Measuring device and measuring method

Abstract

To provide a measurement device capable of accurately measuring birefringence property on a sample surface, and a measurement method.SOLUTION: A measurement device 100 comprises: a light source 11 which generates illumination light L1; a photodetector 43 which detects reflection light L2 from a sample 30 illuminated with the illumination light L1; a confocal optical system 110 including an objective lens 24 which condenses the illumination light L1 onto a surface of the sample 30, guiding the illumination light L1 to the sample 30 and guiding the reflection light L2 reflected by the sample 30 to the photodetector 43; an analyzer 42 which is disposed rotatably within the confocal optical system 110 in such a manner that reflection light from the objective lens 24 is made incident; and a processing unit 60 which calculates birefringence property on the surface of the sample 30 on the basis of a plurality of confocal images captured while changing a rotation angle of the analyzer 42.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a measurement device and a measurement method. [Background technology]

[0002] Patent Document 1 discloses an apparatus for measuring birefringence using an analyzer. In Patent Document 1, linearly polarized or circularly polarized light is incident on a disk substrate. The transmitted or reflected light from the disk substrate is guided to the analyzer. The analyzer is rotated, and the birefringence is measured from the change in the amount of light that passes through the analyzer and enters a photodetector.

[0003] Non-Patent Document 1 discloses a two-dimensional birefringence measurement method using a phase shift method. In Non-Patent Document 1, the incident light incident on a sample is circularly polarized. The transmitted light that passes through the sample is detected by a photodetector via a quarter-wave plate and an analyzer. The quarter-wave plate is changed between 0° and 45°. Furthermore, the analyzer is rotated in 45° increments between 0° and 135°. Then, the principal axis orientation and magnitude of birefringence are determined from eight images. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-5545 [Non-patent literature]

[0005] [Non-Patent Document 1] "Two-dimensional birefringence measurement by phase shift method" Yukitoshi Otani, Toru Yoshizawa, Optics, Vol. 27, No. 12, 1998, pp. 698-703 Summary of the Invention [Problem to be solved by the invention]

[0006] For compound semiconductors such as SiC and GaN, and high-quality crystals such as piezoelectric crystals, various inspections are required in addition to the crystal defects that appear on the surface. For example, it is desirable to inspect and evaluate optical properties that cannot be measured directly, such as crystal distortion, birefringence, and surface roughness.

[0007] These optical properties can be measured using X-ray topography, interferometry, and spectrophotometers. However, since these methods measure transmitted light through the sample, it is difficult to accurately measure the properties of the sample's outermost surface. Furthermore, these measurement methods are susceptible to the influence of surface irregularities, so the surface must be polished.

[0008] In Non-Patent Document 1, transmitted light is detected, making it difficult to measure the characteristics of the surface state of the sample. In Patent Document 1, reflected light from the front surface of the sample and reflected light from the back surface of the sample are also detected, making it difficult to accurately measure the surface state.

[0009] The present disclosure has been made in consideration of such problems, and provides a measurement device and a measurement method that can accurately measure the birefringence characteristics on a sample surface. [Means for solving the problem]

[0010] A measurement device according to one aspect of this embodiment includes a light source that generates illumination light, a photodetector that detects reflected light from a sample illuminated with the illumination light, a confocal optical system that has an objective lens that focuses the illumination light on the surface of the sample and guides the illumination light to the sample and guides reflected light reflected by the sample to the photodetector, an analyzer that is rotatably disposed within the confocal optical system so that reflected light from the objective lens is incident thereon, and a processing unit that calculates the birefringence characteristics of the surface of the sample based on a plurality of confocal images taken by changing the rotation angle of the analyzer.

[0011] In the above measurement apparatus, the processing unit may calculate at least one of a principal axis direction of birefringence and a birefringence phase difference as the birefringence characteristics.

[0012] In the above-described measuring device, when a reference angle is set to 0° in terms of the rotation angle of the analyzer, the confocal images may be captured when the rotation angle of the analyzer is 0°, 45°, 90°, and 135°.

[0013] The measuring device may further include a rotatable quarter-wave plate arranged in the optical path of the reflected light, the reflected light having passed through the quarter-wave plate being incident on the analyzer, and a plurality of confocal images may be captured by changing the rotation angle of the quarter-wave plate.

[0014] In the above-described measuring apparatus, the sample may be illuminated with the illumination light that is circularly polarized.

[0015] The above-described measuring method may further include a differential interference prism disposed in the optical paths of the illumination light and the reflected light.

[0016] A measurement method according to one aspect of this embodiment is a measurement method using a confocal microscope including a light source that generates illumination light, a photodetector that detects reflected light from a sample illuminated with the illumination light, a confocal optical system that has an objective lens that focuses the illumination light on the surface of the sample and guides the illumination light to the sample and guides reflected light reflected by the sample to the photodetector, and an analyzer that is rotatably arranged within the confocal optical system so that reflected light from the objective lens is incident thereon, the measurement method including the steps of: acquiring a plurality of confocal images by changing the rotation angle of the analyzer; and calculating the birefringence characteristics of the surface of the sample based on the plurality of confocal images.

[0017] 8. The measurement method according to claim 7, wherein at least one of a principal axis direction of birefringence and a birefringence phase difference is calculated as the birefringence characteristics.

[0018] 9. The measurement method according to claim 7, wherein the confocal images are captured when the rotation angle of the analyzer is 0°, 45°, 90°, and 135°, where a reference angle is 0° in terms of the rotation angle of the analyzer.

[0019] In the above measurement method, a rotatable quarter-wave plate may be disposed in the optical path of the reflected light, the reflected light having passed through the quarter-wave plate may be incident on the analyzer, and a plurality of confocal images may be captured by changing the rotation angle of the quarter-wave plate.

[0020] In the above measurement method, the sample may be illuminated with the illumination light that is circularly polarized.

[0021] In the above measurement method, a differential interference prism may be disposed in the optical paths of the illumination light and the reflected light. [Effects of the Invention]

[0022] According to the present disclosure, it is possible to provide a measurement device and a measurement method that can accurately measure the birefringence characteristics on the surface of a sample. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram showing the overall configuration of a measurement device according to a first embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating the cross-sectional shape of a sample. [Figure 3] FIG. 1 is a schematic diagram for explaining the disorder of the crystal grain arrangement of a sample. [Figure 4] 10A and 10B are diagrams illustrating the difference in the angle of elliptically polarized light depending on the azimuth angle of crystal particles. [Figure 5] 10 is a graph showing a change in the amount of emitted light depending on the principal axis direction. [Figure 6] 1 is a graph showing the principal axis orientation of a crystal and the azimuth angle obtained by analysis. [Figure 7] 1 is a flowchart showing a measurement method according to the first embodiment. [Figure 8] FIG. 10 is a schematic diagram showing the overall configuration of a measurement device according to a second embodiment. [Figure 9] 10 is a flowchart showing a measurement method according to the second embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the overall configuration of a measurement device according to a third embodiment. [Figure 11] 10 is a flowchart showing a measurement method according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description shows a preferred embodiment of the present invention, and the scope of the present invention is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same content.

[0025] Embodiment 1 The measurement device according to the first embodiment detects light reflected by a sample via a confocal optical system. The measurement device performs measurements on the sample surface based on the detection results of the reflected light. For example, the measurement device performs processing to measure birefringence characteristics such as the principal axis orientation of birefringence and birefringence index. The sample can be a compound semiconductor such as SiC or GaN, or a wafer of piezoelectric crystal.

[0026] A measurement apparatus 100 according to the first embodiment will be described with reference to Fig. 1. The measurement apparatus 100 includes a light source 11, a confocal optical system 110, a stage 31, a photodetector 43, and a processing unit 60. The measurement apparatus 100 is a confocal microscope having the confocal optical system 110.

[0027] The light source 11 generates illumination light L1 that illuminates the sample 30. The light source 11 can be, for example, a laser light source or a lamp light source. The confocal optical system 110 guides the illumination light L1 to the sample 30. For example, it is a line confocal optical system. That is, it forms a linear illumination area on the sample 30.

[0028] The confocal optical system 110 includes a filter 12, a polarizing plate 13, a first quarter-wave plate 14, a lens 15, a slit 16, a half mirror 21, a scanner 22, a lens 23, an objective lens 24, a lens 41, and an analyzer 42.

[0029] Illumination light L1 from light source 11 is incident on filter 12. Filter 12 is, for example, a bandpass filter that transmits only light of a predetermined wavelength. Illumination light L1 from filter 12 is collected by lens 15 and incident on slit 16. Slit 16 is positioned conjugate with the focal plane of objective lens 24. Slit 16 converts the illumination light into a line. Illumination light L1 that passes through slit 16 is converted into circularly polarized light by polarizing plate 13 and first quarter-wave plate 14.

[0030] The circularly polarized illumination light L1 enters the scanner 22 via a half mirror 21. The half mirror 21 is a beam splitter that splits the optical paths of the illumination light L1 and the reflected light L2 from the sample 30. The half mirror 21 transmits half of the incident light and reflects the other half.

[0031] The arrangement of the optical elements in the confocal optical system 110 is not limited to the arrangement shown in Fig. 1. For example, the polarizing plate 13 and the first quarter-wave plate 14 may be arranged between the lens 15 and the filter 12. In other words, the illumination light L1, which has become circularly polarized, may pass through the lens 15 and the slit 16.

[0032] The scanner 22 is a vibrating mirror, a galvanometer mirror, a rotating mirror, etc., and deflects the illumination light L1. For example, the illumination light L1 scans the sample 30 in a direction perpendicular to the longitudinal direction of the linear illumination area.

[0033] The illumination light L1 scanned by the scanner 22 is incident on the objective lens 24 via the lens 23. The objective lens 24 focuses the illumination light L1 on the surface of the sample 30. In other words, the focal point of the objective lens 24 is the surface of the sample 30. Furthermore, since the slit 16 and the focal point of the objective lens 24 have a conjugate imaging relationship, a linear illumination area corresponding to the slit direction is formed on the sample 30. For example, the longitudinal direction of the linear illumination area on the sample 30 can be the X direction, and the scanning direction of the scanner 22 can be the Y direction.

[0034] The sample 30 is placed on a stage 31. The stage 31 is a movable stage that moves the sample 30 in the X, Y, and Z directions. A Z scan is performed by the stage 31. By moving the stage 31 in the Z direction, the focusing position of the illumination light L1 can be aligned with the surface of the sample 30. Of course, the focusing position may be aligned with the surface of the sample 30 by moving the objective lens 24 along the optical axis instead of the stage 31. By performing a Z scan, an all-in-focus image and a height image of the sample 30 can be obtained. Furthermore, if the surface unevenness is small, the sample 30 may be imaged with the focus on the surface without performing a Z scan.

[0035] The reflected light L2 reflected by the sample 30 is refracted by the objective lens 24 and the lens 23 and enters the scanner 22. The reflected light L2 is descanned by the scanner 22 and enters the half mirror 21. The half mirror 21 reflects half of the reflected light L2 in the direction of the lens 41.

[0036] The lens 41 focuses the reflected light L2 from the half mirror 21 onto the light receiving surface of the photodetector 43. The photodetector 43 is, for example, a line sensor in which a plurality of pixels are arranged in a row. The pixels of the photodetector 43 are arranged along a direction corresponding to the linear illumination area. The light receiving surface of the photodetector 43 and the focal plane of the objective lens 24 are arranged in a conjugate position. The photodetector 43 detects the reflected light from the surface of the sample 30 via the confocal optical system 110.

[0037] Of course, the photodetector 43 is not limited to a line sensor, but may be a zero-dimensional sensor. When a zero-dimensional sensor is used, a confocal optical system can be configured by combining it with a pinhole or a point light source. Furthermore, when a zero-dimensional sensor is used as the photodetector 43, the slit 16 is not necessary.

[0038] The stage 31 changes the height of the sample 30 so that the surface of the sample 30 becomes the focal position of the illumination light L1. Figure 2 is a diagram schematically showing the cross-sectional shape of the sample 30. The solid line shows the illumination light L1 when the focal position of the illumination light L1 is aligned with the surface 30a of the sample 30. The dashed line shows the illumination light L1' when the focal position of the illumination light L1 is shifted from the surface 30a of the sample 30. In Figure 2, the surface of the sample 30 facing the objective lens 24 (not shown in Figure 2) is the front surface 30a, and the surface of the sample 30 facing the stage 31 is the back surface 30b.

[0039] In the confocal optical system 110, when the front surface 30a of the sample 30 is the focal position of the illumination light L1, the amount of light detected by the photodetector 43 is the highest. In other words, the photodetector 43 does not detect light reflected from surfaces that are out of the focal plane of the objective lens 24. The photodetector 43 does not detect light reflected from surfaces other than the front surface 30a of the sample 30. The photodetector 43 does not detect light reflected from the back surface 30b of the sample 30. Since the influence of light reflected from the back surface 30b of the sample 30 can be suppressed, it is possible to accurately measure the front surface 30a of the sample 30.

[0040] By using the confocal optical system 110, direct measurement is possible even if the surface 30a is uneven or tilted. In other words, measurement can be performed without being affected by optical constants. Furthermore, even if the surface 30a is uneven, a focus can be formed over the entire surface 30a. As described above, it is possible to cut out reflected light from the back surface 30b. Furthermore, even if a pattern such as a metal film 30c is provided, it does not affect the measurement. The height image of the sample 30 can be used as a correction image to check the effects of polarization and tilt angle.

[0041] When measuring surface irregularities with an optical interferometer, if crystalline and metal surfaces are mixed in the field of view, the steps between them cannot be measured accurately. This is because the optical constants are affected differently depending on the material. On the other hand, height measurements using the confocal optical system 110 are not affected by materials with different optical constants, so steps and slope shapes can be measured accurately. Information on surface roughness, steps, and tilt angle can be obtained from height images accurately measured by the confocal optical system 110. Based on this information, it is possible to evaluate the accuracy of polarization measurement results and make corrections. Because the polarization state changes depending on the tilt angle, the polarization measurement results can be corrected taking this into account.

[0042] As described above, the scanner 22 scans the sample 30 with the illumination light L1. This allows the measurement device 100 to acquire a confocal image of the surface of the sample 30. The photodetector 43 captures a confocal image in which the surface of the sample 30 is the focal point. The confocal image is a two-dimensional image in the X and Y directions. When capturing reflected light with the confocal optical system 110, there are two ways to capture images: normal capture without performing a Z scan, and capture an image (all-in-focus image) in which the entire field of view is in focus using a Z scan (focus scan). The latter all-in-focus image is used for surfaces with large irregularities. By performing a Z scan, the reflected image and the surface irregularities can be measured simultaneously, allowing a height image to be acquired.

[0043] An analyzer 42 is disposed between the lens 41 and the photodetector 43. The analyzer 42 is rotatably disposed in the optical path of the reflected light L2. The rotation axis of the analyzer 42 is parallel to the optical axis. The analyzer 42 is a polarizer that transmits only a predetermined linearly polarized light component. In other words, linearly polarized light parallel to the transmission axis of the analyzer 42 is detected by the photodetector 43. Furthermore, by rotating the analyzer 42, the direction of the linearly polarized light detected by the photodetector 43 can be changed.

[0044] 1, the analyzer 42 is disposed immediately before the photodetector 43, but the position of the analyzer 42 is not particularly limited. The analyzer 42 may be disposed closer to the photodetector 43 than the half mirror 21. The analyzer 42 may be disposed within the confocal optical system 110 so that the reflected light L2 branched from the illumination light L1 by the half mirror 21 is incident on the analyzer 42.

[0045] The processing unit 60 acquires a confocal image captured by the photodetector 43. The processing unit 60 acquires confocal images at each rotation angle of the analyzer 42. The processing unit 60 is an information processing device such as a personal computer. The processing unit 60 has a memory for storing multiple confocal images. The processing unit 60 stores the amount of light detected by the photodetector 43 in association with XYZ coordinates. The processing unit 60 constructs an all-in-focus image, for example, by associating the XYZ coordinates with the amount of detected light. Specifically, the all-in-focus image is a two-dimensional reflection intensity (bright field) image. The processing unit 60 also acquires a height image of the sample 30. The height image is reconstructed within the processing unit 60 so that it is three-dimensional (height is represented by the grayscale of the image).

[0046] The processing unit 60 also has a processor for performing calculations using the phase shift method (phase shift calculations). The processing unit 60 may control a motor for rotating the analyzer 42. Furthermore, the processing unit 60 may control the driving of the stage 31.

[0047] The optical anisotropy due to the crystals of sample 30 will now be described with reference to FIG. 3. FIG. 3 is a plan view schematically showing particles of crystal 30d provided in sample 30. Since crystals have birefringence, the refractive index varies depending on the direction. Refractive index n1 is the refractive index in the slow axis, and refractive index n2 is the refractive index in the fast axis, which is perpendicular to the slow axis.

[0048] If the crystal grain arrangement is disordered, the directions of the refractive indices n1 and n2 change depending on the azimuth angle of the crystal grains. The disorder in the crystal grain arrangement here is not limited to planar disorder in the XY direction, but is a three-dimensional disorder including the Z direction. The angle of the principal axis of birefringence changes depending on the azimuth angle of the crystal grains. Furthermore, distortion on the sample surface can be simulated as a three-dimensional crystalline disorder.

[0049] The polarization state of reflected light L2 when circularly polarized illumination light L1 is irradiated onto sample 30 will be described with reference to Figure 4. Due to the influence of birefringence caused by surface reflection, reflected light L2 becomes elliptically polarized light. When crystal particles are formed so that the major axis of birefringence is 0°, reflected light L2 becomes elliptically polarized light LP1 with the X axis as the major axis and the Y axis as the minor axis. The electric field on the X axis of elliptically polarized light LP1 is defined as E1, and the electric field on the Y axis is defined as E2.

[0050] When a crystal is formed with the principal axis of birefringence at φ, the reflected light L2 becomes elliptically polarized light LP2, with the direction of the elliptically polarized light LP1 rotated by φ. In other words, the angle of the elliptically polarized light changes depending on the principal axis direction φ. Note that φ is an angle between -180° and 180°.

[0051] Here, the rotation angle of the analyzer 42 is θ. The rotation angle θ is the angle of the transmission axis of the analyzer 42 from the Y axis. Since the reflected light L2 is elliptically polarized, changing the rotation angle θ changes the amount of reflected light L2 detected by the photodetector 43. Even if the rotation angle θ is the same, the amount of detected light changes depending on the principal axis orientation, that is, the azimuth angle of the crystal grain. Therefore, detection can be performed at multiple rotation angles θ, and the azimuth angle of the crystal grain can be determined.

[0052] In order to perform measurements using the phase shift method or the like disclosed in Non-Patent Document 1, the rotation angle θ of the analyzer 42 is changed. The rotation angle θ is changed in increments of 45°, and reflected light is detected. For example, the initial rotation angle θ is set to a reference angle of 0°, and reflected light L2 is detected at four rotation angles of 0°, 45°, 90°, and 135°. In other words, by changing the rotation angle of the analyzer 42, four confocal images are captured.

[0053] Here, the detected light intensity when θ=0° is I1, and the detected light intensity when θ=45° is I2. The detected light intensity when θ=90° is I3, and the detected light intensity when θ=135° is I4. Figure 5 is a graph showing the change in the detected light intensity I(φ). Figure 5 shows the results of a simulation where E1=2 and E2=1. The birefringence phase difference is calculated as the phase difference of a quarter wave plate of 90°. Here, the simulation was performed by changing φ in the range of -180° to 180°.

[0054] If the principal axis direction of birefringence obtained by analysis using the phase shift method is taken as the analysis azimuth angle φcal, the analysis azimuth angle φcal can be calculated from the following equation (1).

number

[0055] Figure 6 shows the analytical azimuth angle φcal calculated using equation (1). By calculating the analytical azimuth angle φcal using the phase shift, the principal axis orientation φ of the measurement area can be accurately measured. In this way, the principal axis orientation φ can be determined in the range of -90° to 90°. By converting the principal axis orientations to gray levels, the distribution of the orientation angles of the crystals on the surface of the sample 30 can be visualized as a two-dimensional image. Note that Figures 5 and 6 show the results of calculations under the condition that the birefringence phase difference due to reflection is 0°.

[0056] Next, the birefringence phase difference Δcal calculated by phase shift calculation will be described. Δcal is the birefringence phase difference due to surface reflection, and can be calculated by the following formula (2).

number

[0057] Here, I0=(I1+I2+I3+I4) / 2. In this way, the principal axis direction φ and the birefringence phase difference Δcal can be obtained by the phase shift method. The processing unit 60 calculates the birefringence characteristics of the sample surface based on a plurality of confocal images acquired by changing the rotation angle of the analyzer 42. The measurement method according to this embodiment will be described below with reference to FIG. 7. FIG. 7 is a flowchart showing the measurement method.

[0058] First, the processing unit 60 rotates the analyzer 42 (S101). The analyzer 42 may be rotated automatically by a motor or the like, or may be rotated manually by a user. Here, j=1 to 4, with the rotation angle being set at 45° intervals. When j=1, the rotation angle of the analyzer 42 is 0°, which is the reference angle. When j=2, the rotation angle of the analyzer 42 is 45°. When j=3, the rotation angle of the analyzer 42 is 90°, which is the reference angle, and when j=4, the rotation angle of the analyzer 42 is 135°, which is the reference angle.

[0059] Then, the processing unit 60 performs a Z scan (S102). That is, the stage 31 is moved up and down (Z direction). The focal position is adjusted to the surface 30a of the sample 30. At the height of the stage 31 where the detected light intensity is maximized, the focal position coincides with the surface 30a of the sample 30. Then, the processing unit 60 stores the detected light intensity at the in-focus position for each XY coordinate.

[0060] This results in a polarized image I at the focal point. j Polarized image I j is a two-dimensional confocal image in which the detected light amount (received light intensity) of the reflected light L2 is associated with each pixel. For example, when the rotation angle of the analyzer 42 is 0°, j=1, so a polarization image I1 is acquired. In addition, in S102, a height image H is obtained from the change in the detected light amount when a Z scan is performed. j The height image H j is data showing the surface height of the sample 30 according to the XY coordinates.

[0061] Next, the processing unit 60 determines whether j=4 (S103). If j=4 is not true (NO in S103), the processing of S101 and S102 is repeated until j=4 is true. For example, when the rotation angle of the analyzer 42 is 0°, j=1; therefore, the rotation angle is set to 45°, and j=2. The processing unit 60 then performs the Z scan of S102. This allows a polarized image I2 at a rotation angle of 45° to be acquired. Similarly, the processing unit 60 sets the rotation angle to 90° and acquires a polarized image I3 at j=3. The processing unit 60 sets j=4 and acquires a polarized image I4 at j=4. Of course, the order in which the polarized images I1, I2, I3, and I4 are acquired is not particularly limited.

[0062] By performing the processes of S102 and S103, four confocal images are captured. If j=4 (YES in S103), the processing unit 60 performs a phase shift calculation (S104). Here, the processing unit 60 calculates the principal axis direction φ of birefringence using the following equation (3).

number

[0063] Next, the processing unit 60 performs birefringence calculation (S105). Here, the processing unit 60 calculates the birefringence phase difference Δcal using the following equation (4).

number

[0064] In this way, it is possible to measure changes in the polarization state due to surface reflection of the sample 30. The processing unit 60 can calculate the principal axis orientation φ and the birefringence phase difference Δcal for each pixel of the two-dimensional confocal image. This makes it possible to obtain the distribution of the principal axis orientation φ and the birefringence phase difference Δcal in the XY plane. The processing unit 60 can change the display color and shade depending on the principal axis orientation φ and the birefringence phase difference Δcal and display them on the monitor.

[0065] Although the processing unit 60 calculates both the principal axis orientation φ and the birefringence phase difference Δcal in the above embodiment, it may calculate only one of them. That is, the processing unit 60 may calculate only the principal axis orientation φ. Alternatively, the processing unit 60 may calculate only the birefringence phase difference Δcal.

[0066] In this embodiment, a confocal image is acquired as the polarized image, so the influence of reflected light from the back surface 30b of the sample 30 can be suppressed. In other words, reflected light L2 when the focal position coincides with the front surface 30a of the sample 30 is detected via the confocal optical system 110. Therefore, almost no reflected light from the back surface 30b is detected. This allows accurate measurement of the surface of the sample 30. In particular, accurate measurement can be performed even for samples made of materials that transmit illumination light.

[0067] The measurement method according to this embodiment is a measurement method using a confocal microscope. The measurement method includes the steps of acquiring multiple confocal images by changing the rotation angle of the analyzer 42, and calculating the birefringence characteristics of the surface of the sample 30 based on the multiple confocal images. Because the confocal images are used, the principal axis orientation φ and the birefringence phase can be measured with high spatial resolution.

[0068] The measuring apparatus 100 according to this embodiment is capable of measuring various samples, such as compound semiconductor devices and piezoelectric crystals. For example, in the case of compound semiconductor devices, the surface condition significantly affects the device characteristics. Therefore, by determining the principal axis orientation and birefringence phase of the crystal on the surface, more appropriate evaluation can be performed. It is also possible to evaluate points of interest on the surface, such as the vicinity of crystal defects.

[0069] By using the confocal optical system 110 and performing a Z scan (focus scan) during imaging, it is possible to obtain an image in focus across the entire sample, even if the surface is uneven or tilted. Furthermore, since the surface unevenness can be measured simultaneously, it is possible to investigate the correlation between birefringence and unevenness. Furthermore, if the apparent birefringence due to the slope of the surface is large, the tilt angle can be used to correct the birefringence characteristics. Furthermore, a light source 11 with a single wavelength, such as 546 nm, can be used as the illumination light L1. Alternatively, by performing multi-wavelength measurements, the wavelength dispersion of the refractive index can be obtained.

[0070] Furthermore, if there is a wavelength difference that allows wavelength dispersion to be detected sufficiently, it is possible to separate the apparent birefringence due to surface shape, etc., from the true birefringence through calculation by measuring multiple wavelengths. In this case, simultaneous equations can be solved based on the detection results obtained from measurements at multiple wavelengths. For example, measurements are taken at wavelengths of 546 nm, 450 nm, and 650 nm. In this way, the wavelength dispersion of the birefringence characteristics can be evaluated.

[0071] By measuring the birefringence characteristics using the measurement device 100, highly precise distributions of the birefringence phase difference Δ and the principal axis orientation φ can be obtained. For example, in the case of a uniaxial crystal, the principal axis orientation φ is ideally aligned with the crystallographic c-axis, but in real crystals, the crystal may be distorted due to factors such as the growth method. Therefore, distributions in the principal axis orientation may occur, which could be used to improve crystal growth and polishing methods. By observing the light reflected from the surface, dislocation defects on the observed surface can be observed (by observing strain). Furthermore, even if there are no scratches in the form of surface irregularities on the observed surface, it is possible to observe a processing-affected layer (i.e., latent scratches) that remains as stress strain.

[0072] It is also possible to simultaneously illuminate the area with three monochromatic lights, starting with white light, and use a 3-CCD (Charged Coupled Device) camera to perform simultaneous multi-wavelength measurements and acquire color images. Furthermore, since it is sufficient to detect reflected light L2 from the area illuminated with illumination light L1, measurements can be performed non-destructively. In this case, filter 12 can be a filter that transmits three wavelengths. Furthermore, optical elements such as first quarter-wave plate 14 can be designed to have appropriate characteristics for each of the three wavelengths.

[0073] Embodiment 2 A measurement device according to the second embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram showing the overall configuration of a measurement device 100. In this embodiment, a second quarter-wave plate 44 is added to the configuration of the first embodiment. The basic configuration other than the second quarter-wave plate 44 is the same as that of the first embodiment, and therefore the description will be omitted where appropriate.

[0074] The second quarter-wave plate 44 is rotatably disposed in the optical path of the reflected light L2. Specifically, the second quarter-wave plate 44 is disposed between the analyzer 42 and the lens 41. Of course, the location of the second quarter-wave plate 44 is not limited to the position shown in FIG. 8. The second quarter-wave plate 44 may be disposed anywhere between the analyzer 42 and the half mirror 21.

[0075] The second quarter-wave plate 44 is rotatably provided. The rotation axis of the second quarter-wave plate 44 is parallel to the optical axis of the reflected light L2. For example, the processing unit 60 controls a motor (not shown) for rotating the second quarter-wave plate 44. Alternatively, the user may manually rotate the second quarter-wave plate 44.

[0076] The polarization state of the reflected light L2 changes as it passes through the second quarter-wave plate 44. Then, the reflected light L2 that has passed through the second quarter-wave plate 44 enters the photodetector 43 via the analyzer 42. That is, the photodetector 43 detects the reflected light L2 that has passed through the second quarter-wave plate 44 and the analyzer 42.

[0077] Here, the second quarter-wave plate 44 has two rotation angles of 0° and 45°, with a reference angle of 0°. That is, the second quarter-wave plate 44 is rotated at angles of 0° and 45°, and the reflected light L2 is detected at each rotation angle. The polarization state of the reflected light L2 incident on the analyzer 42 changes depending on the rotation angle of the second quarter-wave plate 44.

[0078] The analyzer 42 has four rotation angles: 0°, 45°, 90°, and 135°, as in the first embodiment. Therefore, four confocal images (polarized images) are acquired when the second quarter-wave plate 44 has a rotation angle of 0° and 45°, respectively. In this embodiment, a total of eight confocal images (polarized images) are acquired.

[0079] The measurement method according to this embodiment will be described with reference to FIG. 9. FIG. 9 is a flowchart showing the measurement method. The processing unit 60 rotates the second quarter-wave plate 44 (S201). Here, when i=1, the rotation angle of the second quarter-wave plate 44 is 0°, and when i=2, the rotation angle of the second quarter-wave plate 44 is 45°. First, the processing unit 60 sets the rotation angle of the second quarter-wave plate 44 to 0°.

[0080] Next, the processing unit 60 rotates the analyzer 42 (S202). Here, similar to step S101 in the first embodiment, j=1 to 4, where j=0°, 45°, 90°, and 135°, respectively. First, j=1, and the rotation angle of the analyzer 42 is set to 0°.

[0081] The processing unit 60 performs a Z scan on the stage 31 (S203). As a result, similar to step S102 in the first embodiment, a polarization image P ij and height image H ij Since the rotation angle of the analyzer 42 is 0° and the rotation angle of the second quarter-wave plate 44 is 0°, the processing unit 60 obtains the polarization image P 11 and height image H 11 Get.

[0082] Next, the processing unit 60 determines whether j=4 (S204). If j=4 is not true (NO in S204), the processing of S202 and S203 is repeated until j=4 is true. Here, the rotation angle of the second quarter-wave plate is 0°. If the rotation angle of the analyzer 42 is 0°, j=1, so the rotation angle is set to 45°, and j=2. Then, the processing unit 60 performs a Z scan in S203. As a result, a polarization image P with a rotation angle of 45° is obtained. 12 can be obtained.

[0083] Similarly, the processing unit 60 sets the rotation angle to 90°, and calculates the polarization image P when i=1 and j=3. 13 The processing unit 60 obtains the polarization image P when j=4 and i=1 and j=4. 14 Of course, the polarization image P 11 , P 12 ,P 13 , P 14 The order of acquisition of the above is not particularly limited.

[0084] If j=4 (YES in S204), the processing unit 60 determines whether i=2 or not (S205). If i=2 is not true (NO in S205), the process returns to S201. That is, with i=2, the processes of S202, S203, and S204 are repeated. For example, when the rotation angle of the second quarter-wave plate 44 is 0°, i=1, so the rotation angle is set to 45° and i=2. The processes of S202, S203, and S204 are performed in the same manner. As a result, the polarization image P 21 , P 22 ,P 23 , P 24 The polarized image P 11 , P 12 ,P 13 , P 14 , P 21 , P 22 ,P 23 , P 24 The order in which these are acquired is not particularly limited.

[0085] If i=2 (YES in S205), the processing unit 60 performs a phase shift calculation (S206). Here, the processing unit 60 calculates the principal axis direction φ using the following equation (5).

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[0086] Next, the processing unit 60 performs birefringence calculation (S207). Here, the processing unit 60 calculates the birefringence phase difference Δcal using the following equation (6).

number

[0087] In this way, in the present embodiment, the principal axis orientation φ and the birefringence phase difference Δcal can be accurately measured, as in the first embodiment. Therefore, the orientation angle and crystalline state of the crystal grains can be evaluated. In the first embodiment, the measurement range of the principal axis orientation φ was -90° to +90°, but in the second embodiment, the measurement range of the principal axis orientation φ can be expanded to -180° to 180°.

[0088] Embodiment 3 A measurement apparatus according to a third embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing the overall configuration of the measurement apparatus 100. In this embodiment, the measurement apparatus 100 is a differential interference microscope. The measurement apparatus performs a phase shift method in a differential interference mode.

[0089] 10, a Nomarski prism 25 is added to the configuration of FIG. 8. Furthermore, the first quarter-wave plate 14 is not disposed in the optical path of the illumination light L1. In other words, the first quarter-wave plate 14 has been removed from the configuration of FIG. 8. The configuration other than the Nomarski prism 25 and the first quarter-wave plate 14 is the same as in the first and second embodiments, and therefore, description thereof will be omitted where appropriate.

[0090] Since the first quarter-wave plate 14 is not provided, linearly polarized illumination light L1 enters the scanner 22. The illumination light L1 reflected by the scanner 22 enters the Nomarski prism 25 via the lens 23. The Nomarski prism 25 is a differential interference prism that splits the linearly polarized illumination light L1 into two light beams. In other words, by passing through the Nomarski prism 25, the illumination light L1 becomes two parallel light beams that are shifted laterally by a predetermined shear amount. Note that the differential interference prism is not limited to the Nomarski prism 25, and a Wollaston prism may also be used.

[0091] The two light beams split by the Nomarski prism 25 are orthogonal linearly polarized light. That is, one of the two light beams is ordinary light and the other is extraordinary light. The two light beams split by the Nomarski prism 25 illuminate the sample 30 that is focused by the objective lens 24. The two light beams illuminate different points on the sample 30. Then, each light beam is reflected by the sample 30. Therefore, the reflected light L2 from the sample 30 contains two light beams.

[0092] The reflected light L2 from the sample 30 passes through the objective lens 24 and enters the Nomarski prism 25. The Nomarski prism 25 combines the two light beams. The reflected light L2 then propagates along the same optical path as in the first and second embodiments and is detected by the photodetector 43.

[0093] In this way, the processing unit 60 obtains the differential interference image D j For example, if there is a height difference between the incident positions of the two light beams on the surface of the sample 30, an optical path difference (phase difference) occurs between the two light beams. Therefore, the photodetector 43 obtains a contrast according to the optical path difference.

[0094] In this embodiment, the rotation angle of the second quarter-wave plate 44 is fixed at 0°, and four differential interference images D1 to D4 are acquired. When the rotation angle of the analyzer 42 is 0°, 45°, 90°, or 135°, j=1, 2, 3, or 4. Differential interference image D1 is the differential interference image when the rotation angle of the analyzer 42 is 0°, and differential interference image D2 is the differential interference image when the rotation angle of the analyzer 42 is 45°. Differential interference image D3 is the differential interference image when the rotation angle of the analyzer 42 is 90°. Differential interference image D4 is the differential interference image when the rotation angle of the analyzer 42 is 135°.

[0095] Next, the measurement method according to this embodiment will be described with reference to Fig. 11. First, the processing unit 60 rotates the analyzer 42 (S301). As described above, the rotation angles of the analyzer 42 are set to 0°, 45°, 90°, and 135°, and j=1, 2, 3, and 4, respectively.

[0096] The processing unit 60 drives the stage 31 up and down to perform a Z scan (S302). j Here, since j=1, a differential interference contrast image D1 is acquired. Note that S302 can be omitted.

[0097] Next, the processing unit 60 determines whether j=4 (S303). If j=4 is not true (NO in S303), the processes of S301 and S302 are repeated until j=4 is true. The rotation angle of the second quarter-wave plate is 0°. When the rotation angle of the analyzer 42 is 0°, j=1, so the rotation angle is set to 45°, and j=2. Then, the processing unit 60 performs a Z scan in S302. This makes it possible to acquire a differential interference contrast image D2 at a rotation angle of 45°.

[0098] Similarly, the processing unit 60 sets the rotation angle to 90° and acquires a differential interference contrast image D3 when j = 3. The processing unit 60 sets j = 4 and acquires a differential interference contrast image D4 when j = 4. Of course, the order in which the differential interference contrast images D1, D2, D3, and D4 are acquired is not particularly limited.

[0099] When j=4 (YES in S303), the processing unit 60 performs a phase shift calculation (S304). The processing unit 60 calculates α using the following equation (7).

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[0100] The processing unit 60 calculates the differential amount (S305). The processing unit 60 calculates the differential amount Δh / ΔS using the following equation (8). ΔS is the shear amount caused by the Nomarski prism 25. If the surface height is h(x, y), the differential amount in the shear S direction is Δh / ΔS. The direction of S may be the X direction or the XY diagonal direction.

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[0101] Here, λ is the wavelength of the illumination light L1. The differential amount corresponds to the gradient of the surface height. In this way, steps such as edges can be quantitatively measured. Furthermore, the surface shape can be measured by integration processing.

[0102] It is possible to combine the first to third embodiments as appropriate. For example, by arranging the second quarter-wave plate 44 so that it can be inserted into or removed from the optical path of the reflected light, it is possible to switch between the measurements of the first and second embodiments. Similarly, by arranging the Nomarski prism 25 so that it can be inserted into or removed from the optical paths of the illumination light L1 and the reflected light L2, it is possible to switch between the measurements of the second and third embodiments.

[0103] The processing unit 60 is not limited to being a single physical device. In other words, the processing in the processing unit 60 may be distributed and performed by multiple devices. For example, the processing unit that acquires the detection data from the photodetector 43 may be separate from the storage device that stores the data. Furthermore, the processing unit 60 may be multiple devices that perform distributed processing.

[0104] Some or all of the processing of the processing unit 60 described above may be executed by a computer program. The above-described program can be stored and supplied to a computer using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)). The program may also be supplied to a computer by various types of transitory computer-readable media. Examples of transitory computer-readable media include electrical signals, optical signals, and electromagnetic waves. The transitory computer-readable media can supply the program to a computer via wired communication paths such as electric wires and optical fibers, or via wireless communication paths.

[0105] Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. [Explanation of symbols]

[0106] 11 Light source 12 Filters 13 Polarizing plate 14 First quarter wave plate 15 Lenses 16 Slit 21 Half Mirror 22 Scanner 23 Lens 24 objective lenses 25 Nomarski Prism 30 samples 30a surface 30b back side 30c metal membrane 31 Stages 41 Lens 42 Analyzer 43 Photodetector 44 Second quarter wave plate 60 Processing section 100 Measuring Device 110 Confocal optical system

Claims

1. a light source that generates illumination light; a photodetector that detects reflected light from the sample illuminated with the illumination light; a confocal optical system having an objective lens that focuses the illumination light on a surface of a sample, and that guides the illumination light to the sample and guides light reflected by the sample to the photodetector; a moving means for moving the sample or the objective lens so that the surface of the sample is in focus; an analyzer rotatably disposed within the confocal optical system so that reflected light from the objective lens is incident thereon; a processing unit that calculates birefringence characteristics of the surface of the sample based on a plurality of confocal images captured by changing the rotation angle of the analyzer, the moving means moves the sample or the objective lens to adjust the focal position to the surface of the sample at each rotation angle of the analyzer; the sample is illuminated with circularly polarized illumination light, A measuring device in which the confocal image is acquired by detecting the amount of light when the surface of the sample is at the in-focus position at each coordinate on a plane perpendicular to the optical axis of the objective lens.

2. 2. The measuring apparatus according to claim 1, wherein the processing unit calculates at least one of a principal axis direction of birefringence and a birefringence phase difference as the birefringence characteristics.

3. 3. The measurement device according to claim 1, wherein the confocal images are captured when the rotation angle of the analyzer is 0°, 45°, 90°, and 135°, where a reference angle is 0° for the rotation angle of the analyzer.

4. a quarter-wave plate rotatably disposed in the optical path of the reflected light, The reflected light transmitted through the quarter-wave plate is incident on the analyzer, 4. The measuring device according to claim 1, wherein a plurality of confocal images are captured by changing the rotation angle of the quarter-wave plate.

5. acquiring a surface topography of the sample based on the confocal image; 5. The measuring device according to claim 1, wherein a correlation between the surface irregularity shape and the birefringence characteristics is obtained.

6. a light source that generates illumination light; a photodetector that detects reflected light from the sample illuminated with the illumination light; a confocal optical system having an objective lens that focuses the illumination light on a surface of a sample, and that guides the illumination light to the sample and guides light reflected by the sample to the photodetector; a moving means for moving the sample or the objective lens so that the surface of the sample is in focus; an analyzer rotatably disposed in the confocal optical system so that reflected light from the objective lens is incident thereon, acquiring a plurality of confocal images by changing the rotation angle of the analyzer; calculating birefringence characteristics of the surface of the sample based on the plurality of confocal images; the moving means moves the sample or the objective lens to adjust the focal position to the surface of the sample at each rotation angle of the analyzer; the sample is illuminated with circularly polarized illumination light, A measurement method in which the confocal image is obtained by detecting the amount of light when the surface of the sample is at a focal point at each coordinate on a plane perpendicular to the optical axis of the objective lens.

7. 7. The measurement method according to claim 6, wherein at least one of a principal axis direction of birefringence and a birefringence phase difference is calculated as the birefringence characteristics.

8. 8. The measurement method according to claim 6, wherein the confocal images are captured when the rotation angle of the analyzer is 0°, 45°, 90°, and 135°, where a reference angle is 0° in the rotation angle of the analyzer.

9. a rotatable quarter-wave plate is disposed in the optical path of the reflected light; The reflected light transmitted through the quarter-wave plate is incident on the analyzer, The measurement method according to any one of claims 6 to 8, wherein a plurality of confocal images are captured by changing the rotation angle of the quarter-wave plate.

10. acquiring a surface topography of the sample based on the confocal image; The measurement method according to any one of claims 6 to 9, further comprising obtaining a correlation between the surface irregularity shape and the birefringence characteristics.

Images