Optical measurement system and optical measurement method

Abstract

Provided is an optical measurement system that can suppress noise and achieve higher-accuracy measurement. This optical measurement system includes a light source, an image sensor, and an optical system including a beam splitter that splits light from the light source into a first light and a second light. The optical system can form a first optical system for using the image sensor to record a first hologram in which the first light has been modified with the second light, which is diverging light, while no sample is present, and a second optical system for using the image sensor to record a second hologram in which light that is obtained by irradiating a sample with the first light is modified with the second light. The second optical system has a restricting part that restricts, to a prescribed range, the spreading of the light obtained by irradiating the sample with the first light.

Description

[Technical Field]

[0001] The present invention relates to an optical measurement system and an optical measurement method that utilize digital holography. [Background technology]

[0002] Known methods for measuring the shape of a sample include a measurement method using white light interference and a measurement method using confocal light.

[0003] Measurement methods using white light interference use a low-coherence light source and a reference mirror to scan the sample in the vertical direction and obtain the shape from the interference fringes. Confocal measurement methods also obtain the shape of the sample by scanning a spot focused by an objective lens in three-dimensional space. These methods have the problem of reduced measurement accuracy due to the effects of vibration.

[0004] Digital holography has been proposed and put into practical use as a method for measuring the shape of a sample with higher accuracy. Digital holography is a technology for measuring the shape of a sample, etc., by observing the interference fringes that occur when a reference light and an object light generated by irradiating a sample with light are superimposed on each other to obtain the shape of the wavefront of the object light. The following prior art documents exist regarding measurement devices using digital holography:

[0005] For example, International Publication No. 2012 / 005315 (Patent Document 1) discloses a configuration that can measure the shape of a sample by employing a reflective optical system.

[0006] International Publication No. 2014 / 054776 (Patent Document 2) discloses a configuration for extracting information in a specific z-plane by tomography.

[0007] International Publication No. 2015 / 064088 (Patent Document 3) and International Publication No. 2019 / 044336 (Patent Document 4) disclose configurations that can improve lateral resolution (XY plane).

[0008] WO 2020 / 045584 (Patent Document 5) discloses a configuration that uses a cube beam combiner and can easily achieve large numerical aperture recording and reflective illumination.

[0009] International Publication No. 2020 / 045589 (Patent Document 6) discloses a configuration that uses pinholes for reference light and illumination light to eliminate scattered light and interference noise, and uses a spherical wave as a reference, eliminating the need for a physical reference plane. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2012 / 005315 [Patent Document 2] International Publication No. 2014 / 054776 [Patent Document 3] International Publication No. 2015 / 064088 [Patent Document 4] International Publication No. 2019 / 044336 [Patent Document 5] International Publication No. 2020 / 045584 [Patent Document 6] International Publication No. 2020 / 045589 Summary of the Invention [Problem to be solved by the invention]

[0011] For optical measurement methods using digital holography as described above, there is a demand for a configuration that can suppress noise caused by scattered light and unnecessary light and achieve more accurate measurements. One object of the present invention is to provide an optical measurement system that can suppress noise and achieve more accurate measurements. [Means for solving the problem]

[0012] An optical measurement system according to one aspect of the present invention includes a light source, an image sensor, and an optical system including a beam splitter that splits light from the light source into first light and second light. The optical system is configured to record a first hologram using the image sensor, modulating light obtained by illuminating a sample with the first light with the second light, which is diverging light. The optical system includes a limiting unit that limits the spread of the light obtained by illuminating the sample with the first light to a predetermined range.

[0013] The limiting section may limit the range of the sample illuminated with the first light to a predetermined range.

[0014] The limiting section may limit the range through which the light obtained by illuminating the sample with the first light passes to a predetermined range.

[0015] The size of the range in which the sample is illuminated with the first light may be determined so that, in the spatial frequency domain of the hologram recorded by the image sensor, the component corresponding to the first light does not overlap with components other than the component corresponding to the first light.

[0016] The limiting portion may include a mask having an opening pattern corresponding to the predetermined range formed on a shielding member.

[0017] The limiting portion may be configured to be able to change the size of the opening pattern. The optical system may be an off-axis holographic optical system.

[0018] The optical system may generate a first hologram from transmitted light obtained by illuminating a sample with a first light, and in this case, the optical system may record a second hologram from transmitted light obtained by illuminating a substrate included in the sample that is not a measurement target with the first light, instead of the sample.

[0019] The optical system may generate a first hologram from reflected light obtained by illuminating a sample with a first light, and in this case, the optical system may record a second hologram from transmitted light obtained by illuminating a fiducial reference surface with the first light instead of the sample.

[0020] The optical measurement system may further include a processing unit that calculates a shape of the sample based on the first hologram and the second hologram.

[0021] According to another aspect of the present invention, there is provided an optical measurement method using an optical system including a beam splitter that splits light from a light source into first light and second light. The optical measurement method includes the steps of: illuminating a sample with the first light, modulating the light obtained with a second light that is diverging light, and recording a first hologram using an image sensor; recording a second hologram using the image sensor, modulating the first light with the second light that is diverging light, in a state where the sample is not present; and calculating the shape of the sample based on the first hologram and the second hologram. The spread of the light obtained by illuminating the sample with the first light is limited to a predetermined range. [Effects of the Invention]

[0022] According to an embodiment of the present invention, noise can be suppressed to achieve more accurate measurements. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing an example configuration of an optical measurement system according to a first embodiment. [Figure 2] 10A and 10B are diagrams for explaining a state in which object light and off-axis reference light are incident on a recording surface of an image sensor. [Figure 3] 5A and 5B are diagrams for explaining the relationship between a sample and an off-axis reference light in the optical measurement system according to the embodiment. [Figure 4] 10A and 10B are diagrams for explaining the relationship of spatial frequency bands regarding an off-axis hologram in the optical measurement system according to the present embodiment. [Figure 5] It is a schematic diagram showing a modification example of an optical system related to a mask in an optical measurement system according to Embodiment 1. [Figure 6] It is a flowchart showing the processing procedure of a measurement method using the optical measurement system according to Embodiment 1. [Figure 7] It is a schematic diagram showing a configuration example of an optical measurement system according to a modification example of Embodiment 1. [Figure 8] It is a schematic diagram showing a configuration example of an optical measurement system according to Embodiment 2. [Figure 9] It is a flowchart showing the processing procedure of a measurement method using the optical measurement system according to Embodiment 2. [Figure 10] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 1 of Embodiment 2. [Figure 11] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 2 of Embodiment 2. [Figure 12] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 3 of Embodiment 2. [Figure 13] It is a schematic diagram showing a hardware configuration example of a processing device included in the optical measurement system according to the present embodiment. [Figure 14] It is a schematic diagram showing a functional configuration example of a processing device included in the optical measurement system according to the present embodiment. [Figure 15] It is a diagram showing an example of the effect by the mask adopted by the optical measurement system according to the present embodiment.

Embodiments for Carrying Out the Invention

[0024] Embodiments of the present invention will be described in detail with reference to the drawings. For the same or corresponding parts in the drawings, the same reference numerals are given and the description thereof will not be repeated.

[0025] <A. Optical Measurement System> First, the optical measurement system according to this embodiment uses digital holography that uses divergent light such as a point light source as reference light. In this embodiment, a configuration example of lensless digital holography in which there is no lens between the sample and the image sensor will be described.

[0026] In the following description, an optical measurement system that mainly employs an off-axis holography optical system will be described. In Embodiment 1, a transmissive optical system will be exemplified, and in Embodiment 2 and its modification examples, a reflective optical system will be exemplified.

[0027] The optical measurement system according to this embodiment measures the shape of a sample. Furthermore, the optical measurement system according to this embodiment can also measure the refractive index of the sample. Although any sample can be measured, for example, it can be used for surface inspection of semiconductors, measurement of the thickness and refractive index distribution of film products, evaluation of the surface roughness and waviness of precision machined surfaces, observation and shape evaluation of living cells, and the like.

[0028] <B. Embodiment 1> (b1: Optical system) FIG. 1 is a schematic diagram showing a configuration example of an optical measurement system 1 according to Embodiment 1. FIG. 1(A) shows an optical system for recording in-line reference light, and FIG. 1(B) shows an optical system for recording object light. The optical measurement system 1 is configured to be able to form the optical systems shown in FIGS. 1(A) and 1(B).

[0029] The optical system shown in FIG. 1(A) corresponds to an optical system for recording an off-axis hologram I obtained by modulating an in-line reference light L serving as a recording reference with an off-axis reference light R. Also, the optical system shown in FIG. 1(B) corresponds to an optical system for recording an off-axis hologram I obtained by modulating an object light O obtained by illuminating a sample S with an illumination light Q with an off-axis reference light R that is divergent light. More specifically, the optical system shown in FIG. 1(B) is an off-axis hologram I from the transmitted light obtained by illuminating the sample S with the illumination light Q. LR is equivalent to the optical system for recording. Also, the optical system shown in FIG. 1(B) is an off-axis hologram I obtained by modulating an object light O obtained by illuminating a sample S with an illumination light Q with an off-axis reference light R that is divergent light. OR is equivalent to the optical system for recording. More specifically, the optical system shown in FIG. 1(B) is an off-axis hologram I from the transmitted light obtained by illuminating the sample S with the illumination light Q.OR The illumination light profile is also obtained using the optical system shown in Figure 1(B). In this case, the sample S is not placed.

[0030] The processing device 100 processes the off-axis hologram I LR and Off-Axis Hologram I OR Based on this, the shape of the sample S is calculated.

[0031] Referring to FIG. 1(A), the optical measurement system 1 measures an off-axis hologram I LR The optical system for recording includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M1 and M2, an objective lens MO, a pinhole P, a lens L1, a mask A1, and an image sensor D.

[0032] The light source 10 is composed of a laser or the like and generates coherent light. The beam expander BE expands the cross-sectional diameter of the light from the light source 10 to a predetermined size. The beam splitter BS1 splits the light expanded by the beam expander BE into two beams. One of the beams split by the beam splitter BS1 corresponds to the in-line reference light L (first light), and the other corresponds to the off-axis reference light R (second light).

[0033] The inline reference light L is reflected by mirror M2 and directed to beam splitter BS2. Furthermore, the inline reference light L passes through half mirror HM2 of beam splitter BS2 and is directed to image sensor D. An objective lens MO and a pinhole P are arranged between mirror M2 and beam splitter BS2. The inline reference light L is focused by objective lens MO, and its cross-sectional diameter is narrowed by pinhole P. The pinhole P corresponds to the position of the point source of the inline reference light L. The objective lens MO and pinhole P realize the point source of the inline reference light L.

[0034] On the other hand, the off-axis reference light R is reflected by mirror M1 and directed to beam splitter BS2. Further, the off-axis reference light R is reflected by half mirror HM2 of beam splitter BS2 and directed to image sensor D. A mask A1 and a lens L1 are disposed between mirror M1 and beam splitter BS2. After passing through mask A1, the off-axis reference light R is focused by lens L1, and the focusing point FP1 corresponds to the position of the point source of the off-axis reference light R. In other words, mask A1 and lens L1 realize the point source of the off-axis reference light R.

[0035] Mask A1 has an aperture pattern SP1 in the region through which off-axis reference beam R passes. An image corresponding to aperture pattern SP1 of mask A1 is formed on image sensor D. The size of aperture pattern SP1 of mask A1 is determined so that off-axis reference beam R that has passed through mask A1 is not irradiated beyond the surface of beam splitter BS2 on the image sensor D side. By determining the size of aperture pattern SP1 of mask A1 in this way, it is possible to suppress the generation of noise due to unnecessary interference.

[0036] In addition, the off-axis reference beam R is adjusted so that the in-line reference beam L can be recorded as a hologram.

[0037] The in-line reference light L and the off-axis reference light R are superimposed by the beam splitter BS2 arranged in front of the image sensor D through the optical path described above. That is, the image sensor D generates an off-axis hologram I, which is obtained by modulating the in-line reference light L with the off-axis reference light R, which is a divergent light. LR is obtained.

[0038] The beam splitter BS2 is preferably configured in a cube shape so that it can be easily placed in front of the image sensor D. The point source of the in-line reference light L and the point source of the off-axis reference light R are placed optically close to each other by the beam splitter BS2.

[0039] Referring to FIG. 1(B), the optical measurement system 1 measures an off-axis hologram I OR The optical system for recording the signal includes a mask A2 and lenses L2 and L3 instead of the objective lens MO and pinhole P. A sample S to be measured is placed between the lens L2 and the beam splitter BS2.

[0040] In addition, if the distance required by the objective lens MO and pinhole P is longer than the distance required by the objective lens MO and pinhole P of the optical system shown in Figure 1(A), the beam splitter BS1 and mirror M2 are positioned closer to the light source 10.

[0041] The light output from one side of the beam splitter BS1 is used as illumination light Q (first light) for illuminating the sample S. That is, the illumination light Q split by the beam splitter BS1 is reflected by the mirror M2 and illuminates the sample S. The object light O (i.e., the light transmitted through the sample S) obtained by illuminating the sample S with the illumination light Q passes through the half mirror HM2 of the beam splitter BS2 and is guided to the image sensor D.

[0042] Between the mirror M2 and the beam splitter BS2, a lens L3, a mask A2, and a lens L2 are arranged in this order.

[0043] The illumination light Q is collected by the lens L3 and passes through the mask A2. The illumination light Q that has passed through the mask A2 is further collected by the lens L2 and forms an image on the sample S.

[0044] The mask A2 corresponds to a limiting unit that limits the spread of light obtained by illuminating the sample S with the illumination light Q (first light) to a predetermined range. As an example of the limiting unit, the mask A2 may have a shielding member formed with an opening pattern SP2 corresponding to the predetermined range. The illumination light Q passes through the area corresponding to the opening pattern SP2.

[0045] An image of the aperture pattern SP2 of the mask A2 passes through the lens L2 and is focused on the sample S. That is, of the light illuminating the mask A2, only the portion of the light corresponding to the aperture pattern SP2 passes through the mask A2. This makes it possible to limit the range in which the illumination light Q that has passed through the mask A2 illuminates the sample S. That is, the mask A2, which is an example of a limiting unit, limits the range in which the illumination light Q (first light) illuminates the sample S to a predetermined range. By limiting the illumination range of the illumination light Q, unnecessary light can be reduced, thereby improving measurement accuracy.

[0046] In the optical measurement system 1, the illumination range may vary depending on the thickness of the sample S. In such cases, the aperture pattern SP2 of the mask A2 may be changed as necessary, or the position of the lens L2 for imaging the illumination light Q onto the sample S may be changed.

[0047] If the mirror M2 and the mask A2 are arranged optically close to each other, the lens L3 may be omitted.

[0048] Further, the off-axis reference light R (second light) output from the other end of the beam splitter BS1 is guided to the image sensor D via the same optical path as in FIG. 1(A).

[0049] (b2: Measurement processing) Next, a process for measuring the shape of sample S in optical measurement system 1 according to embodiment 1 will be described. In the following description, the light receiving surface of image sensor D will be referred to as the "recording surface," and the intersection of the recording surface and the central optical axis of beam splitter BS2 will be referred to as the "origin." The direction of the optical axis will be referred to as the z-axis, and two axes perpendicular to the z-axis will be referred to as the x-axis and y-axis, respectively. In other words, the optical axis is perpendicular to the recording surface of image sensor D, and the x-axis and y-axis are parallel to the recording surface of image sensor D. This also applies to other embodiments.

[0050] The distribution of the object light O, the off-axis reference light R, and the in-line reference light L on the recording surface of the image sensor D can be expressed by the following general formulas (1) to (3).

[0051]

number

[0052] The in-line reference beam L, the object beam O, and the off-axis reference beam R are all coherent beams with angular frequency ω. The off-axis hologram I recorded in the optical system shown in Figure 1(A) is LR is calculated as the light intensity of the composite light of the light expressed by equation (3) and the light expressed by equation (1) using the following equation (4). Also, the off-axis hologram I recorded in the optical system shown in FIG. OR is calculated as the light intensity of the composite light of the light expressed by equation (2) and the light expressed by equation (3) using the following equation (5).

[0053]

number

[0054] In addition, Off-Axis Hologram I LR is invariant regardless of the state of the object beam O, so it only needs to be recorded at least once.

[0055] In equations (4) and (5), the first term on the right-hand side corresponds to the light intensity component of the object light O or the in-line reference light L, the second term on the right-hand side corresponds to the light intensity component of the off-axis reference light R, the third term on the right-hand side corresponds to the direct image component resulting from the modulation of the object light O by the off-axis reference light R, and the fourth term on the right-hand side corresponds to the conjugate image component.

[0056] Applying a bandpass filter to equations (4) and (5) and extracting the direct image component of the third term gives the complex amplitude off-axis hologram J recorded with the in-line reference beam L. LR and the complex amplitude off-axis hologram J recorded with the object beam O. ORare calculated as shown in the following equations (6) and (7), respectively.

[0057]

number

[0058] Here, if we divide equation (7) by equation (6), the component of the off-axis reference beam R is removed, and the complex amplitude in-line hologram J based on the in-line reference beam L is obtained. OL is calculated as shown in the following equation (8).

[0059]

number

[0060] The component of the in-line reference light L is the complex amplitude in-line hologram J shown in equation (8). OL can be removed by multiplying by the inline reference light L. The method described in International Publication No. 2020 / 045584 (Patent Document 5) can be used to calculate the inline reference light L. Through the above processing, an object beam hologram U is obtained as shown in the following equation (9).

[0061]

number

[0062] Here, if the object beam hologram U contains frequency components that do not satisfy the sampling theorem, the following correction process is applied to generate a hologram having information that allows the state of the target position to be reproduced. In the following, the hologram having information that allows the state of the target position to be reproduced is referred to as the reconstruction object beam hologram U Σ If the sampling theorem is satisfied, the object beam hologram U can be used as the reconstruction object beam hologram U. Σ Let's say.

[0063] As an example of the correction process, the number of sampling points constituting the image output from the image sensor D may be increased by interpolation before removing the in-line reference light L. Alternatively, the pixel pitch of the image sensor D may be subdivided by applying the division and overlap process disclosed in International Publication No. 2020 / 045584 (Patent Document 5). By using the division and overlap process, the amount of calculation can be reduced.

[0064] Reconstruction object beam hologram U Σ By performing a diffraction calculation using a plane wave expansion, the light wave distribution at any position can be reconstructed. Σ The hologram U is propagated by a distance d (at a position d away from the recording surface). d Let's say.

[0065] The distance of M media (m=1, 2, . . . , M) included in the distance d from the light receiving surface (recording surface) of the image sensor D to the desired distance d is defined as d m , the refractive index is n m If so, Hologram U d can be generalized as the following equation (10). zm is calculated according to equation (11).

[0066]

number

[0067] When multiple media exist, the boundary surfaces between the media are assumed to be parallel to the recording surface. The transmission coefficient when light is incident from medium m to medium m+1 is T m,m+1 (k x ,k y ) is expressed as T m,m+1 (k x ,k y ) is always considered to be 1.

[0068] For example, if the signal propagates only through the air for a distance d, then M=1 and d1=d,n m =1.

[0069] The transmission coefficient when light enters medium m+1 is given by wave number k x ,k y If it can be considered almost uniform without depending on T m,m+1 You can simplify the calculation by setting ≡1.

[0070] (b3: Restriction section) In order to apply a bandpass filter to equations (5) and (4) and extract the direct image component of the third term, it is necessary to prevent the direct image component from overlapping with the light intensity component and the conjugate image component in the spatial frequency band. Therefore, in this embodiment, a limiting unit such as mask A2 is used to limit the spread of object light O obtained by illuminating sample S with illumination light Q, thereby preventing image degradation due to overlapping of spatial frequency bands.

[0071] By forming an image of the aperture pattern SP2 of the mask A2, which is positioned away from the sample S, on the sample S, the spatial frequency bandwidth contained in the interference fringes can be appropriately controlled while maintaining the freedom of the illumination method, thereby efficiently utilizing the spatial frequency bandwidth that can be recorded by the image sensor D.

[0072] In the optical measurement system 1, the mask A1 and the lens L1 realize a point source of the off-axis reference beam R. The spatial frequency f of the interference fringes at any point on the recording surface is expressed as the incident angle θ of the object beam O at that point. O and the incident angle θ of the off-axis reference beam R R Using these, it can be expressed as the following equation (12).

[0073]

number

[0074] 2A and 2B are diagrams for explaining the state in which the object light O and the off-axis reference light R are incident on the recording surface of the image sensor D. Fig. 2A shows the case in which the off-axis reference light R is a plane wave, and Fig. 2B shows the case in which the off-axis reference light R is a spherical wave.

[0075] 2(A), when the off-axis reference beam R is a plane wave, the angle formed by the object beam O and the off-axis reference beam R at any point on the recording surface of the image sensor D depends on the position on the recording surface of the image sensor D. For example, the angle α formed by the object beam O and the off-axis reference beam R at the upper end of the recording surface of the image sensor D is significantly different from the angle β formed by the object beam O and the off-axis reference beam R at the lower end of the recording surface.

[0076] 2(B), when the off-axis reference beam R is a spherical wave, the angle formed by the object beam O and the off-axis reference beam R at a point on the recording surface of the image sensor D is approximately the same value, independent of the position on the recording surface. For example, the angle α formed by the object beam O and the off-axis reference beam R at the upper end of the recording surface of the image sensor D is approximately the same as the angle β formed by the object beam O and the off-axis reference beam R at the lower end of the recording surface.

[0077] In other words, if the off-axis reference light R is a point light source, the angle between the light ray (object light O) originating from any point on the sample S and the light ray originating from the point light source of the off-axis reference light R can be made almost constant at any point on the recording surface.

[0078] If we consider the object beam O as a collection of wave sources on the same z plane as the point source of the off-axis reference beam R, the position of the wave source on the z plane (x s ,y s ) and the corresponding spatial frequency (u s ,v s ) the relationship shown in the following equation (13) approximately holds between them.

[0079]

number

[0080] z in the formulaL is the distance in the z-axis direction from the point light source of the off-axis reference beam R to the recording surface, and λ is the wavelength. Also, let u be the spatial frequency in the x-direction and v be the spatial frequency in the y-direction.

[0081] As shown in equation (13), there is an approximately linear relationship between the position of the wave source (object light O) on the z-plane and the spatial frequency (coordinates of the spectral component). Therefore, by limiting the area where the wave source (object light O) exists, it is possible to control the spread of the spatial frequency band of the direct image component. This allows for efficient use of the spatial frequency band.

[0082] Here, the "area where the wave source exists" refers to the range in which the sample S is illuminated. In other words, optimizing the aperture pattern SP2 of the mask A2 limits the illumination range, thereby enabling appropriate control of the spatial frequency band. Note that since the mask A2 simply limits the range in which the sample S is illuminated, it does not cause distortion in the reconstructed sample image as long as the complex amplitude of the object light O is correctly recorded.

[0083] Next, a method for determining the size of the opening pattern SP2 of the mask A2 will be described. As described above, the off-axis hologram I recorded in the optical system shown in FIG. OR is calculated as shown in equation (5). In equation (5), the component required for image reconstruction is the direct image component of the third term, and the other terms are superimposed as noise components and must be removed using a band-pass filter.

[0084] The coordinates of the origin of the image sensor D are (0,0,0), and the coordinates of the center of the sample S are (0,0,z L )

[0085] 3 is a diagram illustrating the relationship between the sample S and the off-axis reference light R in the optical measurement system according to the present embodiment. Referring to FIG. 3, the coordinates of the point light source (focus point FP1′) of the off-axis reference light R, which is expanded on the sample S side with respect to the half mirror HM2 of the beam splitter BS2, are expressed as (x R ,y R ,z R =z L ) and the illumination range of the sample S is a rectangle with a size in the x direction and b in the y direction, then for the direct image component of the third term, the bandwidth W in the u direction is x and the bandwidth in the v direction, W y can be approximately expressed as the following equation (14), and the center frequency u in the u direction c and the center frequency in the v direction, v c can be approximately expressed as the following equation (15).

[0086]

number

[0087] Also, the bandwidth W in the u direction of the conjugate image component (4th term) x and the bandwidth in the v direction, W y can also be approximately expressed as in equation (14) above. On the other hand, the central frequency u in the u direction of the conjugate image component (the fourth term) c and the center frequency in the v direction, v c is obtained by inverting the sign of the above equation (15).

[0088] Furthermore, the bandwidth of the combined light intensity component of the first term and the light intensity component of the second term will be twice as large as that of equation (14) with the origin as the center.

[0089] The above relationship can be shown in Figure 4. 4A and 4B are diagrams for explaining the relationship between spatial frequency bands regarding an off-axis hologram in the optical measurement system according to the present embodiment. LThe figure shows the position of the off-axis reference beam R on the recording plane and the illumination range of the sample S. Figure 4(B) shows the spectrum obtained by two-dimensional Fourier transform of the hologram recorded on the recording plane (z = 0).

[0090] Referring to FIG. 4A, in the real space, the sample S is (0,0,z L The point source of the off-axis reference beam R is located at the coordinates (0,0,z L ) in the x direction R and y in the y direction R It exists at a distance of just

[0091] Referring to FIG. 4B, in Fourier space (spatial frequency domain), the direct image component of the third term, which contains information about the object light O, has a bandwidth W x ×W y The center frequency of the direct image component is the coordinate of the point source of the off-axis reference light (x R ,y R ) is determined by the

[0092] In order to extract only the third term (direct image component) containing information about the object light O from the spectrum in Fourier space shown in Figure 4(B) using a bandpass filter, it is necessary to ensure that it does not overlap with the other terms (first, second, and fourth terms).

[0093] On the other hand, the spatial frequency band of the image sensor D is finite, so the center frequency u c and v c It is also not desirable to make σ excessively large. Therefore, in order to efficiently utilize the spatial frequency band of the image sensor D, it is necessary to bring the component of the third term as close as possible to the components of the other terms (the first, second, and fourth terms) so that they do not overlap.

[0094] In order to arrange each band close to each other, the spatial frequency bandwidth is limited to an appropriate range. If the off-axis reference light is a diverging light (point light source), the relationship of the above equation (5) holds. Therefore, by limiting the illumination range of the illumination light Q, the spatial frequency bandwidth of each component can be limited to an appropriate range.

[0095] In this way, the size of the range in which the sample S is illuminated by the illumination light Q is determined so that in the Fourier space (spatial frequency domain) of the hologram recorded by the image sensor D, the component corresponding to the illumination light Q (first light) (third term) does not overlap with components other than the component corresponding to the illumination light Q (first and second terms).

[0096] By limiting the spatial frequency bandwidth of each component to an appropriate range, the spatial frequency band of the image sensor D can be used efficiently, and noise caused by overlapping spatial frequency bands can also be suppressed.

[0097] Although the above description has been given of the case where the mask A2 is applied to an off-axis holography optical system, the above-mentioned mask A2 is also effective in other holography optical systems that use diverging light (i.e., a point light source or a light source that can be regarded as a point light source) as the reference light, for example, when limiting the spatial frequency bandwidth of the direct image component to a range that can be recorded by the image sensor D.

[0098] The mask A2 used in the optical measurement system according to this embodiment may have a similar external shape to a field stop used in an optical microscope. However, a field stop is used to suppress stray light that occurs when excess light (light outside the field of view) strikes a wall along the optical path. While a field stop can reduce the noise level, the amount of stray light suppressed is small, so unless the objective is to detect weak light, no significant problem occurs even if no proactive measures are taken.

[0099] In contrast, limiting the illumination range in digital holography, which uses diverging light as reference light, has the effect of limiting the spatial frequency bandwidth contained in the interference fringes to the range that can be recorded by the image sensor D. The mask A2 used in the optical measurement system according to this embodiment is used for this purpose.

[0100] In this way, the mask A2 used in the optical measurement system according to this embodiment exerts an effect different from that exerted by the field stop used in an optical microscope.

[0101] In the above explanation, a case where a mask A2 having an opening pattern SP2 of a predetermined size formed thereon is used as an example of a limiting section is described, but this is not limited to this, and the limiting section may be realized using any optical element.

[0102] For example, the size of the aperture pattern (the cross-sectional area through which the illumination light passes) may be made arbitrarily changeable by using an optical element that can control the light transmittance, such as a polarizing mirror or liquid crystal. By configuring the size of the aperture pattern to be arbitrarily changeable, it is possible to easily accommodate changes in the distance between the sample S and the image sensor D or changes in the position of the point light source of the off-axis reference light.

[0103] (b4: Modified optical system for mask A2) As an optical system for forming an image of the aperture pattern SP2 of the mask A2 on the sample S, the following optical system may be adopted instead of the configuration shown in FIG.

[0104] FIG. 5 is a schematic diagram showing a modification of the optical system relating to mask A2 in optical measurement system 1 according to the first embodiment.

[0105] 5(A), lenses L31 and L32 may be disposed in place of the lens L3 shown in FIG. 1(B). That is, in the optical system shown in FIG. 5(A), illumination light Q passes through mirror M2, lens L31, lens L32, mask A2, and lens L2 in this order, and is imaged on sample S. Lenses L31 and L32 constitute an imaging optical system 20 such as a 4f optical system.

[0106] The light that passes through the aperture pattern SP2 of the mask A2 is imaged on the sample S in the same shape as the aperture pattern SP2.

[0107] Fig. 5(B) shows an example of an optical system in which the illumination light Q illuminating the sample S is collimated. More specifically, in the optical system shown in Fig. 5(B), lenses L21 and L22 are disposed instead of the lens L2 of the optical system shown in Fig. 5(A). Both the lens L21 and the lens L22 are condensing lenses, and when combined, the illumination light Q that has passed through the mask A2 illuminates the sample S as collimated light.

[0108] The optical systems arranged before and after the mask A2 are not limited to the optical systems shown in Figures 1(B), 5(A), and 5(B). Any configuration may be used for the optical system arranged before the mask A2 as long as it can project the reflected light from the mirror M2 so as to cover the aperture pattern SP2 of the mask A2. Furthermore, any configuration may be used for the optical system arranged after the mask A2 as long as it can form an image of the aperture pattern SP2 of the mask A2 on the sample S. As long as these requirements are met, the number and type of lenses can be designed as desired. Furthermore, this is not limited to lenses, and any optical device may be used to achieve this.

[0109] (b5: Measurement of sample shape using phase information of object light) Next, a description will be given of a method for measuring the shape of sample S using optical measurement system 1 according to embodiment 1. The shape of sample S is measured using the amount of phase change caused by the sample.

[0110] By the above-mentioned procedure, the reconstruction object beam hologram U Σ The light wave distribution obtained by propagating the light to the sample surface using a plane wave expansion is called the object light distribution U S The object light distribution U S The phase distribution of the illumination light Q is Q The phase change amount Δθ caused by the sample S is added to the above.

[0111] Here, when measuring by sequentially replacing the sample S, it is assumed that the distance from the recording surface to the sample surface may change, but it is not necessary to record the illumination light Q (illumination light profile) every time the distance changes. Diffraction calculations can be used to calculate the illumination light Q at a different distance from the illumination light Q at the sample surface a certain distance away from the recording surface.

[0112] If sample S includes a substrate that is not the measurement target, the profile of the illumination light that has passed through the substrate can be calculated by performing a propagation calculation within the medium using a plane wave expansion of the illumination light Q (illumination light profile). In this case, if the approximate thickness and refractive index of the substrate are known, there is no need to prepare a sample of only the substrate in addition to sample S and record the illumination light Q.

[0113] The calculated profile of the illumination light transmitted through the substrate can be used to measure layers other than the substrate of sample S. Furthermore, if recording is possible with only the substrate, the illumination light transmitted through the substrate can be recorded with only the substrate in place, thereby omitting the calculation of propagation within the medium of the substrate.

[0114] Object light distribution U S In order to extract only the phase change amount Δθ caused by the sample S from the phase distribution of the illumination light, information on the illumination light Q is required. In the optical measurement system according to this embodiment, the illumination light Q (illumination light profile) recorded when the sample S is not placed is used to obtain the phase distribution θ of the illumination light. Q The object light distribution U S The phase change amount Δθ caused by the sample S is calculated by subtracting it from the phase distribution of the sample S.

[0115] Phase distribution of illumination light θ Q The object light distribution U S The process of subtracting the phase distribution of the object light of complex amplitude U S By dividing by the illumination light Q, the amplitude and phase distribution U P Calculate the amplitude and phase distribution U P This can be achieved by calculating the argument of

[0116] In the optical measurement system 1 according to the first embodiment, the shape of the sample S is measured using the relational expression shown in the following equation (16) between the amount of phase change Δθ caused by the sample S and the thickness Δd of the sample S.

[0117]

number

[0118] k in the formula z1 is the wave number in the z direction in the sample S, and k z2 is the wave number in the z direction in the medium in which the sample S exists, δ is the phase correction term, and λ is the light source wavelength. z1 and k z2 can be calculated according to the following equations (17) and (18), respectively.

[0119]

number

[0120] In the equation, n1 is the refractive index of the medium in which the sample S exists, and n2 is the refractive index of the sample S. For example, if the sample S exists in a vacuum, the refractive index n1=1.

[0121] The wave number k in the x direction in the formula x and the wave number k in the y direction y is the amount of phase change per unit length in the x and y directions, so the phase distribution θ of the illumination light on the sample surface is expressed as follows, as shown in the following equations (19) and (20): Q It can be calculated by differentiating

[0122]

number

[0123] Furthermore, the phase correction term δ in equation (16) is used to correct the phase change due to the complex transmittance when the transmittance is a complex number due to optical absorption in the sample S. If the phase change due to the complex transmittance can be considered to be uniform across the entire sample S because the samples S are all made of the same material, the phase correction term δ may be omitted.

[0124] When a positional shift occurs in the coordinates of the point light source of illumination light due to disturbance, the illumination light Q may be corrected by translating the pixels on the image sensor D. The amount of translation is typically calculated by S is determined so that the correlation between the illumination light Q and the

[0125] If the wavefront shape of the illumination light is smooth, the amount of information may be reduced by using a low-pass filter or polynomial approximation.

[0126] (b6: Processing procedure) Fig. 6 is a flowchart showing the procedure of a measurement method using optical measurement system 1 according to embodiment 1. The procedure shown in Fig. 6 is an optical measurement method using an optical system including beam splitter BS1 that splits light from light source 10 into a first light and a second light.

[0127] 6, first, a process for acquiring an in-line reference beam L is executed. More specifically, the optical system shown in FIG. 1(A) is configured (step S2). Then, a coherent beam is generated from a light source 10, and a processing device 100 modulates the in-line reference beam L with an off-axis reference beam R to generate an off-axis hologram I, which is recorded on an image sensor D. LR (Step S4). Steps S2 and S4 need only be performed once unless the optical system related to the off-axis reference beam R is changed. Furthermore, the processing of steps S2 and S4 is performed to improve the accuracy of the reconstructed image, and depending on the required accuracy, the processing of steps S2 and S4 may be omitted.

[0128] Next, a process for acquiring an illumination light profile is performed. More specifically, the optical system shown in FIG. 1B is configured (step S6). At this time, a state in which the sample S is not present is maintained. A substrate having the same thickness as the substrate of the sample S may be placed at the position where the sample S is placed (sample position), or nothing may be placed at the sample position. This state corresponds to the measurement reference. Then, coherent light is generated from the light source 10, and the processing device 100 acquires an illumination light hologram Q(x, y) to be recorded on the image sensor D (step S8). In this way, the processing device 100 records a hologram on the image sensor D by modulating the light obtained by illuminating with the illumination light Q with the off-axis reference light R in a state in which the sample S is not present. Alternatively, the processing device 100 may record a hologram on the image sensor D from transmitted light obtained by illuminating with the illumination light Q a substrate that is not a measurement target included in the sample S, instead of the sample S.

[0129] The processing device 100 generates a reconstruction illumination light hologram (illumination light profile Q) from the illumination light hologram Q(x, y). Σ (x, y) is calculated (step S10).

[0130] Next, a process for acquiring the phase amplitude distribution of the sample S is performed. More specifically, the sample S is placed in the original position of the optical system shown in FIG. 1(B) (step S12). Then, coherent light is generated from the light source 10, and the processing device 100 acquires an object beam hologram U(x, y) to be recorded on the image sensor D (step S14). In this way, the processing device 100 acquires an off-axis hologram I(x, y) by modulating the light obtained by illuminating the sample S with the illumination light Q (first light) with the off-axis reference light R (second light). OR is recorded by the image sensor D. At this time, as described above, the limiting section (mask A2) is used to limit the spread of light obtained by illuminating the sample S with the illumination light Q to a predetermined range.

[0131] Hereinafter, the processing device 100 processes the off-axis hologram I LR and Off-Axis Hologram IOR Based on this, a process of calculating the shape of the sample S is performed.

[0132] As a calculation process, first, a process of reconstructing a hologram is executed. More specifically, the processing device 100 derives a reconstruction object beam hologram U(x, y) from the object beam hologram U(x, y). Σ (x, y) is calculated (step S16). Then, the processing device 100 calculates the illumination light profile Q Σ (x,y) and the reconstruction object beam hologram U Σ (x, y) is propagated to the position of the sample surface by plane wave expansion, and the illumination light distribution Q S (x,y) and the object light distribution U S (x, y) is calculated (step S18).

[0133] Next, a process for calculating the amplitude-phase distribution is executed. More specifically, the processing device 100 calculates the object light distribution U S (x, y) is the illumination light distribution Q S Divide by (x, y) to obtain the amplitude and phase distribution U P (x, y) is calculated (step S20).

[0134] Next, a process for calculating the object light phase is executed. More specifically, the processing device 100 calculates the amplitude-phase distribution U P The phase change amount Δθ(x, y) is calculated from the deflection angle (x, y) (step S22).

[0135] Next, a process for calculating the thickness of the sample S is executed. More specifically, the processing device 100 calculates the thickness Δd(x, y) of the sample S using the phase change amount Δθ(x, y) (step S24). The thickness Δd of the sample S is calculated using the relational expression shown in the above-mentioned equation (16).

[0136] Finally, the processing device 100 compiles the thickness Δd(x, y) at each coordinate on the sample surface to calculate the shape profile of the sample S (step S26).

[0137] By the above-described processing, the shape of the sample S can be calculated. In addition, the refractive index and refractive index profile of the sample S can also be measured. In this case, in step S24, the refractive index n2(x, y) of the sample S is calculated, and in step S26, the refractive indices n2(x, y) at each coordinate on the sample surface are collected to calculate the refractive index profile of the sample S.

[0138] <C. Modified Example of Embodiment 1> A modified example of the optical system of the optical measurement system 1 according to Embodiment 1 will be exemplified.

[0139] FIG. 7 is a schematic diagram showing a configuration example of an optical measurement system 1A according to a modified example of Embodiment 1. FIG. 7(A) shows an optical system when in-line reference light is recorded, and FIG. 7(B) shows an optical system when object light is recorded. The optical measurement system 1 A can configure the optical systems shown in FIGS. 7(A) and 7(B).

[0140] The optical system shown in FIG. 7(A) is the same as the optical system when in-line reference light is recorded in the optical measurement system 1 according to Embodiment 1 shown in FIG. 1(A), so a detailed description will not be repeated.

[0141] The optical system shown in FIG. 7(B) is object different in the arrangement position of the mask A2 as compared with the optical system when recording light in the optical measurement system 1 according to Embodiment 1 shown in FIG. 1(B). More specifically, the mask A2 is arranged on the optical path from the sample S to the image sensor D. In the optical system shown in FIG. 7(B), the mask A2 is arranged at a position adjacent to the sample S.

[0142] The object light O obtained by illuminating the sample S with the illumination light Q passes through the mask A2 and is guided to the image sensor D. Thus, the mask A2 corresponds to a limiting portion that limits the spread of the light (object light O) obtained by illuminating the sample S with the illumination light Q (first light) to a predetermined range.

[0143] In the optical system shown in FIG. 7(B), the mask A2, which is an example of a limiting part, limits the range through which the object light O obtained by illuminating the sample S with the illumination light Q passes to a predetermined range. By limiting the spread of the object light O, unnecessary light can be reduced and the measurement accuracy can be improved.

[0144] Details of the mask A2 have been described above, so the description will not be repeated. However, the aperture pattern may be appropriately designed according to the arrangement position of the mask A2.

[0145] Note that the processing procedure and the like are the same as those in the first embodiment, so the detailed description will not be repeated.

[0146] <D. Second Embodiment> (d1: Optical System) FIG. 8 is a schematic diagram showing a configuration example of the optical measurement system 2 according to the second embodiment. FIG. 8(A) shows the optical system in the case of recording in-line reference light, and FIG. 8(B) shows the optical system in the case of recording object light. The optical measurement system 2 is configured to be able to form the optical systems shown in FIGS. 8(A) and 8(B).

[0147] The optical system shown in FIG. 8(A) is the same as the optical system in the case of recording in-line reference light in the optical measurement system 1 according to the first embodiment shown in FIG. 1(A), so the detailed description will not be repeated.

[0148] The optical system shown in FIG. 8(B) corresponds to an optical system for recording an off-axis hologram I obtained by modulating the object light O obtained by illuminating the sample S with the illumination light Q with an off-axis reference light R. More specifically, the optical system shown in FIG. 8(B) generates an off-axis hologram I from the reflected light obtained by illuminating the sample S with the illumination light Q. Note that the illumination light profile is also acquired using the optical system shown in FIG. 8(B). In this case, as will be described later, a reference reference surface is arranged instead of the sample S. OR The optical system shown in FIG. 8(B) corresponds to an optical system for recording an off-axis hologram I obtained by modulating the object light O obtained by illuminating the sample S with the illumination light Q with an off-axis reference light R. More specifically, the optical system shown in FIG. 8(B) generates an off-axis hologram I from the reflected light obtained by illuminating the sample S with the illumination light Q. OR Note that the illumination light profile is also acquired using the optical system shown in FIG. 8(B). In this case, as will be described later, a reference reference surface is arranged instead of the sample S.

[0149] The optical system shown in Fig. 8(B) differs from the optical system when recording object light in optical measurement system 1 according to embodiment 1 shown in Fig. 1(B) in the configuration for illuminating sample S with illumination light Q. Therefore, off-axis reference light R output from the other side of beam splitter BS1 is guided to image sensor D via the same optical path as in Figs. 1(A), 1(B), and 8(A).

[0150] The light output from one side of the beam splitter BS1 is used as illumination light Q for illuminating the sample S.

[0151] More specifically, the beam splitter BS 1 The illumination light Q split by is reflected by mirror M2 and mirror M3, respectively, and then passes through lens L3, mask A2, and lens L4 before being directed to beam splitter BS2. The illumination light Q is further reflected by half mirror HM2 of beam splitter BS2 to illuminate sample S. Object light O (i.e., light reflected by sample S) obtained by illuminating sample S with illumination light Q passes through half mirror HM2 of beam splitter BS2 and is directed to image sensor D.

[0152] Between mirror M2 and beam splitter BS2, mirror M3, lens L3, mask A2, and lens L4 are arranged in this order. As in the first embodiment, illumination light Q is collected by lens L3 and passes through mask A2. After passing through mask A2, illumination light Q is further collected by lens L4 and forms an image on sample S. That is, the image of aperture pattern SP2 of mask A2 passes through lens L4 and forms an image on sample S. This makes it possible to limit the range of illumination on sample S by illumination light Q that has passed through mask A2. By limiting the illumination range of illumination light Q, unnecessary light can be reduced, improving measurement accuracy.

[0153] Optical Measurement System 2Even in this case, the illumination range may vary depending on the thickness of the sample S. In such a case, the aperture pattern SP2 of the mask A2 may be changed as necessary, or the lens L for imaging the illumination light Q onto the sample S may be changed. 4 The position of the

[0154] If the mirror M2 and the mask A2 are arranged optically close to each other, the lens L3 may be omitted.

[0155] (d2: Measurement processing) Next, a process for measuring the shape of sample S in optical measurement system 2 according to the second embodiment will be described.

[0156] The phase shift Δθ caused by the sample S and the height Δh of the sample S and The relationship is as shown in equation (21) below.

[0157]

number

[0158] k in the formula z teeth z The wave number in the direction the law of nature, δ is a phase correction term.

[0159] wave number k x and wave number k y can be calculated using the above equations (19) and (20). The phase correction term δ may also be omitted if the phase change due to the complex reflectance can be considered to be uniform across the entire sample S, for example, because the samples S are all made of the same material.

[0160] Next, the illumination light profile in the optical measurement system 2 will be described. In the reflective optical system employed by the optical measurement system 2, a reference surface is placed at the position where the sample S is to be placed (sample position), and reflected light from the reference surface is used as the illumination light Q. The reference surface is preferably a flat surface, and for example, an optical flat can be used. That is, the optical system shown in FIG. 8(B) acquires an illumination light profile from reflected light obtained by illuminating the reference surface, placed at the position where the sample S is to be placed, with the illumination light Q.

[0161] By propagating the recorded illumination light Q, the illumination light distribution Q on the sample surface at different distances is obtained. S Therefore, as in the first embodiment (transmissive optical system), it is not necessary to record the illumination light Q every time the distance from the recording surface changes. Furthermore, if a positional shift occurs in the coordinates of the point light source of the illumination light due to disturbance, the illumination light Q may be corrected by translating the pixels on the image sensor D.

[0162] In order to remove shape errors contained in the fiducial reference surface, multiple illumination lights may be recorded while translating the fiducial reference surface in the x and y directions, and the average value of the recorded illumination lights may be used as the illumination light Q.

[0163] Furthermore, when measuring the shape (in-plane profile) of the entire sample surface, an optical system in which the illumination light Q is parallel (see, for example, FIG. 5(B)) may be used. When the illumination light Q is a spherical wave, the focus deviation with respect to the sample surface may be detected as a false concave or convex shape. Such false shapes are caused by the illumination light being a spherical wave, so when measuring the shape (in-plane profile) of the entire sample surface, it is preferable to use an optical system in which the illumination light Q is parallel.

[0164] (d3: Processing procedure) Fig. 9 is a flowchart showing the procedure of a measurement method using optical measurement system 2 according to embodiment 2. The procedure shown in Fig. 9 is an optical measurement method using an optical system including beam splitter BS1 that splits light from light source 10 into a first light and a second light.

[0165] 9, first, a process for acquiring an in-line reference beam L is executed. More specifically, the optical system shown in FIG. 8(A) is configured (step S52). Then, a coherent beam is generated from the light source 10, and the processing device 100 modulates the in-line reference beam L with the off-axis reference beam R to generate an off-axis hologram I, which is recorded on the image sensor D. LR (Step S54). Steps S52 and S54 need only be performed once unless the optical system related to the off-axis reference beam R is changed. 5 2 and S 5 The process of step S4 is intended to improve the accuracy of the reconstructed image. Depending on the required accuracy, 5 2 and S 5 Step 4 may be omitted.

[0166] Next, a process for acquiring an illumination light profile is performed. More specifically, the optical system shown in FIG. 8(B) is configured (step S56). At this time, the sample S is not placed, and a fiducial reference surface is placed at the position where the sample S would be placed (sample position). This state corresponds to the measurement reference. Then, coherent light is generated from the light source 10, and the processing device 100 acquires an illumination light hologram Q(x, y) to be recorded on the image sensor D (step S58). In this way, the processing device 100 records a hologram in the image sensor D, obtained by modulating the light obtained by illuminating the fiducial reference surface with the illumination light Q, instead of the sample S, with the off-axis reference light R.

[0167] The processing device 100 generates a reconstruction illumination light hologram (illumination light profile Q) from the illumination light hologram Q(x, y). Σ (x, y) is calculated (step S60).

[0168] Next, a process for acquiring the phase amplitude distribution of the sample S is performed. More specifically, the sample S is placed in the original position of the optical system shown in FIG. 8(B) (step S 6 Then, the light source 10 generates coherent light, and the processing device 100 acquires the object light hologram U(x, y) recorded in the image sensor D (step S 6 4). In this way, the processing device 100 generates an off-axis hologram I by modulating the light obtained by illuminating the sample S with the illumination light Q (first light) and the off-axis reference light R (second light). OR is recorded by the image sensor D. At this time, as described above, the limiting section (mask A2) is used to limit the spread of light obtained by illuminating the sample S with the illumination light Q to a predetermined range.

[0169] Hereinafter, the processing device 100 processes the off-axis hologram I LR and Off-Axis Hologram I OR Based on this, a process of calculating the shape of the sample S is performed.

[0170] As a calculation process, first, a process of reconstructing a hologram is executed. More specifically, the processing device 100 derives a reconstruction object beam hologram U(x, y) from the object beam hologram U(x, y). Σ (x, y) is calculated (step S66). Then, the processing device 100 calculates the illumination light profile Q Σ (x,y) and the reconstruction object beam hologram U Σ (x, y) is propagated to the position of the sample surface by plane wave expansion, and the illumination light distribution Q S (x,y) and the object light distribution U S (x, y) is calculated (step S68).

[0171] Next, a process for calculating the amplitude-phase distribution is executed. More specifically, the processing device 100 calculates the object light distribution U S (x, y) is the illumination light distribution Q S Divide by (x, y) to obtain the amplitude and phase distribution U P (x, y) is calculated (step S70).

[0172] Next, a process for calculating the object light phase is executed. More specifically, the processing device 100 calculates the phase change amount Δθ(x, y) from the deflection angle of the amplitude-phase distribution U P (x, y) of the sample surface (step S72).

[0173] Next, a process for calculating the height of the sample S is executed. More specifically, the processing device 100 calculates the height h(x, y) of the sample S using the phase change amount Δθ(x, y) (step S74). The relational expression shown in the above equation (21) is used for calculating the height h of the sample S.

[0174] Finally, the processing device 100 aggregates the thicknesses h (x, y) at each coordinate of the sample surface to calculate the shape profile of the sample S (step S76).

[0175] Through the above-described processes, the shape of the sample S can be calculated. <E. Variation of Embodiment 2> Some variations of the optical system of the optical measurement system 2 according to Embodiment 2 will be exemplified.

[0176] (e1: Variation 1) FIG. 10 is a schematic diagram showing a configuration example of an optical measurement system 2A according to Variation 1 of Embodiment 2. FIG. 10(A) shows an optical system when in-line reference light is recorded, and FIG. 10(B) shows an optical system when object light is recorded. The optical measurement system 2A can configure the optical systems shown in FIGS. 10(A) and 10(B).

[0177] The optical system shown in FIG. 10(A) is the same as the optical system when in-line reference light is recorded in the optical measurement system 1 according to Embodiment 1 shown in FIG. 1(A), and thus a detailed description will not be repeated.

[0178] The optical system shown in FIG. 10(B) differs from the optical system when recording an in-line reference beam in the optical measurement system 2 according to the second embodiment shown in FIG. 8(B) in that the mask A2 is disposed at a different position. More specifically, the mask A2 is disposed between the sample S and the image sensor D. 10 ( B In the optical system shown in Fig. 1, the mask A2 is To S are placed adjacent to each other.

[0179] The illumination light Q is reflected by the half mirror HM2 of the beam splitter BS2 and illuminates the sample S. At this time, the illumination light Q passes through the mask A2, so that the range of the sample S illuminated by the illumination light Q is limited to a predetermined range.

[0180] Then, the object light O obtained by illuminating the sample S with the illumination light Q (i.e., the light reflected by the sample S) passes through the half mirror HM2 of the beam splitter BS2 and is guided to the image sensor D. At this time, the object light O generated by illuminating the sample S with the illumination light Q also passes through the mask A2, so the range through which the object light O passes is limited to a predetermined range.

[0181] 10(B), the mask A2 not only limits the illumination range of the illumination light Q, but also limits the transmission range of the object light O obtained by illuminating the sample S with the illumination light Q. In this way, the mask A2 corresponds to a limiting unit that limits the spread of the light (object light O) obtained by illuminating the sample S with the illumination light Q (first light) to a predetermined range. By limiting the spread of the object light O, unnecessary light can be reduced, and measurement accuracy can be improved.

[0182] The details of mask A2 have been described above, and therefore will not be described again. However, the opening pattern may be appropriately designed depending on the arrangement position of mask A2.

[0183] The processing procedure and the like are the same as those in the second embodiment, and therefore detailed description will not be repeated.

[0184] (e2: Variation 2) Fig. 11 is a schematic diagram showing an example configuration of an optical measurement system 2B according to Modification 2 of Embodiment 2. Fig. 11(A) shows an optical system when recording an in-line reference beam, and Fig. 11(B) shows an optical system when recording an object beam. The optical measurement system 2B is capable of configuring the optical systems shown in Figs. 11(A) and 11(B).

[0185] 11, the optical path of the off-axis reference light R is located on the back side of the image sensor D. According to the optical system shown in FIG. 11, except when recording the in-line reference light L, the optical path does not cross the sample S, making it easy to measure samples S with larger areas.

[0186] The optical system of the optical measurement system 2B shown in Figure 11(A) differs from the optical systems shown in Figures 1(A) and 8(A) in that mirrors M11 and M12 are arranged instead of mirror M1.

[0187] The off-axis reference light R split by the beam splitter BS1 is reflected by a mirror M11, and then reflected by a mirror M12 to be guided to the beam splitter BS2. That is, the mirrors M11 and M12 guide the off-axis reference light R from the rear side of the image sensor D to the beam splitter BS2.

[0188] The rest of the configuration is substantially the same as the optical system shown in FIG. 1(A) and FIG. 8(A). The optical system of the optical measurement system 2B shown in FIG. 11(B) is substantially the same as the optical system shown in FIG. 8(B) except that the mirror M2 is omitted.

[0189] 11(B), the optical measurement system 2B according to the second modification of the second embodiment can measure a sample S having a wider sample surface. Note that in order to change the relative relationship between the optical measurement system 2B and the sample S, the optical measurement system 2B or the sample S may be moved.

[0190] The processing procedure and the like are the same as those in the second embodiment, and therefore detailed description will not be repeated.

[0191] (e3: Variation 3) Fig. 12 is a schematic diagram showing a configuration example of an optical measurement system 2C according to Modification 3 of Embodiment 2. Fig. 12(A) shows an optical system when recording an in-line reference beam, and Fig. 12(B) shows an optical system when recording an object beam. The optical measurement system 2C is capable of configuring the optical systems shown in Fig. 12(A) and Fig. 12(B).

[0192] In the optical system shown in Fig. 12, the illumination position of illumination light Q is located outside beam splitter BS2. According to the optical system shown in Fig. 12, it is possible to reduce unnecessary light generated by reflection at beam splitter BS2 and suppress noise.

[0193] The optical system of the optical measurement system 2C shown in FIG. 12(A) is the same as the optical system shown in FIG. 11(A).

[0194] The optical system of the optical measurement system 2C shown in Figure 12(B) differs from the optical system shown in Figure 11(B) in that the position of the sample S has been changed to the outside of the beam splitter BS2. In addition, the sample S is positioned so that the sample surface of the sample S is inclined at a predetermined angle with respect to the optical axis of the lens L3. Corresponding to the inclination of the sample S, the mask A2 is also positioned so that it is inclined at a predetermined angle with respect to the optical axis of the lens L3. By positioning the mask A2 at an angle, an image of the aperture pattern SP2 of the mask A2 can be formed on the sample S.

[0195] FIG. 12(B) shows an example of an optical system in which the optical path of the off-axis reference light R is configured below the plane of the drawing of the beam splitter BS2. However, the beam splitter BS2 may be inverted and configured above the plane of the drawing, or the beam splitter BS2 may be rotated 90 degrees and configured in the front or back direction of the plane of the drawing.

[0196] Since the sample S is arranged obliquely, in the process of reproducing the hologram, the object light hologram for reproduction is propagated to the sample surface by plane wave expansion to calculate the light wave distribution, and the calculated light wave distribution is rotationally transformed in the coordinate system according to the inclination of the sample S. Thereby, the light wave distribution of the sample surface of the obliquely arranged sample S can be calculated.

[0197] Note that regarding other processing procedures and the like, they are the same as those in the second embodiment, so detailed descriptions will not be repeated.

[0198] (e4: Modification Example 4) In the above-mentioned modification examples 2 and 3 as well, the mask A2 may be arranged at the same arrangement position as the arrangement position of the mask A2 shown in the above-mentioned modification example 1.

[0199] <F. Processing Device 100> (f1: Hardware Configuration Example) FIG. 13 is a schematic diagram showing a hardware configuration example of a processing device 100 included in the optical measurement system according to the present embodiment. Referring to FIG. 13, the processing device 100 includes, as main hardware elements, a processor 102, a main memory 104, an input unit 106, a display unit 108, a storage 110, an interface 120, a network interface 122, and a media drive 124.

[0200] The processor 102 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and reads one or more programs stored in the storage 110 into the main memory 104 and executes them. The main memory 104 is a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and functions as a working memory for the processor 102 to execute the programs.

[0201] The input unit 106 includes a keyboard, a mouse, etc., and receives operations from the user. The display unit 108 outputs the results of program execution by the processor 102 to the user.

[0202] Storage 110 is made up of nonvolatile memory such as a hard disk or flash memory, and stores various programs and data. More specifically, storage 110 holds an operating system (OS) 112, a measurement program 114, hologram data 116, and measurement results 118.

[0203] Operating system 112 provides an environment in which processor 102 executes programs. Measurement program 114 is executed by processor 102 to realize the optical measurement method according to the present embodiment. Hologram data 116 corresponds to image data output from image sensor D. Measurement results 118 include measurement results obtained by executing measurement program 114.

[0204] The interface 120 mediates data transmission between the processing device 100 and the image sensor D. The network interface 122 mediates data transmission between the processing device 100 and an external server device.

[0205] The media drive 124 reads necessary data from a recording medium 126 (e.g., an optical disk) that stores programs to be executed by the processor 102, and stores the data in the storage 110. The measurement program 114 to be executed by the processing device 100 may be installed via the recording medium 126, or may be downloaded from a server device via the network interface 122.

[0206] The measurement program 114 may execute processing by calling necessary modules in a predetermined sequence at a predetermined timing among the program modules provided as part of the operating system 112. In such a case, a measurement program 114 that does not include such modules is also included in the technical scope of the present invention. The measurement program 114 may be provided as part of another program.

[0207] In addition, all or part of the functions provided by the processor 102 of the processing device 100 executing a program may be realized by a hardwired logic circuit (e.g., an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit)).

[0208] Note that the hardware configuration example of the processing device 100 is similar to that of the other embodiments, and therefore detailed description thereof will not be repeated.

[0209] (f2: Functional configuration example) Fig. 14 is a schematic diagram showing an example of the functional configuration of processing device 100 included in the optical measurement system according to this embodiment. Typically, each functional element shown in Fig. 14 may be realized by processor 102 of processing device 100 executing measurement program 114. Note that the hardware that realizes the functional configuration shown in Fig. 14 is selected appropriately according to the times.

[0210] Referring to Figure 14, the processing device 100 includes, as its main functional elements, an inline reference light acquisition module 150, an illumination light hologram acquisition module 152, an object light hologram acquisition module 154, a hologram reproduction module 156, an amplitude phase distribution calculation module 158, an object light phase calculation module 160, and an object shape calculation module 162.

[0211] The in-line reference beam acquisition module 150 converts the hologram to be recorded on the image sensor D into an off-axis hologram I when the optical system for recording the in-line reference beam is configured. LR Record as.

[0212] The illumination light hologram acquisition module 152 acquires the illumination light hologram Q(x, y) to be recorded on the image sensor D in a state where the optical system for recording the object light is configured.

[0213] Object beam hologram acquisition module 154 acquires object beam hologram U(x, y) to be recorded on image sensor D in a state where the optical system for recording object beam is configured.

[0214] Both the illumination light hologram acquisition module 152 and the object light hologram acquisition module 154 are configured to record the detection signal of the image sensor D, and either one is enabled depending on a status signal that is set manually or automatically.

[0215] The hologram reproducing module 156 reproduces the illumination light hologram (illumination light profile Q) from the illumination light hologram Q(x, y) acquired by the illumination light hologram acquisition module 152. Σ (x, y)) and reconstructs the object beam hologram U(x, y) from the object beam hologram U(x, y) acquired by the object beam hologram acquisition module 154. Σ Calculate (x,y).

[0216] Furthermore, the hologram reproducing module 156 is configured to have an illumination light profile Q Σ(x, y) and the object light hologram U for reproduction Σ (x, y) is propagated to the position of the sample surface by plane wave expansion to obtain the illumination light distribution Q of the sample surface S (x, y) and the object light distribution U S (x, y) is calculated.

[0217] The amplitude-phase distribution calculation module 158 Object light distribution U S (x,y) divides by the illumination light distribution Q S (x, y) to calculate the amplitude-phase distribution U of the sample surface P (x, y).

[0218] The object light phase calculation module 160 calculates the phase change amount Δθ(x, y) from the deflection angle of the amplitude-phase distribution U (x, y) of the sample surface. P (x, y).

[0219] The object shape calculation module 162 uses the phase change amount Δθ(x, y) to calculate information (such as thickness and refractive index) for specifying the shape of the sample. The object shape calculation module 162 outputs the calculation result as the shape information of the sample S.

[0220] <G. Experimental Example> Next, an example of the effect of the mask A2 for restricting the range of the illumination light Q adopted by the optical measurement system according to the present embodiment will be described.

[0221] FIG. 15 is a diagram showing an example of the effect of the mask adopted by the optical measurement system according to the present embodiment. FIG. 15 shows an example of the intensity reproduction image of the USAF 1951 test target recorded using the optical measurement system 1 adopting the transmission optical system shown in FIG. 1.

[0222] FIG. 15(A) shows an example of the intensity reproduction image based on the hologram recorded with the mask A2 removed, and FIG. 15(B) shows an example of the intensity reproduction image based on the hologram recorded with the mask A2 arranged.

[0223] In the intensity reproduction image shown in FIG. 15(A), it can be seen that significant image degradation has occurred. This is because the range of the illumination light is not restricted, so in the spectral band, the direct image component overlaps with the conjugate image component and the folded light that occurs because the sampling theorem is not satisfied. As a result, significant image degradation has occurred.

[0224] In contrast, in the intensity reproduction image shown in FIG. 15(B), the irradiation range of the illumination light is restricted approximately within the dashed line in the figure. As a result, in the spectral band, it can be seen that the direct image component does not overlap with the conjugate image component and the folded light, and image degradation is suppressed.

[0225] Furthermore, according to the intensity reproduction image shown in FIG. 15(B), by imaging the image corresponding to the aperture pattern SP1 using the mask A2 on the image sensor D, it is possible to suppress the knife-edge diffraction that can occur at the edge of the illumination range, and it can be confirmed that the illumination range can be controlled in units of several tens of μm.

[0226] <H. Other Embodiments> As described above, the process of obtaining the off-axis hologram I LR (the processes of steps S2 and S4 in FIG. 6, and the processes of steps S52 and S54 in FIG. 9) is for improving the accuracy of the reproduction image, and may be omitted depending on the required accuracy.

[0227] When the off-axis hologram I LR is not obtained, the calculation process according to the above-mentioned equation (8) is not performed, and the complex amplitude off-axis hologram J OR shown in equation (7) may be directly used as the object light hologram U(x, y).

[0228] Alternatively, after removing the component (=R0exp(iφ OR )) of the off-axis reference light R from the complex amplitude off-axis hologram J R shown in equation (7), it may be used as the object light hologram U(x, y). When removing the off-axis reference light R, the complex amplitude off-axis hologram JOR It may be divided by the complex conjugate of the off-axis reference light R. The distribution of the off-axis reference light R can be obtained by a method such as calculation from the analytical solution of the spherical wave based on the physical arrangement of the point light source of the off-axis reference light R.

[0229] In addition, when the off-axis hologram I LR is not acquired, in addition to the above formula (8), formulas (4), (6), and (9) are not used.

[0230] <I. Modified Example> The above-described optical system is an example, and any optically equivalent change can be made according to restrictions such as required specifications and space. For example, a single lens may be changed to a compound lens, or any reflecting member may be used instead of the mirror.

[0231] Also, in the above description, an implementation example in which the processing device 100 executes arithmetic processing related to the shape measurement of the sample S has been illustrated, but it is not limited to this, and any implementation form can be adopted. For example, part or all of the processing performed by the processing device 100 may use computing resources on the cloud.

[0232] <J. Summary> In the optical measurement device according to the present embodiment, by restricting the range in which the sample is illuminated with the illumination light to a predetermined range, overlap in the Fourier space (spatial frequency domain) between the component including the information of the object light, the light intensity component, and the conjugate light component can be avoided. As a result, noise due to overlap between components can be suppressed, and more accurate measurement can be realized.

[0233] Also, by designing so as to secure the maximum area within the range where no overlap occurs between components in the Fourier space (spatial frequency domain), more information can be acquired, and the measurement accuracy can be improved.

[0234] In this way, in the optical measuring device according to this embodiment, by forming an image of a restricting portion (mask) positioned at a position different from the sample surface at the sample position, the illumination range of the sample can be controlled to any shape, and the frequency band of the image sensor capable of recording holograms can be efficiently utilized.

[0235] Furthermore, in the optical measuring device according to this embodiment, the image that has passed through a restricting section (mask) arranged downstream of the sample surface is made incident on the image sensor, thereby making it possible to efficiently utilize the frequency band of the image sensor capable of recording holograms.

[0236] The optical measurement system according to this embodiment measures the shape of a sample using phase information of the object light, so the depth resolution (resolution on the z-axis) is not limited by the focal depth, and the shape of the sample can be measured on the order of nm. Furthermore, the optical measurement system according to this embodiment employs an off-axis holography optical system, which allows the distribution of the complex amplitude of light to be recorded in one shot. This eliminates the need for physical scanning or phase shifting, and ensures that the measured thickness (or height) of the sample surface is not affected by vibration. Furthermore, the hologram recorded in one shot is complete as the complex amplitude of the light wave, and measurement accuracy can be maintained even when correction processes such as software focusing and coordinate correction are performed.

[0237] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0238] 1, 1A, 2, 2A, 2B, 2C Optical measurement system, 10 Light source, 20 Imaging optical system, 100 Processing device, 102 Processor, 104 Main memory, 106 Input unit, 108 Display unit, 110 Storage, 112 Operating system, 114 Measurement program, 116 Hologram data, 118 Measurement result, 120 Interface, 122 Network interface, 124 Media drive, 126 Recording medium, 150 In-line reference light acquisition module, 152 Illumination light hologram acquisition module, 154 Object light hologram acquisition module, 156 Hologram reconstruction module, 158 Amplitude phase distribution calculation module, 160 Object light phase calculation module, 162 Object shape calculation module, A1, A2 Mask, BE Beam expander, BS1, BS2 Beam splitter, D Image sensor, FP1 Focus point, I LR ,I OR Off-Axis Hologram, J LR ,J OR Complex amplitude off-axis hologram, J OL Complex amplitude in-line hologram, L in-line reference beam, L1, L2, L3, L4, L21, L22, L31, L32 lenses, M1, M2, M3, M11, M12 mirrors, MO objective lens, O object beam, P pinhole, Q illumination beam profile, Q illumination beam, Q S Illumination light distribution, R Off-axis reference light, S Sample, SP1, SP2 Aperture pattern, U Σ Reconstruction object beam hologram, U Object beam hologram, U P Amplitude-phase distribution, U S Object light distribution, U d Hologram, Wx,Wy bandwidth, d distance, f spatial frequency, h height, kx,ky,kz1 wave number, n1,n2 refractive index, uc,vc center frequency.

Claims

1. A light source and An image sensor; an optical system including a beam splitter that splits the light from the light source into a first light and a second light, the optical system is configured to record, with the image sensor, a first hologram obtained by modulating light obtained by illuminating a sample with the first light with the second light, which is divergent light; the optical system includes a limiting unit that limits the spread of light obtained by illuminating the sample with the first light to a predetermined range; an optical measurement system in which the size of the predetermined range is determined so that, in the spatial frequency domain of the hologram recorded by the image sensor, the component corresponding to the first light does not overlap with components other than the component corresponding to the first light.

2. The optical measurement system according to claim 1 , wherein the limiting unit limits the range in which the sample is illuminated with the first light to the predetermined range.

3. The optical measurement system according to claim 1 , wherein the limiting unit limits a range through which light obtained by illuminating the sample with the first light passes to the predetermined range.

4. 4. The optical measurement system according to claim 1, wherein the limiting section includes a mask having an opening pattern corresponding to the predetermined range formed in a shielding member.

5. The optical measurement system according to claim 4 , wherein the limiting section is configured to be able to change the size of the opening pattern.

6. 6. The optical measurement system according to claim 1, wherein the optical system is an off-axis holographic optical system.

7. the optical system generates the first hologram from transmitted light obtained by illuminating the sample with the first light; The optical measurement system according to any one of claims 1 to 6, wherein in the optical system, a second hologram is recorded from transmitted light obtained by illuminating a substrate that is not a measurement target included in the sample with the first light, instead of the sample.

8. the optical system generates the first hologram from reflected light obtained by illuminating the sample with the first light; 7. The optical measurement system according to claim 1, wherein in the optical system, a second hologram is recorded from transmitted light obtained by illuminating a reference surface with the first light instead of the sample.

9. The optical measurement system according to claim 7 or 8, further comprising a processing device that calculates a shape of the sample based on the first hologram and the second hologram.

10. An optical measurement method using an optical system including a beam splitter that splits light from a light source into a first light and a second light, a step of recording a first hologram by an image sensor, the first hologram being obtained by illuminating a sample with the first light and modulating the light with the second light, which is divergent light; recording a second hologram by the image sensor in the absence of the sample, the second hologram being obtained by modulating the first light with the second light, which is divergent light; calculating a shape of the sample based on the first hologram and the second hologram; an optical measurement method, wherein the step of recording the second hologram with the image sensor includes a step of limiting the spread of light obtained by illuminating the sample with the first light to a predetermined range so that a component corresponding to the first light does not overlap with a component other than the component corresponding to the first light in the spatial frequency domain of the second hologram recorded by the image sensor.

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