Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
  • H01J37/3174—Particle-beam lithography, e.g. electron beam lithography
  • H01J37/3177—Multi-beam, e.g. fly's eye, comb probe
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
  • H01J37/10—Lenses
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
  • H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/22—Optical, image processing or photographic arrangements associated with the tube

Definitions

• Charged particle optical system comprising an electrostatic deflector
• the present invention relates to a charged particle optical system comprising an electrostatic deflector for the deflection of at least one beamlet of charged particles, which deflector comprises a first and a second electrode between which the said beamlet passes, which beamlet is deflected upon setting a potential difference between the electrodes.
• the invention further relates to the use of such charged particle optical system
• One such charged particle system is known from US6, 897,458.
• This system is a maskless lithography system.
• a beam of charged particles such as electrons
• the beamlets are subsequently focused to a desired diameter and pass a beamlet blanker array comprising blanking electrostatic deflectors.
• a beamlet is deflected so as to terminate at a beamlet stop array located behind the beamlet blanker array. Without deflection, the beamlet reaches a set of lenses to focus the beamlet on the target surface.
• Scanning deflection means move the beamlets together in one direction over the target surface.
• Electrostatic deflectors may be used for the blanking deflectors and the scanning deflectors in such a maskless lithography system and in other high-speed deflection applications. Typical examples are oscilloscope tubes, electron beam lithography systems and inspection systems, and streak cameras.
• a common type of electrostatic deflector is a planar deflector, which comprises two parallel plates with opposite voltages +V and -V. An electric field is therewith generated in the (x-) direction normal to the plates. Such planar deflector deflects a beam in one direction only.
• the disadvantage of planar deflectors is that x and y deflections must be applied sequentially at different distances (i.e. different z-positions) to a target, for instance a wafer of semiconductor material.
• deflector is a multipole deflector, the most common instance thereof is an octopole deflector consisting of curved plates with cylindrical or conical segments. By applying a suitable combination of electrode potentials to the plates, deflections in two orthogonal directions (x and y) can be applied simultaneously.
• a disadvantage of this deflector type is its complex construction.
• the said prior art reference US 6,897,458 specifies a specific electrostatic deflector of the planar type for use as scanning deflection means.
• This deflector comprise electrodes arranged to deflect an assembly of electron beamlets in a single direction.
• the electrodes may be deposited in the form of strips on a suitable plate.
• the strip- shaped electrodes may be deposited on the set of projection lenses, at the side facing the target surface, or alternatively on a separate plate between said set of lenses and the target surface.
• Fig. 10 shows a diagrammatical cross-sectional view of a portion of said prior art electrostatic deflector 11.
• the deflector 11 comprises a first strip 131, a second strip 132 and a third strip 133, which are present on a substrate 150. Passing windows 140, e.g. through-holes, extend through the substrate 150 between said strips 131,
• the lithography system is designed in such a manner that beamlets of charged particles, i.e. electrons, pass through the passing windows 140.
• the first and third strip 131, 133 are part of the first electrode, while the second strip 132 forms part of the second electrode. Therefore, the second strip 132 has an opposite polarity of that of the first and the second strip 131, 133. In this example, the second strip 132 is the negative pole.
• an electric field is generated towards the second strip 132.
• the electric field generated between the first and the second strip 131, 132 has a direction opposite to the electric field generated between the second and the third strip 132,
• the beamlets 7 are deflected by the electric field in opposing directions.
• Such deflection turns out disadvantageous; a surface area covered by a grid of the beamlets 7 is larger when the beamlets 7 are deflected than when not deflected. That difference in surface area causes problems for writing a pattern on a target surface that is much larger than the surface area. Then, the patterns of neighbouring surface areas need to fit together without any undesired overlaps or gaps in between.
• EP1993118 Another type of electrostatic deflector is known from EP1993118.
• This type is a blanker deflector using an array of electrodes protruding from a substrate.
• the array is designed to enable deflection in two directions simultaneously and to allow individual addressing of individual electrodes in the array; the latter feature results from the requirement that each beamlet in a blanker deflector is to be deflected separately.
• Holes are present in the substrate between the electrodes - one active, one ground or opposite polarity - to allow any beamlet to pass.
• the electrodes have a wall- shaped form and may be formed on two substrates stacked together in such a manner that the electrodes at least partially face each other.
• the height of these electrodes is in the order of 35-50 ⁇ m, the mutual distance may be less than lO ⁇ m. In the event that the electrodes are present on the same substrate, the height may be less than 10 ⁇ m and their mutual distance in the order of 0.5-2 times their height.
• the substrate may be thinned below the membrane with the protruding electrodes.
• this type of deflector has the limitation that it provides insufficient uniformity if intended for application as a scanning deflector.
• the presence of one of the electrodes on a second substrate leads to the generation of stray fields and hardly controllable effects.
• This is not problematic for its use as a blanker deflector; if a potential difference is applied between the electrodes in the blanker deflector, a beamlet will be deflected to terminate at a beam stop.
• a slightly larger or smaller deflection does not matter as long as it terminates anywhere at the beam stop. But when applied as scanning deflector, such variation would immediately result in a decrease of the resolution of the provided pattern.
• the stray fields may lead to a reduction of homogeneity of the beamlet. This may result in insufficient resist development and/or wrong beam positioning, and therewith non-adequate (i.e. failed) pattern generation.
• the prior art has shortcomings that are to be overcome by the invention.
• a charged particle optical system comprising an electrostatic deflector for the deflection of at least one beamlet of charged particles.
• the deflector comprises a first and a second electrode between which the said beamlet passes, wherein each of said electrode comprises at least one strip, which is at least partially freestanding.
• the deflector in the charged particle optical system of the invention has due to its electrodes comprising at least partially freestanding strips the advantage that an electric field with uniform field strength can be provided. This better uniformity is based on contributions from several effects: first, the use of freestanding strips implies the absence of a continuous character that easily impacts the uniformity in a negative way.
• an insulating carrier may affect the system as a parasitic capacitor.
• freestanding electrodes can be made in a single etching step. This allows a reduction in the distance between electrodes, and therewith a reduction of the potential voltage difference over the electrodes. Such reduction leads again to a better uniformity of the deflector, particularly when applied in combination with a high scanning frequency, e.g. more than 100 kHz, preferably in the range of 300-3000 kHz, more preferably between 500 and 1500 kHz.
• the strip may be provided with a relatively large surface area at the strip's side face normal to the direction of the electric field.
• the provision of such large surface area additionally will improve the mechanical stability of the freestanding strips.
• the contribution of the electric field span up between two opposing strips is big in comparison to that of the stray component of the electric field.
• the field is uniform over a grid of beamlets instead of individually addressing a single beamlet. Due to these features the deflector is particularly advantageous for the scanning deflection operation, though any other use is not excluded. Particularly its fine precision and homogeneous output enables its use for other deflection and/or filtering operations.
• each electrode comprises at least one strip, the strips extending substantially in parallel and defining a passing window through which a plurality of beamlets passes, said passing window having a width in a direction normal to the strips, in which direction an electric field is generated upon setting the potential difference between the electrodes, said strips having a height, a width and a lateral direction in three mutually perpendicular directions, the height of the strip being larger than the width of the passing window.
• relatively short distances enable relatively small driving voltages, while still meeting requirements of deflection angles.
• a design with small driving voltages, for instance smaller than 10V is effective for a more than one reason; first, the driving electronics to provide the voltages at switching frequencies of 1 MHz or more can be kept relatively simple; no dedicated high voltage power transistors are needed which would consume a lot of power and/or may constitute components that have a life time that may be critical and limiting overall. Additionally, with a small voltage, the risk of a uncontrolled discharge between electrodes with damaging effectively is strongly reduced. That is good for reliability and robustness.
• a plurality of passing windows is present, the orientation of the electric field in each passing window being the same.
• the term 'same orientation' is not intended to imply that the electric field in one passing window has a constant orientation in time. Effectively, it is preferable that the orientation of the electric field is reversed within one single scanning period.
• the term is intended that the electric field in different passing windows at any moment in time has the same orientation.
• the electric field in different passing windows has at any moment in time the same magnitude as well.
• an isolation domain preferably an isolation window
• an isolation window is present between a first and a second passing window.
• the specified pitch between beamlets can be met, even though the addition of such an isolation window.
• the term 'short distance' is used herein to express a short distance relative to the distance of the electrodes in a prior art macroscopic deflector as well as relative to the other dimensions within the deflector, such as the height of the strips and/or the distance between neighbouring passing windows.
• At least one terminating resistance is present.
• a terminating resistance accelerates positioning of a beamlet, between a first and a second scanning period.
• the term 'positioning' herein particularly refers to positioning of the beamlet to a starting position for scanning of a subsequent line during the second scanning period.
• a beamlet is deflected in the same orientation in both the first and the scanning period, and preferably in all scanning periods.
• Positioning of a beamlet, without simultaneously writing is achieved by bringing the voltage over the electrodes to a starting value corresponding to the starting position and additionally switching the beamlet off through operation of a beamlet blanker upwards in the column.
• the deflection of a beamlet in the same orientation in subsequent scanning periods turns out to simplify the provision of patterning data to the beamlets.
• all beamlets are deflected in the same orientation.
• the terminating resistance is electrically coupled in parallel to the electrode system.
• a first terminating resistance is electrically coupled between the first electrode and ground, and a second terminating resistance is electrically coupled between the second electrode and ground.
• the provision of the terminating resistance in one of the implementations damps out a parasitic capacitance in the deflector, which capacitance tends to slow down any switch back of the potential difference. It is not excluded to use the first and second implementations in combination.
• the terminating resistance is suitably integrated into the deflector; examples include resistors of polysilicon, TaN, TiWN,
• an edge zone is present, which at least partially overlies the aperture in the substrate.
• the edge zones comprise strips of the electrodes to define an electric field in the same orientation as the above mentioned electric field, but being devoid of passing windows for beamlets.
• the edge zone is embodied as an extension of an interdigitated pair of electrodes. However, it is designed to be free of beamlets. The addition of such edge zone turns out to be very beneficial for the uniformity of the electric field. It is most beneficial in a design wherein the first and second electrodes are put to voltages of opposite polarity and an additional ground electrode is defined adjacent to the electrode system.
• the freestanding electrodes are covered with a coating so as to provide an electrically substantially homogeneous surface.
• a coating is to prevent that local variations in the surface structure are more or less active to set up the electric field between the electrodes. Therewith, it contributes to the uniformity of the electric field. Moreover, such homogeneity tends to reduce the risk of electrostatic discharge.
• a second electrostatic deflector is present that deflects in a different direction than the - first - deflector.
• the different direction may be a direction opposite or perpendicular to the scanning direction, or any other direction different from the scanning direction. It is in particular a direction within the optical plane (e.g. a plane from which the optical axis exits as a normal). Corrections perpendicular to the scanning directions are useful in view of the simultaneously ongoing movement of the lithography system with respect to the target surface. This movement, also referred to as the mechanical scan, is suitably in the same direction as that of the further deflector. Such a correction is suitably carried out at a lower frequency than the scanning frequency.
• a deflection in opposite direction to the scanning direction is suitably carried out with a deflector of the same type as the one used for the scanning.
• deflection is a part of the scanning. It is herewith accomplished that a beamlet passes through the centre part of the optical axis in the effective lens plane of the projection lens arrangement even when deflected. In this manner, spherical aberrations caused by deflection through the projection lens arrangement are reduced.
• a charged particle optical system comprising a scanning electrostatic deflector for the deflection of at least one beamlet of charged particles.
• the deflector comprises a first and a second electrode between which the said beamlet passes through a passing window and is deflected under operation of an electric field, if any, between said electrodes, wherein a plurality of passing windows is present, the orientation of the electric field in each passing window being the same.
• the deflector is designed to a have a substantially uniform electric field within an active area of the deflector. Surprisingly, it has turned out possible to get a deflector with a uniform field, even though electrodes are defined within this active area. Any potential field disturbers, such as interconnects, capacitors, are defined outside the active area. Additionally, edge zones may be specified bordering the active area to flatten non-uniformities due to edge effects. In one embodiment the field is suppressed outside the active area. Such suppression is for instance implemented by the provision of isolating materials. In a preferred embodiment, the field is generated only within the active area.
• One preferred embodiment of achieving the operation within the active area only is the use of an interdigitated pair of strip-like shaped electrodes.
• Another manner of getting such operation is to a structure, wherein the active area is defined by absence of a underlying carrier. The absence of such underlying carrier immediately implies that in that area the field is not disturbed by any unavoidable interaction with the underlying carrier. Most suitably, a combination of both manners is applied.
• An elegant manner hereof is the provision of freestanding electrode strips.
• the deflector is used for deflection of at least one beamlet of charged particles.
• the deflector is used for the deflection of a plurality of beamlets. It is most suitable that voltages of opposite polarity to the first and the second electrode of the deflector. It has turned out that driving the deflector with opposite voltages around a ground value (either 0 Volt or another value) provides best results.
• a ground value either 0 Volt or another value
• a sawtooth profile turns out highly advantageous, particularly in combination with a structure in which anywhere within the deflector the electric field has the same orientation.
• the opposite voltages on the electrodes are equal in magnitude and smaller than 10V.
• the 10V is herein the maximum applied voltage difference with the ground for the positive polarity; this will be -10V for the negative polarity. More suitably, the voltages are even smaller, for instance with a maximum voltage of 7, 5 or 4 Volt.
• Such small voltages are enabled through the inventive deflector, where the freestanding electrodes at short distance of each other provide a deflection strength similar to those of a prior art deflectors.
• the scanning frequency is relatively large, suitably in the RF range, more preferably in medium RF between 300 and 3000 kHz, for instance 0.5-1.2 MHz.
• the -modulated- beamlet is positioned to a starting position in a positioning period without exposing a target surface, and deflected from the starting position in a writing period.
• This alternation of positioning and scanning is particularly done as a sawtooth profile. It turns out to improve the uniformity of the scanning.
• the scanning frequency is in a radio frequency (RF) range and each beamlet is deflected in the same orientation as other beamlets both within a scanning period and in subsequent scanning periods; and the positioning period is shorter than the writing period.
• RF radio frequency
• the use is particularly exploited in a method of projecting a predetermined pattern on a target surface by means of a maskless lithography system. It is therein applied for scanning said pattern on the target surface.
• This method comprises the steps of generating a plurality of beamlets; modulating a magnitude of a beamlet using modulation means provided with data of the predetermined pattern retrieved from a data storage; focusing said modulated beamlets onto the target surface using focusing means, and scanning said pattern on the target surface by electrostatically deflecting said modulated beamlets.
• the electrostatic deflector comprises a first and a second electrode which are at least partially freestanding, said deflector deflecting the said plurality of beamlets by operation of an electric field between the electrodes between which the said plurality of beamlets passes, the said plurality of beamlets defining a passing window and a dimension of said passing window in a direction transverse to said first direction matching a diameter of said beamlets, said passing window extending in a first direction, said plurality of beamlets is arranged in a single row extending in said first direction and wherein a substantial part of the electrostatic deflector extends beyond the passing window in said first direction.
• the said substantial part extends in said first direction a number of times the pitch of the beams in the passing window.
• the deflector deflects the beamlets transverse to said first direction over a subdivision within said surface of said target, such as a field on a wafer, wherein the deflector is a scanning deflector for performing the final writing projection of the system.
• FIG. 1 shows a simplified schematic drawing of an embodiment of a charged particle multi-beamlet lithography system
• Fig 2 shows a top view of a preferred embodiment of the invention
• Fig. 3 shows a detail of Fig. 2 in enlarged view
• Fig.4 shows a diagrammatical cross-sectional drawing of the embodiment of Fig. 2;
• Fig. 5 shows a diagrammatical cross-sectional drawing of the embodiment of Fig. 2 in a direction perpendicular to that of Fig. 4
• Fig. 6 shows a top view of a second embodiment according to the invention
• Fig. 7 shows a third embodiment according to the invention
• Fig. 8 is a simplified representation in cross section of a deflector system with a deflector according to the invention
• Fig. 9 shows a simplified, diagrammatical cross-sectional view of a portion of the electrostatic deflector of the invention.
• Fig. 10 shows a diagrammatical cross-sectional view of a portion of a prior art electrostatic deflector
• Fig. 1 shows a simplified schematic drawing of an embodiment of a charged particle multi-beamlet lithography system based upon an electron beam optical system without a common cross-over of all the electron beamlets.
• Such lithography systems are described for example in U.S. patent Nos. 6,897,458 and 6, 958,804 and 7.084,414 and 7,129,502, which are hereby incorporated by reference in their entirety, assigned to the owner if the present invention.
• Such a lithography system suitably comprises a beamlet generator generating a plurality of beamlets, a beamlet modulator patterning said beamlets into modulated beamlets, and a beamlet projector for projecting said beamlets onto a surface of a target.
• the beamlet generator typically comprises a source and at least one aperture array.
• the beamlet modulator is typically a beamlet blanker with a blanking deflector array and a beam stop array.
• the beamlet projector typically comprises a scanning deflector and a projection lens system.
• the lithography system suitably includes the functionality of a redundancy scan.
• a redundancy scan Such a functionality is known from WO-A 2007/013802 assigned to the assignee of the present application and is included herein by reference.
• compensation for failing, i.e. invalid beamlets is provided.
• the reliability of the lithography system may be increased dramatically.
• a lithography system for redundancy scanning may include a sensor and control unit coupled thereto, so as to identify invalid beamlets with properties outside predefined specifications.
• This control unit is coupled to a system control for switching specific beamlets on or off and actuating the system with respect to the target - or vice versa - to replace invalid beamlets with valid beamlets.
• projection of any invalid beamlets is prevented.
• unwritten pattern elements are left. The unwritten pattern elements are thereafter transferred onto the target surface by scanning valid replacement beamlets over said surface.
• the lithography system 1 of the invention is very well suitable for implementing the redundancy scan functionality. Its achieved improvement of the accuracy of scanning lines onto the target surfaces enables that a second scan is carried out that exactly fills a gap left open in a first scanning sequence.
• the lithography system comprises an electron source 3 for producing a homogeneous, expanding electron beam 4. Beam energy is preferably maintained relatively low in the range of about 1 to 10 keV. To achieve this, the acceleration voltage is preferably low, the electron source preferably kept at between about -1 to -10 kV with respect to the target at ground potential, although other settings may also be used.
• the electron beam 4 from the electron source 3 passes a double octopole and subsequently a collimator lens 5 for collimating the electron beam 4.
• the collimator lens 5 may be any type of collimating optical system.
• the electron beam 4 impinges on a beam splitter, which is in one suitable embodiment an aperture array 6.
• the aperture array 6 blocks part of the beam and allows a plurality of beamlets 7 to pass through the aperture array 6.
• the aperture array preferably comprises a plate having through-holes.
• a plurality of parallel electron beamlets 7 is produced.
• the system generates a large number of beamlets 7, preferably about 10,000 to 1,000,000 beamlets, although it is of course possible to use more or less beamlets. Note that other known methods may also be used to generate collimated beamlets.
• the plurality of electron beamlets 7 pass through a condenser lens array - not shown in the figure - which focuses each of the electron beamlets 7 in the plane of beamlet blanker array 9.
• This beamlet blanker array 9 preferably comprises a plurality of blankers, which are each capable of deflecting one or more of the electron beamlets 7.
• the beamlet blanker array 9 constitutes with a beam stop array 10 a modulating means 8.
• the modulating means 8 add a pattern to the electron beamlets 7. The pattern will be positioned on the target surface 13 by means of components present within an end module.
• the beam stop array 10 comprises an array of apertures for allowing beamlets to pass through.
• the beam stop array in its basic form, comprises a substrate provided with through-holes, typically round holes although other shapes may also be used.
• the substrate of the beam stop array 8 is formed from a silicon wafer with a regularly spaced array of through-holes, and may be coated with a surface layer of a metal to prevent surface charging.
• the metal is of a type that does not form a native-oxide skin, such as CrMo.
• the passages of the beam stop array 10 are aligned with the elements of the beamlet blanker array 9.
• the beamlet blanker array 9 and the beamlet stop array 10 operate together to block or let pass the beamlets 7. If beamlet blanker array 9 deflects a beamlet, it will not pass through the corresponding aperture in beamlet stop array 10, but instead will be blocked by the substrate of beamlet block array 10. But if beamlet blanker array 9 does not deflect a beamlet, then it will pass through the corresponding apertures in beamlet stop array 10 and will then be projected as a spot on a target surface 13 of the target 24.
• the lithography system furthermore comprises a control unit 60 comprising data storage 61, a read out unit 62 and data converter 63.
• the control unit 60 may be located remote from the rest of the system, for instance outside the inner part of a clean room.
• optical fibers 64 modulated light beams holding pattern data are transmitted to a projector 65 which projects the ends of the fibers (schematically depicted in plate 15) into the electron optical unit 18, here on to the modulation array 9.
• Modulated light beams 8 from each optical fiber end are projected on a light sensitive element of a modulator on the beamlet blanker array 9.
• Each light beam 14 holds a part of the pattern data for controlling one or more modulators.
• transmitting means 17 enabling that the projector 65 is appropriately aligned with the plate 15 at the ends of the fibers.
• the electron beamlets 7 enter the end module.
• the term 'beamlet' to refer to a modulated beamlet.
• Such a modulated beamlet effectively comprises time- wise sequential portions. Some of these sequential portions may have a lower intensity and preferably have zero intensity - i.e. portions stopped at the beam stop. Some portions will have zero intensity in order to allow positioning of the beamlet to a starting position for a subsequent scanning period.
• the end module is preferably constructed as an insertable, replaceable unit, which comprises various components.
• the end module comprises a beam stop array 10, a scanning deflector array 11, and a projection lens arrangement 12, although not all of these need be included in the end module and they may be arranged differently.
• the end module will, amongst other functions, provide a demagnification of about 100 to 500 times, preferably as large as possible, e.g. in the range 300 to 500 times.
• the end module preferably deflects the beamlets as described below. After leaving the end module, the beamlets 7 impinge on a target surface 13 positioned at a target plane.
• the target usually comprises a wafer provided with a charged-particle sensitive layer or resist layer.
• the thus modulated beamlets 7 pass through a scanning deflector array 11 that provides for deflection of each beamlet 7 in the X- and/or Y-direction, substantially perpendicular to the direction of the undeflected beamlets 7.
• the deflector array 11 is a scanning electrostatic deflector enabling the application of relatively small driving voltages, as will be explained hereinafter.
• the beamlets 21 pass through projection lens arrangement 12 and are projected onto a target surface 13 of a target, typically a wafer, in a target plane.
• the projection lens arrangement 12 focuses the beamlet, preferably resulting in a geometric spot size of about 10 to 30 nanometers in diameter.
• the projection lens arrangement 12 in such a design preferably provides a demagnification of about 100 to 500 times.
• the projection lens arrangement 12 is advantageously located close to the target surface 13.
• protection means may be located between the target surface 13 and the focusing projection lens arrangement 12.
• the protection means may be a foil or a plate, evidently provided with needed apertures, and are to absorb the released resist particles before they can reach any of the sensitive elements in the lithography system.
• the scanning deflection array 9 may be provided between the projection lens arrangement 12 and the target surface 13. [0059] Roughly speaking, the projection lens arrangement 12 focuses the beamlets 7 to the target surface 13. Therewith, it further ensures that the spot size of a single pixel is correct.
• the scanning deflector 11 deflects the beamlets 7 over the target surface 13. Therewith, it needs to ensure that the position of a pixel on the target surface 13 is correct on a microscale. Particularly, the operation of the scanning deflector 11 needs to ensure that a pixel fits well into a grid of pixels which ultimately constitutes the pattern on the target surface 13. It will be understood that the macroscale positioning of the pixel on the target surface is suitably enabled by wafer positioning means present below the target 13.
• the target surface 13 comprises a resist film on top of a substrate. Portions of the resist film will be chemically modified by application of the beamlets of charged particles, i.e. electrons. As a result thereof, the irradiated portion of the film will be more or less soluble in a developer, resulting in a resist pattern on a wafer.
• the resist pattern on the wafer can subsequently be transferred to an underlying layer, i.e. by implementation, etching and/or deposition steps as known in the art of semiconductor manufacturing.
• the current invention addresses this object of precise and uniform projection of the plurality of scanning beamlets on the target surface 13.
• at least freestanding electrodes in the scanning deflector 11 allow the creation of a very uniform electric field, and therewith result in a uniform deflection meeting its objective. Additionally, it turned out possible to manufacture the freestanding electrodes with an appropriate mechanical strength and without giving rise to new engineering problems that would be even more difficult to solve.
• the freestanding electrodes had one or more mechanical resonance frequencies well below and/or above a chosen operating frequency of the scanning deflector. In other words, in this embodiment the provision of voltage differences over the electrodes does not lead to vibrations of the freestanding electrodes. Such vibrations would be the end of a uniform field between the electrodes.
• the freestanding electrodes were provided with a surface structure that results in merely minor fluctuations and/or disturbances in the electric field.
• Fig 2 shows a top view of a preferred embodiment of the electrostatic scanning deflector 11 of the invention.
• Fig. 3 shows an enlarged view of a portion of Fig. 2.
• Fig. 4 discloses a schematic cross-sectional view in a first direction.
• Fig. 5 shows a schematic cross-sectional view in a direction perpendicular to that of Fig. 4.
• Fig. 9 shows a simplified view.
• Fig 2 shows a number of consecutive strips 31-38, which are part of the comb- structured first electrode 21 or the comb- structured second electrode 22 respectively.
• the strips 31-38 together constitute an interdigitated pair of electrodes; this will hereinafter also be referred to as an electrode system.
• the substrate 50 herein supports the electrode system; however the electrode system at least partially and suitably largely overlies an aperture 51 in the substrate 50.
• Fig 4 merely shows consecutive strips 31-35, but it illustrates even with such reduced number of strips the principle adequately.
• the consecutive strips from bridges extending from a first side 101 to a second side 102 of the aperture 51. However, that is not deemed necessary, as will be shown with reference to Fig. 7.
• the field is generated effectively in an active area 20, as indicated with a dotted line in Fig. 2.
• the freestanding electrodes of the present embodiment generate the field primarily via their side faces. There are no such side faces outside the active area 20.
• the active area 20 may be defined alternatively.
• the term 'at least partially freestanding electrodes' is meant to describe that any portion of the relevant conductors present within the active area are freestanding or partly freestanding.
• the term 'freestanding' is meant to describe that these conductors are not supported by means of any membrane or other carrier in the active area.
• the term 'partly freestanding' is intended to describe the situation in which these conductors are locally and/or over a limited area supported by a membrane, by mechanical posts or by any other support structure.
• the term 'at least partially freestanding electrodes' is implemented in that the consecutive strips are freestanding in the active area.
• Windows 40, 41 extend between the strips. Some of those are passing windows 40; others are isolation domains 41. In this preferred example, the isolation domains 41 are windows, e.g. are free space not filled with any dielectric or other material.
• the passing windows 40 have a width b.
• Passing windows 40 are windows through which a beamlet 7 is designed to pass. Passing windows may be holes designed for a couple of beamlets 7, or grooves fully extending between the strips of the electrodes. If a passing window 40 is limited to a couple of beamlets 7, the limitation may well be due to the provision of a support structure (such as posts or beams for instance extending perpendicular to the strips). However, there may be other reasons to limit a passing window 40. The provision of a relatively long passing window is however advantageous to obtain a maximum uniformity; any interruption or limitation of a passing window likely gives rise to a variation of the electric field.
• the number of consecutive strips is relatively large and their mutual distance short.
• the strips 31-38 have a lateral dimension, a width a and a height z.
• An isolation window 41 has a width c.
• the width b of a passing window 40 is smaller than the total distance 2a+c between passing windows 40. More suitably, the width b of a passing window 40 is chosen such that at most three rows of electron beamlets 7 pass through the passing window 40. More preferably, the number of rows is two and most preferably, the number of rows is one. A reduction of the number of rows turns out beneficial for the generation of a uniform field.
• the field lines mostly run in a direction normal to the lateral extension of the strips 31-38.
• the field strength of such a deflector is not uniform. Particularly near to corners of the electrodes, the field strength is higher and the sides anyhow lead to disturbances of the electric field.
• the scanning deflector 11 according to the invention the field strength is extremely uniform and clearly more uniform than in the prior art.
• the scanning deflector demonstrates a variation in deflection strength of less than 5%, more preferably less than 3% and most preferably even less than 2%. In one embodiment of the invention, a variation in deflection strength between 1 and 1.5% has been achieved.
• the deflector can be driven electrically in a better way; i.e. the provision of the - varying - voltage difference over the electrodes may be increased in speed and/or with a higher bandwidth.
• the term 'bandwidth' is used herein as a measure for the uniformity of application of the electrical signal. A bandwidth that is too low, may cause problems such as uncontrollable delay and variations in the timing of providing the voltage difference and variations in the magnitude of the voltage difference.
• the risk of damage to the deflector as a consequence of electrostatic discharge is reduced.
• the height z of the strips 31 is designed to be relatively large.
• the height z is larger than the width b of the passing window 40.
• the larger height serves to increase the so-called deflection strength, or alternatively reduce the needed potential difference for a given deflection angle.
• Fig. 9 is a simplified cross-sectional view of a portion of the electrostatic deflector according to the invention. Comparison with the prior art Fig. 10 will elucidate the major improvements made in the invention. First of all, the field in the deflector extends directly from the first to the second electrode; in the prior art it extended above the electrode. Thus results in a larger uniformity and a better controlled field strength. Second, the height z of the electrodes 31-36 is larger in the invention than in the prior art. Since a beamlet 7 is deflected in the invention over the full height z, the deflection occurs more gradually. The field strength needed for a predefined deflection angle can thus be reduced.
• the height z is larger than the width b of a passing window 40.
• the deflector of the invention includes isolation windows 41 in addition to passing windows 40. This results therein that beamlets 7 are all deflected in the same direction. In the prior art shown in Fig. 10, the beamlets 7 were deflected in opposite directions. Even though the invention thus has additional strips in comparison to the prior art of Fig. 10, a pitch between a first and a second beamlet is not increased. If desired, the pitch may even be reduced. Such a small pitch is one step towards patterning of smaller critical dimensions in the lithography system of the invention. Though not shown in this figure or in Fig. 10, the prior art deflector comprises specific holes through which individual beamlets pass.
• a plurality of beamlets passes between a first and a second strip.
• the construction of the deflector of the invention as a series of freestanding strips does not need additional holes. Additionally, the passing of a plurality of beamlets between a first and second strip instead of through individual holes contributes to uniformity.
• ground electrode 25 is not located adjacent to a positively or negatively charged electrode, but is present on the substrate in an area not or substantially not overlying the aperture.
• the distance between such charged electrode and the ground electrode has become much larger. This helps to meet the boundary condition that no electrostatic discharge is to occur with a damage that destroys the deflector.
• the consecutive strips of the first and second electrodes 21, 22 may be located at smaller distances.
• the potential of the ground electrode need not to be equal to that of the ground in an ordinary environment (OV).
• the ground electrode may f.i.
• the potentials applied to the first and second electrodes 21, 22 are then potentials around this ground, f.i. -1OkV -/+ 10V.
• the potential difference between the first and second electrode 21, 22 is at most 50V, more suitably at most 20V and even more suitably at most 10V.
• potential differences of less than 10V have been achieved, for instance 8V, 6V, 5V.
• the bandwidth is at least 5 times the scanning frequency. A bandwidth of 10 times the scanning frequency provides a result that is very appropriate in terms of uniformity.
• the scanning frequency is at least 100 kHz, more preferably at least 500 kHz or even 1 MHz or more.
• the structure is provided with bondpads 28. These bond pads 28 are coupled to each of the electrodes through interconnects 29.
• the interconnects 29 are present between ground plane areas 25. This is particularly suitable in case of higher switching frequencies in the order of 500 kHz or more. RF effects then start to be relevant. By implementing the interconnect as a waveguide, such RF aspects are suppressed substantially. It will be understood by the skilled person that other transmission line implementations - stripline, transmission line etc - may be chosen alternatively.
• the orientation of the electric field in each passing window 40 is the same. Due to the equal orientation of the electric field, the deflection of all beamlets 7 goes in the same orientation. As a result, the surface area as well as the shape of the projected grid of beamlets 7 is the same, independent or not whether there is a deflection.
• This principle is embodied, in the shown embodiment in the following manner: the first electrode comprises a first and a third strip, while the second electrode comprising a second and fourth strip.
• a first passing window is present between the first and the second strip.
• a second passing window is located between the third and the fourth strip.
• an isolation domain is present between the second and third strip; i.e. the isolation domain is free of a passing window.
• the isolation domain is suitably a window for manufacturing reasons.
• the present design allows to reduce driving voltages, the risk of discharge is substantially reduced.
• a terminating resistance is coupled in parallel to the electrode system of first and second electrode 21,22.
• a terminating resistance may be integrated on the substrate of the deflector.
• the terminating resistance may be a separate component, such as one or more surface mountable resistors that are assembled separately. It is provided to remove any effects on positioning time of parasitic capacitance in the system. Specifically, the resistance dampens the capacitance and/or the resistance and the parasitic capacitance operate together as filter. As a result, it is achieved that a positioning period is shorter than a writing period. Together these define the time needed for scanning one line, and therewith the scanning frequency.
• the resistance is mechanically coupled to a heat removal path.
• the heat removal path may include a heatspreader, a heatsink and the like.
• the use of such resistance is enabled in that due to the relatively low driving voltage, the potential difference over the electrodes is relatively small. This implies that the heat dissipation over the resistance will be limited.
• the benefit of the resistance is that the potential difference over the electrodes may be reduced more quickly. Effectively, the parasitic capacitance of the electrode system is damped by the resistor and therewith does not counteract this reduction of potential difference.
• the said reduction of the potential difference directly corresponds to a reduced time to bring a beamlet to its starting position for a subsequent deflection. Therewith, it increases the scanning frequency.
• Fig. 4 and 5 show diagrammatical cross-sectional drawings of the embodiment of Fig. 2.
• Fig 4 shows even more clearly the mutual positioning of strips 31-38 and aperture 51 in the substrate.
• Fig. 5 shows that a strip 31 extends from a first side 101 to an opposite second side 102 of the aperture 51 in this embodiment.
• an electrode effectively constitutes a bridge covering the underlying aperture. That is a construction that is favourable from mechanical stability perspective.
• This structure is suitably manufactured on the basis of a semiconductor substrate that can be etched and patterned selectively both from its top side and from its bottom side.
• a silicon-on-insulator (SOI) substrate turns out very advantageous for this purpose; the buried oxide 52 therein acts as etch stop.
• an etch stop can be created with a pn-junction or other doping transition, as is known in the art.
• the electrodes will be made in the top semiconductor layer (device layer) 53.
• the substrate 50 is created in the bottom semiconductor layer (handling wafer).
• the aperture 51 may be created by any type of etching, such as dry etching and wet etching.
• the silicon wafers preferably are doped, either p-type or n-type.
• a pn- junction is absent so as to prevent current generation within the freestanding electrodes.
• the doping level may be chosen freely as known to the skilled person in the field of etching and microfabrication.
• the freestanding electrodes are provided with a coating 54. It has been found that the addition of a coating further improves the uniformity of the electric field. Various materials could be used to improve the smoothness, including dielectric and conductive materials. However, metal coatings are considered most suitable; contrarily to a coating of a dielectric material, a metal coating does not result in additional capacitance in the system.
• the semiconductor material of the freestanding electrode is not oxidized prior to provision of the metal coating.
• the metal coating could be provided on all surfaces of the freestanding electrodes simultaneously, e.g. by a suitable CVD process, but that is not deemed necessary.
• Fig. 6 shows a top view of a second embodiment according to the invention. This embodiment shows an interdigitated pair of electrodes 21, 22. Edge zones 23 are present located at opposite edges of the deflector 11. The edge zones 23 comprise a set of parallel oriented strips of the first and the second electrode 21, 22. Nonetheless, no passing windows 40 have been designed within the edge zones 23. Suitably, the design of the strips is equal to the design in the main portion of the deflector 9, but that is not necessary. Although shown to be equal, the edge zones 23 might well be implemented in different designs.
• edge zones 26 are advantageous to create edge zones 26 in a direction normal to the electric field, i.e. near the distal ends of the freestanding portion of electrodes or strips.
• Such edge zones 26 support to prevent artifacts in the electric field as a consequence of interactions with the substrate and/or conductors, such as leads and interconnects.
• these edge zones each have an extension of between 2 and 20% of the lateral extension of a strip 31, more preferably between 4 and 12%.
• the deflector 11 of the invention is assembled together with the projection lens arrangement 12. This is achievable without grave electrostatic discharge problems observed with the prior art planar deflector shown in Fig. 10.
• the deflector with at least partially freestanding electrode strips and a more uniform field turns out to better withstand electrostatic voltages.
• the deflector may be assembled near or directly up or below the projection lens arrangement 12.
• the scanning deflector 11 of the invention has in one embodiment the further advantage that its thickness is less than that of a prior art deflector.
• the overall thickness of substrate 50 and the electrodes may be less than 500 micrometer, and preferably less than 300 micrometer. This enables a position of the deflector 11 near to the projection lens arrangement 12.
• Fig. 7 shows a third embodiment according to the invention.
• the electrode system comprises several portions 91-94.
• the number is four, but that is not necessary or limiting. The number might be larger (for instance 9 or 16), it could be smaller (2).
• the electrode system may be subdivided into a series of portions adjacent to each other, instead of a plurality of blocks. Each of the portions comprises consecutive strips of electrodes 21, 22 that overlie an aperture 51a-d in the substrate 50. In this embodiment, there are four apertures 51a-d corresponding to the four portions 91-94. However, this is not strictly necessary; an additional layer could act as a carrier for the electrode system of all strips.
• FIG. 8 is a schematic view of an embodiment of a scanning electrostatic deflection system in accordance with the invention. This embodiment comprises a first electrostatic scanning deflector 11a and a second electrostatic scanning deflector l ib.
• At least one of the deflectors 11a, l ib is a deflector in accordance with the invention.
• both are scanning deflectors in accordance with the invention.
• two deflectors 11a and l ib are located one behind the other, each with opposite voltages on their electrodes. For deflection purposes, the sign of these voltages on each deflector 11a, l ib is switched simultaneously. Centering of the deflected beamlet 7 in the effective lens plane 19, and near the optical axis 0 of the projection lens system, is performed by fine tuning the ratios of the deflection angles in view of distance d5 between deflector 9b and the effective lens plane 19 of the projection lens arrangement. The mutual distance d6 between the two deflectors 1 Ia, 1 Ib, and the potential difference applied between the electrodes may also be used in this fine-tuning operation.
• the applied potential difference in the first scanning deflector 11a and that in the second scanning deflector 1 Ib are herein mutually coupled. They are changed in such a way that the pivot point of beamlet 7 is in the optical plane of projection lens arrangement and crosses the optical axis 0 of the projection lens system.
• the driving circuits of the first and the second deflector l la, 1 Ib are thereto controlled through a single controller.
• portions of the driving circuits for instance a portion thereof generating the scanning frequency, may be integrated or otherwise coupled together.
• first deflector 11a deflects beamlet 7 at an angle ⁇ l away from the optical axis 0, and second deflector 1 Ib deflects the beamlet 7 back in the opposite direction and at angle ⁇ 2. In that way, beamlet 7 is deflected over an angle ⁇ 3 when crossing the effective lens plane 19 of the projection lens arrangement.
• a charged particle system comprising a scanning electrostatic deflector for the deflection of at least one beamlet of charged particles.
• the deflector comprises a first and a second electrode between which the said beamlet passes, wherein each electrode comprises at least one strip, the strips extending substantially in parallel and defining a passing window through which a plurality of beamlets passes, said passing window having a width in a direction normal to the strips, in which direction an electric field is generated upon setting the potential difference between the electrodes, said strips having a height, a width and a lateral direction in three mutually perpendicular directions, the height of the strip being larger than the width of the passing window.
• the deflector comprises freestanding electrode strips.
• a method of scanning a surface with a scanning frequency using an electrostatic deflector comprises a first and a second electrode between which a passing window is present.
• each beamlet scans a line on the surface in a single scanning period.
• the scanning comprises the positioning of the beamlet to a starting position in a positioning period, and the deflection of the beamlet from the starting position by varying the electric field strength over the electrodes in a writing period.
• the scanning frequency is in a radio frequency (RF) range.
• the beamlet is deflected in the same direction in each scanning period.
• Each beamlet is deflected under operation of the electric field that is oriented in the orientation for each beamlet; moreover, the positioning period is shorter than the writing period.
• the present invention effectively enables scanning in a different regime governed by different rules than the prior art.
• the governing regime is that of high- frequency scanning. More specifically, the high scanning frequency is a frequency within the radio frequency (RF) range, and most suitably in the medium range thereof between 300 and 3000 kHz.
• RF radio frequency
• the deflection needs to obey rules of RF electronics in order to prevent delays and non-uniformities due to the RF behaviour of the conductors and materials involved.
• One prominent RF property is the parasitic capacitance. Particularly when changing and reversing voltages, parasitic capacitance may introduce major delays. Additionally, parasitic capacitance tends to lead to deformation of the field, and therewith to a scanning that is easily out of specification.
• the inventors proposed to deflect beamlets over relatively small angles only, but to carry out the scanning within the radio frequency range. Such smaller deflection angles provide better accuracy and enable a reduction in the applied voltage difference over the electrodes of the deflector. Moreover in order to get an appropriate and reliable result for such high frequency scanning, it was understood that to limit the deflection to a single orientation. Such single orientation deflection requires more repositioning of the beamlets, which costs time. However, a deflection into opposite orientations was found to lead to difference in surface area of the grid of beamlets between the situation with deflection and without deflection. Correction of such difference in surface area was considered undoable at high frequencies.
• the voltages are applied onto the electrodes of the deflector by means of a sawtooth characteristic.
• the exact sawtooth shape may be tuned to optimize performance.
• the reverse setting of the voltage results in the desired repositioning, together with mechanical repositioning of the target relative to the lithography system, which is carried out simultaneously.
• the positioning time is reduced through filtering and/or damping out parasitic capacitance.
• filtering out is suitably achieved by adding components to the deflector so as to obtain filtering performance.
• Filter topologies are known to skilled persons in the field of analog electronic engineering. Examples include RC filters, RCL-filters, pi-filters and LC filters and networks. Most suitably, use is made of an RC filter. This may be implemented through a terminating resistance.
• the voltages applied to the electrodes of the deflector are less than 10V. This voltage reduction is particularly relevant to reduce power losses as a consequence of the said filtering.
• the deflector of the invention is used as the deflector operating at a small potential difference. With freestanding electrodes, this deflector further reduces parasitic capacitance of the deflector and thus supports reduction
• the positioning period has a duration of at most half of the writing period. More suitably, the positioning period has a duration of less than 40%, and most preferred less than 25% of the writing period.

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