Calculation method, imaging method, and imaging device

Abstract

To provide a calculation method, an imaging method, and an imaging device with which it is possible to easily calculate the amount of shear generated by a an optical element disposed in the optical path of an interference optical system.SOLUTION: A calculation method according to the present invention calculates the amount of shear generated by a prescribed optical element that is disposed in the optical path of an imaging optical system 110. The calculation method includes the steps of: capturing the interference image of a quadratic surface by the imaging optical system 110 that is included in an object surface; measuring the fringe interval of interference fringes included in the interference image; and calculating the amount of shear on the basis of the constant in an expression that represents the quadratic surface and the fringe interval.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a calculation method, an imaging method, and an imaging apparatus, and particularly to a technique for calculating a shear amount. Background Art

[0002] Techniques for performing high-speed defect inspection and classification on compound semiconductor wafers, glass substrates, and the like are indispensable for quality control and improvement of devices and products. Patent Document 1 describes a defect inspection apparatus using a differential interference microscope. A differential interference microscope separates illumination light into ordinary light and extraordinary light by a differential interference prism such as a Nomarski prism. The amount of positional deviation between the ordinary light and the extraordinary light is referred to as the shear amount.

[0003] The optical path difference between ordinary light and extraordinary light will be described with reference to FIG. 1. The vertical direction (Z direction) in FIG. 1 represents the height direction. The horizontal direction (S direction) in FIG. 1 represents the direction in which illumination light is separated into ordinary light and extraordinary light, that is, the shear direction. The ordinary light and the extraordinary light are respectively linearly polarized light vibrating in the S direction and linearly polarized light vibrating in a direction perpendicular to the S direction.

[0004] FIG. 1 includes ordinary light and extraordinary light when the shear amount is ΔS1, and ordinary light and extraordinary light when the shear amount is ΔS2. ΔS2 is larger than ΔS1. The upper surface of the sample 50 is inclined at an angle Φ with respect to the horizontal direction. d1 represents the height difference when ordinary light and extraordinary light are reflected on the sample 50 when the shear amount is ΔS1. d2 represents the height difference when ordinary light and extraordinary light are reflected on the sample 50 when the shear amount is ΔS2. d2 is larger than d1. Prior Art Documents Patent Documents

[0005] Patent Document 1 Japanese Unexamined Patent Publication No. 1997-061370 Patent Document 2 Japanese Unexamined Patent Publication No. 2004-037429 [Patent Document 3] Japanese Patent Publication No. 1989-219605 [Patent Document 4] Japanese Patent Publication No. 1989-069933 [Patent Document 5] Patent No. 2527176 [Overview of the project] [Problems that the invention aims to solve]

[0006] When performing inspection or classification using differential interference contrast images, it is preferable to keep the intensity of the received light signal constant in the defect-free planar areas in order to maintain accuracy. This allows inspection to be performed using the same threshold. In order to keep the intensity of the received light signal constant, it is necessary to keep the path difference between normal light and abnormal light generated by the Nomarski prism constant.

[0007] The path difference between normal and abnormal light is determined by the shear amount of the differential interference prism and the position adjustment of the differential interference prism. Therefore, if the shear amount of the differential interference prism can be calculated, the intensity of the received light signal can be kept constant by adjusting the position of the differential interference prism according to the calculation result. Also, if the shear amount of the differential interference prism can be calculated, the intensity of the received light signal can be kept constant by using a differential interference prism with an appropriate shear amount. By keeping the intensity of the received light signal constant, inspection conditions can be kept constant when inspecting various samples using the same device. In addition, differences between different devices of the same design can be reduced. This section describes the challenges of inspecting various samples using the same apparatus. The path difference of a differential interference prism (e.g., Nomarski prism) can be adjusted using a horizontally positioned step. Note that the path difference of a differential interference prism represents the path difference between normal and abnormal light, independent of the sample. However, actual samples (e.g., wafers) contain inclination. In particular, defective areas of a sample contain inclination even if the sample itself is horizontal. Therefore, even if the path difference of the differential interference prism is the same and the same defective area is observed, if the shear amount ΔS is different, the path difference between normal and abnormal light will not be the same, and the brightness will not be the same. Since even areas without defects contain inclination, even if the differential interference prism is adjusted to have the same path difference, if the shear amount ΔS is different, the brightness will not be the same. In this case, it is difficult to perform defect inspection at a predetermined brightness threshold. This section describes an example of a method for reducing machine differences between different devices of the same design. In device A, the differential interference prism is adjusted, i.e., the path difference of the differential interference prism is determined, and the inspection is performed in device B under the same conditions. If the shear amount of the differential interference prism can be measured, it can be determined that the shear amount of the differential interference prism in device A and the shear amount of the differential interference prism in device B are different. If the shear amounts are different, the differential interference prism in device B can be replaced with one whose shear amount falls within the acceptable range, or the position of the differential interference prism can be finely adjusted to compensate for changes in brightness of defective parts, etc., caused by the difference in shear amount.

[0008] Therefore, there is a need to calculate the shear amount of differential interference prisms. However, it is difficult to calculate the shear amount of differential interference prisms based on the step shape of a sample or the inclination angle of a plane. Even when imaging a step shape of a sample with differential interference prisms that have different shear amounts, sufficient differences may not be observed between the differential interference images. In general, the shear amount of a Nomarski prism is about 1 to 2 pixels in the microscopic observation image, and it is difficult to measure it by measuring the width of the interference intensity profile. In addition, changing the inclination angle of the object surface is time-consuming, and there is the problem that the change in reflected light intensity due to the inclination angle must be taken into consideration.

[0009] The present invention was made to solve these problems and provides a calculation method, an imaging method, and an imaging apparatus that can easily calculate the amount of shear generated by a predetermined optical element arranged in the optical path of an interference optical system. [Means for solving the problem]

[0010] The calculation method according to the present invention is A method for calculating the amount of shear generated by a predetermined optical element arranged in the optical path of an interference optical system, The interference optical system captures an interference image of a quadratic surface contained on the surface of an object, The steps include measuring the fringe spacing of interference fringes included in the aforementioned interference image, A step of calculating the shear amount based on the constant in the formula representing the quadratic surface and the fringe spacing, Includes.

[0011] Furthermore, the imaging method according to the present invention is The above calculation method and, The steps include adjusting the position of the predetermined optical element based on the shear amount so that the path difference between the two beams of light separated by the interference optical system becomes a predetermined value, After the adjustment step, the interference image of the sample is captured using the interference optical system. Includes.

[0012] Furthermore, the imaging device according to the present invention is Interferometric optics and, A predetermined optical element arranged in the optical path of the interference optical system, The interference optical system captures an interference image of a quadratic surface contained on the object surface, and then performs a processing to calculate the shear amount of the predetermined optical element based on the fringe spacing of the interference fringes contained in the interference image and a constant in the formula representing the quadratic surface. It is equipped with. [Effects of the Invention]

[0013] According to the present invention, a calculation method, an imaging method, and an imaging apparatus that can easily calculate the shear amount generated by a predetermined optical element arranged in an optical path of an interference optical system can be provided. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0014] [Figure 1] It is a diagram for explaining the relationship between the shear amount and the optical path difference. [Figure 2] 1 shows the configuration of an imaging apparatus used in the calculation method according to Embodiment 1. [Figure 3] It is a flowchart showing the flow of the calculation method and the imaging method according to Embodiment 1. [Figure 4] It shows measurement results of the three-dimensional shape of a spherical surface. [Figure 5] It is a diagram for explaining a method of estimating the radius of a sphere. [Figure 6] It is a differential interference image of a spherical surface when white light is used. [Figure 7] It shows a differential interference image of a spherical surface when monochromatic light is used. [Figure 8] It is a diagram showing a profile of a differential interference image along the shear direction. [DESCRIPTION OF EMBODIMENTS]

[0015] Hereinafter, a specific configuration of the present embodiment will be described with reference to the drawings. The following description illustrates preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, components denoted by the same reference signs have substantially the same content.

[0016] (Embodiment 1) The calculation method, imaging method, and imaging apparatus according to Embodiment 1 will be described below with reference to the drawings. The calculation method according to Embodiment 1 (hereinafter referred to as "this calculation method") is a method for evaluating a predetermined optical element (e.g., a differential interference prism) arranged in the optical path of an imaging optical system (e.g., a confocal optical system). The imaging optical system is an interference optical system. The following description will mainly focus on the case where the imaging optical system is a confocal optical system. Furthermore, although the following description will mainly focus on the case where the imaging optical system is a differential interference optical system, the imaging optical system may be other interference optical systems (e.g., a shearing interference optical system).

[0017] First, the imaging device 100 used in this calculation method will be described with reference to Figure 2. The imaging device 100 detects reflected light from a sample (not shown) via a confocal optical system. The imaging device 100 images the surface of the sample based on the detection result of the reflected light. The sample may be a compound semiconductor such as SiC or GaN, or a piezoelectric crystal wafer. The sample may also be a transparent wafer or a transparent substrate.

[0018] Furthermore, a predetermined optical element, such as a differential interference prism (e.g., a Nomarski prism), is placed in the optical path of the confocal optical system. The predetermined optical element imparts a relative lateral displacement to the two light beams separated by the interference optical system. The following description will focus on the case where the predetermined optical element is a differential interference prism, but the predetermined optical element is not limited to a prism and may be a lens or a diffraction grating. The imaging device 100 captures a differential interference image of a quadratic surface (e.g., a sphere) contained on the surface of an object in order to evaluate the differential interference prism. When the quadratic surface is a sphere, the sphere may be the surface of a steel ball for a ball bearing, or the surface of a glass bead. The following description will focus on the case where the quadratic surface is a sphere, but the quadratic surface may be a paraboloid or a cylinder.

[0019] The imaging device 100 comprises a light source 11, an imaging optical system 110, a stage 31, a photodetector 43, and a processing unit 60. The imaging device 100 is a confocal microscope having an imaging optical system 110, which is a confocal optical system. The imaging optical system 110 is also called an interference optical system.

[0020] The light source 11 generates illumination light L1 to illuminate the sphere 30 and the sample. The light source 11 is, for example, a laser light source or a lamp light source. The imaging optical system 110 guides the illumination light L1 to the surface of the sphere 30. The imaging optical system 110 is, for example, a line confocal optical system, which forms a line-shaped illumination area on the sphere 30.

[0021] The imaging optical system 110 includes a filter 12, a polarizer 13, a lens 15, a slit 16, a half mirror 21, a scanner 22, a lens 23, a Nomarski prism 24, an objective lens 25, a lens 41, and an analyzer 42.

[0022] Illumination light L1 from light source 11 enters filter 12. Filter 12 is, for example, a bandpass filter that transmits only a predetermined wavelength. Illumination light L1 from filter 12 is linearly polarized by polarizer 13. Illumination light L1 is focused by lens 15 and enters slit 16. Slit 16 is positioned conjugate to the focal plane of objective lens 25. Slit 16 makes the illumination light linear.

[0023] Linearly polarized illumination light L1 enters the scanner 22 via a half-mirror 21. The half-mirror 21 is a beam splitter that divides the optical paths of the illumination light L1 and the reflected light L2 from the sphere 30. The half-mirror 21 transmits half of the incident light and reflects the other half.

[0024] The scanner 22 is a vibrating mirror, a galvanometer mirror, a rotating mirror, etc., and deflects the illumination light L1. For example, on the sphere 30, the illumination light L1 is scanned in a direction perpendicular to the longitudinal direction of the linear illumination area.

[0025] The illumination light L1 reflected by the scanner 22 enters the Nomarski prism 24 via the lens 23. The Nomarski prism 24 is a differential interference prism and splits the linearly polarized illumination light L1 into two light beams. In other words, the illumination light L1 passes through the Nomarski prism 24 and then through the objective lens 25, resulting in two parallel light beams that are shifted laterally by a predetermined amount. Note that the differential interference prism is not limited to the Nomarski prism 24, but may also be a Wollaston prism.

[0026] The two light beams split by the Nomarski prism 24 are orthogonal and linearly polarized. That is, one of the two light beams is normal light and the other is abnormal light. The two light beams split by the Nomarski prism 24 are focused by the objective lens 25 and illuminate the surface of the sphere 30. The two light beams illuminate different points on the sphere 30. After passing through the objective lens 25, the normal light and the abnormal light become parallel beams with a lateral shift relative to each other. The amount of lateral shift is called the shear amount.

[0027] The focal point of the objective lens 25 is on the surface of the sphere 30. Furthermore, because the slit 16 and the focal point of the objective lens 25 are in a conjugate imaging relationship, a linear illumination region corresponding to the direction of the slit is formed on the sphere 30. For example, the longitudinal direction of the linear illumination region on the sphere 30 is the X direction, and the scanning direction of the scanner 22 is the Y direction.

[0028] The sphere 30 and the sample are placed on the stage 31. The stage 31 is a drive stage that moves the sphere 30 and the sample in the XYZ directions. The stage 31 performs a Z scan. 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 sphere 30. Of course, instead of the stage 31, the objective lens 25 may be moved along the optical axis to align the focusing position with the surface of the sphere 30. By performing a Z scan, a focused image and a height image of the sphere 30 can be obtained. Also, if the surface irregularities are small, the sphere 30 may be imaged with the surface in focus without performing a Z scan.

[0029] The reflected light L2 reflected by the sphere 30 contains two light beams. The reflected light L2 reflected by the sphere 30 enters the Nomarski prism 24 via the objective lens 25. The Nomarski prism 24 combines the two light beams. The reflected light L2 is refracted by 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 towards the lens 41.

[0030] 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 multiple pixels are arranged in a row. The pixels of the photodetector 43 are arranged along the direction corresponding to the line-shaped illumination area. The light-receiving surface of the photodetector 43 and the focal plane of the objective lens 25 are positioned conjugate to each other. The photodetector 43 detects the reflected light from the sphere 30 via the imaging optical system 110.

[0031] Of course, the photodetector 43 is not limited to a line sensor; it may also be a zero-dimensional sensor. When using a zero-dimensional sensor, a confocal optical system can be constructed by combining it with a pinhole or a point light source. In such cases, the slit 16 becomes unnecessary.

[0032] The stage 31 adjusts the height of the sphere 30 so that its surface becomes the focal point of the illumination light L1. In the imaging optical system 110, the amount of light detected by the photodetector 43 is highest when the surface of the sphere 30 is at the focal point of the illumination light L1. In other words, reflected light from surfaces outside the focal plane of the objective lens 25 is not detected by the photodetector 43.

[0033] As described above, the scanner 22 scans the sphere 30 with illumination light L1. Therefore, the imaging device 100 can acquire confocal images of the sphere 30 and the surface of the sample. The photodetector 43 captures a confocal image where the surface of the sphere 30 is at the focal point. The confocal image is a two-dimensional image in the XY direction. When imaging reflected light with the imaging optical system 110, there are two methods: normal imaging without Z-scanning, and capturing a fully focused image (all-focus image) with Z-scanning (focus scan). For surfaces with large irregularities, the latter all-focus image is used. By performing Z-scanning, the reflected image and surface irregularities can be measured simultaneously, allowing for the acquisition of a height image.

[0034] An analyzer 42 is positioned between the lens 41 and the photodetector 43. The analyzer 42 is rotatably positioned in the optical path of the reflected light L2. The axis of rotation of the analyzer 42 is parallel to the optical axis. The analyzer 42 is a polarizer that transmits only a predetermined linear polarization component. In other words, linear polarization 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 linear polarization detected by the photodetector 43 can be changed.

[0035] In Figure 2, the analyzer 42 is positioned directly in front of the photodetector 43, but the position of the analyzer 42 is not particularly limited. The analyzer 42 should be positioned within the imaging optical system 110 so that reflected light L2, branched from the illumination light L1 by the half-mirror 21, is incident on it. The analyzer 42 may also be positioned in crossed nicols relative to the polarizer 13. Rotating the analyzer 42 does not change the path difference between normal and abnormal light, but it does change the amplitude of the interference fringes, which will be discussed later. The amplitude of the interference fringes is maximized when the analyzer 42 and polarizer 13 are positioned in crossed nicols.

[0036] The processing unit 60 acquires the confocal image captured by the photodetector 43. The processing unit 60 is an information processing device such as a personal computer. The processing unit 60 has a memory for storing the confocal image. The processing unit 60 stores the amount of light detected by the photodetector 43 in association with XYZ coordinates. For example, the processing unit 60 constructs a full-focus image by associating the XYZ coordinates with the amount of light detected. Specifically, the full-focus image is a two-dimensional reflection intensity (bright-field) image. The processing unit 60 also acquires a height image of the sphere 30. The height image is reconstructed within the processing unit 60 so that it is three-dimensional (height is represented in grayscale). The processing unit 60 may also control the driving of the stage 31.

[0037] Next, with reference to Figure 3, the calculation method and the imaging method according to Embodiment 1 (referred to as the imaging method) will be described. The calculation method includes steps S101 to S106. The imaging method includes steps S101 to S108.

[0038] First, the three-dimensional shape of the surface of the sphere 30 is measured using the imaging optical system 110, which is a confocal optical system (step S101). At this time, the polarizer 13, Nomarski prism 24, and analyzer 42 may be removed from the optical path of the imaging optical system 110. In addition, only the polarizer 13 and analyzer 42 may be removed. The objective lens 25 used in step S101 may be different from the objective lens 25 used in differential interference contrast observation.

[0039] Figure 4 shows an example of the three-dimensional shape of the sphere 30 as measured by the imaging device 100. The surface height of the sphere 30 is shown in grayscale. The AB line indicates a line along the shear direction.

[0040] Returning to Figure 3, we continue the explanation. Next, we estimate the radius R of the sphere 30 based on the three-dimensional shape of the surface of the sphere 30 (step S102).

[0041] Refer to Figure 5 to specifically explain how to calculate the radius R. Figure 5 shows the height profile along line AB in Figure 4. The radius R (e.g., 4126.033 μm) is calculated by least-squares fitting the height profile with a circle.

[0042] Let's return to Figure 3 and continue the explanation. Next, we switch to differential interference contrast observation (step S103). Here, the objective lens 25 for which we want to calculate the shear amount is selected. As an example, let's explain the case where an objective lens 25 with an NA (Numerical Aperture) of 0.15 and a magnification of 5x is selected. The limiting angle θ at which reflected light can be received, as seen from the optical axis, is determined from the NA. θ is 8.6 degrees, and the radius r of the partial circle visible in the field of view is 600 μm. In the case of NA=0.15, the field of view of the objective lens (3 mm) includes the entire region that can be observed by reflection. In the case of R=4000 μm, even if the shear amount is 1 to 10 μm, the path difference within the partial circle is sufficiently larger than the illumination wavelength λ (e.g., 546 nm). Thus, it is necessary to set the radius R, NA, and field of view so that the path difference within the partial circle is several times λ.

[0043] Next, the imaging optical system 110 and the Nomarski prism 24 capture a differential interference image of the surface of the sphere 30 (step S104). The differential interference image of the surface of the sphere 30 will be described in detail with reference to Figures 6 and 7.

[0044] Figure 6 shows the differential interference image obtained using white light, and Figure 7 shows the differential interference image obtained using monochromatic light. Note that while color interference fringes are obtained when using white light, Figure 6 shows the color interference fringes converted to grayscale. The central black fringe represents the 0th order interference fringe. The diameter φ of the visible subcircle in the field of view is 1170 μm.

[0045] The s-direction (the direction in which the interference fringes are aligned) shown in Figure 7 represents the Shear direction of the Nomarski prism 24. In the following steps, a differential interference image obtained using monochromatic light will be used. Therefore, in step S104, only a differential interference image obtained using monochromatic light may be acquired.

[0046] Returning to Figure 3, we continue the explanation. Next, we measure the fringe spacing of the interference fringes contained in the differential interference image acquired in step S104 (step S105).

[0047] The method for measuring the fringe spacing will be specifically explained with reference to Figure 8. Figure 8 shows the profile of a differential interference image along the shear direction. The vertical axis represents interference brightness, and the horizontal axis represents the position in the shear direction. Figure 8 includes profiles I_dic and I_dihc. I_dic is obtained from a differential interference image acquired using a first differential interference prism (referred to as DIC), and profile I_dihc is obtained from a differential interference image acquired using a second differential interference prism (referred to as DIHC). The shear amount of DIC is smaller than the shear amount of DIHC. Note that in this calculation method, the fringe spacing can be measured from a single differential interference image, so it is not necessary to acquire two types of differential interference images in step S104. When measuring the fringe spacing, for example, the distance between peaks included in I_dic or I_dihc is measured. Alternatively, the valley width of the 0th-order interference fringe (the distance at which the valley depth is halved) may be measured. By doubling the valley width, the fringe spacing of the interference fringe can be measured.

[0048] Returning to Figure 3, we continue the explanation. Next, based on the radius R estimated in step S102 and the fringe spacing measured in step S105, we calculate the shear amount of the Nomarski prism 24 using equation (1): Δs = (λ·R) / (2w) (step S106). Here, Δs represents the shear amount of the Nomarski prism 24. λ represents the wavelength of the monochromatic light used to capture the differential interference image. R represents the radius of the sphere. w represents the fringe spacing measured in step S105.

[0049] Next, we will explain why equation (1) holds. First, if s is the Shear direction, the profile z(s) of the height z on the surface of the sphere can be approximated by a quadratic function with sufficient accuracy in the range -r≦s≦r. When z(s) is approximated by a quadratic function, it is expressed as dz / ds=-s / R. The change in the inclination of the surface of the sphere 30 in the Shear direction of the Nomarski prism 24 is approximated by a linear equation.

[0050] Therefore, the path difference L(s) = 2*(dz / ds)*Δs = 2*(-s / R)*Δs between the normal and abnormal light separated by the Nomarski prism 24. Converting the path difference L(s) to the phase difference δ(s), we get δ(s) = (2π / λ)*2*(-s / R)*Δs. When s=w, the phase difference is 2π, so equation (1): Δs = (λ·R) / (2w) holds.

[0051] Returning to Figure 3, the explanation continues. Next, the position of the Nomarski prism 24 is adjusted based on the shear amount calculated in step S106 (step S107). Specifically, the Nomarski prism 24 is moved in a direction that crosses the optical axis of the imaging optical system 110 to adjust the path difference between normal and abnormal light. For example, if the relationship between the amount of movement of the Nomarski prism 24 and the amount of change in the path difference is known, the amount of movement of the Nomarski prism 24 may be determined after calculating the path difference between normal and abnormal light based on the shear amount, so that the path difference becomes a predetermined value. At this point, in addition to adjusting the position of the Nomarski prism 24, brightness and contrast may also be adjusted. Furthermore, if the shear amount is not within the reference range, the Nomarski prism 24 may be replaced.

[0052] Next, the sample is placed on the stage 31, and a differential interference image of the sample is captured by the imaging optical system 110 and the Nomarski prism 24 (step S108). Before placing the sample on the stage 31, the sphere 30 may be removed from the stage 31. Since the path difference between normal light and abnormal light is adjusted in step S106, the inspection can be performed under the same inspection conditions.

[0053] The samples described above may be transparent substrates or transparent wafers. For transparent substrates and wafers, removing back-surface reflections is important for improving the accuracy of defect detection. Therefore, defect detection accuracy can be improved by capturing differential interference images using a confocal optical system.

[0054] Note that the order in which the radius of the sphere is estimated in steps S101-S102 and the fringe spacing of the interference fringes is measured in steps S103-S105 is arbitrary. Also, if the radius R of the sphere 30 is known, steps S101-S102 may be omitted. The case where the radius R is known is, for example, when the sphere 30 is manufactured with high precision or when the radius R has been measured in advance by means other than a confocal optical system. In such cases, the imaging optical system 110 does not have to be a confocal optical system.

[0055] Next, the imaging device according to Embodiment 1 will be described with reference to Figures 2 and 3. The processing unit 60 of the imaging device according to Embodiment 1 has a function to perform step S106 shown in Figure 3. The processing unit 60 may also further have a function to perform step S102 shown in Figure 3.

[0056] According to the calculation method, imaging method, and imaging apparatus of Embodiment 1, the shear amount of a differential interference prism can be easily calculated from the fringe spacing of interference fringes included in the differential interference image of a sphere.

[0057] Furthermore, both the measurement of the surface shape of the sphere and the imaging of interference fringes produced by the sphere can be performed using the confocal optical system used to image the sample. Therefore, there is no need to prepare any other equipment in addition to the confocal microscope. Moreover, meaningful calculation results can be obtained by performing measurements using the confocal optical system used for inspection.

[0058] The above explanation uses the example of calculating the shear amount of a differential interference optical system, but it is also possible to calculate the shear amount of interference optical systems other than differential interference optical systems (e.g., shearing interference optical systems). Assume that a predetermined optical element is placed in the optical path of the interference optical system to give a relative lateral displacement to the two divided light beams. The predetermined optical element is not limited to a prism type element, but may also be a wedge type or a planar type element.

[0059] In the explanation above, a sphere was used as an example of a quadratic surface for capturing interference images, but interference images can also be captured of other quadratic surfaces such as cylinders or parabolas. If the radial direction of a cylinder coincides with the shear direction, the shear amount can be calculated in the same way as for a sphere, by taking the radius of the cylinder as R. Furthermore, in the explanation above, equation (1) was derived by approximating the height profile of a sphere with a quadratic function, so if the height profile is expressed by a quadratic function, the same equation as equation (1) can be derived. For example, z(s)=as 2 When expressed as such, dz / ds = 2as, and the equation corresponding to equation (1): Δs = (λ / 2a) / (2w) is derived. In generalization, the shear quantity can be calculated based on the constants in the equation representing the quadratic surface (e.g., the coefficient a of the quadratic order and the radius R) and the fringe spacing. Note that for a sphere, x 2 +y 2 +z 2 =R 2 It is expressed as such, and the radius R is a constant in the equation representing a sphere.

[0060] In general, in step S101 of Figure 3, the three-dimensional shape of the quadratic surface contained in the object surface is measured by an interference optical system. In step S102, the constants in the equation representing the quadratic surface are estimated. In step S104, an interference image of the quadratic surface is captured. In step S106, the shear amount is calculated based on the constants in the equation representing the quadratic surface and the fringe spacing. In step S107, the position of the optical elements is adjusted so that the path difference between the two beams of light separated by the interference optical system is a predetermined value.

[0061] If the quadratic surface is a sphere, it is possible to determine not only the amount of shear but also the direction of the shear. If the shear direction is unknown, the evaluation can begin by determining the direction in which the interference fringes in the interference image are aligned and then determining the orientation of the S-axis.

[0062] Although embodiments of the present invention have been described above, the present invention includes appropriate modifications that do not impair its purpose and advantages, and is not limited by the above embodiments. [Explanation of Symbols]

[0063] 100 Imaging device 11 Light source 110 Imaging Optical System 12 filters 13 Polarizer 15 lenses 16 slits 21 Half Mirror 22 Scanners 23 lenses 24 Nomarski prism 25 Objective lens 41 lenses 42 Analyzers 43 Photodetector 30 spheres 31 stages 50 samples 60 Processing Unit L1 illumination light L2 reflected light

Claims

1. A method for calculating the amount of shear generated by a predetermined optical element arranged in the optical path of an interference optical system, The interference optical system captures an interference image of a quadratic surface contained on the surface of an object, The steps include measuring the fringe spacing of interference fringes included in the aforementioned interference image, A step of calculating the shear amount based on the constant in the formula representing the quadratic surface and the fringe spacing, Includes, The aforementioned interference optical system is a confocal optical system, The steps include: measuring the three-dimensional shape of the quadratic surface using the confocal optical system; A step of estimating the constant based on the three-dimensional shape, A calculation method characterized by having an additional feature.

2. A method for calculating the amount of shear generated by a predetermined optical element arranged in the optical path of an interference optical system, The steps include: capturing an interference image of the surface of an object having a quadratic curved surface using the interference optical system; The steps include measuring the fringe spacing of interference fringes included in the aforementioned interference image, The steps include: calculating the shear amount, Includes, A calculation method for calculating the shear amount, wherein if the quadratic surface of the object is a sphere, the shear amount is calculated using the following equation (1), and if the quadratic surface of the object is a paraboloid, the shear amount is calculated using the following equation (2). ΔS=(λ・R) / (2w) (Formula 1) ΔS=(λ / 2a) / (2w) (Formula 2) However, ΔS is the shear amount, λ is the wavelength of light used to capture the interference image, R is the radius of the sphere, and a is the parabolic equation z(s) = as ２ The s inside ２ Let a be the coefficient of .

3. The calculation method according to either claim 1 or 2, The steps include adjusting the position of the predetermined optical element based on the shear amount so that the path difference between the two beams of light separated by the interference optical system becomes a predetermined value, After the adjustment step, the interference image of the sample is captured using the interference optical system. An imaging method that includes this.

4. The aforementioned sample is a transparent substrate or a transparent wafer. The imaging method according to claim 3.

5. Interferometric optics and, A predetermined optical element arranged in the optical path of the interference optical system, The interference optical system captures an interference image of a quadratic surface contained on the object surface, and then performs a processing to calculate the shear amount of the predetermined optical element based on the fringe spacing of the interference fringes contained in the interference image and a constant in the formula representing the quadratic surface. Equipped with, The aforementioned interference optical system is a confocal optical system, The aforementioned processing unit, Based on the three-dimensional shape of the quadratic surface measured using the aforementioned confocal optical system, a process is further performed to estimate the constant. Imaging device.

6. An interference optical system, A predetermined optical element arranged in the optical path of the interference optical system, A processing unit that performs the following steps: captures the surface of an object having a quadratic curved surface using the interference optical system to obtain an interference image, measures the spacing between interference fringes included in the interference image, and calculates the amount of shear generated by the predetermined optical element; Equipped with, The processing unit is an imaging device that calculates the shear amount using the following equation (1) when the quadratic surface of the object is a sphere, and calculates the shear amount using the following equation (2) when the quadratic surface of the object is a parabolic surface. ΔS=(λ・R) / (2w) (Formula 1) ΔS=(λ / 2a) / (2w) (Formula 2) However, ΔS is the shear amount, λ is the wavelength of light used to capture the interference image, R is the radius of the sphere, and a is the coefficient a of s² in the equation z(s) = as² representing the parabolic surface.

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