JP5330749B2 - measuring device - Google Patents

Description

  The present invention relates to a measuring apparatus for observing and inspecting the surface or internal irregularities of a sample (object to be measured) such as a wafer using an interferometer, for example, an interference microscope typified by a Michelson type or a Linnik type.

  Conventionally, the incident light is divided into two optical paths, one light is irradiated to the sample (object to be measured), the other light is irradiated to the reference mirror, and the reflected light reflected from the sample interferes with the reference light. A measuring apparatus using an interferometer is known that forms interference fringes and observes and inspects the inside of the surface of a sample.

  In Patent Document 1, when forming interference fringes, the reference mirror can be moved in the optical axis direction by the piezo element PZT, and the usable measurement range is expanded by using phase shift means for changing the phase of the reference light ( The same applies to Non-Patent Document 1.)

  In Patent Document 2, a part of the inspected inspection surface is compared and displaced by an amount δz, the reference mirror is displaced by δz, and the optical measurement surface reliably contacts an appropriate part of the inspection surface. become.

  In Patent Document 3, the movable mirror is arranged so that it can freely move in the incident direction of light. When generating interference light, constant speed movement control is performed by a known piezo drive device. ing.

  Further, in Patent Document 4, the reference mirror can be fixedly arranged substantially perpendicular to the light irradiation direction (including a case where the reference mirror is slightly tilted so that several interference fringes can be formed), and in the light irradiation direction. On the other hand, it is described that it can be tilted.

Further, in Non-Patent Document 2, a phase shift is performed in a non-scanning manner by a two-dimensional image sensor, and the reference mirror is tilted to give different incident angles to the object light and the reference light incident on the CCD, and the CCD spatial axis On the other hand, the interference fringes with different phases are developed linearly, and this is taken and measured. In addition, this method makes it possible to perform a phase shift while suppressing an increase in detection time.
Japanese Patent Laid-Open No. 2006-116028, line number 0067, FIG. JP 2005-530147 A, line number 0044, FIG. 1, FIG. Japanese Patent Laying-Open No. 2006-300792, line number 0023, FIG. Japanese Patent Laid-Open No. 11-83457, line number 0032, FIG. University of Tsukuba, Department of Physical Engineering, University of Tsukuba, Nanoscience Special Project Research Organization Shuichi Makida, Yoshiaki Anno, Takashi Endo, Masahide Ito, Toyohiko Yadagai, “Phase-Shift Spectrum Interferometric Coherence Tomography by Reference Wavefront Gradient Method”, 64th JSAP Conference Proceedings, Autumn 2003, Fukuoka University One-shot-phase-shifting Fourier domain optical coherence tomography by reference wavefront tilting, Yoshiaki Yasuno, Shuichi Makita, Takashi Endo, Gouki Aoki, Hiroshi Sumimura, Masahide Itoh and Toyohiko Yatagai, 2004, Optical Sociaty of America

  However, in the measurement apparatus using the above-described conventional interferometer, the optical path on the measurement object side and the optical path of the reference optical path on which the reference mirror is arranged coincide with each other. It becomes so large that a simple configuration cannot be realized.

  In Patent Document 3, it is necessary to arrange a transmission limiting device to correct the optical path length from the reference optical path, which requires a complicated configuration.

  In Patent Document 4, a voltage-controlled variable wavelength filter must be provided to change the optical path length. Similar to Patent Document 3, a complicated configuration is required, and the entire apparatus is downsized. I can't.

  Accordingly, an object of the present invention is to provide a measuring apparatus capable of measuring the surface shape of a sample (measurement object) such as a wafer by simply tilting a reference mirror with a simple configuration. .

  In order to solve the above-mentioned problems, the present invention is characterized by matters described in the claims.

  According to the present invention, the surface shape of an object to be measured (sample) such as a wafer can be measured with a simple configuration by slightly tilting the reference mirror. Furthermore, it is possible to identify the exact coordinate position such as dust and pole piece and transmit / receive the accurate data to / from a charged particle beam device such as an electron microscope or a drawing device, thereby further contributing to the improvement of work efficiency.

  The measurement apparatus according to the present invention uses various interferometers.

  In the best mode of the present invention, a Michelson interferometer is used. However, a Linnik type (phase shift type) interferometer may be used as long as the effect of the present invention is achieved.

  For reference, it is also conceivable to perform a fine tilt (amount of fine movement Δλ) of the reference mirror (Ref) described below, for example, by using a Time domain Refractometry interferometer as the interferometer.

λ = 800nm
Δλ = 30nm
Resolution: ΔZ = 2lm / π · λ ² / Δλ
= 9.4μ
Lateral resolution: ΔX = 4λ / π · f / d
The scanning area in the optical axis direction is 2Z ₀ = ΔX ² π / 2λ.

  In this case, however, the resolution is limited, and it is not easy to inspect the shape of dust and pole pieces such as dust on a measurement object (sample) such as a wafer.

  It is also conceivable to use a Fourier domain Refractometry interferometer. In this case, there is a limit to spectroscopy and wavelength scanning, and it is not easy to inspect the shape of ultrafine regions such as dust and pole pieces on a measurement object such as a wafer.

  In the present invention, the position of the interference end is preferably measured by tilting the Reference Mirror (reference mirror) in a minute amount fixed type or tilting type (particularly vibration type). For example, if the reference mirror is fixed in a slight amount (15 minutes in the best mode) in a gently tilted state, or tilted in a tilting manner (especially a vibration type) as necessary, it is placed on the line sensor. Interference fringes are formed. In this way, an interference image in the height direction can be obtained with one shot without scanning with laser light. In addition, the position of the interference end can be measured using a Michelson-type interferometer with low coherence.

  In another preferred embodiment of the present invention, a laser beam is applied to a sample such as a wafer, preferably two wavelengths of laser light, particularly a semiconductor laser (LD), a light emitting diode (LED) and a super light emitting diode (SLD). Are irradiated with two laser beams, and the inside of the surface of the sample is observed and inspected using an interferometer. When a semiconductor laser (LD) is used, the intensity (power) of the laser beam is proportional to the current (linear relation) when the intensity (power) with respect to the current exceeds a predetermined threshold value (Ith). However, up to a predetermined threshold (Lth), LED emission or SLD-like emission occurs, so by setting a very small current value and using a semiconductor laser (LD) that emits light with a constant light amount, In addition, the inside of the surface of the sample can be observed and inspected through a single light source (for example, a semiconductor laser (LD)) through an interferometer.

Preferably, a reference optical path for guiding light to the reference mirror is provided between the reference mirror and the beam splitter. Then, an optical optical path difference is provided between the measurement optical path for guiding light to the object to be measured (sample) and the reference optical path.

  Preferably, an optical system (lens system) is provided in the measurement optical path for guiding the measurement light, while an optical system (lens system) is not provided in the reference optical path for guiding the reference light. The difference can be changed.

  In the measurement apparatus using the interferometer according to the present invention, when the reference mirror itself for guiding the reference light is tilted by a small amount, an interference image in the height direction of the sample is obtained in one shot without scanning the laser light. be able to.

  In another preferred embodiment of the present invention, an incident optical path, a measurement optical path, a reference optical path, and a detection optical path are provided along a cross shape around the beam splitter, and an optical optical path difference is provided between the reference optical path and the measurement optical path. In addition, the reference mirror is tilted by a minute amount (fixed or tilted) to form interference fringes on the detection means. Thereby, it is possible to obtain an interference image in the height direction of the sample in one shot without scanning the laser beam.

  A beam splitter is provided as a polarizing means, and part of the light is guided by the beam splitter to reflect the light.

  The detection means provided in the detection optical path receives reflected light from the object to be measured and reflected light from the reference mirror by a beam splitter (polarization means). Then, interference fringes are formed on the detection means.

  In order to make it possible to use laser light of two wavelengths, a semiconductor laser (LD) or a light emitting diode (LED) and a super light emitting diode (SLD) are provided in two branched light paths of the incident light path of the laser light, respectively. .

  In another preferred embodiment of the present invention, a lens is arranged on the measurement optical path side, and no lens is arranged on the reference optical path side. Doing so gives an optical path difference. Furthermore, the surface shape of the object to be measured such as a wafer can be measured by slightly tilting the reference mirror (fixed type or tilting type).

  As a modification, in order to give an optical optical path difference, a lens is not arranged on the measurement optical path side that guides light to the object to be measured (sample), but a lens is arranged on the reference optical path side that guides light to the reference mirror. It is also possible to do.

  According to the best mode of the present invention, the surface shape of a sample (object to be measured) such as a wafer and the accurate coordinate position of dust (foreign matter) or pole piece on the surface are specified, and an electron microscope and a drawing apparatus are specified. Send and receive accurate data to and from charged particle beam equipment, etc., and further quickly inspect the surface shape, foreign matter such as dust, and inspection of pole pieces, etc., to further contribute to the improvement of work efficiency such as semiconductor inspection Can do.

  FIG. 1 schematically shows a measuring apparatus according to a preferred embodiment of the present invention.

  As shown in FIG. 1A, any two light sources of the semiconductor laser (LD) or the light emitting diode (LD) 10 and the super light emitting diode (SLD) 12 are used as the light sources of the two-wavelength laser light, and particularly low coherence. Provided on the incident side as a light source. Preferably, a light emitting diode (LED) having a wavelength λ = 650 nm, a super light emitting diode (SLD) having a wavelength λ = 800 nm, a semiconductor laser (LD) having a wavelength λ = 800 nm to 900 nm, or the like is used.

  However, in the present invention, it is also possible to use two-wavelength laser light from other low-coherence light sources.

  Centering on the beam splitter 2, at least four optical paths, that is, an incident optical path 4, a measurement optical path 6, a reference optical path 8, and a detection optical path 9 are arranged along a cross shape.

  The incident optical path 4 is branched into two branched optical paths 4a and 4b at the incident beam splitter 13. The lens 11 and the light emitting diode 10 are arranged in one branched optical path 4a, and the lens 15 and the super light emitting element are arranged in the other branched optical path 4b. A diode 12 is arranged.

  The detection optical path 9 is also branched into two branch optical paths 9a and 9b at the incident beam splitter 17, and one CCD a18 of the detecting means 16 is arranged in one branch optical path 9a, and detected in the other branch optical path 9b. The other CCDb 20 of the means 16 is arranged.

  In the illustrated example, a lens 21 is disposed in the measurement optical path 6. The laser beam is irradiated onto the sample 23 through the measurement optical path 6.

  No lens is disposed in the reference optical path 8. Therefore, the laser light is guided directly to the reference mirror 30 through the reference light path 8.

  The reference mirror 30 is fixed by being tilted by a small amount with respect to the optical axis of the reference optical path 8 as indicated by a one-dot chain line 29 in FIG. For example, the inclination angle is preferably about 15 minutes (that is, 15/60 degrees).

  The reference mirror 30 does not have the above-described fixing method, and as a modification, the reference mirror 30 tilts within a desired tilt angle (particularly, from several seconds (for example, 4, 5 seconds) to several tens of seconds (20, 30 seconds)). You may make it incline by the system which vibrates with a period).

  In the illustrated example, the optical path difference is provided between the reference optical path 8 and the measurement optical path 6 by providing the lens 21 in the measurement optical path 6 and not providing the lens in the reference optical path 8, but as a modification, An optical optical path difference may be provided between the reference optical path 8 and the measurement optical path 6 by providing a lens (not shown) in the reference optical path 8.

  As another modification, the same lens as the lens 21 in the measurement optical path 6 for guiding the measurement light can be provided in the reference optical path 8 for guiding the reference light in a detachable manner. The lens may be taken out from the reference optical path 8 for guiding the reference light, and the reference optical path 8 may have an optical path length (optical optical path length) different from that of the measurement optical path 6.

  Thus, in any form, an optical optical path difference is provided between the reference optical path 8 and the measurement optical path 6, and the reference mirror 30 is slightly tilted. For example, the reference mirror 30 is slightly tilted by an angle of about 15 minutes (that is, 15/60 degrees). Due to the inclination of the reference mirror 30, the reflected light from the sample 23 interferes with the reference light from the reference mirror 30 without scanning the surface of the sample 23, and interference fringes are generated in the detection means 16.

  The detection means 16 includes a CCD a 18 that detects a focused wave (waveform) and a CCD b 20 that detects a standing wave (waveform). One CCDa 18 has a plurality of detectors, and these detectors detect a plurality of focused waves (waveforms) having different frequencies according to the light intensity.

  FIG. 1B shows an example of three detectors 18a, 18b, and 18c. In FIG. 1B, three detectors 18a, 18b, and 18c are arranged in order from the bottom. Corresponding to these, three half mirrors 18d, 18e, and 18f are provided to detect a focused wave (9/10, 9/100, 1/100) as shown on the right side.

  As shown in FIG. 1C, when obtaining the maximum value (peak) of the waveform (focused wave), the waveform (focused wave) acquired by the CCDa 18 is multiplied by the stationary wave of the CCDb 20 to obtain the waveform (focused wave). It is preferable that the maximum value (peak) of the above is raised to facilitate detection.

  Preferably, calibration is performed using one bit (for example, 256) of the CCDb 20 as a reference of the scale. For example, it subdivides by 1/256 and multiplies by 1 bit (for example, 256).

  For a focused wave (waveform), it is not always necessary to detect a signal from the convergence end. For example, a signal from a predetermined position on the horizontal axis (x axis, space axis) in FIG. 2 may be detected. By using one bit of the CCDb 20, the signal detection range can be freely determined.

  In the preferred embodiment of the present invention, as shown in FIG. 2A, the envelope waveform of the CCDa 18 is detected in the processing step 1, and x is obtained from the following relational expression.

Te <ex
However, x represents a DC (current) component, and T represents one cycle.

  The position of the maximum value of the envelope waveform shown in FIG. 2A is detected as a reference position.

  It is preferable to obtain the position indicating the maximum value of the envelope waveform of the CCDa 18 as the reference position using the position indicated by the arrow in FIG.

  FIG. 2C shows one periodic waveform. Thus, it is preferable to obtain the phase measurement of the waveform of the CCDb 20 shown in FIG.

  Also, the phase can be obtained by precision Fourier transform. That is, the spatial frequency is detected and the phase is measured by Fourier with a slight bit length variation. In this case, the spatial frequency at which the accuracy of N times the accuracy obtained in one cycle is obtained is determined by the measuring device. Therefore, as long as there is no change in conditions such as temperature, it is constant, so that the spatial frequency may be detected from time to time.

  FIG. 3 shows an outline of a measuring apparatus according to the second preferred embodiment of the present invention.

  In FIG. 3, the measuring apparatus includes a pulse laser 66, a collimating lens 68, a beam splitter 69, a long working objective lens 74, a glass plate 75, a test surface 77, a reference mirror 70, a cylinder lens 72, a long working objective lens 74, and a cylinder. A lens 76, an area sensor 78, and the like are included. The reference mirror 70 is arranged slightly tilted as indicated by a broken line 71.

  Also in the case of the second embodiment, a laser light source of a semiconductor laser (LD), a light emitting diode (LD), or a super light emitting diode (SLD) is used, but the light emitting diode (LD) and the super light emitting diode (SLD) have two wavelengths. As a laser light source, particularly as a low coherence light source, it is provided on the incident side. Preferably, a light emitting diode (LED) having a wavelength λ = 650 nm, a super light emitting diode (SLD) having a wavelength λ = 800 nm, or the like is used. When a semiconductor laser (LD) is used, a pulse laser with a wavelength of about 800 nm to 900 nm (center wavelength: 850 nm to 890 nm) may be used. In the case of a semiconductor laser, when the intensity (power, P) in relation to the current (I) exceeds a predetermined threshold value (Ith), the intensity (power) of the laser light is proportional to the current (linear relation). However, up to a predetermined threshold (Lth), LED light emission or SLD light emission is used, so a semiconductor laser (LD) that emits light with a constant amount of light is set to a very small current value. Thus, the inside of the surface of the sample can be observed and inspected by passing the interferometer with one light source (for example, a semiconductor laser (LD)). When a light-emitting diode (LED) is used as a light source, the light is condensed by a collimator lens or the like and then provided with a very narrow slit having a width of several nanometers or several micrometers, thereby providing a line width of several μm (for example, 2 to 3 μm). The sample may be irradiated with a linear light beam having a length of about 250 to 300 μm.

  In the present invention, the pulse laser 66, which is a semiconductor laser (LD), emits LEDs as described above, and an extremely narrow slit 80 having a width of several nanometers or several micrometers is disposed on the image side of the collimator lens immediately after the pulse laser 66. Thus, the sample is irradiated with a linear light beam having a line width of several μm (for example, 2 to 3 μm) and a length of about 250 to 300 μm. Further, the reference mirror 70 (Reference Mirror) is tilted to a minute amount fixed type or tilted type (particularly vibration type) as indicated by reference numeral 71, and the position of the interference end is measured. For example, the reference mirror 70 is fixed to a minute amount (in the best form, an angle of 15 minutes (that is, 15/60 degrees)) or is tilted (especially vibration) as necessary. By tilting, an interference fringe is formed on the area sensor 78. In this way, an interference image in the height direction can be obtained with one shot without scanning with laser light. In addition, the position of the interference end can be measured using a Michelson-type interferometer with low coherence.

(A) is explanatory drawing which shows the outline of the measuring apparatus by the preferable 1st Example of this invention. (B) shows the waveforms of the three detectors of CCDa side by side. (C) shows the waveforms of CCDa and CCDb side by side. (A) is explanatory drawing in the case of detecting the envelope roll waveform of CCDa. (B) is explanatory drawing in the case of detecting the reference position shown with an arrow. (C) is explanatory drawing in the case of measuring the phase of a CCDb waveform by precise measurement. Explanatory drawing which shows the outline of the measuring apparatus by the preferable 2nd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light emitting diode 12 Super light emitting diode 16 Detection means 18 CCDa
20 CCDb

Claims (2)

In an interference microscope that observes and inspects fine irregularities on the sample surface and internal height information using a two-beam interferometer that divides a light beam having a finite coherence distance into two parts and irradiates the sample and a reference mirror.
A means for shaping and dividing a linear light beam, a reference optical path for guiding and irradiating the light beam to the reference mirror, a condensing means for condensing and irradiating the sample with the light beam at a point, and a fine reflection from the sample, By providing a measurement optical path that condenses scattered light, converts it into a light beam, and guides it, and by providing a small amount of inclined optical path difference in the reference light path, the reference mirror and the line on the sample surface are positioned where the light flux from the sample overlaps. An interference fringe distribution having the height distribution information in the direction is formed, and the height distribution information can be obtained without moving the sample in the vertical direction or moving the interference fringes , and the detection means for generating the interference fringes is provided. The detection means includes a CCDa for detecting a focused wave (waveform) and a CCDb for detecting a standing wave (waveform). The CCDa has a plurality of detectors, and the detectors according to the light intensity. Multiple focused waves (waveforms) with different frequencies When detecting the maximum value (peak) of the waveform (focused wave), the waveform (focused wave) acquired by the CCDa is multiplied by the CCDb stationary wave to obtain the maximum value (peak) of the waveform (focused wave). ), And a calibration is performed using one bit of CCDb as a scale reference . Using a two-beam interferometer that divides a light beam shaped from a point light source with a finite coherence distance and irradiates the sample and a reference mirror, observation and inspection of minute irregularities on the sample surface and internal height information In the interference microscope that
A reference optical path for guiding and irradiating a light beam to a reference mirror, a condensing means for condensing and irradiating the sample with a light beam at a point, and a fine reflection and scattered light from the sample are collected and converted into a light beam and guided. By providing a measurement optical path to be measured and providing a slight amount of inclined optical path difference in the reference optical path, a reference mirror and an interference fringe having height information are formed at a position where light beams from the sample overlap, Alternatively , the height information can be acquired without moving the interference fringes , and furthermore, a detection means for generating the interference fringes is provided. The detection means includes a CCDa for detecting the focused wave (waveform) and a standing wave (waveform). The CCDa has a plurality of detectors and detects a plurality of focused waves (waveforms) having different frequencies according to the light intensity by the detectors. ) Maximum value (peak) When that, in the waveform (focused wave) acquired by CCDA, over a standing wave of ccdB, was embossed maximum value of the waveform (focusing wave) (peak), and, to calibrate the 1-bit ccdB as a reference scale A measuring device.

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