- the He ion source also provides a greater depth of focus than an electron source.
- images of a sample obtained using an ion microscope e.g., a gas field ion microscope
- images of a sample obtained using an ion microscope can show a larger portion of the sample, measured along the direction perpendicular to the sample surface, in focus than comparable images obtained from secondary electrons in a SEM.
- He ion beams can also provide a more sensitive contrast mechanism for secondary electron images of a sample due to a larger range of secondary electron yields for different materials available when causing the secondary electrons to leave the sample due to the interaction of the ion beam with the sample, as compared to when causing the secondary electrons to leave the surface due to the interaction of an electron beam with the sample.
- secondary electron yields for common materials such as semiconductors and metals vary from 0.5 to 2.5 for an incident electron beam.
- secondary electron yields for the same materials exposed to a He ion beam can vary from 0.5 to 8.
- identification of different materials from secondary electron images can be performed more accurately using a gas field ion microscope (e.g., a He ion microscope) than in comparable SEM systems.
- Auger electrons can be detected using one or more appropriate detectors capable of detecting electrons in an energy-resolved fashion (see discussion above regarding types of detectors). If multiple detectors are used, the detectors may all be the same type of detector, or different types of detectors may be used, and may generally be configured as desired.
- the detectors can be configured to detect Auger electrons leaving surface 181 of sample 180 (the surface on which the ion beam impinges), surface 183 of sample 180 (the surface on the opposite side from where the ion beam impinges) or both (see discussion above regarding configurations of detectors).
- electron collection optics e.g., an electrostatic lens system
- that are adjacent the surface of the sample and that can direct the electrons to the detector can be used (e.g., to increase the effective solid angle of detection for the Auger electrons).
- detecting the energy of Auger electrons can yield material constituent information (e.g., elemental information, chemical environment information) about a sample.
- the information is predominantly related to the surface of the sample.
- the Auger electrons emitted by the element or material will have a particular energy or band of energies.
- the energy of the Auger electrons at a given location on a surface generally depends on the material present at that location.
- the change in the energy of the Auger electrons as a function of the location of the ion beam on the surface of the sample can be correlated to a change in the element(s) and/or material(s) present at the surface of the sample, providing material constituent information about the surface of the sample.
- Auger electrons detected in a gas field ion microscope can arise from a smaller region than the region giving rise to Auger electrons in a SEM with a similar spot size.
- the Auger electrons which leave the surface due to the interaction of the sample and the He ion beam can correspond to a more localized interrogation of the surface of the sample (e.g., with less lateral averaging of material properties) than the Auger electrons generated in a SEM.
- the He ion source also provides a greater depth of focus than an electron source.
- images of a sample obtained using an ion microscope e.g., a gas field ion microscope
- Auger electron detection Another advantage of using an ion beam, as opposed to an electron beam, for Auger electron detection is that when using an electron beam the Auger electrons are detected on a baseline of backscattered electrons, and, using an ion beam, the
- backscattered electrons are not present.
- it can be possible to obtain a relatively high signal to noise ratio for detected Auger electrons while collecting a relatively small number of Auger electrons, which can reduce the amount of time it takes to obtain a relatively good quality Auger electron spectrum from a sample when using an ion beam.
- a scattered ion is generated when an ion from the ion beam
- scattered ions generally provide information about the surface of the sample.
- the particular arrangement of the detector(s) generally depends on the type of information that is desired to be obtained.
- topographical information about a sample surface can be obtained via detected scattered ions.
- FIG. 34A generally depicts an embodiment of an approach to detecting scattered ions from different regions of a surface to determine topographical information about the surface of a sample.
- FIG. 34A shows a sample 7010 having regions 7012, 7014 and 7016 with surfaces 7013, 7015 and 7017, respectively.
- Scatter patterns 7020, 7030 and 7040 represent the angular distribution of ions scattered from surfaces 7013, 7015 and 7017, respectively, when the ion beam is perpendicularly incident thereon.
- each of scatter patterns 7020, 7030 and 7040 is a cosine-type distribution.
- topographic information is obtained from He ions that are scattered at large scattering angles.
- topographic information from scattered ions is determined by detecting scattered ions at an angle of 60° or greater (e.g., 65° or greater, 70° or greater, 75° or greater) relative to the direction of the ion beam.
- FIG. 34A depicts the use of two detectors, in some embodiments a single detector is used (e.g., detector 7041 or detector 7050). Alternatively, in certain embodiments, more than two (e.g., three, four, five, six, seven, eight) detectors can be used.
- FIGS. 35A-35I generally depict various embodiments of approaches to detecting scattered ions from different regions of a surface to determine topographical information about the surface of a sample.
- FIGS. 35A, 35D and 35G shows a sample 8050 having regions 8052, 8054, 8056 and 8058 with surfaces 8053, 8055, 8057, 8059 and 8061, respectively.
- surfaces 8055 and 8059 are oblique relative to surfaces 8053, 8057 and 8061.
- Scatter patterns 8070, 8090 and 80110 represent the angular distribution of ions scattered from surfaces 8053, 8057 and 8061, respectively, when the ion beam is perpendicularly incident thereon.
- each of scatter patterns 8070, 8090 and 80110 is a cosine-type distribution.
- Scatter patterns 8080 and 80100 represent the angular distribution of ions scattered from surfaces 8055 and 8059 when the ion beam is perpendicular with respect to regions 8054 and 8058.
- the angular distribution of scatter patterns 8080 and 80100 is not a cosine-type distribution.
- FIGS. 35B and 35C depict the total yield of scattered ions and the relative abundance of detected scattered ions when a hemispherical detector (which may be capable of angularly resolving the scattered ions, spectrally-resolving the scattered ions, or both) 80120 is used to detect the scattered ions.
- a hemispherical detector which may be capable of angularly resolving the scattered ions, spectrally-resolving the scattered ions, or both
- FIG. 35C there is a shadow effect in the relative abundance of the detected ions when using detector 80120.
- the relative abundance profiles from detector 80120 can be used to determine the topography of sample 8050.
- the contribution to the total abundance of the scattered ions detected that is due to topography alone can be removed from the total abundance of the detected scattered ions to determine the contribution to the total detected scattered ions due to other effects (e.g., changing material across the surface of sample 8050).
- FIGS. 35E and 35F depict the total yield of scattered ions and the relative abundance of detected scattered ions when a top detector 80130 having a relatively small acceptance angle for scattered ions is used to detect the scattered ions.
- the relative abundance of scattered ions decreases at regions 8054 and 8056.
- the contribution to the total abundance of the scattered ions detected that is due to topography alone can be removed from the total abundance of the detected scattered ions to determine the contribution to the total detected scattered ions due to other effects (e.g., changing material across the surface of sample 8050).
- FIGS. 35H and 351 depict the total yield of scattered ions and the relative abundance of detected scattered ions when a top detector 80140 a relatively large acceptance angle for scattered ions is used to detect the scattered ions. As shown in FIG. 351, by selecting the appropriate acceptance angle of detector 80140, the relative abundance of the detected scattered ions is substantially the same across the sample. Changes in the total abundance of detected scattered ions would be due to effects other than changes in surface topography (e.g., changing material across the surface of sample 8050).
- the detection of scattered ions can be used to determine material constituent information about the surface of the sample.
- One such approach involves measuring the total abundance of scattered ions.
- the total abundance of scattered ions can be detected using a single detector (e.g., a hemispherical detector) configured to detect scattered ions leaving surface 181 of sample 180 (the surface on which the ion beam impinges), or multiple detectors (e.g., located at different solid angles with respect to the surface of the sample) configured to detect scattered ions leaving surface 181 of sample 180 (the surface on which the ion beam impinges the sample surface at a range of angles and energies).
- a single detector e.g., a hemispherical detector
- multiple detectors e.g., located at different solid angles with respect to the surface of the sample
- the scattering probability of a He ion (and therefore the total abundance of scattered He ions, assuming no effects from other factors, such as topographical changes in the surface sample) is approximately proportional to the square of the atomic number (Z value) of the surface atom from which the He ion scatters.
- Z value the atomic number of the surface atom from which the He ion scatters.
- the total abundance of scattered He ions from a tungsten atom at a surface of the semiconductor article will be approximately 25 times the total abundance of scattered ions from a silicon atom at the surface of the semiconductor article.
- the total abundance of scattered He ions from a gold atom at a surface of the semiconductor article will be approximately 25 times the total abundance of scattered ions from a silicon atom at the surface of the semiconductor article.
- the total abundance of scattered He ions from a indium atom at a surface of the semiconductor article will be approximately 10 times the total abundance of scattered ions from a silicon atom at the surface of the semiconductor article.
- Another approach to determining material constituent information about the surface of a sample by detecting scattered He ions involves measuring the scattered He ions in an energy-resolved and angle-resolved fashion.
- second lens 226 focuses He ion beam 192 onto surface 181 of sample 180.
- He ions 1102 scatter from surface 181 and are detected by detector 1100.
- Detector 1100 is designed so that the angle and energy of each detected scattered He ion is known for each angle ⁇ within the acceptance angle of detector 1100.
- the mass of the atom at the surface that scatters the scattered He ion can be calculated based on the following relationship: where E s is the energy of the scattered He ion, E; is the incident energy of the He ion, MHe is the mass of the He ion, ⁇ s is the scattering angle, and M a is the mass of the atom that scatters the He ion.
- Detector 1100 can, for example, be an energy-resolving phosphor-based detector, an energy-resolving scintillator-based detector, a solid state detector, an energy-resolving electrostatic prism-based detector, an electrostatic prism, an energy-resolving ET detector, or an energy-resolving microchannel. In general, it is desirable for detector 1100 to have a substantial acceptable angle. In some embodiments, detector 1100 is stationary (e.g., an annular detector). In certain embodiments, detector 1100 can sweep through a range of solid angles.
- such a system can contain multiple (e.g., two, three, four, five, six, seven, eight) detectors. Often, the use of multiple detectors is desirable because it can allow for a larger acceptance angle of detected scattered He ions.
- detecting the total abundance of scattered He ions can provide crystalline information about a sample.
- the total abundance of scattered He ions can vary depending on whether the ion beam is aligned with the crystal structure of the sample or not. If the ion beam is aligned with the crystal structure of the sample, the probability that ions in the ion beam can generally penetrate into a given distance into the sample without undergoing a collision with a sample atom (commonly referred to as channeling) is relatively high, resulting in a lower total abundance of scattered He ions.
- the ions in the ion beam will have a lower probability of penetrating into the sample the given distance without undergoing a collision with a sample atom, resulting in a higher total abundance of scattered He ions. Therefore, the change in the total abundance of scattered He ions as a function of the ion beam location at the sample surface can be correlated to the crystalline information of the material at that location. For example, there may be regions of the sample surface where the scattered He ions' total abundance is substantially the same.
- Such regions can, for example, have the same crystal orientation, and the size of the regions can provide grain size and/or crystal size information (e.g., in a polycrystalline sample that includes multiple, oriented crystal domains), and/or can provide information regarding strained regions of sample (whether amorphous or crystalline) because the magnitude of the scattered He ions' total abundance for a material of a given chemical composition (e.g., elemental composition, material composition) can depend on the strain of the material.
- a material of a given chemical composition e.g., elemental composition, material composition
- crystalline information about the surface of a sample can be obtained by exposing a region of the surface to an ion beam (without rastering the ion beam) and then measuring a pattern of the scattered He ions (e.g., similar to a Kikuchi pattern obtained due to backscattered electrons from a sample surface exposed to an electron beam).
- the pattern of the scattered He ions can be analyzed to determine, for example, the orientation, lattice spacing, and/or crystal type (e.g., body centered cubic, face centered cubic) of the material at the location of the sample surface that is exposed to the ion beam.
- Scattered ion imaging techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Scattered ion imaging techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. Optionally, this approach can similarly be used for purposes of mask repair.
- Another example of a sample class for which scattered ion imaging techniques can be used is metals and alloys. For example, images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- Yet another example of a sample class where scattered ion imaging techniques can be used is read/write structures for data storage. Additional examples of classes of materials for which scattered ion imaging techniques can be used are biological materials and pharmaceutical materials.
- scattered ions are not formed when a sample surface is exposed to an electron beam of the type used in conventional SEMs, and thus none of the crystalline information or material constituent information obtainable via detected scattered He ions is available with such SEMs.
- This is a significant advantage of a gas field ion microscope (e.g., a He ion microscope) as described herein relative to a conventional SEM.
- Measurement of scattered He ions using a gas field ion microscope can offer a number of advantages relative to conventional Rutherford backscattering measurement devices.
- the spot size to which the incident He ions can be focused at the surface of the sample can be significantly smaller than the spot size of conventional Rutherford backscattering measurement devices (typical spot sizes of 100 ⁇ m to 1 mm or more), allowing for the material constituent information about the sample surface to be more precisely localized than achieved with conventional Rutherford backscattering measurement devices.
- a gas field ion microscope e.g., a He ion microscope
- a gas field ion microscope allows for pixel-by-pixel rastering across the sample surface, whereas Rutherford backscattering measurement devices do not have this capability. This can reduce the cost and/or complexity associated with material constituent information about the sample surface at various locations of the surface.
- a primary neutral particle is a neutral particle generated when the ion beam interacts with the sample and an ion (e.g., a He ion) from the ion beam leaves the sample as an un-charged neutral particle (e.g., an un-charged He atom).
- an ion e.g., a He ion
- un-charged neutral particle e.g., an un-charged He atom
- primary He atoms are a relatively sensitive probe of the sub-surface region of a sample.
- the sub-surface region is the region of a sample that is more than five nm beneath the sample surface (e.g., 10 nm or more beneath the sample surface, 25 nm or more beneath the sample surface, 50 nm or more beneath the sample surface), and 1000 nm or less beneath the sample surface (e.g., 500 nm or less beneath the sample surface, 250 nm or less beneath the sample surface, 100 nm or less beneath the sample surface).
- the probe depth of the ion beam increases as the energy of the ions increase.
- a higher energy ion beam can be used.
- material constituent information based on the detection of primary He atoms can be determined using total abundance detection, energy-resolved/angle-resolved detection, or both, using detector arrangements as described above with respect to the corresponding techniques for scattered He ions and also using the same mathematical relationships as described above for scattered He ions.
- the detector(s) used for primary He atoms is capable of detecting a neutral species. Examples of such detectors include microchannel plates, channeltrons and scintillator/PMT detectors.
- Primary neutral particle (e.g., He atom) techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Primary neutral particle techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. Optionally, this approach can similarly be used for purposes of mask repair.
- Another example of a sample class for which primary neutral particle imaging techniques can be used is metals and alloys. For example, images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- Yet another example of a sample class where primary neutral particle imaging techniques can be used is read/write structures for data storage. Additional examples of classes of materials for which primary neutral particle imaging techniques can be used are biological materials and pharmaceutical materials.
- Primary neutral particles are generally not generated when a sample surface is exposed to an electron beam of the type used in conventional SEMs, and thus none of the crystalline information or material constituent information obtainable via detected scattered He ions is available with such SEMs. This is a significant advantage of a gas field ion microscope (e.g., a He ion microscope) as described herein relative to a conventional SEM.
- a gas field ion microscope e.g., a He ion microscope
- Typical photons of interest include X-ray photons, UV photons, visible photons and IR photons.
- an IR photon is a photon having a wavelength of more than 700 nm to 100,000 nm (e.g., from 1.2xlO "5 keV to 1.7xlO "3 keV )
- a visible photon is a photon having a wavelength of from more than 400 nm to 700 nm (e.g., from 1.8x10 "3 keV to 3x10 "3 keV)
- a UV photon is a photon having a wavelength of more than 10 nm to 400 nm (e.g., from 3.IxIO "3 keV to 125 eV)
- an X-ray photon is a photon having a wavelength of from 0.01 nm to 10 nm (e.g., from 125 eV to 125 keV).
- such photons are e
- the photons can be detected using one or more appropriate detectors capable of detecting photons in a wavelength- resolved or energy-resolved fashion (see discussion above regarding types of detectors). If multiple detectors are used, the detectors may all be the same type of detector, or different types of detectors may be used, and may generally be configured as desired.
- the detectors can be configured to detect photons leaving surface 181 of sample 180 (the surface on which the ion beam impinges), surface 183 of sample 180 (the surface on the opposite side from where the ion beam impinges) or both (see discussion above regarding
- the system can include one or more optical elements (e.g., one or more lenses, one or more mirrors) that are adjacent the surface of the sample and that can direct the photons to the detector can be used (e.g., to increase the effective solid angle of detection of the detected photons).
- optical elements e.g., one or more lenses, one or more mirrors
- detecting the energy and/or wavelength of the photons can yield material constituent information (e.g., elemental information, chemical environment information) about a sample.
- the information is predominantly related to the surface of the sample.
- the photons emitted by the element or material will have a particular energy/band of energies and wavelength/band of wavelengths.
- the energy and wavelength of the photons emitted from a given location on a surface generally depends on the material present at that location.
- the change in the energy or wavelength of the photons as a function of the location of the ion beam on the surface of the sample can be correlated to a change in the element(s) and/or material(s) present at the surface of the sample, providing material constituent information about the surface of the sample.
- material constituent information about the sample can be obtained detecting photons by determining the de-excitation time of the sample material. This can be achieved, for example, by pulsing the ion beam to expose the sample to the ion beam for a brief period, followed by measuring the amount of time it takes to detect the photons, which relates to the de-excitation time of the sample material that emits the photons.
- each element or material in a given chemical environment will have a particular de-excitation time period.
- Crystalline information about a sample can be obtained using photon detection in combination with a polarizer because the polarization of the photons can depend upon the crystal orientation of the material in the sample.
- the polarization of the photons emitted by a sample can be determined, providing information relating to the crystal orientation of the sample.
- the information contained in the detected photons will predominantly be information about the surface of the sample.
- detected photons can contain information relating to the sub-surface region of the sample.
- detected photons can be used to determine optical properties of the sample.
- Photon imaging techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Photon imaging techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. Optionally, this approach can similarly be used for purposes of mask repair.
- Another example of a sample class for which photon imaging techniques can be used is metals and alloys. For example, images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- Yet another example of a sample class where photon imaging techniques can be used is read/write structures for data storage. Additional examples of classes of materials for which photon imaging techniques can be used are biological materials and pharmaceutical materials.
- Imaging samples using photons generated by exposure to a He ion beam can provide a number of advantages relative to photon imaging via other techniques, such as SEM.
- the spot size of the He ion beam on the sample can be smaller than the spot size of an electron beam from a SEM.
- the region of the sample that is exposed to the He ion beam is more carefully controlled than the exposed region in a SEM.
- He ions are heavier than electrons, scattering events do not disperse He ions as readily within the sample as electrons are dispersed by scattering.
- He ions incident on the surface of a sample can interact with the sample in a smaller interaction volume than electrons in a SEM.
- photons detected in a gas field ion microscope e.g., a He ion microscope
- a gas field ion microscope can arise from a smaller region than the region giving rise to photons in a SEM with a similar spot size.
- the photons which are generated by the interaction of the sample and the He ion beam can correspond to a more localized interrogation of the surface of the sample (e.g., with less lateral averaging of material properties) than the photons generated in a SEM.
- the He ion source also provides a greater depth of focus than an electron source.
- images of a sample obtained using an ion microscope e.g., a gas field ion microscope
- Detection of secondary ions from the sample can provide material constituent information about the sample via calculation of the masses of detected particles. In general, this information will correspond to material at the surface of the sample.
- the mass(es) of the secondary ions is(are) determined using a combination of time-of-flight and a mass-resolved detector, such as a quadrupole mass spectrometer.
- a mass-resolved detector such as a quadrupole mass spectrometer.
- Such secondary ion detection can be performed as follows.
- the ion beam is operated in pulsed mode by changing the electrical potentials applied to ion optical elements in the ion optics. Pulses of incident ions are incident on a surface of the sample.
- Secondary ion imaging techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Secondary ion imaging techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. Optionally, this approach can similarly be used for purposes of mask repair.
- sample class for which secondary ion imaging techniques can be used is metals and alloys.
- images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- sample class where secondary ion imaging techniques can be used is read/write structures for data storage.
- materials for which secondary ion imaging techniques can be used are biological materials and pharmaceutical materials.
- a secondary neutral particle is a neutral particle generated when the ion beam interacts with the sample to remove a mono-atomic or poly-atomic species from the sample in an un-charged state. Interactions between the incident ion beam and the sample can produce secondary neutral particles. Typically, this method is more effective when using a noble gas ion of mass greater than He (Ar ions, Ne ions, Kr ions, Xe ions). In general, to access the information available from secondary neutral particles, the particles are ionized (e.g., via laser induced ionization, electron induced ionization) prior to detection.
- Detection of secondary neutral particles (post-ionization) from the sample can provide material constituent information about the sample via calculation of the masses of detected particles. In general, this information will correspond to material at the surface of the sample.
- the mass(es) of the secondary neutral particles (post- ionization) is(are) determined using a combination of time-of-flight and a mass-resolved detector, such as a quadrupole mass spectrometer.
- a mass-resolved detector such as a quadrupole mass spectrometer.
- Such secondary neutral particle (post- ionization) detection can be performed as follows.
- the ion beam is operated in pulsed mode by changing the electrical potentials applied to ion optical elements in the ion optics. Pulses of incident ions are incident on a surface of the sample.
- the mass of the particle can be calculated, and the type chemical species (e.g., atom) can be identified. This information is used to determine material constituent information for the sample.
- Secondary neutral particle imaging techniques can be applied to a variety of different classes of samples.
- An example of such a class of materials is semiconductor articles, such as patterned wafers, which can include, for example, multiple electrical conductors surrounded by a matrix of insulating material.
- Secondary neutral particle imaging techniques can be used to identify defects in the device, such as incomplete electrical connections between conductors, and/or electrical shorts between circuit elements. Optionally, this approach can similarly be used for purposes of mask repair.
- Another example of a sample class for which secondary neutral particle imaging techniques can be used is metals and alloys. For example, images of samples that contain mixed materials such as alloys can be used to determine the surface distribution of each of the materials in the sample.
- Yet another example of a sample class where secondary neutral particle imaging techniques can be used is read/write structures for data storage. Additional examples of classes of materials for which secondary neutral particle imaging techniques can be used are biological materials and pharmaceutical materials.
- Secondary neutral particle are generally not generated when a sample surface is exposed to an electron beam of the type used in conventional SEMs, and thus none of the material constituent information obtainable via detected secondary neutral particle is available with such SEMs. This is a significant advantage of a gas field ion microscope (e.g., a He ion microscope) as described herein relative to a conventional SEM.
- a gas field ion microscope e.g., a He ion microscope
- Semiconductor fabrication typically involves the preparation of an article that includes multiple layers of materials sequentially deposited and processed to form an integrated electronic circuit, an integrated circuit element, and/or a different
- Such articles typically contain various features (e.g., circuit lines formed of electrically conductive material, wells filled with electrically non-conductive material, regions formed of electrically semiconductive material) that are precisely positioned with respect to each other (e.g., generally on the scale of within a few nanometers).
- compositions and related properties can have an important impact on the performance of the article. For example, in certain instances, if one or more of these parameters is outside an appropriate range, the article may be rejected because it cannot function as desired. As a result, it is generally desirable to have very good control over each step during
- the term semiconductor article refers to an integrated electronic circuit, an integrated circuit element, a microelectronic device or an article formed during the process of fabricating an integrated electronic circuit, an integrated circuit element, a microelectronic device.
- a semiconductor article can be a portion of a flat panel display or a photovoltaic cell.
- Regions of a semiconductor article can be formed of different types of material (electrically conductive, electrically non-conductive, electrically semiconductive).
- Exemplary electrically conductive materials include metals, such as aluminum, chromium, nickel, tantalum, titanium, tungsten, and alloys including one or more of these metals (e.g., aluminum-copper alloys).
- Exemplary electrically non-conductive materials include borides, carbides, nitrides, oxides, phosphides, suicides, and sulfides of one or more of the metals (e.g., nickel suicides, tantalum borides, tantalum germaniums, tantalum nitrides, tantalum suicides, tantalum silicon nitrides, and titanium nitrides).
- Exemplary electrically semiconductive materials include silicon, germanium and gallium arsenide.
- a electrically semiconductive material can be doped (p-doped, n-doped) to enhance the electrical conductivity of the material.
- fabrication of a semiconductor article involves sequentially depositing and processing multiple layers of material. Typical steps in the deposition/processing of a given layer of material include imaging the article (e.g., to determine where a desired feature to be formed should be located), depositing an appropriate material (e.g., an electrically conductive material, an electrically
- a photoresist such as a polymer photoresist
- a photoresist is deposited/exposed to appropriate radiation/selectively etched to assist in controlling the location and size of a given feature.
- the photoresist is removed in one or more subsequent process steps, and, in general, the final semiconductor article desirably does not contain an appreciable amount of photoresist.
- the gas field ion microscope (e.g., He ion microscope) described herein can be used to investigate a semiconductor article at various steps (e.g., each step) in the fabrication process.
- the gas field ion microscope e.g., He ion microscope
- the gas field ion microscope can be used to determine topographical information about the surface of the semiconductor article, material constituent information of the surface of the semiconductor article, material constituent information about the sub-surface region of the semiconductor article, crystalline information about the semiconductor article, voltage contrast information about the surface of the semiconductor article, voltage contrast information about a sub-surface region of the sample, magnetic information about the semiconductor article, and/or optical information about the semiconductor article.
- Using an ion microscope or ion beam as described herein can provide a variety of different advantages, which, in general, can reduce the time, cost and/or complexity associated with semiconductor article fabrication.
- Exemplary advantages associated with using the ion microscope or ion beam described herein include relatively high resolution, relatively small spot size, relatively little undesirable sample damage, relatively little undesirable material deposition and/or implantation, relatively high quality imaging in a relatively short time period, relatively high throughput. Certain examples of process steps in semiconductor fabrication are discussed below.
- the patterning step involves exposing the photoresist to a radiation pattern of an appropriate wavelength so that some regions of the photoresist are etch resistant and other regions of the photoresist are not etch resistant.
- the radiation pattern can be formed on the photoresist by forming an image of a mask onto the photoresist or covering certain regions of the photoresist with a mask, and exposing the uncovered regions of the photoresist through the mask.
- an ion beam generated by the interaction of gas atoms with the gas field ion source (e.g., He ion source) described herein can be used to irradiate to pattern the photoresist to create desired etch-resistant regions and non-etch resistant regions. This can be achieved, for example, by rastering the ion beam across the photoresist so that desired regions of material are exposed to the ions (e.g., by turning the ion beam on at regions where exposure of the photoresist to radiation is desired and by turning the ion beam off at regions where exposure of the photoresist to radiation is not desired).
- a semiconductor article can be fabricated in a maskless process.
- the relatively deep penetration depth of ions that can be achieved with the ion beam can further assist in processing relatively thick photoresist materials, as well as assisting in good quality processing of more standard thickness photoresist materials.
- the ion beam has higher resolution relative to what is generally achieved with an electron beam, allowing for the fabrication of smaller sized features with higher precision. Further, ion beam patterning of photoresist can be faster than electron beam patterning of photoresist.
- a focused ion beam is commonly used during the fabrication of a semiconductor article to obtain a sample for inspection.
- Gallium (Ga) ions are commonly used in the FIB.
- a FIB can be used for a variety of reasons, such as cross-sectional imaging through a semiconductor article, circuit editing, failure analysis of a
- a FIB can be used to deposit one or more materials on a sample (e.g., as an ion source in a chemical vapor deposition process).
- the FIB is used to remove material from a semiconductor article via sputtering.
- the FIB is used to slice through a semiconductor article to expose a cross-section of the article for subsequent imaging using the ion microscope.
- the FIB is used to sputter away material from an article to form a trench or via in the article. This technique can be used, for example, to expose portions of the article that are underneath the article's surface.
- a FIB can also be used as a selective sputtering tool to remove portions of a semiconductor article, such as portions of conductive material on the article.
- a FIB is used to cut out a portion of a sample so that the portion can be subsequently analyzed (e.g., using TEM).
- a gas field ion microscope e.g., a He ion microscope
- a cross-beam tool with both a FIB instrument and a gas field ion microscope can be used so that the location of the FIB can be determined using the gas field ion microscope without moving the sample.
- the gas field ion source can be used to image the sample and provide information that can be used to precisely position the FIB as desired.
- Such an arrangement can offer numerous advantages relative to using a SEM to determine location of the FIB.
- a SEM can result in a magnetic field adjacent the sample surface, which can result in isotope separation of the Ga ions, resulting more than one location of the FIB at the sample. In many instances, this problem results in the FIB and SEM being used in series rather than simultaneously. In contrast, however, a gas field ion microscope can be operated in the absence of such a magnetic field, thereby eliminating complications associated with Ga ion isotope separation, while also allowing the FIB and gas field ion microscope to be used
- An additional advantage for using a gas field ion microscope is that it has a longer working ⁇ distance than typically used with a SEM, while still maintaining very good resolution because the ion beam has a smaller virtual source than the electron beam. This can relieve certain spacing constraints that may exist for a tool that combines a FIB instrument and a SEM.
- a further advantage of a gas field ion microscope as described herein is that it can be used to obtain sub-surface information about a sample, which can enhance the ability to precisely locate the FIB, whereas a SEM generally cannot provide such sub-surface information.
- the process generally involves interacting electrons with an activating gas to form a reactive gas that can then participate in chemistry at the surface of a semiconductor article to add material to the surface, remove material from the surface, or both.
- the electrons are generated as secondary electrons resulting from the interaction of a Ga ion beam with the sample and/or the electrons are generated as secondary electrons resulting from the interaction of an electron beam (e.g., produced by a SEM) with the sample.
- an appropriate pumping system can be used to remove undesirable volatile products of the surface chemistry.
- activating gases that can be used to remove material from the surface include Cl 2 , O 2 , 1 2 , XeF 2 , F 2 , CF 4 and H 2 O.
- a surface region formed of chrome, chrome oxide, chrome nitride and/or chrome oxynitride can be at least partially removed by interacting electrons with Cl 2 and/or O 2 , and allowing the resulting chemical species to etch the surface region.
- a surface region formed of a tantalum nitride can be at least partially removed by interacting electrons with XeF 2 , F 2 and/or CF 4 , and allowing the resulting chemical species to etch the surface region.
- a surface region formed of a carbon-containing material can be at least partially removed by interacting electrons with H 2 O and/or O 2 , and allowing the resulting chemical species to etch the surface region.
- An example of an activating gas that can be used to deposit a material on the surface is WF 6 (to deposit W, such as a W plug).
- a gas field ion beam e.g., a He ion beam
- a gas field ion beam can provide improved resolution relative to a Ga ion beam and/or an incident electron beam (e.g., an incident electron beam produced by a SEM), which can allow for the more precise and/or controllable use of the chemistry.
- This can, for example, reduce (e.g., eliminate) the undesirable interaction of ions with certain portions of a sample (e.g., such as can occur with a Ga ion beam where the beam profile has tails that extend to
- An advantage to using an ion beam to remove material is that the material can be removed in a relatively controlled and/or precise manner.
- An additional advantage is that sputtering can be achieved without undesirable implantation of ions (e.g., such as often results when using Ga ion sputtering, where Ga implantation is a common undesired side effect of sputtering).
- voids in certain features or layers may be inadvertently formed.
- the voids can undesirably impact the properties (e.g., electrical, mechanical) of the feature and/or the overall device.
- subsequent processing steps may open the void, and the void may, for example, fill with liquid and/or gaseous components. This can cause corrosion of the underlying structures, particle defects and/or residue defects on the surrounding wafer surface.
- a TiN x protective layer is commonly used to protect an adjacent dielectric material (e.g., boron and phosphor doped silicon glass) from corrosion (e.g., from HF that is liberated during W formation). ' Discontinuities in the TiN x layer can result in significant void formation.
- material e.g., dielectric material
- trenches e.g., relatively high aspect ratio trenches
- void formation can occur during dielectric filling of shallow trench isolation structures.
- voids can be formed during the formation of electrically conductive lines of material (e.g., copper lines), which can result in undesirable reduction in electrical conductance. In some cases, such voids can result in a lack of electrical conductance where electrical conductance is desired.
- electrically conductive lines of material e.g., copper lines
- a gas field ion microscope e.g., a He ion microscope
- a gas field ion microscope can be used to investigate void formation by taking advantage of its ability to provide sub-surface information about a sample, such as a semiconductor article. This property can be used during the semiconductor article fabrication process to determine the existence and/or location of voids. This is a distinct advantage over using an electron beam because an electron beam generally does not provide this kind of sub-surface information for a sample.
- Overlay shift registration generally refers to the alignment of a feature of a given layer of a semiconductor article with a feature in a different layer of the semiconductor article.
- the formation of a semiconductor article generally involves the proper formation of many layers.
- a semiconductor article contains well over 20 layers.
- each layer can contain multiple different features, each of which is desirably located with high precision so that the semiconductor article can function properly.
- a semiconductor article can contain lateral features, such as electrically conductive wires, which are in different layers and connected to each other by a via.
- nm e.g., 75 nm, 50 nm, 25 ⁇ m, 15 ran, 10 nm, nine nm, eight nm, seven nm, six nm, five nm, four nm, three nm, two nm, 1 nm). Misalignment of a single one of these many features can render the entire semiconductor article useless.
- Test structures which are ⁇ m-sized structures (significantly larger than microelectronic circuit feature sizes).
- optical test structures typically cannot be placed intra-dye on a wafer due to the amount of wafer space they occupy.
- the test structures can be placed, for example, nearer to the edges of wafer, but they still occupy valuable space on the wafer surface.
- Optical test structures are also expensive, because they are
- the He ion microscope can permit alignment of circuit features in multiple layers at higher resolution than can typically be achieved using optical test structures.
- overlay shift registration can be performed without using purpose-fabricated test structures (e.g., optical test structures) because, for example, the gas field ion microscope (e.g., He ion microscope) described herein can image sub-surface features of samples, such as semiconductor articles. Accordingly, the wasted space on a wafer taken up by purpose-fabricated test structures (e.g., optical test structures) can be avoided, as well as the associated cost and/or complexity associated with including such test structures.
- Critical dimension measurements frequently involve, e.g., the determination of the length of a patterned feature on a wafer, for example.
- Wafers containing multiple dies, with each die forming a semiconductor article
- Wafers may be selected at random from a fabrication line for inspection, or all wafers on the line can be inspected.
- An imaging instrument can be used to measure selected critical dimensions at a relatively high throughput rate. If the measured critical dimension does not fall within acceptable limits, the wafer may be discarded. If multiple samples originating from a particular fabrication machine have critical dimensions outside acceptable limits, the machine may be taken out of service, or its operating parameters changed.
- He ion microscope systems disclosed herein can be used for critical dimension measurement.
- the He ion beam can be raster-scanned over a region of a wafer, and the resulting image(s) of the wafer can be used to determine the critical dimension(s).
- He ion microscope systems can provide a number of advantages relative to SEMs and other inspection systems.
- He ion microscope images generally exhibit less edge blooming (generally, excessive signal, approaching the point of saturation of the detector, due to enhanced yield at topographic features with slopes nearly parallel to the beam) than comparable SEM images.
- the reduced edge blooming is a result of the smaller interaction volume between He ions and the surface of the sample, relative to the interaction volume of electrons with the surface.
- the incident He ions can be focused to a smaller spot size than a comparable incident electron beam.
- the smaller beam spot size in combination with the smaller interaction volume, results in images of the sample having resolution that is superior to images produced with SEMs, and more accurate determination of critical dimensions of samples.
- the depth of focus of a He ion beam is relatively large compared to a SEM.
- the resolution of sample features at varying depths is more consistent when using an ion beam, as compared to an electron beam. Therefore, using an ion beam can provide information at various sample depths with better and more consistent lateral resolution than can be provided using an electron beam.
- better critical dimension profiles can be achieved using an ion beam than can be achieved with an electron beam.
- the relatively high yield of secondary electrons provided by an ion beam, as compared to an electron beam can result in a relatively high signal to noise ratio for a given current. This can, in turn, allow for sufficient information about the sample to be obtained in a relatively short period of time, increasing throughput for a given current.
- Imaging of the samples for determination of critical dimensions can be performed using scattered He ions. This provides the added advantage of material information in addition to high resolution distance determination.
- a flood gun can be used to prevent excessive charging of the sample surface (see discussion above).
- very low He ion beam currents e.g., 100 fA or less
- the use of low ion currents reduces ion beam-induced damage to certain resist materials.
- wafer samples selected for critical dimension measurement may first need to be sectioned (e.g., to measure a cross-sectional dimension of the sample).
- heavier gases such as Ne and Ar can be used in the ion microscope to form an ion beam which can be used to slice through the sample.
- a Ga- based FIB can be used to section the sample. Then, the microscope system can be purged of these gases and He can be introduced, so that critical dimension measurements are made with a He ion beam, avoiding sample damage during metrology.
- Line edge roughness generally refers to the roughness of the edge of a line of material in a semiconductor article
- line width roughness generally refers to the roughness of the width of a line of material in a semiconductor article. It can be desirable to understand these values to determine whether actual or potential problems exist in a given semiconductor article. For example, if adjacent lines formed of electrically conductive material have edges that bulge outward toward each other, the lines may contact each other resulting in a short.
- line edge roughness and/or line width roughness can be desirable to understand the dimensions of line edge roughness and/or line width roughness to within five nm or less (e.g., four nm or less, three nm or less, two nm or less, one nm or less, 0.9 nm or less, 0.8 nm or less, 0.7 nm or less, 0.6 nm or less, 0.5 nm or less).
- the line edge roughness and/or line edge width is measured multiple times to provide statistical information regarding the size of the feature.
- fabrication tolerances for parameters such as line edge roughness can be very high.
- line edge roughness of semiconductor article features may have to be controlled within 5 nm or less (e.g., within 4 nm or less, within 3 nm or less, within two nm or less, within one nm or less, within 0.5 nm or less, within 0.1 nm or less, within 0.05 nm or less, within 0.01 nm or less).
- wafers When determining line edge roughness and line width roughness, wafers may be selected at random from a fabrication line for inspection, or all wafers on the line can be inspected.
- An imaging instrument can be used to measure line edge roughness and line width roughness at a relatively high throughput rate. If the measured line edge roughness and line width roughness does not fall within acceptable limits, the wafer may be discarded. If multiple samples originating from a particular fabrication machine have line edge roughness and line width roughness outside acceptable limits, the machine may be taken out of service, or its operating parameters may be changed.
- the gas field ion microscope (e.g., He ion microscope) disclosed herein can be used for metrology of line edge roughness and line width roughness.
- the He ion beam can be raster-scanned along the length of a feature, and the resulting information can be used to determine the line edge roughness and line width roughness with relatively high precision.
- He ion microscope systems can provide a number of advantages relative to SEMs and other inspection systems.
- He ion microscope images generally exhibit less edge blooming (generally, excessive signal, approaching the point of saturation of the detector, due to enhanced yield at topographic features with slopes nearly parallel to the beam) than comparable SEM images.
- the reduced edge blooming is a result of the smaller interaction volume between He ions and the surface of the sample, relative to the interaction volume of electrons with the surface.
- the incident He ions can be focused to a smaller spot size than a comparable incident electron beam.
- the smaller beam spot size in combination with the smaller interaction volume, results in images of the sample having resolution that is superior to images produced with SEMs, and more accurate determination of line edge roughnesses and line width roughnesses of samples.
- the depth of focus of a He ion beam is relatively large compared to a SEM.
- the resolution of sample features at varying depths is more consistent when using an ion beam, as compared to an electron beam. Therefore, using an ion beam can provide information at various sample depths with better and more consistent lateral resolution than can be provided using an electron beam.
- better line width profiles than can be achieved using an ion beam than can be achieved with an electron beam.
- the relatively high yield of secondary electrons provided by an ion beam, as compared to an electron beam can result in a relatively high signal to noise ratio for a given current. This can, in turn, allow for sufficient information about the sample to be obtained in a relatively short period of time, increasing throughput for a given current.
- Imaging of the samples for determination of critical dimensions can be performed using scattered He ions. This provides the added advantage of material information in addition to high resolution distance determination.
- a flood gun can be used to prevent excessive charging of the sample surface (see discussion above).
- very low He ion beam currents e.g., 100 fA or less
- the use of low ion currents reduces ion beam-induced damage to certain resist materials.
- wafer samples selected for line edge roughness and line width roughness measurement may first need to be sectioned (e.g., to measure a cross- sectional dimension of the sample).
- heavier gases such as Ne and Ar can interact with a gas field ion source to generate an ion beam which can be used to slice through the sample.
- the microscope system can be purged of these gases and He can be introduced, so that critical dimension measurements are made with a He ion beam, avoiding sample damage during metrology.
- the process of forming a semiconductor article typically involves stacking many different layers of material in a desired fashion, and performing appropriate processes on each layer. Generally, this involves depositing on and/or removing material from a given layer.
- the final semiconductor article includes many different features in different layers (e.g., to form a desired circuit). In general, it is desirable for the features to be properly aligned for the final device to function as desired. Alignment marks are commonly used in semiconductor articles to assist in properly aligning features in a given layer with features in a different layer. However, using alignment marks can add extra steps to the overall fabrication process, and/or can introduce other complexities or expenses to the fabrication process.
- the mere presence of the alignment marks means that there are areas and/or volumes of the semiconductor article that are not available for use (e.g., for the fabrication of active components).
- an ion beam can be used to investigate the sub-surface region of a material. This property can be used to determine the location of certain features in a layer beneath a surface layer, allowing features in different layers of the semiconductor article to be aligned as desired without the use alignment marks.
- the gas field ion microscope (e.g., the He ion microscope) described herein can be used to remove and/or deposit material (e.g., from an electrical circuit) using, for example, the gas assisted chemistry and/or sputtering techniques noted above.
- An advantage of using an ion microscope to perform these processes is that the ion beam can also be used to assess the resulting product to determine, for example, whether the desired material was properly deposited or removed. This can reduce the cost and/or complexity associated with device fabrication, and/or increase the throughput of device fabrication.
- Removal and/or addition of material capabilities can be combined to perform sub-surface circuit repair. To repair a sub-surface defect, material from the device is first removed down to a depth that exposes the defect. The defect is then repaired by either adding or removing material from the device. Finally, the overlying layers of the device are repaired, layer-by- layer, by adding appropriate thicknesses of new material.
- the gas field ion microscope (e.g., the He ion microscope) described herein can provide particular advantages for circuit editing applications including small spot sizes and low ion currents for controlled and highly accurate editing of fabricated devices.
- Photoresist e.g., polymer photoresist, such as poly(methyl methacrylate) (PMMA) or epoxy-based photoresists, allyl diglycol carbonate, or photosensitive glasses
- PMMA poly(methyl methacrylate)
- photosensitive glasses e.g., silicon dioxide, silicon dioxide, or silicon dioxide
- PMMA poly(methyl methacrylate)
- etchant epoxy-based photoresists, allyl diglycol carbonate, or photosensitive glasses
- etching the non-etch resist regions of the material depositing appropriate materials (e.g., one or more electrically conductive materials, one or more non-electrically conductive materials, one or more semiconductive materials), and optionally removing undesired regions of material.
- the patterning step involves exposing the photoresist to a radiation pattern of an appropriate wavelength so that some regions of the photoresist are etch resistant and other regions of the photoresist are not etch resistant.
- the radiation pattern can be formed on the photoresist by forming an image of a mask onto the photoresist or covering certain regions of the photoresist with a mask, and exposing the uncovered regions of the photoresist through the mask.
- Photolithographic masks used to fabricated integrated circuits and other microelectronic devices in the semiconductor industry can be fragile and/or expensive.
- mask fabrication processes can be time-consuming and/or delicate, hi some circumstances, despite the care which is typically used during the manufacturing of such masks, fabrication errors produce mask defects.
- mask defects can arise from handling and general use. If circuits or other devices were produced using the defective masks, the circuits or devices may not operate correctly. Given the time and expense required to fabricate a new mask, it may be more cost-effective to edit a defective mask than to fabricate an entirely new mask.
- Mask defects generally include an excess of mask material in a region of the mask where there should be no material, and/or an absence of mask material where material should be present.
- the gas field ion microscope e.g., the He ion microscope
- the gas field ion microscope described herein may be used to inspect and/or repair a mask.
- the gas field ion microscope e.g., He ion microscope
- the gas field ion microscope can be used to inspect the mask to determine whether a defect and present, and, if a defect is present, where the defect is.
- Many of the various advantageous featured provided by the gas field ion microscope (e.g., He ion microscope) disclosed herein are desirably used to image the mask.
- the article is inspected for potential defects.
- the inspection is performed using an in-line tool which is always running and being fed wafers and that is fully automatic.
- the tool is often used to examine a small area of wafer whether there are regions where a defect will occur. This inspection is performed prior to defect review (see discussion below).
- the goal of defect inspection typically is to determine whether a defect may exist, as opposed to determining the exact nature of a given defect.
- a region of a wafer is analyzed to see whether certain anomalous properties (e.g., voltage contrast properties, topographical properties, material properties) are exhibited by the sample, relative to other regions of the same wafer and/or to regions of other wafers.
- the coordinates e.g., X 5 Y coordinates
- the location of the wafer is more carefully inspected during defect review.
- a gas field ion microscope e.g., a He ion beam
- a gas field ion microscope can be used to gather information about a sample during defect inspection.
- Such a microscope can be used for relatively high throughput and high quality defect inspection.
- the different contrast mechanisms provided by the gas field ion microscope e.g., He ion microscope
- a sample is noted as having a potential defect during defect inspection, that sample is then submitted to defect review where the particular region(s) of the sample having the potential defect is(are) investigated to determine the nature of the defect. Based on this information, modifications to the process may be implemented to reduce the risk of defects in final product.
- defect inspection is conducted at slower speed and higher magnification than defect review, and may be automated or conducted manually to obtain specific information regarding one or more defects. The information is used to attempt to understand why anomalous results were obtained during defect review, and the nature and cause of the defects that gave rise to the anomalous results.
- the gas field ion microscope (e.g., He ion microscope) described herein can be used to investigate a semiconductor article at various steps (e.g., each step) in the fabrication process.
- the gas field ion microscope e.g., He ion microscope
- the gas field ion microscope can be used to determine topographical information about the surface of the semiconductor article, material constituent information of the surface of the semiconductor article, material constituent information about the sub-surface region of the semiconductor article, crystalline information about the semiconductor article, voltage contrast information about the surface of the semiconductor article, voltage contrast information about a sub-surface region of the semiconductor article, magnetic information about the semiconductor article, and/or optical information about the semiconductor article.
- the different contrast mechanisms provided by the He ion microscope can permit visualization of defects that would otherwise not appear using SEM-based techniques.
- Using an ion microscope or ion beam as described herein can provide a variety of different advantages, which, in general, can reduce the time, cost and/or complexity associated with semiconductor article fabrication.
- Exemplary advantages associated with using the ion microscope or ion beam described herein include relatively high resolution, relatively small spot size, relatively little undesirable sample damage, relatively little undesirable material deposition and/or implantation, relatively high quality imaging in a relatively short time period, relatively high throughput.
- He ion microscopes can be used to identify and examine metal corrosion in various devices and material. For example, metal fixtures and devices used in nuclear power plants, military applications, and biomedical applications can undergo corrosion due to the harsh environments in which they are deployed. He ion microscopes can be used to construct images of these and other devices based on the relative abundance of hydrogen (H) in the devices, which serves as reliable indicator of corrosion.
- H hydrogen
- a detector for these ions or atoms is positioned on the back side of a sample, opposite to an incident He ion beam. Exposing the sample to He ions generates scattered H atoms and ions from within the sample, and these scattered H atoms and ions can be detected and used to construct images of the sample. The H abundance images can then be used to assess the extent of corrosion within the sample.
- the small spot size and interaction volume of the He ion beam can result in high resolution H images of the sample to be obtained without damaging the sample.
- a gas field ion microscope e.g., a He ion microscope
- the gas field ion microscope can be used to image immuno-labeled cells and internal cell structures. The microscope can be used in this manner while providing certain advantages disclosed herein.
- a therapeutic agent e.g., small molecule drug
- a crystal e.g., as it comes out of solution. It can be desirable to determine the crystalline structure of the crystallized small molecule because this can, for example, provide information regarding the degree of hydration of the small molecule, which, in turn, can provide information regarding the bioavailability of the small molecule. In certain instances, the crystalline information may turn out to demonstrate that the small molecule is actually in an amorphous (as opposed to crystalline) form, which can also impact the bioavailability of the small molecule.
- a gas field ion microscope e.g., a He ion microscope
- a gas field ion microscope as described herein can be used to determine, for example, topographical information about a biological sample, material constituent information of a surface of a biological sample, material constituent information about the sub-surface region of a biological sample and/or crystalline information about a biological sample.
- the microscope can be used in this manner while providing certain advantages disclosed herein.
- any of the analysis methods described above can be implemented in computer hardware or software, or a combination of both.
- the methods can be
- Program code is applied to input data to perform the functions described herein and generate output information.
- the output information is applied to one or more output devices such as a display monitor.
- Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system.
- the programs can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language.
- the program can run on dedicated integrated circuits preprogrammed for that purpose.
- Each such computer program is preferably stored on a storage medium or device (e.g., ROM or magnetic diskette) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein.
- the computer program can also reside in cache or main memory during program execution.
- the analysis methods can also be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein.
- a SEM can be used in one or more of the preceding embodiments in combination with a gas field ion microscope.
- a SEM can be used to produce secondary electrons, Auger electrons, X-ray photons, IR photons, visible photons and/or UV photons.
- a SEM can be used to promote gas assisted chemistry.
- the gas field ion microscope can be configured in any of the operating modes disclosed herein, so that the SEM and the gas field ion microscope perform complementary functions.
- crystallographic orientations of W can also be used in a tip.
- a W(112), W(110) or W(IOO) tip may be used.
- a 25 mm length of emitter wire formed of single crystal W(111) was obtained from FEI Company (Hillsboro, OR). The emitter wire was trimmed to a 3 mm length and set aside.
- a V-shaped heater wire was prepared as follows. A 13 mm length of polycrystalline tungsten wire (diameter 180 ⁇ m) was obtained from Goodfellow (Devon, PA) and cleaned by sonication for 15 minutes in distilled water to remove the carbon residue and other impurities. The wire was bent at its midpoint to form an angle of 115 degrees.
- the region near the apex of the "V" was electrochemically etched to prepare it for welding in a IN aqueous solution of sodium hydroxide (NaOH) with an applied AC potential of 1 V and frequency 60 Hz for a duration of approximately 15 seconds.
- NaOH sodium hydroxide
- the heater wire was then removed from the etching solution, rinsed with distilled water, and dried.
- the V-shaped heater wire was mounted in a fixture to ensure that the ends of the wire remained coplanar.
- the emitter wire was spot welded to the V-shaped apex of the heater wire.
- the two ends of the heater wire were spot welded to two posts of a support base of the type shown in FIGS. 1 IA and 1 IB.
- the support base was obtained from AEI Corporation (Irvine, CA). The resulting assembly was then cleaned
- the end of the emitter wire was etched by an electrochemical process as follows.
- a resist material e.g., nail polish obtained from Revlon Corporation, New York, NY
- a drop of resist was placed on the surface of a clean glass microscope slide, and the wire was dipped ten times into the resist solution, allowing the resist to dry slightly between each dipping. Care was taken to assure that the upper boundary of the resist was in the shape of a circle, and that the plane of the circle was maintained perpendicular to the axis of the wire.
- the wire was allowed to dry for 1 hour in air.
- the support base with the resist-coated emitter wire attached was then attached to an etching fixture that included: (a) a translation apparatus for vertically translating the support base; (b) a dish; and (c) a counter electrode, formed of stainless steel to minimize undesired chemical reactions, that extended into the dish.
- the dish was filled with an etching solution to a level such that the solution was in contact with the counter electrode. Approximately 150 mL of solution was present in the etching fixture dish.
- the orientation of the support base was adjusted to ensure that the longitudinal axis of the emitter wire was approximately parallel to the vertical direction (e.g., the direction along which the translation apparatus provided for translation of the support base).
- the support base was lowered toward the dish using the translation apparatus until the exposed emitter wire just contacted the etching solution.
- a high magnification camera mounted to the etching fixture allowed the resist layer and etching solution surface to be seen easily, and permitted accurate positioning of the emitter wire with respect to the solution surface.
- the wire was lowered an additional 0.2 mm into the etching solution. In this position, the resist coated portion of the emitter wire was fully immersed in etching solution.
- the etching solution consisted of 150 mL of 2.5 M aqueous NaOH. To facilitate wetting, 1 drop of surfactant (PhotoFlo 200, obtained from Eastman Kodak, Rochester, NY) was added to the etching solution. Gentle stirring of the etching solution using a magnetic stirrer was also employed during the etching process.
- surfactant PhotoFlo 200, obtained from Eastman Kodak, Rochester, NY
- An external power supply was connected to the support base posts and the counter electrode.
- the voltage maximum amplitude, pulse duration, and waveform shape of the external power supply could be controlled to provide particular etching conditions in the etching fixture.
- a sequence of AC pulses at a frequency of 60 Hz was applied to the emitter wire to facilitate the electrochemical etching process.
- Portions of the emitter wire which were immersed in solution but not covered by resist material began to etch away. Because the emitter wire was positioned so that only a small uncoated region of the wire above the edge of the photoresist material was immersed in solution, localized etching of the emitter wire in this region was observed. As the electrochemical reaction proceeded, the diameter of the wire in this region began to get narrower due to the etching process.
- the pulse duration of the external power supply was adjusted to 325 ms, and sixty pulses of this duration were applied to the emitter wire over a total time window of 5 minutes. These pulses further promoted the electrochemical etching process, resulting in an etched region of the emitter wire with a very small diameter.
- the pulse duration of the external power supply was adjusted to 35 ms, and individual pulses were applied to the emitter wire until etching was complete and the resist-coated portion of the emitter wire dropped off into the etching solution.
- the support base was then removed from the etching fixture, rinsed with distilled water, and dried under a flow of nitrogen.
- the emitter wire - still attached to the support base - was then examined using a
- the support base was installed in a sample region of the SEM, on a sample manipulator equipped with a tilt and rotate manual stage. Images of the source were acquired from several different observation perspectives and magnifications to verify that the tip was approximately correctly shaped.
- the SEM images were then used to characterize the average full cone angle, the average tip radius, and average cone direction, as discussed previously of the apex of the tip of the wire.
- the images used for these measurements were taken at a magnification of 65,000 X, and along a viewing axis oriented at right angles to the axis of the emitter wire.
- the emitter wire tilt was adjusted using the SEM sample manipulator to ensure that the emitter wire was oriented orthogonally with respect to the viewing axis.
- the SEM sample manipulator was used to rotate the tip by 45° (about the axis of the emitter wire) between successive images.
- FIGS. 37A-37D This yielded a set of eight images of the tip - each from a different perspective - which were then used to determine the cone angle, radius of curvature, and cone direction of the tip.
- Four of the eight perspective images are shown in FIGS. 37A-37D.
- Each of the SEM images was digitized into bitmap format and then analyzed using custom algorithms developed using the MathCAD software package (PTC Inc., Needham, MA).
- MathCAD software package PTC Inc., Needham, MA
- each of the images was smoothed by applying a Gaussian convolution algorithm to reduce image noise, particularly noise due to vibrations of the SEM that occurred during imaging.
- a filtering step based upon a threshold intensity value was then applied to each of the images to emphasize the boundary between the tungsten tip and the black background.
- the tip boundary in each image was then determined as the set of nonzero-intensity (X 5 Y) points that formed a demarcation between image pixels corresponding to the tip and image pixels corresponding to the black (e.g., zero-intensity) background.
- One such set of (X, Y) points for one of the views of the tip is shown in FIG. 38. Similar sets of boundary points were determined for each of the eight perspective views of the tip.
- a smoothing algorithm was applied to the curve to ensure that the local slope of the curve was relatively insensitive to noise and other small signal variations.
- the smoothing algorithm consisted of fitting the raw (X 5 Y) data points to a fourth-order polynomial, which has been found to describe the shape of the tip well. The effect of the smoothing algorithm was to ensure that, on either side of the apex position, the first derivative of this curve is not excessively influenced by small variations in the shape.
- the position on the boundary curve corresponding to that view where the slope acquired a zero value was identified as the tip apex and given the label X ape ⁇ .
- the position on the boundary curve corresponding to the (X, Y) point, closest to the tip apex, where the slope of the boundary curve acquired a value of 1 was given the label X +1 .
- the position on the boundary curve corresponding to the (X, Y) point, closest to the tip apex, where the slope of the boundary curve acquired a value of -1 was given the label X -1 .
- the left radius of the tip in a particular view was calculated as the absolute value of the difference between X +1 and X apex5 multiplied by 1.414.
- the right radius of the tip in a particular view was calculated as the absolute value of the difference between X -1 and X apex , multiplied by 1.414.
- the radius of curvature of the tip in a particular view was calculated as the average of the left radius and the right radius values.
- the calculations of the right radius, left radius, and tip radius of curvature were repeated for each of the eight perspective views of the tip.
- the average tip radius was then calculated as the average of the tip radius of curvature measurements in all of the views of the tip.
- the average tip radius was determined to be 62 nm.
- the standard deviation of all of the tip left and right radii was also calculated, and expressed as a percentage of the average tip radius.
- the eccentricity was determined to be 11.9%.
- the cone angle of the tip in each of the eight perspective views was also determined.
- left and right tangent points on the boundary curve were located on the left and right sides of the tip apex, respectively, at positions 1 ⁇ m from the tip apex, measured along the Y direction, as discussed previously.
- the left cone angle of the tip in a particular view was then determined as the angle between a tangent to the boundary curve at the left tangent point and a line parallel to the Y axis and extending through the left tangent point.
- the right cone angle of the tip in a particular view was determined as the angle between a tangent to the boundary curve at the right tangent point and a line parallel to the Y axis and extending through the right tangent point. Finally, the full cone angle was determined as the sum of the magnitudes of the left and right cone angles.
- the average full cone angle of the tip was then determined by calculating the average of the eight measurements of the full cone angle of the tip from the eight perspective views of the tip. For the tip shown in FIGS. 37A-37D, for example, the average full cone angle was determined to be 34.5°.
- the cone direction was calculated as the half of the absolute value of the difference between the magnitudes of the left and right cone angles. Repeating this determination for each of the eight views of the tip yielded eight measurements of the cone direction of the tip. The average cone direction of the tip was then calculated as the average of these eight measurements of the cone direction. For the tip shown in FIGS. 37A-37B, the average cone direction was determined to be 2.1°.
- a set of criteria based on the measurements of average tip radius, radius eccentricity, average cone angle, and average cone direction were used to determine whether a given tip would be accepted for use in the He ion microscope. In general, these criteria were as follows.
- the tip was accepted for use if the measured average cone angle was between 15° and 45°, the average tip radius was between 35 nm and 110 nni, the standard deviation of the tip radius of curvature measurements was less than 30%, and the average cone direction was less than 7°.
- the tip shown in FIGS. 37A-37D satisfied each of these criteria, and so this tip was accepted for use in the He ion microscope.
- the tip was inspected in a custom-built FIM.
- the FIM included a mounting area for the support assembly supporting the tip, a high voltage power supply for biasing the tip, an extractor adjacent to the tip, and a detector for recording ion emission patterns from the tip.
- the extractor was spaced from the tip by a distance of 5 mm and had an opening of 10 mm.
- the extractor was grounded to an external ground.
- the detector a combination microchannel plate (MCP) and image intensif ⁇ er (obtained from Burle Electro-Optics Inc., Sturbridge, MA) was positioned at a distance of 75 mm from the extractor.
- MCP microchannel plate
- image intensif ⁇ er obtained from Burle Electro-Optics Inc., Sturbridge, MA
- the support assembly including the tip was installed in the FIM and the FIM chamber was evacuated to a background pressure of 1x10 " Torr.
- the tip was cooled to 77 K using liquid nitrogen as a coolant.
- the source was heated to 900 K for 5 minutes to desorb condensates or other impurities that had formed on the tip during processing. Heating of the tip was accomplished by applying an electrical current to the heater wire to which the tip was welded. The current was applied using a power supply with constant power capabilities (Bertan Model IB-30A, available from Spellman High Voltage Inc., Hauppauge, NY). Temperature measurements were made using an optical pyrometer (obtained from Pyro Corporation, Windsor, NJ).
- the tip was sharpened to obtain a terminal atomic trimer at the tip apex.
- Helium gas was pumped out of the FIM chamber until the background pressure in the chamber was less than 1.2x10 "8 Torr.
- the tip was then heated, via application of current to the heater wires as described above, to a temperature of 1500 K for 2 minutes.
- Oxygen gas was introduced into the FIM chamber in the vicinity of the tip at a pressure of 1x10 "5 Torr. After 2 minutes, the tip temperature was reduced to 1100 K. After 2 minutes at 1100 K, the oxygen supply was shut off and the tip was allowed to cool to approximately 77 K. During cooling, and about 15 minutes after the oxygen supply was shut off, the residual oxygen gas was pumped out of the FIM chamber until the background pressure in the chamber was less than 1.2xlO "8 Torr.
- the extractor was biased as above, and the tip was again biased at +5 kV relative to the extractor.
- He gas at a pressure of IxIO "5 Torr was introduced into the FIM chamber, and the FIM was once again operated as described above to acquire He emission images of the tip.
- the tip voltage was
- the observed FIM pattern included adatoms - extra atoms in addition to the desired three atom trimer structure at the tip apex.
- the adatoms were slowly removed by field evaporation at the tip bias potential of +18 kV. During field evaporation, images of the tip were captured periodically and monitored to determine when to halt the field evaporation process. The adatoms were removed one by one until a clear FIM image of an atomic trimer at the tip apex was observed. In addition to the atomic trimer, the ridges of a 3 sided pyramid were also clearly observed.
- the atomic trimer was slowly removed by further field evaporation of the tip. By increasing the tip bias slowly beyond +18 kV, the trimer atoms were removed one by one, resulting in rounded tip that was observed in FIM images recorded by the detector.
- the tip bias potential was further increased up to +28 kV. Field evaporation of the tip atoms continued during this process.
- a bias potential of +28 kV another atomic trimer was obtained at the apex of the tip.
- a FIM image of the second trimer is shown in FIG. 40.
- the tip bias potential was reduced to attain the highest angular intensity in the FIM emission pattern. This occurred at a tip bias of +23 kV.
- the highest angular intensity was determined by adjusting the tip bias to obtain the largest observed brightness of a selected atom in the FIM emission pattern.
- the bias at which the highest angular emission intensity occurred was verified by measuring the He ion current from the trimer as the potential bias of the tip was adjusted. The He ion current was measured using a Faraday cup positioned in the path of the He ion beam.
- the tip was then blunted to a nearly spherical end-shape by slowly increasing the bias potential of the tip above +28 kV and field evaporating atoms from the tip apex. Field evaporation was continued until another atomic trimer was obtained at the surface of the tip at a bias potential of +34 kV. To verify the repeatability of the tip re-building procedure, the sharpening process was repeated twice more to obtain new atomic trimers at the tip apex. After two successive trimer re-builds, the Helium gas supply was shut off, the applied tip bias was removed, the tip was allowed to warm to room temperature, and the FIM chamber pressure was slowly equalized to atmospheric pressure. The tip, still mounted in the support assembly, was stored on a shelf for a period of 2 weeks until it was used in a helium ion microscope.
- the support assembly including the tip was installed in a helium ion microscope system similar to the system shown in FIGS. 1 and 5.
- the elements of the system were configured as follows.
- the extractor was positioned 1 mm from the tip, and had an opening of diameter 3 mm.
- the first lens of the ion optics was positioned at a distance 30 mm from the extractor. After passing through the first lens, ions passed through the alignment deflectors, which were configured as quadrupole electrodes.
- An aperture with an opening of diameter of 20 ⁇ m was positioned further along the path of the ions to selectively block a portion of the ion beam.
- a cross-over point of the ion trajectories was positioned at a distance of 50 mm in front of the aperture.
- the astigmatism corrector configured as an octupole electrode, was positioned after the aperture to adjust
- the ion microscope system was evacuated so that the base pressure in the tip area was about 2xlO "9 Torr.
- the tip was cooled to about 80 K using liquid nitrogen.
- the extractor was grounded, and a bias of +5 kV, relative to the extractor, was then applied to the tip.
- the tip was heated by applying electrical power of 8 W to the heater wire, until it was visibly glowing (corresponding to a tip temperature of about 1100 K). Photons emitted from the glowing tip were observed from a side port of the ion optics, using a mirror tilted at 45° with respect to a plane perpendicular to the longitudinal axis of the ion optics. The mirror was introduced for this purpose into the ion optics, in a position just below the alignment deflectors, via a side port in the ion column. The tip was tilted and shifted iteratively until the glowing tip was aimed roughly along the longitudinal axis of the ion optics. Proper alignment of the tip with the longitudinal axis was achieved when the glowing tip appeared as a circular point source. The tip was misaligned if it appeared to be rod-shaped.
- the tip was allowed to cool while maintaining the tip at a potential bias of +5 kV relative to the extractor. Once the tip had cooled to liquid nitrogen temperature, He gas was introduced into the tip region at a pressure of IxIO "5 Torr.
- the ion microscope system was run in SFIM mode, as described above, to generate an image showing the He ion emission pattern of the tip. The image indicated the shape of the tip to atomic precision.
- the alignment electrodes were used to raster the ion beam generated from the tip over the surface of the aperture.
- Sawtooth voltage functions were applied to each of the alignment deflectors to achieve rastering at a frame rate of 10 Hz, with a maximum voltage of the sawtooth functions of 150 V relative to the common external ground of the microscope system.
- the raster pattern scanned 256 points in each of two orthogonal directions transverse to the axis of the ion optics. The astigmatism corrector and the scanning deflectors were not used in this imaging mode.
- the acquisition system sampled the detector signal at each raster point and generated a SFIM image of the tip, which was displayed on a monitor.
- the potential of the first lens in the ion column was set to be 77% of the tip bias.
- the SFIM image was maintained with roughly constant magnification and intensity.
- the tip bias was slowly increased to eliminate undesired adatoms and to produce a tip with an atomic trimer at its apex. This trimer was removed by further increasing the tip bias potential to cause field evaporation of the tip atoms. Field evaporation continued until a new atomic trimer was fo ⁇ ned on the apex of the tip at an applied tip potential of +23 kV.
- the resulting SFIM image of this tip is shown in FIG. 41.
- one atom of the trimer was selected and the tip was tilted and translated while the strength of the first lens was modulated by 100 V.
- the microscope system was operated in FIM mode and the detector collected FIM emission images of the tip.
- the tip was tilted and translated iteratively until the position of the center of the tip on the FIM images was unchanged from one image to another when the strength of the first lens was modulated.
- the aperture was put in place and the potentials applied to the alignment deflectors were adjusted to control the position of the ion beam at the aperture.
- the portion of the ion beam transmitted through the aperture was imaged by the detector, and the detector images were used to iteratively adjust the alignment deflectors.
- the scanning deflectors were used to raster the ion beam transmitted through the aperture over the surface of the sample.
- a recognizable, high contrast feature (a copper grid) on the surface of the sample (part number 02299C-AB, obtained from Structure Probe International, West Chester, PA) was placed in the path of the ion beam under the second lens, and secondary electron images of the feature were measured by the detector using the configuration discussed above.
- the strength of the second lens was adjusted to roughly focus the ion beam on the sample surface; the potential bias applied to the second lens was about 15 kV, relative to the common external ground. The quality of the focus was assessed visually from the images of the sample recorded by the detector.
- the alignment of the ion beam with respect to the axis of the second lens was evaluated by slowly modulating the strength of the second lens— at a frequency of 1 Hz and an modulation amplitude of about 0.1% of the operating voltage of the second lens - and observing the displacement of the feature.
- the beam alignment in the final lens was optimized by adjusting the voltages of the alignment deflectors. The alignment was optimized when the position of the center of the image measured by the detector did not change significantly during modulation of the strength of the second lens.
- the sample was imaged at a higher magnification by adjusting the strength of the second lens, so that the field of view on the sample was about 2 ⁇ m square.
- the asymmetry of the focus was minimized by adjusting the astigmatism corrector controls. These controls were adjusted while observing the image and specifically the sharpness of edges in all directions.
- the astigmatism correction was complete when the sharpness of the focused image was the same in all directions. Typically, no more than 30 volts were applied to the astigmatism corrector to achieve this condition. At this point, the helium ion microscope was fully operational.
- the imaging conditions included a wide range of beam currents (100 pA to 1 fA).
- the beam current was controlled by several methods. First, different apertures with different diameter holes were put into position using a motorized aperture mechanism. The aperture mechanism included apertures whose diameters ranged from 5 ⁇ m to 100 ⁇ m. Second, the first lens focus strength was adjusted to move the beam crossover closer to the aperture plane in the ion optics so that a larger ion current reached the sample.
- the first lens focus strength was adjusted to move the beam further from the aperture plane so that less ion current passed through the aperture.
- the helium gas pressure in the tip region was increased or decreased to increase or decrease the ion beam current, respectively.
- the beam energy was typically selected for best angular intensity; the beam energy was typically in a range from 17 keV to 30 keV.
- the beam energy changed over time in response to the changing shape of the tip.
- the type of detector used, and the detector's settings, were selected according to the type of sample that was examined with the ion microscope.
- an ET detector was used with a metal grid biased at about +300 V relative to the common external ground.
- a scintillator internal to the ET detector was biased at +10 kV relative to the external ground, and the gain of the internal PMT adjusted to produce the largest possible signal without saturation.
- a MCP detector obtained from Burle Electro-Optics, Sturbridge, MA was also used to detect secondary electrons and/or scattered He from samples.
- the MCP grid, front face, and back face could each be biased relative to the external ground.
- the gain of the detector was attained by biasing the back face of the MCP positive with respect to the front end. Typical gain voltages were 1.5 kV. A collector plate adjacent to the back face was biased at +50 V with respect to the back face. From the collector plate, the detection signal was in the form of a small varying current which was superimposed on the large positive voltage. For collection of secondary electrons, the front face and grid of the MCP were biased to +300 V. For collection of scattered He, the front face and grid were biased to -300 V.
- the image shown in FIG. 42 is an image of a plurality of carbon nanotubes on a silicon substrate.
- the image was acquired by detecting secondary electrons from the surfaces of the nanotubes.
- An ET detector was positioned at a distance of 8 mm from the sample and 15 mm off-axis from the ion beam, and oriented at an angle of 20° with respect to the plane of the sample.
- the He ion beam current was 0.5 pA and the average ion energy was 21 keV.
- the ion beam was raster-scanned with a dwell time of 200 ⁇ s per pixel, and the total image acquisition time was 200 s.
- the field of view of the image was 4 ⁇ m.
- the image shown in FIG. 43 is an image of an aluminum post on a silicon substrate.
- the image was acquired by detecting secondary electrons from the surfaces of the nanotubes.
- the He ion beam current was 0.5 p A and the average ion energy was 24 keV.
- the ion beam was raster-scanned with a dwell time of 200 ⁇ s per pixel.
- the field of view at the surface of the sample was 1 ⁇ m, obtained by applying a maximum voltage of 1 V to the scanning deflectors.
- a W(111) tip was mounted in a support assembly and electrochemically etched following the procedure described in Example 1.
- a SEM image of the tip is shown in FIG. 46.
- Geometrical characterization of the tip was performed according to the procedure in Example 1. For this tip, the average tip radius was determined to be 70 nm. The tip was accepted for use based on the criteria in Example 1.
- the source assembly including the etched tip was installed into the FIM described in
- the tip was sharpened to produce an atomic trimer at the apex.
- Helium was pumped out of the FIM chamber, and the tip was heated by applying a constant current of 4.3 A to the tip for 20 seconds.
- a tilted mirror installed in the FIM column and angled to re-direct light propagating along the column axis to a side port of the column, was used to observed the tip. No glow (e.g., photons emitted from the tip) was visible to the eye, so the tip was allowed to cool for 5 minutes.
- the tip was heated by applying a constant current of 4.4 A to the tip for 20 seconds. No glow was visible to the eye, so the tip was allowed to cool for 5 minutes.
- the tip was heated by applying a constant current of 4.5 A to the tip for 20 seconds. No glow was visible to the eye, so the tip was allowed to cool for 5 minutes. Then the tip was heated by applying a constant current of 4.6 A to the tip for 20 seconds. At this temperature, a glow was clearly visible from the tip. Thus, the current necessary to induce tip glow was established to be 4.6 A. The source was then allowed to cool for 5 minutes.
- a negative bias was applied to the tip while monitoring electron emission current from the tip.
- the bias was made increasingly negative until an electron emission current of 50 pA from the tip was observed.
- the tip bias at this current was -1.98 kV.
- the heating current of 4.6 A was applied to the tip.
- Tip glow was again observed after about 20 seconds. Heating of the tip extended another 10 seconds after tip glow was observed.
- the bias potential and heating current applied to the tip were then removed from the tip, and the tip was allowed to cool to liquid nitrogen temperature.
- Scan voltages of maximum amplitude 1 V were introduced on the scanning deflectors to produce a 10 ⁇ m field of view on the sample.
- the potentials of the first and second lenses, the alignment deflectors, and the astigmatism corrector were adjusted to control the portion of the He ion beam that passed through the aperture, and to control the quality of the beam focus at the sample position, as described in Example 1.
- the sample was tilted and rotated during imaging to reveal the three dimensional nature and the details of the sidewalls.
- the image shown in FIG. 51 was recorded by measuring secondary electrons from the surface of the sample.
- a MCP detector was positioned at a distance of 10 mm from the sample, and oriented parallel to the surface of the sample.
- the MCP grid and front surface were biased at +300 V, relative to the common external ground.
- the He ion beam current was 4 pA and the average ion energy was 21.5 keV.
- the total image acquisition time was 30 s.
- FIG. 52 An image of another semiconductor sample taken using this tip is shown in FIG. 52.
- the sample was a multilayer semiconductor device with surface features formed of a metal.
- the image was recorded by measuring secondary electrons that left the sample of the sample due to the interaction of the sample with the incident He ions. Maximum scan voltages of 150 volts were applied to the scanning deflectors to produce a 1.35 mm field of view at the sample surface.
- the sample was observed from a top down perspective, which shows many features on the surface of the sample.
- a MCP detector with grid and front surface biased at +300 V relative to the common external ground was positioned at a distance 10 mm from the sample, and oriented parallel to the surface of the sample.
- the He ion beam current was 15 pA and the average ion energy was 21.5 keV.
- the ion beam was raster-scanned with a dwell time of 10 ⁇ s per pixel. 3.
- the tip in this example was prepared and aligned in the helium ion microscope using a procedure as described in Example 2. Geometrical characterization of the tip was performed according to the procedure in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the sample was a gold grid sample with topographic features (part number 02899G-AB, obtained from Structure Probe International, West Chester, PA).
- the sample was imaged by measuring secondary electron emission from the sample surface in response to incident He ions.
- a 40 mm diameter annual, chevron-type MCP detector (obtained from Burle Electro-Optics, Sturbridge, MA) was positioned at a distance 10 mm from the sample, and oriented parallel to the surface of the sample. The detector consumed a solid angle of about 1.8 steradians and was symmetric with respect to the ion beam. The detector was mounted directly to the bottom of the second lens, as shown in FIG. 66.
- the front surface of the MCP was biased positively (+300 V) with respect to the common external ground, and there was also a positively biased (with respect to the common external ground) internal metal grid (+300 V).
- the image size was 1024x1024 pixels.
- the image size was 512x512 pixels.
- maximum scan voltages of about 2 V were applied to the scanning deflectors to produce a 20 ⁇ m field of view at the sample surface.
- a tip was mounted in a support assembly and fabricated using methods as described in Example 1, except that in the support assembly, the two posts attached to the source base were pre-bent towards each other, as shown in FIG. 56.
- the bend permitted the heater wire to span a significantly shorter length.
- the heater wire was as described in Example 1 , a polycrystalline tungsten wire with a diameter of 180 ⁇ m. With the bent posts, a heater wire length of 5 mm was used. The advantage of a shorter heater wire length that the stiffness of a length of wire increases as the length of the wire decreases.
- the emitter wire was affixed in the usual way as described in Example 1.
- the increased stiffness of the shorter heater wire was observed by applying the same force to a two different tips, one mounted in a support assembly of the type described in Example 1, and the other mounted in the support assembly shown in FIG. 56.
- the deflections of the two tips in response to the applied force were compared.
- the bent post support assembly was deflected by an amount that was a factor of 6 smaller. Consequently the natural vibration frequency of the bent post-type support assembly (approximately 4 kHz) was about 2.5 times higher than the natural frequency of the support assembly of Example 1.
- the support base and the tip moved in unison (e.g., with negligible phase shift) when excited at vibrational frequencies substantially below the natural vibration frequency.
- the relatively low vibration of the tip in the bent post source assembly reduced the likelihood that ion microscope images would have appreciable image artifacts, such as beam landing errors, due to tip vibrations.
- a tip was prepared according to the procedure described in Example 1, except that a different heater wire was used.
- the heater wire used in this example had a diameter that was larger than the diameter of the heater wire in Example 1 by about 25%.
- the thicker heater wire was less compliant with respect to vibrational motion, because, in general, the stiffness of a wire increases with increasing diameter.
- the thicker heater wire was formed from a tungsten-rhenium alloy (74% Tungsten, 26% Rhenium).
- the alloy wire had a significantly higher electrical resistivity than the tungsten heater wire of Example 1; the overall heater wire resistance was measured to be approximately 0.5 ohms.
- Suitable tungsten-rhenium alloy wires were obtained from Omega Engineering (Stamford, CT).
- the thicker heater wire increased the natural frequency of the support assembly, including the tip, from about 1.5 kHz (Example 1) to about 2.2 kHz (this example).
- the relatively low vibration of the tip in the source assembly with this heater wire assembly reduced the likelihood that ion microscope images would have appreciable image artifacts, such as beam landing errors, due to tip vibrations.
- a tip was formed by a process as described in Example 1 , except that the heater wire was replaced by blocks of pyrolytic carbon (obtained from MINTEQ International Pyrogenics Group, Easton, PA).
- the posts of the source assembly were bent towards one another and were machined to have parallel flat surfaces.
- To mount the emitter wire the posts were pried apart and two blocks of pyrolytic carbon were inserted between the posts.
- the emitter wire was placed between the carbon blocks and then the posts were released.
- the compressive force applied to the carbon blocks by the posts held the blocks and the emitter wire in place on the support assembly, preventing relative motion of the emitter wire with respect to the support base.
- a portion of the support assembly, including the bent posts, the two carbon blocks, and the emitter wire, is shown in FIG. 57.
- the size of the pyrolytic carbon blocks was chosen so that the carbon blocks and the emitter wire were in compression. Without the carbon blocks in place, the space between the bent posts was 1.5 mm.
- the carbon blocks each had a length 700 ⁇ m along a direction between the two bent posts.
- the emitter wire had a diameter of 250 ⁇ m.
- the pyrolytic carbon blocks were oriented with respect to the bent posts for maximum electrical resistance and minimum thermal conductivity (e.g., with carbon planes in the pyrolytic carbon blocks oriented approximately perpendicular to a line joining the posts).
- the electrical resistance of the support assembly was measured to be 4.94 ohms at 1500 K 5 which is larger than the resistance of the support assembly of Example 1 (0.56 ohms).
- the power required to heat the tip to 1500 K was 6.4 W
- Example 1 (compared to about 11 W required to heat the tip in Example 1 to 1500 K).
- the tip was held relatively rigid with respect to the source base, due to the absence of a heater wire.
- the natural vibration frequency of the support assembly was greater than 3 kHz.
- a tip was prepared following a procedure as described in Example 1, and characterization of geometrical tip properties was performed in as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1, with changes to the configuration noted below.
- the microscope system was configured to measure secondary electrons that left the sample due to the interaction of the sample with the incident He ions.
- a MCP detector (similarly configured to the detector described in Example 3) was used to record sample images.
- the sample was steel, and was spherical in shape and of uniform composition.
- the He ion beam current was 1.0 pA and the average ion energy was 20 keV.
- the ion beam was raster-scanned with a dwell time of 10 ⁇ s per pixel.
- the maximum potentials applied to the scanning deflectors (about 100 V) yielded a field of view at the surface of the sample of about 1 mm.
- FIG. 58 An image of the sample is shown in FIG. 58.
- the image reflects a measurement of the total secondary electron yield for the sample.
- the image reveals enhanced secondary electron yield at the right-hand edge.
- the enhanced yield resulted from the increased path length of the ion beam near the surface of the sample, where secondary electrons can escape.
- the secondary electron yield was found to increase approximately in proportion to sec( ⁇ ), where ⁇ represents the angle between the incident He ion beam and a normal to the surface of the sample.
- FIGS. 59A and 59B Images of a second sample are shown in FIGS. 59A and 59B.
- the imaging conditions for the sample shown in FIG. 59A were as discussed above in connection with the first sample in this example.
- the He ion beam penetrated deeply into the sample (about 100 nm) before diverging significantly.
- the edges of sample images showed a relatively narrower bright edge effect (e.g., reduced edge blooming).
- the image in FIG. 59A was recorded from the He ion microscope, while the image in FIG. 59B was recorded using a standard SEM. In both images, the signal arises from a measurement of secondary electrons only.
- the SEM image shown in FIG. 59B the SEM was operated under imaging conditions which were 2 keV electron beam energy and 30 pA beam current.
- the bright edges were observed to be appreciably narrower in the He ion microscope images, which is believed to be a consequence of the smaller interaction volume of He ions at the surface of the sample in comparison to incident electrons.
- the He ion beam remains relatively collimated as it passes into the sample.
- the SEM' s electron beam yields an interaction volume which is considerably wider immediately adjacent to the surface of the sample.
- secondary electrons generated by the incident electron beam arise from a surface region that extends several nanometers from the nominal electron beam position on the surface. Consequently, the SEM's bright edge effect was substantially wider, as can be seen by visually comparing the images in FIGS. 59A and 59B.
- FIGS. 67 A and 67B which correspond to FIGS. 59 A and 59B, respectively.
- the line scan area was 1 pixel wide by 50 pixels long.
- the intensity peak in the line scan— which corresponds to the edge feature - has a full width at half-maximum (FWHM) that is 40% wider in the SEM image than in the corresponding He ion microscope image.
- FWHM half-maximum
- the reduced edge width observed in the He ion microscope image is a result of the smaller interaction volume of He ions at the surface of the sample, relative to electrons.
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1.
- the tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- Each experiment began with a measurement of the He ion current by positioning the He ion beam such that it was incident on the Faraday cup in each sample. Next, the He ion beam was rastered over the sample while a variable bias, relative to the common external ground, was applied to the screen, and the secondary electron current from the sample was measured.
- the He ion beam was intentionally defocused (to a spot size of 100 nm) to minimize any contamination or charging artifacts.
- the screen bias potential was adjusted in increments from -30 V to +30 V, and the secondary electron current was measured for each bias potential. Each measurement was conducted with a He ion beam energy of 22.5 keV and a beam current of 13 pA.
- the graph in FIG. 60 shows the results for a silicon sample. On the left of the graph, where the screen was biased negatively, all of the secondary electrons that left the sample due to the interaction of the sample with the incident He ions were returned to the silicon sample. The He ion beam current and the secondary electron current were approximately equal, so that negligible amounts of free secondary ions and scattered helium ions were produced.
- FIG. 61 A is a secondary electron image of an alignment cross on the surface of a substrate, recorded using the helium ion microscope. Scan voltages of maximum amplitude of about 1.5 V were introduced on the scanning deflectors to produce a 15 ⁇ m field of view on the sample. A MCP detector was positioned at a distance of 10 mm from the sample, and oriented parallel to the surface of the sample. The grid and front face of the MCP were biased at +300 V, relative to the common external ground. The He ion beam current was 5 pA and the average ion energy was 27 keV. The ion beam was raster-scanned with a dwell time of 150 ⁇ s per pixel.
- the He ion microscope image shows greater contrast between the different materials that form the alignment cross because of the larger differences in secondary electron yield for an incident He ion beam, relative to an incident electron beam.
- the two materials in the alignment cross can readily be distinguished visually in the image of FIG. 61 A. However, as observed qualitatively in FIG. 6 IB, the two materials have similar secondary electron yields for the incident electron beam of the SEM.
- a tip was prepared following a procedure as described in Example 1, and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1. The tip was then installed and configured in the He ion microscope. The microscope system was configured as described in Example 1, with changes to the configuration noted below.
- Regions of the sample were positively biased due both to arriving positive charges from the incident He ion beam, and to departing negative charges (secondary electrons).
- the magnitude of the induced voltage bias on the sample for a given He ion beam current was dependent upon the electrical capacitance and/or resistance of the exposed region of the sample, relative to the surrounding portions of the sample. These differences lead to different secondary electron collection for different regions of the sample, according to capacitive and/or resistive properties of the sample.
- the differences in detected secondary collection produces contrast in images of the sample recorded using the He ion microscope. In this manner, electrical properties of the sample were determined based on secondary electron images.
- the sample image shows a series of bright, periodic aluminum lines. In the spaces between these bright lines are a series of darker lines. The middle bright line in the image shows a distinct boundary, beyond which the line is dark. Based on the nature of the sample, the bright lines have a low resistance path to ground, or perhaps a very high capacitance relative to ground, and hence they were not substantially biased due to . the action of the He ion beam.
- the dark lines were biased positively under the influence of the He ion beam, and hence the secondary electrons produced there returned back to the sample. To determine whether this effect was due to the capacitive or resistive properties of the dark lines, the dark lines were observed over a period of time under the He ion beam. If the effect was capacitive in nature, the lines became increasingly dark over time.
- FIG. 63 shows an image of another sample recorded using the measurement configuration described above.
- the sample includes lines and other features formed of copper on a silicon substrate. The smallest features are in the form of letters ("DRAIN").
- the positive potential bias on these features increased over the course of image acquisition, as evidenced by the observation that the top of each character appears bright while the bottom of each character appears dark.
- the raster scan in this image proceeded from top to bottom. As a result, biasing mechanism on the surface features of the sample is primarily capacitive. 10.
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1, with changes to the configuration noted below.
- the microscope system was configured to measure secondary electrons that left the sample due to the interaction of the sample with the incident He ions.
- a MCP detector (as described in Example 3) was used to record sample images.
- the front end of the MCP was biased to +300 V, relative to the common external ground, as was the grid in front of it. In this configuration, the measured signal arose almost entirely from secondary electrons. This was verified by biasing the MCP front end to -300 V, without changing the MCP gain, and observing that the measured signal was diminished to nearly zero.
- Scan voltages of maximum amplitude 3 V were introduced on the scanning deflectors to produce a 30 ⁇ m field of view on the sample.
- the He ion beam current was 10 pA and the average ion energy was 22 keV.
- the ion beam was raster-scanned with a dwell time of 100 ⁇ s per pixel.
- the top most metal layer consisted of patterned lines formed of copper.
- the next layer consisted of a dielectric material.
- the bottom layer consisted of another, differently patterned metal layer formed of copper.
- the image of the sample is shown in FIG. 64.
- the image clearly shows the topmost metal layer pattern in bright white, superimposed upon grey image features that correspond to the bottom (sub-surface) metal layer.
- the sub-surface metal layer appears both dimmer and slightly blurred in the image.
- the measured signal was the result of secondary electrons generated at the surface of the sample by both scattered He ions and neutral He atoms. This assessment was verified by biasing the MCP and screen negative and noting that almost no signal was detected. Secondary electrons that left the sample due to the interaction of the sample with the incident He ions produced the image of the surface metal layer in FIG. 64. The image of the sub-surface metal layer is produced He ions that have penetrated into the sample and become neutralized. The neutral He atoms scatter from the sub-surface layer, and a fraction of them return to the surface where they produce secondary electrons upon their exit. This accounts for the blurred and dimmed image of the sub-surface features.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1, with changes to the configuration noted below.
- the microscope system was configured to measure secondary electrons that left the sample due to the interaction of the sample with the incident He ions.
- a MCP detector (as described in Example 3) was used to record sample images.
- the front end of the MCP was biased to +300 V, relative to the common external ground, as was the grid in front of it. In this configuration, the measured signal arose almost entirely from secondary electrons. This was verified by biasing the MCP front end to -300 V, without changing the MCP gain, and observing that the measured signal was diminished to nearly zero.
- Scan voltages of maximum amplitude 15 V were introduced on the scanning deflectors to produce a 150 ⁇ m field of view on the sample.
- the He ion beam current was 10 pA and the average ion energy was 21.5 keV.
- the ion beam was raster-scanned with a dwell time of 100 ⁇ s per pixel.
- the sample that was imaged consisted of a piece of a tungsten weld.
- the tungsten had been heated to above its melting point and had subsequently cooled, forming distinct crystallographic domains, with abrupt boundaries between crystal grains.
- the sample was imaged by measuring secondary electrons that left the sample due to the interaction of the sample with the incident He ions.
- FIG. 65 An image of the sample is shown in FIG. 65.
- the image shows distinctly brighter and darker grains.
- the bright features correspond to surface topographic relief patterns, which enhance secondary electron production due to the topographic effects disclosed herein.
- the contrasting image intensities of the various crystal grains were due to the relative orientations of the crystal domains with respect to the incident He ion beam.
- the scattering probability at the surface was low, and so the ion beam penetrated deeply into the grain.
- the secondary electron yield at the surface of the material was relatively lower, and the grain appeared darker in the image.
- the tungsten lattice in a particular grain was oriented so that the He ion beam was incident upon a high index
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1 , with changes to the configuration noted below.
- Scan voltages of maximum amplitude 15 V were introduced on the scanning deflectors to produce a 150 ⁇ m field of view on the sample.
- the He ion beam current was 10 pA and the average ion energy was 21.5 keV.
- the ion beam was raster-scanned with a dwell time of 100 ⁇ s per pixel.
- the sample was imaged by detecting the abundance of He atoms and He ions incident on the MCP.
- An image of the sample obtained using this measurement procedure is shown in FIG. 68.
- the image shows both bright and dark grains.
- tungsten lattice in the grain was oriented so that the He ion beam was incident along a relatively low index crystallographic direction, there was a low probability of He scattering at the surface of the grain.
- the He ions or He neutral atoms, produced when He ions combine with an electron in the sample
- Grains having these properties appeared dark in the recorded image.
- topographic information in the image of FIG. 68 was significantly reduced because the image was recorded based on scattered He particles, rather than on secondary electrons.
- the series of bright lines that appeared on the image in FIG. 65 were largely removed from the image in FIG. 68.
- the absence of topographic information can make the image in FIG. 68 relatively easier to interpret, especially where the measured intensities in FIG. 68 are used to quantitatively identify the crystallographic properties (such as the relative orientation) of crystalline domains in the sample.
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1 , with changes to the configuration noted below.
- the detector was positioned at a distance of 30 mm from the sample.
- the motor permitted rotation of the MCP detector with respect to the sample to detect He ions and/or neutral atoms leaving the sample surface at a range of different angles. Typically, for example, the motor permitted rotation of the MCP through approximately 180°.
- the sample was a copper ball of diameter of approximately 1 mm.
- the motor was positioned relative to the sample such that the sample was located along the axis of the motor shaft.
- the copper ball sample when exposed to the He ion beam, provided scattered He ions and neutral He atoms at a wide range of angles, due to the shape of the sample surface. That is, by scanning the incident He ion beam across the surface of the sample, a variety of different angles of incidence (e.g., the angle between the He ion beam and a normal to the sample surface) can be realized. For example at the center of the copper ball, the angle of incidence of the He ion beam is 0°. At the edge of the ball (as observed from the perspective of the He ion beam), the angle of incidence is
- the angle of incidence is approximately 30° from simple trigonometry.
- the sample was positioned under the He ion beam, and the detector was positioned with respect to the sample as described above.
- the He ion beam current was 15 pA, and the average ion energy in the He ion beam was 25 keV.
- a maximum voltage of 100 V was applied to the scanning deflectors to achieve a 1 mm field of view at the surface of the sample.
- the distance from the second lens of the microscope system to the sample (e.g., the working distance) was 75 mm. This provided enough open space to allow the MCP detector to rotate with respect to the sample.
- the measurements were performed by recording images of the copper ball while the detector was swept through a 180° range of angles in a hemispherical arc with respect to the sample.
- the He ion beam effectively partitioned the surface of the sample into two sides and, due to the convex surface of the copper ball, scattered He ions and neutral He particles could only be detected from the side on which the detector was positioned.
- the intensity profile of the image of the sample appears crescent- shaped, with the bright region on the left corresponding to the position of the detector.
- the right side of the sample was relatively dark, since scattered He ions and neutral He particles left the surface of the sample in directions such that they could not be measured by the detector.
- FIGS. 69B and 69C correspond to images of the sample recorded with the detector positioned nearly directly above the sample and on the right side of the sample, respectively.
- FIG. 69C a crescent-shaped intensity profile is observed that is analogous to the profile observed in FIG. 69A.
- topographic information about the sample could be determined from images measured with the detector in off-axis positions (e.g., FIGS. 69A and 69C).
- the information acquired from these measurements could be combined with secondary electron measurements of the sample, for example, to ascertain whether image contrast observed in the secondary electron images was due to the surface topography of the sample, or due to another contrast mechanism such as sample charging or material composition.
- the detector With the detector in a known position, it was possible, based on the recorded images, to distinguish a bump on the surface of the sample from a depression.
- the small detector acceptance angle and the known position of the detector for each recorded image could also be used to determine quantitative surface relief (e.g., height) information for the sample by measuring the shadow lengths of surface features in the image and making use of the known angle of the incident He ion beam with respect to the surface features.
- quantitative surface relief e.g., height
- Images of the sample also revealed that, depending upon the orientation of the detector with respect to the sample, certain edges of the sample exhibited a bright edge effect, while other edges exhibited a dark edge effect (see FIG. 69 A, for example).
- This information was used in the design of a detector that was configured to reduce the measurement of topographic information from a sample. The detector design balanced the detection angles to provide a nearly uniform edge effect. As a result, images of a sample such as a copper ball would appear uniformly bright, with variations in intensity arising from material differences in the sample.
- FIG. 7OA shows an image of the sample recorded with the detector nearly on-axis with the incident He ion beam; that is, the detector measured scattered He ions and neutral He atoms at an angle of approximately 0°.
- a region of the sample surface denoted by the rectangular box, was isolated in a series of images and subjected to further analysis.
- the thick horizontal line schematically represents the surface of the sample, and the thin vertical represents the incident He ion beam.
- the dots represent the average measured intensity of scattered He ions and neutral He atoms at various detector positions. The dots are plotted on a polar scale, where the origin of the polar plot is the point of incidence of the He ion beam on the surface of the sample.
- the angular position of a given dot corresponds to the angular position of the detector, and the radial distance from the origin to each dot represents the average measured intensity at that particular angular detector position.
- Each dot corresponds to an image recorded at a different detector position.
- FIG. 71 A an image of the sample is shown with a superimposed rectangular box denoting a different region of the sample surface that was analyzed using multiple sample images to determine the angular intensity distribution of scattered He ions and neutral atoms from the sample.
- the scattering or emission angle was about 40° with respect to the incident He ion beam.
- the polar plot of angular emission intensity shown in FIG. 71B was constructed in the manner described in connection with FIG. 7OB above.
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1, with changes to the configuration noted below.
- the microscope system was configured to measure He ions and neutral He atoms scattered from a sample in response to incident He ions.
- a MCP detector (as described in Example 3) was used to record sample images.
- the front end of the MCP was biased to - 300 V, relative to the common external ground, as was the grid in front of it. hi this configuration, secondary electrons do not reach the MCP due the negative applied potential bias.
- the signal measured by the MCP arises from scattered He ions and neutral He atoms that are incident on the front face of the MCP. From the sample's perspective, the MCP detected He ions and He atoms from within a solid angle of approximately 1.8 steradians. The solid angle was azimuthally symmetric with respect to the incident beam as shown in FIG. 66.
- the bright and dark edge effects observed for the copper ball sample provided information regarding the design and configuration of a detector which, when used to image a sample by measuring scattered He ions and/or neutral He atoms, reduced the amount of topographic information in the measured signals, and more accurately reflected differences in material composition rather than differences in local surface topography of the sample.
- a reduction in topographic information in images formed based on measurements of scattered He ions and neutral He atoms was observed if the MCP was positioned at a working distance of approximately 25 mm from the sample.
- Samples that included different materials could then be imaged and the materials reliably distinguished visually from one another.
- a sample that included four different materials - a nickel base layer, a carbon coating, a copper grid, and a gold wire - was imaged using the He ion microscope.
- the He ion beam current was 1.1 pA and the average He ion energy was 18 keV.
- Maximum voltages of 4 V were applied to the scanning deflectors to realized a field of view at the sample surface of 40 ⁇ m.
- the total image acquisition time was 90 s.
- the resulting image is shown in FIG. 72.
- Different intensities were observed for each of the four different materials in the sample. This is a consequence of the fact that the scattering probability a He ions incident upon a particular material depends upon the atomic number of the material.
- even materials with similar atomic numbers can be distinguished. For example, copper (atomic number 29) is distinguishable visually from nickel (atomic number 28).
- FIG. 73 shows an image of a sample that includes a copper layer underlying a silicon wafer, with an oxide layer overlying the wafer.
- the image was measured using a He ion microscope system configured for detection of scattered He ions and neutral He atoms as described earlier in this example.
- the sample includes surface structural features that were produced by directing a laser to be incident on the sample surface. The laser caused an explosive eruption of the underlying copper layer.
- Visual inspection of the image reveals image contrast (e.g., image intensity variations) that result from the different materials present in the sample. From images such as the image in FIG. 73, the distribution of different materials in a sample can be determined. 75.
- a tip was prepared following a procedure as described in Example 1, and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1 , with changes to the configuration noted below.
- the microscope system was configured to measure photons emitted from a sample in response to the incident He ion beam.
- An image of the sample was constructed from the signal generated by a photomultiplier tube (model R6095, Hamamatsu Photonics K.K., Toyooka, Japan).
- the photomultiplier tube had an end-on window, a relatively high quantum efficiency, and a broad spectral response from 200 nm to 700 nm.
- the tube was operated with a signal gain that could be increased up to 1200 V, or to the point where the output signal reached the signal chain's white noise level without excessive saturation.
- the photomultiplier tube was positioned at a distance of 15 mm from the sample and was oriented to face the sample, hi this configuration, the tube subtended a solid angle of about 2 steradians.
- a sample of sodium chloride (NaCl) was imaged using the photomultiplier tube detector.
- the He ion beam current was 10 pA and the average He ion energy was 25 keV.
- the sample was raster-scanned with a dwell time per pixel of 500 ⁇ s.
- a maximum voltage of 150 V was applied to the scanning deflectors to yield a field of view at the sample surface of 1.35 mm.
- Photons can be produced in the sample via two different mechanisms. First, photons can be produced via processes that are analogous to the cathodoluminescence that is observed in SEM images. In this mechanism, atoms of the sample are excited to higher-lying energy states. Photons are emitted during the subsequent de-excitation process. When the He ions from the incident beam return to lower-lying energy states, photons are emitted.
- a tip was prepared following a procedure as described in Example 1 , and characterization of geometrical tip properties was performed as described in Example 1.
- the tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was biased at +19 kV, relative to the extractor, and He gas was introduced in the vicinity of the tip at a pressure of 2x 10 ⁇ 5 Torr.
- a Faraday cup was placed beyond the second lens, and the first lens and alignment deflectors were used to focus the beam so that substantially all of the He ions originating from one of the tip trimer atoms passed through the aperture (diameter 600 ⁇ m, positioned 370 mm from the tip), and substantially all of the He ions originating from the other two trimer atoms were blocked by the aperture.
- the He ion beam was focused by the first lens into the Faraday cup. hi this configuration, the astigmatism corrector, the scanning deflectors, and the second lens were off.
- the total He ion current originating from the tip atom was measured to be 300 pA using a pico-ammeter (model 487, Keithley Instruments, Cleveland, OH) together with the Faraday cup.
- the Faraday cup was a cylindrical metal cup with a depth-to-diameter ratio of about 6 to 1.
- each of the He ions generated at the tip continued to travel in a straight line, diverging from the tip.
- the aperture intercepted most of the He ion beam and allowed only a small central portion of it to pass further down the remainder of the ion column.
- the portion of the He ion beam that passed through the aperture was detected with the Faraday cup, yielding a measured He ion current of 5 pA passing through the aperture.
- the angular intensity of the He ion beam was then calculated as the He ion beam current passing through the aperture (5 pA) divided by the solid angle of the aperture from the perspective of the tip.
- the corresponding solid angle was calculated as 2.1 x 10 "6 steradians (sr). Based upon the solid angle, the angular intensity of the He ion beam was determined to be 2.42 ⁇ A /sr.
- the brightness of the He ion source was determined from the He ion beam angular intensity and the virtual source size.
- the virtual source size was estimated by examining a FIM image of the tip recorded during sharpening of the tip. From this image, it was evident that individual ionization discs corresponding to the tip trimer atoms were not overlapping. Further, it was known from the crystallography of tungsten that the trimer atoms were separated by approximately 5 Angstroms. Therefore, the actual ionization disks were estimated to have a diameter of about 3 Angstroms.
- the virtual source size is generally smaller than the actual ionization area.
- the virtual source size was determined using the general procedure discussed previously: by back-projecting asymptotic trajectories of 100 He ions once the ions were beyond the electric field region (e.g., the region in the vicinity of the tip and the extractor) of the ion source.
- the back-projected trajectories moved closer to one another until they passed through a region of space in which they were most closely spaced with respect to one another, and then they diverged again.
- the circular diameter of the closest spacing of the back-projected trajectories was defined to be the virtual source size.
- the virtual source size can be considerably smaller.
- the brightness of the ion source was 3.4 x lO 9 A/cm 2 sr.
- the reduced brightness was calculated as the brightness divided by the voltage used to extract the beam (e.g., the voltage bias applied to the tip).
- the tip to extractor voltage was 19 kV, and the reduced brightness was 1.8 x 10 9 A/m 2 srV.
- the etendue is a measure of the product of the He ion beam's virtual source size and its angular divergence (as a solid angle). Using the brightness determined above, the etendue was determined to be 1.5 x 10 "21 cm 2 sr. The reduced etendue is the etendue multiplied by the He ion beam voltage. The reduced etendue, based on the etendue calculated above, was determined (using the tip bias voltage of +19 kV) to be 2.8 x 10 "17 cm 2 srV. 17.
- a tip was prepared following a procedure as described in Example 1, and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the tip was sharpened in the FIM using the procedure described in Example 1.
- the tip was then installed and configured in the He ion microscope.
- the microscope system was configured as described in Example 1, with changes to the configuration noted below.
- the microscope system was configured to measure secondary electrons using an ET detector.
- the detector was positioned at a distance of 10 mm vertically (parallel to the He ion beam) from the sample, displaced 25 mm laterally from the sample, and inclined towards the sample.
- the ET screen was biased at a potential of +300 V, relative to the common external ground.
- the He ion beam current was 1 pA, and the average ion energy in the beam was 22 keV.
- the He ion beam was raster-scanned across the surface of the sample with a dwell time per pixel of 100 ⁇ s.
- a maximum voltage of 100 mV was applied to the scanning deflectors to yield a field of view of 1000 nm on the surface of the sample.
- FIG. 77 shows a graph on which pixel intensity values for one particular line (line #14) before smoothing (dots) and after smoothing (curve) are plotted.
- the vertical axis corresponds to the image intensity, ranging from 0 (black) to 255 (white).
- the horizontal axis corresponds to the pixel number, ranging from 0 (left edge) to 57 (right edge).
- the center of the left to right light-to-dark transition was determined by locating the minimum value of the first derivative of the intensity line scan. For edges with a left to right dark-to-light transition, the center of the transition would have been found by determining the location of the maximum value of the first derivative of the intensity line scan.
- Each line was then trimmed to contain just 21 pixels.
- the trimming operation such that the transition point, the 10 pixels preceding the transition point, and the 10 pixels following the transition point were retained in each line.
- Intensity values for the first five pixels in each trimmed line were averaged together and the average was identified as the 100% value.
- Intensity values for the final five pixels in each trimmed line were averaged together and the average was identified as the 0% value.
- the smoothed data from each line scan was then rescaled in terms of the 100% and 0% values.
- the rescaled data from FIG. 77 is shown in FIG. 78.
- the 75% and 25% values were determined with reference to the 0% and 100% values.
- the spot size of the He ion beam was subsequently determined as the separation along the horizontal axis between the 25% and 75% values. Based upon the data in FIG. 78, the spot size was determined to be 3.0 pixels. The pixel size was converted to nanometers using the known field of view in the measurement configuration and the number of pixels in the image. For this measurement, the field of view was 641 run, and there were 656 pixels spanning the field of view. The spot size of the He ion beam was therefore determined to be 2.93 nm. This was repeated for each of the 20 lines in the selected region of the image, and the results were averaged to yield a mean He ion beam spot size of 2.44 nm.
- a tip was prepared following a procedure as described in Example 1, and characterization of geometrical tip properties was performed as described in Example 1. The tip was accepted for use based on the criteria in Example 1.
- the microscope system was configured to measure scattered He ions and neutral He atoms leaving a sample surface in response to incident He ions.
- a MCP detector as described in Example 3 was positioned 10 mm from the sample.
- a potential bias of 0 V relative to the external ground was applied to the MCP grid and front face.
- FIG. 79 shows an image of the sample recorded using the measurement configuration described above.
- Various features on the surface of the sample have measured intensities which are relatively uniform, and different from the intensity of the substrate.
- Visual inspection of the edges of the surface features reveals that there are no apparent bright edge effects (e.g., edge blooming) which can lead to saturation of the signal chain, and can make the precise location of the edge difficult to find.
- edge blooming e.g., edge blooming
- FIG. 80 A horizontal line scan through one of the sample's surface features is shown in FIG. 80.
- the horizontal axis of the line scan shows the pixel number, and the vertical axis indicates the measured image intensity at particular pixels.
- the same sample was imaged in a Schottky Field Emission SEM (AMRAY model 1860) with a beam energy of 3 keV and a beam current of 30 pA, at a magnification of 30,000 X (corresponding to a field of view of about 13 um).
- the resulting image is shown in FIG. 81, and a horizontal line scan through the same feature that was scanned in FIG. 80 is shown in FIG. 82.
- Multiple measurements of a particular feature on the surface of the sample could also have been performed. If multiple measurements of a feature were made, it would have been possible to ascertain statistical data about the dimensions of the measured feature. For example, the mean feature width, the standard deviation of the feature width, and/or the mean and standard deviation of the location of the first edge and/or the second edge of the feature could have been measured. Fourier methods could also have been used to analyze the positions of the edges of one or more features to determine the spectrum of spatial wavelengths corresponding to the edge shapes.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured to expose a 100 ⁇ m 2 FOV on the surface of the sample to a He ion beam having a beam current of 1 pA, an average ion energy of 20 keV, and a beam spot size on the surface of the sample of 0.1% of the FOV.
- the He ion beam is raster- scanned in discrete steps over the FOV region of the sample surface.
- a two-dimensional detector is used to capture an image of scattered He ions from the surface of the sample at each step.
- Each two-dimensional image corresponds to a Kikuchi pattern at a particular position on the surface of the sample. Based on the Kikuchi pattern, the sample's crystal structure, lattice spacing, and crystal orientation at that position can be determined.
- Kikuchi patterns By measuring Kikuchi patterns at discrete steps throughout the FOV, a complete map of the sample's surface crystal structure is obtained.
- a detector is configured to measure a total intensity of secondary electrons from the sample produced in response to the incident He ion beam.
- the He ion beam is raster-scanned in discrete steps over the entire FOV region of the sample surface, and the total intensity of secondary electrons is measured as a function of the position of the He ion beam on the sample surface.
- the measured crystalline information is then used to remove contributions to the secondary electron intensity measurements that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the corrected intensities of secondary electrons at a corresponding He ion beam position on the sample.
- Topographic information is provided by the image, which shows the surface relief pattern of the sample in the FOV.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- the He ion beam is raster- scanned in discrete steps over the FOV region of the sample surface.
- a detector is used to measured a total abundance of scattered He ions as a function of the position of the He ion beam on the sample surface.
- the measured total abundance values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the total measured abundance of He ions at a corresponding He ion beam position on the sample.
- Differently-oriented crystal grains at the surface of the sample have different yields of scattered He ions, and the image shows the differently-oriented crystal grains as variable gray levels. Using the information in the image, crystal grains and grain boundaries can be identified at the sample surface.
- the total secondary electron intensity is measured as described in Example 19.
- the measured crystalline information is then used to remove contributions to the secondary electron intensity measurements that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the corrected intensities of secondary electrons at a corresponding He ion beam position on the sample.
- Topographic information is provided by the image, which shows the surface relief pattern of the sample in the FOV.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- the He ion beam is raster- scanned in discrete steps over the FOV region of the sample surface.
- a detector is used to measured a total abundance of scattered He ions as a function of the position of the He ion beam on the sample surface.
- the measured total abundance values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the total measured abundance of He ions at a corresponding He ion beam position on the sample.
- Differently-oriented crystal grains at the surface of the sample have different yields of scattered He ions, and the image shows the differently-oriented crystal grains as variable gray levels. Using the information in the image, crystal grains and grain boundaries can be identified at the sample surface.
- the He ion beam is scanned from one grain to another on the surface of the sample.
- a two- dimensional detector is used to capture an image of scattered he ions from the surface of the sample.
- Each two-dimensional image corresponds to a Kikuchi pattern for a particular crystal grain at the surface of the sample. Based on the Kikuchi pattern, the grain's crystal structure, lattice spacing, and crystal orientation can be determined. By measuring a single Kikuchi pattern for each grain rather than at each pixel throughout the FOV, a complete map of the sample's surface crystal structure is obtained in a shorter time.
- the total secondary electron intensity is measured as described in Example 19.
- the measured crystalline information is then used to remove contributions to the secondary electron intensity measurements that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the corrected intensities of secondary electrons at a corresponding He ion beam position on the sample.
- Topographic information is provided by the image, which shows the surface relief pattern of the sample in the FOV.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- Crystalline information from the sample is measured as described in Example 19.
- a detector is configured to measure a total intensity of secondary electrons from the sample produced in response to the incident He ion beam.
- the sample is tilted with respect to the He ion beam, so that the He ion beam is incident at a non-normal angle to the surface of the sample.
- the He ion beam is raster-scanned in discrete steps over the entire FOV region of the sample surface, and the total intensity of secondary electrons is measured as a function of the position of the He ion beam on the sample surface.
- the measured crystalline information is then used to remove contributions to the secondary electron intensity measurements that arise from crystal structure variations in the sample.
- the corrected total intensity values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the corrected total intensities of secondary electrons at a corresponding He ion beam position on the sample.
- Topographic information is provided by the image, which shows the surface relief pattern of the sample in the FOV. Tilting the sample with respect to the He ion beam can reveal topographic information that would otherwise remain hidden if the He ion beam was incident on the sample surface only at normal angles.
- the sample tilt can then be adjusted so that the He ion beam is incident at a different non-normal angle to the surface of the sample, and the He ion beam is raster- scanned is discrete steps over the entire FOV region of the sample surface.
- the total intensity of secondary electrons is measured as a function of the position of the He ion beam on the sample surface, and the measured crystalline information is used to remove contributions to the secondary electron intensity measurements that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct a second grayscale image of the sample corresponding to the second non-normal incidence angle of the He ion beam, where the gray level at a particular image pixel is determined by the corrected total intensities of secondary electrons at a
- Crystalline information from the sample is measured as described in Example 20.
- the total intensity of secondary electrons from the sample is measured as described in Example 22.
- the measured crystalline information is used to remove contributions to the secondary electron intensity measurements, at each ion beam angle of incidence, that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct grayscale images of the sample as described in Example 22.
- the information from the two images measured at different He ion beam angles of incidence can then be combined and used to determine quantitative three-dimensional topographic information about the surface of the sample.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 192.
- Crystalline information from the sample is measured as described in Example 21.
- the total intensity of secondary electrons from the sample is measured as described in Example 22.
- the measured crystalline information is used to remove contributions to the secondary electron intensity measurements, at each ion beam angle of incidence, that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct grayscale images of the sample as described in Example 22.
- the information from the two images measured at different He ion beam angles of incidence can then be combined and used to determine quantitative three-dimensional topographic information about the surface of the sample.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- the corrected total intensity values are used to construct a series of grayscale images of the sample, each image corresponding to one of the detectors, where the gray level at a particular pixel in a particular image is determined by the corrected total intensity of secondary electrons at a corresponding He ion beam position on the sample.
- Information from the images measured by the multiple detectors can then be combined and used to determine quantitative three-dimensional topographic information about the surface of the sample.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- Crystalline information from the sample is measured as described in Example 20.
- To measure topographic information from the sample the total intensity of secondary electrons from the sample is measured as described in Example 25.
- the measured crystalline information is used to remove contributions to the secondary electron intensity measurements, at each detector, that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct grayscale images of the sample as described in Example 25. Information from the images measured by the multiple detectors can then be combined and used to determine quantitative three-dimensional topographic information about the surface of the sample. 27. Measurement of Topographic and Crystalline Information from a Sample
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- Crystalline information from the sample is measured as described in Example 21.
- To measure topographic information from the sample the total intensity of secondary electrons from the sample is measured as described in Example 25.
- the measured crystalline information is used to remove contributions to the secondary electron intensity measurements, at each detector, that arise from crystal structure variations in the sample.
- the corrected total secondary electron intensity values are used to construct grayscale images of the sample as described in Example 25. Information from the images measured by the multiple detectors can then be combined and used to determine quantitative three-dimensional topographic information about the surface of the sample.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- Crystalline information from the sample is measured as described in Example 19.
- a detector configured to measure He ions is positioned to detect He ions scattered from the surface of the sample at large scattering angles.
- the He ion beam is raster-scanned in discrete steps over the entire FOV region of the sample surface, and the total abundance of He ions is measured by the detector as a function of the position of the He ion beam on the sample surface.
- the total abundance values are used to construct a grayscale image of the sample, where the gray level at a particular image pixel is determined by the total measured abundance of scattered He ions at a corresponding He ion beam position on the sample.
- Topographic information is provided by the image, which shows the surface relief pattern of the sample in the FOV.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
- Crystalline information from the sample is measured as described in Example 20.
- Topographic information from the sample is measured as described in Example 28.
- the sample is fixed in position on a sample mount in a gas field ion microscope as described herein.
- the gas field ion microscope is configured as described in Example 19.
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Abstract
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EP11183110.3A EP2416344B1 (en) | 2005-12-02 | 2006-11-15 | Ion sources, systems and methods |
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US78450006P | 2006-03-20 | 2006-03-20 | |
US11/385,215 US7601953B2 (en) | 2006-03-20 | 2006-03-20 | Systems and methods for a gas field ion microscope |
US11/385,136 US20070228287A1 (en) | 2006-03-20 | 2006-03-20 | Systems and methods for a gas field ionization source |
US79580606P | 2006-04-28 | 2006-04-28 | |
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EP11183110.3A Not-in-force EP2416344B1 (en) | 2005-12-02 | 2006-11-15 | Ion sources, systems and methods |
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EP06837735.7A Not-in-force EP1955351B1 (en) | 2005-12-02 | 2006-11-15 | Sample manipulator, ion sources, systems and methods of use |
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