Optical measurement system, optical measurement method, and optical measurement program

Abstract

To provide a technology that can measure samples with higher accuracy while reducing the effort required for adjustment. [Solution] The optical measurement method includes the steps of: configuring an optical system for recording a hologram generated by modulating object light obtained by illuminating a sample with illumination light using reference light coherent with the illumination light; placing a calibration unit including an optical system that generates a known light wave distribution on the optical path of the illumination light in a state where no sample is present; recording a first hologram generated when the calibration unit is generating the light wave distribution; and calculating information on the light wave distribution of the reference light based on information indicating the placement position of the calibration unit, the known light wave distribution, and the first hologram.

Description

[Technical Field]

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

[0002] 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 illuminating a sample are superimposed on each other to obtain the shape of the wavefront of the object light. Typical prior art technologies include the following:

[0003] US Pat. No. 6,411,406 (Patent Document 1) discloses a method for reconstructing a holographic image.

[0004] WO 2013 / 047709 (Patent Document 2) discloses a practical digital holography method that operates in both reflection and transmission modes.

[0005] International Publication No. 2011 / 089820 (Patent Document 3) discloses a method for creating a complex amplitude in-line hologram.

[0006] International Publication No. 2012 / 005315 (Patent Document 4) discloses a method for creating a hologram for high-resolution image reproduction, for reproducing an image with increased resolution from a complex amplitude in-line hologram of a minute subject obtained using in-line spherical wave light.

[0007] International Publication No. 2020 / 045584 (Patent Document 5) discloses a holographic imaging device and the like that has improved performance by taking into account the influence of the refractive index of a cube-shaped beam combiner that constitutes an optical system. More specifically, the publication discloses a method for generating an inline reference beam hologram that represents a light wave on a hologram surface by performing a light propagation calculation, including propagation inside the beam combiner, for a spherical wave emitted from the focal point of an inline spherical wave reference beam, taking into account the refractive index of the beam combiner. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 6,411,406 [Patent Document 2] International Publication No. 2013 / 047709 [Patent Document 3] International Publication No. 2011 / 089820 [Patent Document 4] International Publication No. 2012 / 005315 [Patent Document 5] International Publication No. 2020 / 045584 Summary of the Invention [Problem to be solved by the invention]

[0009] The method disclosed in US Pat. No. 6,411,406 (Patent Document 1) has a problem in that accurate object light cannot be obtained due to superposition of conjugate images.

[0010] The method disclosed in International Publication No. 2013 / 047709 (Patent Document 2) is configured using an imaging optical system, and therefore has the problem that aberration occurs in the imaging optical system, making it impossible to accurately record the three-dimensional distribution.

[0011] WO 2011 / 089820 (Patent Document 3) has a problem in that the reference beam is not perfectly determined, which may cause distortion in the recorded object beam data.

[0012] International Publication No. 2012 / 005315 (Patent Document 4) and International Publication No. 2020 / 045584 (Patent Document 5) have the problem that the inline spherical wave light needs to be accurately adjusted to the inline axis, which requires a lot of time and effort for adjustment.

[0013] The present invention provides a technique that can measure a sample with higher accuracy while reducing the effort required for adjustment. [Means for solving the problem]

[0014] An optical measurement method according to one aspect of the present invention includes the steps of: configuring an optical system for recording a hologram generated by modulating object light obtained by illuminating a sample with illumination light using reference light coherent with the illumination light; placing a calibration unit including an optical system that generates a known light wave distribution on the optical path of the illumination light in a state where no sample is present; recording a first hologram generated while the calibration unit is generating the light wave distribution; and calculating information about the light wave distribution of the reference light based on information indicating the placement position of the calibration unit, the known light wave distribution, and the first hologram.

[0015] The calibration unit may be configured to spatially move the generated light wave distribution. The optical measurement method may further include the steps of moving the generated light wave distribution to a plurality of positions different from the position where the first hologram is recorded and recording a plurality of second holograms generated at the plurality of positions, calculating wavefront aberration from a spectrum calculated from the known light wave distribution and a spectrum calculated from the light wave distributions corresponding to the plurality of second holograms, and adjusting information indicating the placement position of the calibration unit so as to minimize the wavefront aberration.

[0016] The optical measurement method may further include the steps of applying spatial frequency filtering to each of the plurality of second holograms and calculating a plurality of object light holograms corresponding to the plurality of second holograms, respectively, based on the filtering result and information on the light wave distribution of the reference light; and calculating a plurality of light wave distributions corresponding to the plurality of second holograms, respectively, by correcting each of the plurality of object light holograms based on the known light wave distribution.

[0017] The step of calculating the wavefront aberration may include a step of calculating a phase difference distribution spectrum, which is a phase difference distribution between a spectrum calculated from a known light wave distribution and a spectrum calculated from a light wave distribution corresponding to the second hologram, and a step of calculating the root mean square of the average value of the entire phase difference distribution spectrum as an error.

[0018] The optical measurement method may further include a step of recording a third hologram generated by modulating, with reference light, object light obtained by illuminating a sample with illumination light, and a step of applying spatial frequency filtering to the third hologram and calculating an object light hologram based on the filtering result and information on the light wave distribution of the reference light.

[0019] The information on the light wave distribution of the reference light may include a complex conjugate of the light wave distribution of the reference light. An optical measurement method according to another aspect of the present invention includes the steps of configuring an optical system for recording a hologram generated by modulating object light obtained by illuminating a sample with illumination light using a reference light coherent with the illumination light; acquiring information on the light wave distribution of the reference light in the optical system; recording a hologram generated by modulating object light obtained by illuminating a sample with illumination light using the illumination light and a reference light coherent with the illumination light; and applying spatial frequency filtering to the hologram. and calculating an object beam hologram based on the filtering result and information on the light wave distribution of the reference beam.

[0020] Information on the light wave distribution of the reference light may be calculated in advance based on a hologram recorded when a calibration unit including an optical system that generates a known light wave distribution is placed on the optical path of the illumination light in the absence of a sample, information indicating the placement position of the calibration unit, and the known light wave distribution.

[0021] According to yet another aspect of the present invention, an optical measurement system includes a light source that generates coherent light, a beam splitter that generates illumination light and reference light from the coherent light from the light source, an optical system that uses an image sensor to record a hologram generated by modulating object light obtained by illuminating a sample with the illumination light and the coherent reference light, and a processing device having a storage unit that stores information about the light wave distribution of the reference light in the optical system. The processing device applies spatial frequency filtering to the hologram recorded by the image sensor and calculates an object light hologram based on the filtering result and the information about the light wave distribution of the reference light.

[0022] Information on the light wave distribution of the reference light may be calculated in advance based on a hologram recorded when a calibration unit including an optical system that generates a known light wave distribution is placed on the optical path of the illumination light in the absence of a sample, information indicating the placement position of the calibration unit, and the known light wave distribution. [Effects of the Invention]

[0023] According to an embodiment of the present invention, samples can be measured with higher accuracy while reducing the amount of adjustment required. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a schematic diagram showing a configuration example (for measurement processing) of an optical measurement system according to the present embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a configuration example (calibration process) of the optical measurement system according to the present embodiment. [Figure 3] FIG. 2 is a schematic diagram showing an example of the configuration of a profile generating unit of the optical measurement system according to the present embodiment. [Figure 4]It is a schematic diagram showing an example of the hardware configuration of a processing device included in an optical measurement system according to this embodiment. [Figure 5] It is a flowchart showing the processing procedure of measurement processing executed in an optical measurement system according to this embodiment. [Figure 6] It is a flowchart showing the processing procedure of calibration processing executed in an optical measurement system according to this embodiment. [Figure 7] It is a flowchart showing another processing procedure of calibration processing executed in an optical measurement system according to this embodiment. [Figure 8] It is a diagram showing a measurement example in the initial stage of the calibration process of an optical measurement system according to this embodiment. [Figure 9] It is a diagram showing a measurement example after the calibration process of an optical measurement system according to this embodiment. [Figure 10] It is a diagram showing a measurement example of a sample by an optical measurement system according to this embodiment. [Figure 11] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 1 of this embodiment. [Figure 12] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 2 of this embodiment. [Figure 13] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 3 of this embodiment. [Figure 14] It is a schematic diagram showing a configuration example of an optical measurement system according to Modification Example 4 of this embodiment.

Embodiments for Carrying Out the Invention

[0025] 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 attached and the description thereof will not be repeated.

[0026] <A. Configuration Example of Optical Measurement System> The optical measurement system according to this embodiment utilizes digital holography, which uses diverging light such as a point light source as a reference light, and employs a lensless digital holography configuration in which no lens exists between the sample and the image sensor.

[0027] FIG. 1 is a schematic diagram showing an example of the configuration (for measurement processing) of an optical measurement system 1 according to this embodiment. By using the example of the configuration shown in FIG. 1, a light wave distribution indicating the shape of a sample is recorded. More specifically, the optical system shown in FIG. 1 records a hologram I generated by modulating object light O obtained by illuminating a sample S with illumination light Q using reference light R arranged off-axis. OR This corresponds to the optical system for recording.

[0028] 1, the optical measurement system 1 includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M1 and M2, a field mask A1, condenser lenses L1 and L2, and an image sensor D.

[0029] 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.

[0030] Beam splitter BS1 splits the light expanded by beam expander BE into two. One of the split lights (light on the reflection side of beam splitter BS1) corresponds to illumination light Q, and the other light (light on the transmission side of beam splitter BS1) corresponds to reference light R positioned off-axis. Therefore, illumination light Q and reference light R are mutually coherent. In this way, beam splitter BS1 generates illumination light Q and reference light R from the coherent light from light source 10.

[0031] The illumination light Q is reflected by mirror M1 to change its propagation direction, and then passes through field mask A1.

[0032] The field mask A1 limits the range of illumination of the sample S with the illumination light Q to a predetermined range. As an example of a limiting section, the field mask A1 may be configured with a light-shielding member having an opening SP1 formed therein that corresponds to the predetermined range. The illumination light Q passes through the area corresponding to the opening SP1.

[0033] The image of the aperture SP1 of the field mask A1 passes through the condenser lens L1 and is focused on the sample S. That is, of the light illuminating the field mask A1, only the portion of the light corresponding to the aperture SP1 passes through the field mask A1. This makes it possible to limit the range of the sample S illuminated by the illumination light Q that has passed through the field mask A1.

[0034] The range of illumination of the sample S is determined so as to avoid overlap in Fourier space (spatial frequency domain) between the component containing the information of the object light O and the light intensity component and conjugate light component. By limiting the illumination range of the illumination light Q in this way, noise due to overlap between components can be suppressed. However, the field mask A1 may be omitted.

[0035] Illumination light Q passes through sample S to generate object light O. Object light O passes through half mirror HM2 of beam splitter BS2 and enters image sensor D.

[0036] On the other hand, the reference light R is reflected by mirror M2, changes its propagation direction, and then is focused by condenser lens L2. The focus point FP1 of condenser lens L2 corresponds to the position of the point light source. In other words, the off-axis positioned reference light R can be considered as light irradiated from a point light source. Finally, the reference light R is reflected by half mirror HM2 and enters image sensor D.

[0037] In this way, the object light O obtained by illuminating the sample S with the illumination light Q is modulated by the reference light R arranged off-axis in the half mirror HM2. The hologram I generated by the modulation OR is recorded by image sensor D.

[0038] The processing device 100 detects the hologram I recorded by the image sensor D. OR and the complex conjugate R of the light wave distribution of the reference light R obtained by calibration. * and calibration information 114 including the above, to calculate the information required for image reconstruction of the sample S.

[0039] FIG. 1 shows an example of a configuration that employs a cube-shaped beam splitter BS2, but the refractive index of the beam splitter BS2 may be made relatively high or the cube shape may be modified into any other shape in order to increase the numerical aperture or ensure the working distance.

[0040] Hologram I OR The beam splitter for recording may have any shape as long as the boundary surface between different media can be considered as a plane. For example, a plate-shaped beam splitter may be used instead of a cube-shaped one.

[0041] Furthermore, the beam splitter BS2 may be tilted with respect to the wavefront of the object light. Such tilting can suppress stray light. Although the example shown has the sample S and image sensor D facing each other across the beam splitter BS2, it is also possible to employ an example in which the condenser lens L2 and image sensor D are positioned facing each other across the beam splitter BS2.

[0042] Fig. 2 is a schematic diagram showing an example configuration (calibration process) of an optical measurement system 1 according to this embodiment. The optical measurement system 1 shown in Fig. 2 is configured by replacing the sample S, field mask A1, and condenser lens L1 in the configuration shown in Fig. 1 with a calibration unit 20. Note that the configuration related to the reference light R (mirror M2 and condenser lens L2) remains the same as in Fig. 1.

[0043] By using the configuration example shown in Figure 2, the calibration hologram I PiR Calibration hologram I PiRis a set of holograms generated by translating a known light wave distribution P(x, y, z) to multiple positions and modulating each of them with an off-axis reference beam R.

[0044] In this specification, the term "known light wave distribution" means a light wave distribution that can be specified with the accuracy required for the required measurement performance. PiR The light wave distribution of the light used to generate the light wave distribution of the light only needs to be approximately expressed with the required accuracy, and does not need to be completely described without any error. However, the light wave distribution itself does not change with translation.

[0045] Calibration Hologram I PiR By recording the in-line spherical wave light, unlike the configurations disclosed in the above-mentioned Patent Documents 4 and 5, it is not necessary to precisely align the in-line spherical wave light with the in-line axis. No. Calibration Hologram I PiR The image reconstruction process using the method will be described later.

[0046] The calibration unit 20 includes a profile generator 30 and a field-of-view mask FA. The profile generating unit 30 is an optical system that generates a known light wave distribution. In this manner, in a state where the sample S is not present, the calibration unit 20 including the optical system (profile generating unit 30) that generates a known light wave distribution is placed on the optical path of the illumination light Q.

[0047] The profile generating unit 30 may be configured to be able to spatially move the generated light wave distribution. More specifically, the profile generating unit 30 may have a function to translate (shift) the light wave distribution in the x-axis direction, y-axis direction, and z-axis direction. The illumination light Q split by the beam splitter BS1 is reflected by the mirror M1, its propagation direction is changed, and then it enters the profile generating unit 30, whereby a known light wave distribution P that can be moved spatially is generated.

[0048] The field-limiting mask FA has an aperture SP2 corresponding to the field-of-view range recordable by the image sensor D. Note that the position of the field-limiting mask FA is fixed. The light-wave distribution P generated by the profile generation unit 30 is movable in the x-axis direction, y-axis direction, and z-axis direction, respectively. However, the aperture SP2 of the field-limiting mask FA is designed so as not to block the light-wave distribution P generated by the profile generation unit 30. That is, the light-wave distribution P will move parallel within the range that can pass through the aperture SP2 of the field-limiting mask FA. However, the field-limiting mask FA may be omitted.

[0049] <B. Configuration Example of Profile Generation Unit 30> Next, a configuration example of the profile generation unit 30 of the calibration unit 20 will be described. As described above, the profile generation unit 30 may adopt any optical system as long as it can generate a known light-wave distribution. Some typical configuration examples of the profile generation unit 30 will be described.

[0050] FIG. 3 is a schematic diagram showing a configuration example of the profile generation unit 30 of the optical measurement system 1 according to the present embodiment. Any of the optical systems shown in FIGS. 3(A) to 3(D) generates a known light-wave distribution P when illumination light Q, which is a plane wave, is incident.

[0051] [[ID=1'4]]The profile generation unit 30A shown in FIG. 3(A) is an optical system using a pinhole and includes a light-shielding plate 31 movable parallel in three axes. A pinhole 32 is provided within the illumination range of the illumination light Q of the light-shielding plate 31. The beam diameter of the illumination light Q is set to a size that can sufficiently illuminate the range including the pinhole 32.

[0052] The profile generation unit 30B shown in FIG. 3(B) is an optical system using a pinhole and a condenser lens, and includes a light shielding plate 33 and a light shielding plate 34 that are each movable in parallel in three axes. The light shielding plate 33 and the light shielding plate 34 are connected to each other and move in parallel integrally. A condenser lens 35 is provided within the illumination range of the illumination light Q of the light shielding plate 33, and a pinhole 36 is provided within the illumination range of the illumination light Q that has passed through the light shielding plate 34. The beam diameter of the illumination light Q is set to a size such that a sufficient amount of light can pass through the condenser lens 35 and the pinhole 36.

[0053] The profile generation unit 30C shown in FIG. 3(C) is an optical system that does not use a pinhole and uses a condenser lens with known aberration. The profile generation unit 30C includes a light shielding plate 31 that is movable in parallel in three axes. A condenser lens 37 is provided within the illumination range of the illumination light Q of the light shielding plate 31. The beam diameter of the illumination light Q is set to a size such that the range including the condenser lens 37 can be sufficiently illuminated.

[0054] The profile generation unit 30D shown in FIG. 3(D) is an optical system that does not use a pinhole and uses an objective lens with known aberration. The profile generation unit 30D includes a light shielding plate 31 that is movable in parallel in three axes. An objective lens 38 is provided within the illumination range of the illumination light Q of the light shielding plate 31. The beam diameter of the illumination light Q is set to a size such that the range including the objective lens 38 can be sufficiently illuminated.

[0055] Note that the present invention is not limited to the configuration examples shown in FIGS. 3(A) to 3(D), and any optical system that can generate a known light wave distribution can be adopted.

[0056] <C. Measurement Process> Next, the measurement process of the sample S by the optical measurement system 1 will be described. In the following description, the light receiving surface of the image sensor D will be referred to as the "recording surface," and the intersection of the recording surface and the central optical axis of the 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 the 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 the image sensor D, and the x-axis and y-axis are parallel to the recording surface of the image sensor D.

[0057] Moreover, the surface under consideration, which is a predetermined distance away from the recording surface, is called a "sample surface." In the optical system shown in FIG. 1, the light wave distribution of the object light O and the reference light R recorded by the image sensor D can be expressed by the following general formulas (1) and (2).

[0058]

number

[0059] The object beam O and the off-axis reference beam R are mutually coherent beams with an angular frequency ω. For ease of explanation, the coordinates (x, y) may be omitted as appropriate in the following equations.

[0060] Hologram I recorded by image sensor D in one shot OR is calculated as the light intensity of the composite light of the light expressed by equation (1) and the light expressed by equation (2) using the following equation (3).

[0061]

number

[0062] By applying spatial frequency filtering to equation (3), the complex amplitude hologram J OR is calculated as shown in the following equation (4).

[0063]

number

[0064] Complex Amplitude Hologram J OR The complex conjugate R of the light wave distribution of the reference light R obtained by the calibration process * (=R0exp(-iφ R )), the object beam hologram U is calculated as shown in the following equation (5).

[0065]

number

[0066] The object beam hologram U shown in equation (5) corresponds to the light wave distribution of the object beam O on the recording surface of the image sensor D minus the time term (-ωt). Therefore, by using diffraction calculations that do not use approximations such as plane wave expansion, accurate image reconstruction without aberrations can be achieved.

[0067] If the object light hologram U contains frequency components that do not satisfy the sampling theorem, the complex conjugate R of the light wave distribution of the reference light R * Before dividing by, the complex amplitude hologram J is obtained by interpolation. OR After increasing the number of samples, the increased complex amplitude hologram J OR is divided into a grid and the divided grids are superimposed to form a complex amplitude hologram J OR The hologram may be reduced in size. Note that the size of the grating is preferably larger than the size of the image reconstructed from the hologram. By increasing the number of samples and superimposing them in this way, the increase in the amount of calculations can be suppressed.

[0068] Furthermore, the properties of the Fourier transform may be utilized to realize processing equivalent to increasing the number of sampling points and superimposing them on the Fourier spectrum.

[0069] The complex amplitude distribution obtained by increasing the number of samples and superposing them is used as the reconstructed object beam hologram U ΣHowever, if there is no need to increase the number of samples or to superimpose, the object beam hologram U can be used as the reconstruction object beam hologram U Σ Treat as.

[0070] Reconstruction object beam hologram U Σ is a hologram that contains information that can reconstruct the state of the sample surface.

[0071] Next, the calculation of diffraction within the medium and the image reconstruction on the inclined surface will be explained. Reconstruction object beam hologram U Σ By performing a diffraction calculation using a plane wave expansion for , the light wave distribution on any sample surface can be reconstructed. Σ The light wave distribution propagated by a distance d (on the sample surface at a distance d from the recording surface) is called the complex amplitude distribution U d Let's say.

[0072] The distance of M media (m=1, 2, . . . , M) included in the distance d from the recording surface of the image sensor D to the reproduced distance d is defined as d m , the refractive index is n m Then, the complex amplitude distribution U d can be generalized as the following equation (6). zm is calculated according to equation (7).

[0073]

number

[0074] 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.

[0075] For example, if the signal propagates only through the air for a distance d, then M=1 and d1=d,n m =1.

[0076] 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.

[0077] Furthermore, if the boundary surface between the media does not coincide with the optical wavefront, the coordinate system is rotated so that the optical wavefront coincides with the boundary surface. In this case, the boundary surface between the media does not need to be parallel to the recording surface. The rotational transformation can be performed on the spatial frequency spectrum. According to the following equations (8) and (9), the spatial frequency vector ν = (u, v, w) at the coordinates (u, v) of the spatial frequency spectrum is calculated by Fourier transforming the optical wavefront in the medium with refractive index n.

[0078]

number

[0079] According to the following equation (10), a new spatial frequency vector (u', v', w') is calculated by performing a rotational transformation on the spatial frequency vector ν using a matrix A that defines the rotational transformation to the new coordinate system.

[0080]

number

[0081] The coordinates u' and v' of the calculated spatial frequency vector correspond to the coordinates of the spatial frequency spectrum after the rotational transformation. By performing the above-mentioned rotational transformation operation on all data of the wavefront before the boundary, the spatial frequency spectrum of the wavefront after the boundary can be calculated.

[0082] Furthermore, it can also be used to reproduce the image of the inclined surface. By performing an inverse Fourier transform on the spatial frequency spectrum of the wavefront after rotational transformation, the light wave distribution on the surface after rotational transformation can be calculated.

[0083] The light wave distribution obtained as a result of the diffraction calculation is the complex amplitude distribution U of the object light d and becomes. Therefore, the complex amplitude distribution U d can be visualized by any arithmetic processing. For example, by extracting the amplitude component from the complex amplitude distribution U d and imaging it, an image corresponding to the bright field of an optical microscope can be obtained.

[0084] <D. Calibration Process> Next, the calibration process using the configuration example shown in FIG. 2 will be described. In the calibration process, information on the light wave distribution of the reference light R is determined. The information on the light wave distribution of the reference light R includes the complex conjugate R * of the light wave distribution of the reference light R.

[0085] In the configuration example shown in FIG. 2, the known light wave distribution P generated by the calibration unit 20 is translated to arbitrary offset coordinates (x pi , y pi , z pi )(i = 0 to N - 1), thereby generating the light wave distribution P i (i = 0 to N - 1). For example, as shown in FIGS. 3(A) to 3(D), by arbitrarily moving the profile generation unit 30 in one or more directions of the x-axis direction, y-axis direction, and z-axis direction (that is, by arranging the optical unit that generates the light wave distribution P at arbitrary offset coordinates), the light wave distribution P i can be generated.

[0086] The light wave distribution P i is obtained by translating the known light wave distribution P along each axis direction. Therefore, the light wave distribution P i on the recording surface (z = 0) of the image sensor D is the light wave distribution P (which is known) on the recording surface (z = 0) of the image sensor D and the offset coordinates (x pi , y pi , z pi) can be expressed as the following equation (11).

[0087]

number

[0088] Calibration hologram I recorded by image sensor D PiR can be expressed as the following equation (12): By filtering the third term of equation (12), the complex amplitude hologram J PiR is calculated as shown in the following equation (13).

[0089]

number

[0090] Offset coordinate (x pi ,y pi ,z pi ) is known, the complex conjugate R of the light wave distribution of the reference light R * (=R0exp(-iφ R )) is calculated as shown in the following equation (14).

[0091]

number

[0092] In this case, one offset coordinate (x p0 ,y p0 ,z p0 ) from the light wave distribution P0 corresponding to the complex conjugate R of the light wave distribution of the reference light R * The profile generating unit 30 does not need to have a function for translating the known light wave distribution P to a plurality of positions.

[0093] On the other hand, if the offset coordinate is unknown or cannot be obtained with the required accuracy, the complex conjugate R of the light wave distribution of the reference light R can be calculated using the following parameter fitting: * Determine.

[0094] More specifically, the offset coordinate (x p0 ,y p0 ,z p0 ) and set an appropriate initial value. The initial value is determined taking into consideration the optical positional relationship of the calibration unit 20. i is the complex conjugate R of the light wave distribution of the reference light R shown in equation (14). * Using this, it can be expressed as the following equation (15).

[0095]

number

[0096] In this case, the relationship of the following equation (16) must be established for all numbers i (i=0 to N-1).

[0097]

number

[0098] It is clear that the relationship of equation (16) holds when number i=0. When number i≠0, the complex conjugate R of the light wave distribution of the reference light R shown in equation (14) holds. * If is calculated correctly, equation (16) can be transformed into equation (17), and the relationship in equation (16) will hold.

[0099]

number

[0100] In other words, for all numbers i (i=0 to N-1), if the relationship of equation (16) does not hold, the complex conjugate R of the light wave distribution of the reference light R * This means that the complex conjugate R of the light wave distribution of the reference light R has not been calculated correctly. * The reason why it is not calculated correctly is because the offset coordinate (x p0 ,yp0 ,z p0 ) is incorrect, and the offset coordinate (x p0 ,y p0 ,z p0 ) needs to be adjusted to the correct value.

[0101] Offset coordinate (x p0 ,y p0 ,z p0 ) before adjusting the calibration hologram I PiR It is preferable to modify the light wave distribution calculated from

[0102] More specifically, for each of the numbers i=1 to N−1, the object beam hologram U i The light wave distribution P is determined so that the light wave distribution of the image reproduced from the recording surface coincides with the known light wave distribution P on the recording surface. i The corrected light wave distribution is corrected as P i ' is called.

[0103] From equations (11) and (15) to (17), the relationship shown in equation (18) below is established. Note that the complex conjugate R of the light wave distribution of the reference light R * In this state, the object light hologram U is calculated so that it matches the known light wave distribution P, as shown in the following equation (19): i By correcting the x-axis, y-axis, and z-axis, the corrected light wave distribution P i ' to determine.

[0104]

number

[0105] The x- and y-axis adjustments are performed by the object beam hologram U i This is achieved by shifting (offsetting) the target pixel group of the image sensor D corresponding to (x, y). Correction in the z-axis direction (focus position) is achieved by diffraction calculation using the plane wave expansion shown in equation (6). In other words, correction in the z-axis direction is achieved by iThis is achieved by changing the distance at which the image is reconstructed when calculating the diffraction.

[0106] In addition, the light wave distribution P i When (i=1 to N-1) passes through a medium such as a half mirror, it is preferable to apply the same processing as the above-mentioned calculation of diffraction within the medium and processing of image reconstruction on the inclined surface.

[0107] In this way, for numbers i=1 to N-1, the corrected light wave distribution P i ' is calculated.

[0108] Finally, the complex conjugate R of the light wave distribution of the reference light R * Specifically, for all numbers i (i=0 to N-1), the known light wave distribution P and the corrected light wave distribution P i ' are Fourier transformed to obtain the spectrum F[P] and the spectrum F[P i ']. Then, the spectrum F[P] and the spectrum F[P i The phase difference distribution spectrum W i (u,v)(=arg(F[P i '] / F[P])) where arg() is a function that calculates the argument (phase) of a complex number.

[0109] The phase difference distribution spectrum W i It is preferable to perform processing to make the phase continuous for portions of (u, v) where phase discontinuity (gaps) occurs due to the influence of phase periodicity.

[0110] Phase difference distribution spectrum W i Using (u, v), the wavefront aberration W is calculated as shown in the following equation (20): i_err The wavefront aberration W i_err is the phase difference distribution spectrum W i Overall average value W ave is taken as the true value, and the root mean square of the true value is calculated as the error.

[0111]

number

[0112] Here, the average value W ave is the phase difference distribution spectrum W i is the average value of (u,v), and S W is the phase difference distribution spectrum W i The area of ​​the range in which (u,v) is integrated. The integration range is the phase difference distribution spectrum W i (u,v) is the part where valid data exists, and the wavefront aberration W i_err and the mean value W ave This is common in the calculation of

[0113] In the narrow sense, "wavefront aberration" refers to the wavefront aberration W i_err It means the value obtained by multiplying by λ / 2π (λ: wavelength). i_err ×λ / 2π may be referred to as wavefront aberration. However, since λ / 2π is a fixed coefficient, the following processing will be explained without including the coefficient λ / 2π. However, in the measurement examples shown in Figures 8 and 9 described later, evaluation is performed using wavefront aberration in the narrow sense.

[0114] The complex conjugate R of the light wave distribution of the correct reference light R * When the light wave distribution is reconstructed based on i_err On the other hand, the complex conjugate R of the light wave distribution of the reference light R * If there is an error in the wavefront phase, the wavefront aberration W i_err will not be 0.

[0115] Therefore, the wavefront aberration W for all numbers i (i = 0 to N-1) i_err (absolute value) (=ΣW i_err ) to minimize the offset coordinate (x p0 ,y p0 ,z p0 ) is adjusted. A general optimization algorithm can be used for parameter fitting.

[0116] Note that the larger the number of the generated light wave distribution P i , the more reliable the parameter fitting can be. Also, the light wave distribution P i is preferably set evenly over the entire visual field range recordable by the image sensor D.

[0117] <E. Processing device 100> Next, a hardware configuration example of the processing device 100 included in the optical measurement system 1 will be described.

[0118] FIG. 4 is a schematic diagram showing a hardware configuration example of the processing device 100 included in the optical measurement system 1 according to the present embodiment. Referring to FIG. 4, 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.

[0119] The processor 102 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and reads and executes one or more programs stored in the storage 110 into the main memory 104. 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 programs.

[0120] The input unit 106 includes a keyboard, a mouse, etc., and receives operations from the user. The display unit 108 outputs to the user the execution results of programs by the processor 102, etc.

[0121] ​The storage 110 is made up of a nonvolatile memory such as a hard disk or flash memory, and stores various programs and data. More specifically, the storage 110 stores an operating system (OS) 111, a measurement program 112, and It holds a calibration program 113, calibration information 114, hologram data 115, and measurement results 116.

[0122] The operating system 111 provides an environment in which the processor 102 executes programs. The measurement program 112 is executed by the processor 102 to realize the measurement process and the like according to this embodiment. The calibration program 113 is executed by the processor 102 to realize the calibration process and the like according to this embodiment. The calibration information 114 is a parameter determined by the calibration process and is referenced in the measurement process. The hologram data 115 corresponds to the image data output from the image sensor D. The measurement result 116 includes the measurement result obtained by executing the measurement program 112.

[0123] In this way, the storage 110 stores information (calibration information 114) about the light wave distribution of the reference light R in the optical system shown in FIGS.

[0124] 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.

[0125] The media drive 124 stores programs to be executed by the processor 102. Necessary data is read from a recording medium 126 (for example, an optical disk) and stored in the storage 110. Note that the measurement program 112 and / or the calibration program 113 executed in the processing device 100 may be installed via the recording medium 126 or downloaded from a server device via the network interface 122 or the like.

[0126] The measurement program 112 and / or the calibration program 113 may call necessary modules of the program modules provided as part of the operating system 111 in a predetermined array at a predetermined timing to execute processing. In such a case, the measurement program 112 and / or the calibration program 113 that do not include such modules are also included in the technical scope of the present invention. The measurement program 112 and / or the calibration program 113 may be provided by being incorporated into a part of another program.

[0127] Note that 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 (for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit)). How) may be realized.

[0128] For convenience of explanation, FIG. 4 shows a configuration example of the processing device 100 capable of executing both measurement processing and calibration processing, but only one of the measurement processing and calibration processing may be made executable. For example, before the optical measurement system 1 is shipped from the factory, calibration processing is executed, and the complex conjugate R of the light wave distribution of the reference light R * is determined in advance. Therefore, after the factory shipment, there is no need to execute the calibration processing, and only the measurement processing may be executed. In such a case, a processing device capable of executing the calibration processing and a processing device capable of executing the measurement processing may be prepared respectively.

[0129] <F. Processing procedure> Next, the measurement processing and calibration processing executed in the optical measurement system 1 will be described.

[0130] (f1: Measurement processing) 5 is a flowchart showing the procedure of a measurement process executed in the optical measurement system 1 according to the present embodiment. In the measurement process shown in FIG. 5, a complex conjugate R, which is information on the light wave distribution of the reference light R in the optical system shown in FIGS. * are acquired in advance by some method. The steps executed by the processing device 100 shown in FIG.

[0131] 5, the optical system shown in FIG. 1 is configured, and a sample S is placed (step S100). Then, a coherent light is generated from a light source 10, and a processing device 100 detects a hologram I by an image sensor D. OR In this way, the hologram I is generated by illuminating the sample S with the illumination light Q and modulating the object light O with the reference light R (step S102). OR A process of recording (third hologram) is performed.

[0132] The processing device 100 processes the recorded hologram I OR By applying spatial frequency filtering to the complex amplitude hologram J OR (Step S104) (see the above-mentioned formula (4)). Then, the processing device 100 calculates the calculated complex amplitude hologram J OR is the complex conjugate R of the light wave distribution of the reference light R * By dividing by , the object beam hologram U is calculated (step S106) (see the above equation (5)). In this way, the hologram I OR (third hologram), and the filtering result is the complex conjugate R of the light wave distribution of the reference light R. * (information on the light wave distribution of the reference light R) and the object light hologram U are calculated based on the information. It will be executed.

[0133] The processing device 100 performs processing for increasing the number of sampling points and superimposing the object beam hologram U to generate a reconstruction object beam hologram U ΣIn the case where the increase in the number of sampling points and the superposition process are omitted, the object beam hologram U can be used as the reconstruction object beam hologram U Σ Treat as.

[0134] The processing device 100 calculates the reconstruction object beam hologram U Σ By calculating the diffraction up to the sample surface, the complex amplitude distribution U d (step S108) (see the above-mentioned formulas (6) and (7)). Then, the processing device 100 calculates the calculated complex amplitude distribution U d A measurement result is generated using some or all of the information in the complex amplitude distribution U d By extracting and imaging the amplitude component from the signal, an image equivalent to the bright field of an optical microscope is generated.

[0135] 5 is executed for each sample S. Note that the holograms I corresponding to the multiple samples S are OR may be recorded in advance, and a process for generating the measurement results may be executed afterwards.

[0136] (f2: Calibration process) Fig. 6 is a flowchart showing the procedure of the calibration process executed in the optical measurement system 1 according to the present embodiment. The calibration process shown in Fig. 6 is a procedure when a known light wave distribution P and correct offset coordinates are obtained. The steps executed by the processing device 100 shown in Fig. 6 are typically realized by the processor 102 of the processing device 100 executing the calibration program 113.

[0137] 6, the optical system shown in FIG. 2 is configured, and the calibration unit 20 is placed (step S200). At this time, the offset coordinates (x p0 ,y p0 ,z p0) is accurately set (step S202). In this way, a process of configuring an optical system (optical measurement system 1 shown in FIGS. 1 and 2) for recording a hologram generated by modulating object light O obtained by illuminating sample S with illumination light Q using reference light R, and a process of placing calibration unit 20 including an optical system (profile generator 30) that generates a known light wave distribution P on the optical path of illumination light Q in a state where sample S is not present are performed.

[0138] Then, the light source 10 generates coherent light, and the processing device 100 detects the calibration hologram I P0R In this way, the calibration hologram I generated in the state where the calibration unit 20 generates the light wave distribution P0 is recorded (step S204). P0R A process of recording (first hologram) is performed.

[0139] The processing device 100 calculates the known light wave distribution P and the offset coordinate (x p0 ,y p0 ,z p0 ) to calculate the light wave distribution P0 (step S206) (see the above-mentioned equation (11)), and the calculated light wave distribution P0 and the recorded calibration hologram I P0R Using the complex conjugate R of the light wave distribution of the reference light R, * (Step S208) (see the above-mentioned formula (14)). In this way, the information indicating the arrangement position of the calibration unit 20 (offset coordinates), the known light wave distribution P, and the calibration hologram I P0R (first hologram) and the complex conjugate R, which is information on the light wave distribution of the reference light R, * A process of calculating

[0140] Then, the processing device 100 calculates the complex conjugate R of the light wave distribution of the calculated reference light R. * Then, the calibration information 114 including the above is output (step S210). This completes the calibration process.

[0141] FIG. 7 shows another example of the calibration process executed in the optical measurement system 1 according to the present embodiment. 7 is a flowchart showing a processing procedure when correct offset coordinates cannot be obtained. The steps executed by the processing device 100 shown in FIG. 7 are typically realized by the processor 102 of the processing device 100 executing the calibration program 113.

[0142] 7, the optical system shown in Fig. 2 is configured, and calibration unit 20 is arranged (step S250). In this way, a process of configuring an optical system (optical measurement system 1 shown in Figs. 1 and 2) for recording a hologram generated by modulating object light O obtained by illuminating sample S with illumination light Q with reference light R, and a process of arranging calibration unit 20 including an optical system (profile generator 30) that generates a known light wave distribution P on the optical path of illumination light Q when sample S is not present are executed.

[0143] Next, the profile generating unit 30 is translated in sequence to generate N calibration holograms I PiR More specifically, the calibration unit 20 is moved to the offset coordinate (x pi ,y pi ,z pi ) (step S252). Then, the light source 10 generates coherent light, and the processing device 100 uses the image sensor D to capture the calibration hologram I PiR The processes of steps S252 and S254 are repeated from the number i of 0 to N-1.

[0144] In this way, the calibration hologram I generated when the calibration unit 20 generates the light wave distribution P0 P0R The calibration unit 20 then records the light wave distribution as a calibration hologram I (first hologram). P0R The position where the (first hologram) was recorded (offset coordinates (x p0 ,y p0 ,z p0 Multiple positions (offset coordinates (x)) different from pi ,y pi ,z pi:i>0) and generate a plurality of calibration holograms I PiR A process of recording (a plurality of second holograms) is performed.

[0145] Next, the complex conjugate R of the light wave distribution of the reference light R * More specifically, the offset coordinate (x p0 ,y p0 ,z p0 ) and set an appropriate initial value (step S256). Then, the processing device 100 calculates the known light wave distribution P and the offset coordinate (x p0 ,y p0 ,z p0 ) is used to calculate the light wave distribution P0 (step S258) (see the above-mentioned equation (11)), and the calculated light wave distribution P0 and the recorded calibration hologram I P0R Using the complex conjugate R of the light wave distribution of the reference light R, * is provisionally calculated (step S260) (see equation (14) above).

[0146] In this way, the information indicating the placement position of the calibration unit 20 (initial values ​​of the offset coordinates), the known light wave distribution P, and the calibration hologram I P0R (first hologram) and the complex conjugate R, which is information on the light wave distribution of the reference light R, * A process of calculating

[0147] Subsequently, a process for correcting the light wave distribution is performed. More specifically, the processing device 100 performs a process for correcting the light wave distribution by adjusting the recorded calibration hologram I PiR By applying spatial frequency filtering to the complex amplitude hologram J PiR (step S262) (see the above-mentioned formula (4)). Then, the processing device 100 calculates the calculated complex amplitude hologram J PiR The current complex conjugate R * By dividing by i (Step S264) (see the above equations (6) and (7)). In this way, the multiple calibration holograms IPiR Applying spatial frequency filtering to each of the (plurality of second holograms), and calculating the complex conjugate R of the filtering result. * (information on the light wave distribution of the reference light R) PiR Multiple object beam holograms U i A process of calculating

[0148] Next, the processing device 100 calculates the object beam hologram U i From the light wave distribution P i Determine Then, the processing device 100 calculates the object beam hologram U so that it matches the known light wave distribution P (step S266). i By correcting the modified light wave distribution P i ' is calculated (step S268) (see the above equations (18) and (19)). In this way, the processing device 100 calculates a plurality of object light holograms U i By correcting each of these, multiple calibration holograms I PiR Multiple modified lightwave distributions P corresponding to i ' are calculated respectively.

[0149] Next, the processing device 100 calculates a spectrum calculated from the known light wave distribution P and a plurality of calibration holograms I PiR (multiple second holograms) i The wavefront aberration is calculated from the spectrum calculated from .

[0150] More specifically, the processing device 100 calculates the known light wave distribution P and the modified light wave distribution P i ' are Fourier transformed to obtain the spectrum F[P] and the spectrum F[P i Then, the processing device 100 calculates the spectrum F[P] and the spectrum F[P i The phase difference distribution spectrum W i (u,v)(=arg(F[P iIn this way, the processing device 100 calculates the spectrum F[P] calculated from the known light wave distribution P and the calibration hologram I PiR (second hologram) i ' is calculated from the spectrum F[P i '] and the phase difference distribution spectrum W i Calculate (u,v).

[0151] Finally, the processing device 100 calculates the phase difference distribution spectrum W i Using (u,v), the wavefront aberration W i_err (Step S274). As shown in the above equation (20), the processing device 100 calculates the wavefront aberration W i_err In the calculation process of the phase difference distribution spectrum W i Overall average value W ave The root mean square of the error is calculated.

[0152] The processing of steps S262 to S274 is repeated from the number i of 1 to N-1. Next, the processing device 100 calculates the wavefront aberration W i_err The offset coordinate (x p0 ,y p0 ,z p0 ) value (information indicating the placement position).

[0153] More specifically, the processing device 100 calculates the wavefront aberration W calculated in step S274. i_err The sum of (=ΣW i_err ) is calculated (step S276), and the calculated wavefront aberration W i_err It is determined whether the sum satisfies the convergence condition (step S278). i_err may include that the sum of the values ​​is equal to or less than a predetermined value.

[0154] Wavefront aberration W i_errIf the sum does not satisfy the convergence condition (NO in step S278), the processing device 100 changes the values of the offset coordinates (x p0 , y p0 , z p0 ) (step S280) and repeats the processing from step S260 onward.

[0155] If the sum of the wavefront aberration W i_err does not satisfy the convergence condition (YES in step S278), the processing device 100 outputs calibration information 114 including the current complex conjugate R * (step S282). Then, the calibration process ends.

[0156] <G. Measurement Example> Next, a measurement example by the optical measurement system according to the present embodiment is shown. The following measurement example is for explaining the improvement in accuracy by determining the complex conjugate R * of the light wave distribution of the reference light R using the calibration unit 20.

[0157] First, an optical system shown in FIG. 2 was configured. The wavelength of the light source 10 was set to 532 nm, and an optical system with a numerical aperture N A = 0.5 was configured. Then, the light wave distributions P i (i = 0 to N - 1) generated by the calibration unit 20 were recorded. In the measurement examples shown in FIGS. 8 and 9, the light wave distributions P i were recorded at 11 points (N = 11; i = 0 to 10).

[0158] As described above, the light wave distribution P i is obtained by translating a known light wave distribution P parallel in the x-axis direction, y-axis direction, and z-axis direction within the field of view of the image sensor D. A point source was used as the known light wave distribution P.

[0159] As the offset coordinates (x p0 , y p0 , z p0 ) corresponding to the light wave distribution P0, initial values determined in consideration of the optical positional relationship of the calibration unit 20 were set, and the complex conjugate R of the light wave distribution of the reference light R was obtained using the set initial values.* was calculated.

[0160] 8A and 8B are diagrams showing an example of measurement in the initial stage of the calibration process of the optical measurement system 1 according to this embodiment. FIG. 8A shows the amplitude distribution near the focal point of the object beam hologram U1 reconstructed using the initial values ​​of the offset coordinates. FIG. 8B shows the wavefront aberration W calculated using the amplitude distribution near the focal point of the object beam hologram U1. 1_err The wavefront aberration W when the initial offset coordinate is used is shown. 1_err was 2.924λ.

[0161] The initial values ​​of the offset coordinates do not accurately reflect the optical positional relationship of the calibration unit 20, and therefore the complex conjugate R of the light wave distribution of the reference light R * As a result, as shown in Figure 8(A), the focal point (Airy disk spot) is not a spot but varies. Also, as shown in Figure 8(B), a large wavefront aberration occurs in the object beam hologram U1.

[0162] Next, following the procedure described above, the offset coordinate (x p0 ,y p0 ,z p0 ) is adjusted. p0 ,y p0 ,z p0 ) to obtain the complex conjugate R of the light wave distribution of the reference light R. * was calculated.

[0163] 9A and 9B are diagrams showing an example of measurement after the calibration process of the optical measurement system 1 according to this embodiment. FIG. 9A shows the amplitude distribution near the focal point of the object beam hologram U1 reconstructed using the adjusted offset coordinates. FIG. 9B shows the wavefront aberration W calculated using the amplitude distribution near the focal point of the object beam hologram U1. 1_err The wavefront aberration W when the initial offset coordinate is used is shown. 1_err As shown in FIG. 9A, the complex conjugate R of the light wave distribution of the reference light R* By accurately determining the above, a focal point (Airy disk spot) is formed on the object beam hologram U1, and no obvious wavefront aberration is observed, as shown in FIG. 9(B).

[0164] Generally, a wavefront aberration of 0.07λ or less is considered to be the diffraction limit, and the wavefront aberration W 1_err is 0.023λ, it can be said that the imaging performance is sufficient. In addition, when the wavefront aberration is calculated for the cases where the number i is 2 to 10, the wavefront aberration W i_err is 0.07λ or less, and the imaging performance is diffraction-limited over the entire field of view.

[0165] 10 is a diagram showing an example of measurement of a sample by the optical measurement system 1 according to the present embodiment. FIG. 10 shows a hologram I recorded using the optical measurement system 1 shown in FIG. OR The reconstructed image of a sample (USAF 1951 resolution test target) is shown.

[0166] Figures 10(A1) and 10(A2) show reconstructed images using the initial offset coordinate values. Figure 10(A1) shows the overall image of the resolution test target, and Figure 10(A2) shows an enlarged view of a portion of the resolution test target.

[0167] In the reconstructed images shown in FIGS. 10(A1) and 10(A2), significant distortion occurs, and the pattern lines in group 9 of the resolution test target are not resolved sufficiently.

[0168] Figures 10(B1) and 10(B2) show the reconstructed images using the adjusted offset coordinates. Figure 10(B1) shows the overall image of the resolution test target, and Figure 10(B2) shows an enlarged view of a portion of the resolution test target.

[0169] In the reproduced image shown in Fig. 10(B1), no significant distortion occurs. Also, in Fig. 10(B2), the 9-6 pattern lines (width 0.548 μm) of the test target indicated by the rectangular frame lines can be decomposed into three lines, indicating that performance comparable to the theoretical resolution of 0.532 μm determined by the optical system is obtained.

[0170] As described above, by accurately determining the complex conjugate R of the light wave distribution of the reference light R through the calibration process as described above, it can be understood that the sample can be measured with high precision. *

[0171] <H. Modified Example> In Figs. 1 and 2, a configuration example of the optical measurement system 1 employing a transmission-type optical system is illustrated, but the present invention is not limited to this configuration example, and various modifications as described below are possible.

[0172] (h1: Modified Example 1) As a first modified example of the present embodiment, a configuration example in which the reference light is arranged near the sample will be described.

[0173] Fig. 11 is a schematic diagram showing a configuration example of the optical measurement system 1A according to the first modified example of the present embodiment. Fig. 11(A) shows a configuration example for measurement processing, and Fig. 11(B) shows a configuration example for calibration processing.

[0174] Referring to Fig. 11(A), in the optical measurement system 1A, instead of the half mirror HM2, a mirror M3 is arranged. The mirror M3 is arranged outside the range irradiated by the object light O from the sample S. The reference light R is reflected by the mirror M4, its propagation direction is changed, and it is guided to the mirror M3. The reference light R is further reflected by the mirror M3 and guided to the light receiving surface of the image sensor D. That is, on the light receiving surface of the image sensor D, the object light O obtained by illuminating the sample S with the illumination light Q is modulated by the reference light R.

[0175] In this way, when it is not necessary to ensure a working distance, the mirror M3 may be used in place of the half mirror HM2. The mirror M3 may be a plane mirror, a convex mirror, or a concave mirror.

[0176] 11(B), in the optical measurement system 1A, the profile generating section 30 including the calibration unit 20 is arranged so as to replace the field mask A1 and the condenser lens L1, which are the illumination optical system. The calibration process is the same as that described above.

[0177] (h2: Variation 2) As a second modification of this embodiment, a configuration example in which the illumination optical system is omitted will be described.

[0178] Fig. 12 is a schematic diagram showing an example configuration of an optical measurement system 1B according to Modification 2 of this embodiment. Fig. 12(A) shows an example configuration for measurement processing, and Fig. 12(B) shows an example configuration for calibration processing.

[0179] 12(A), in the optical measurement system 1B, a field-limiting mask FA is placed near the sample S. By using such a field-limiting mask FA, the illumination optical system can be simplified or eliminated. FIG. 12(A) shows an example configuration in which the coupling optical system (field mask A1 and condenser lens L1) corresponding to the illumination optical system is eliminated.

[0180] Furthermore, any optical system may be used to illuminate the sample S with the illumination light Q, as long as it can maintain coherence between the illumination light Q and the reference light R. For example, the illumination light Q may be incident obliquely, or diffuse illumination may be used as the illumination light Q.

[0181] 12(B), in the optical measurement system 1B, the profile generating section 30 including the calibration unit 20 is placed on the optical path of the illumination light Q after removing the sample S. Since the illumination optical system is omitted, it is not necessary to remove the illumination optical system when placing the calibration unit 20. The calibration process is the same as that described above.

[0182] (h3: Variation 3) As a third modification of this embodiment, a configuration example employing a reflective optical system will be described.

[0183] 13A and 13B are schematic diagrams showing an example configuration of an optical measurement system 1C according to a third modification of this embodiment. Fig. 13A shows an example configuration for measurement processing, and Fig. 13B shows an example configuration for calibration processing.

[0184] 13(A), in optical measurement system 1C, illumination light Q split by beam splitter BS1 is reflected by mirror M1 and mirror M5, respectively, to change its propagation direction, and then passes through condenser lens L3, field mask A1, and condenser lens L4 before being directed to half mirror HM2. Furthermore, illumination light Q is reflected by half mirror HM2 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 and enters image sensor D.

[0185] On the other hand, the reference light R is reflected by mirror M2, changes its propagation direction, and then is focused by condenser lens L2. The focus point FP1 of condenser lens L2 corresponds to the position of the point light source. Finally, the reference light R is reflected by half mirror HM2 and enters image sensor D.

[0186] 13(B), the calibration process in the optical measurement system 1C is performed using a transmissive optical system, similar to that in FIGS. 2 and 12(B). More specifically, the profile generating section 30 including the calibration unit 20 is placed on the optical path of the illumination light Q after removing the sample S. The calibration process is similar to that described above.

[0187] (h4: Variation 4) As a fourth modification of this embodiment, a configuration example suitable for measuring scattered light from the sample S will be described.

[0188] FIG. 14 is a schematic diagram showing a configuration example of an optical measurement system 1D according to Modification 4 of the present embodiment. FIG. 14(A) shows a configuration example for measurement processing, and FIG. 14(B) shows a configuration example for calibration processing.

[0189] Referring to FIG. 14(A), in the optical measurement system 1D, the illumination light Q branched by the beam splitter BS1 is reflected by the mirror M6 and its propagation direction is changed, and then irradiates the sample S. The scattered light generated by illuminating the sample S with the illumination light Q becomes object light O and enters the image sensor D.

[0190] In the optical measurement system 1D, the scattered light generated by the sample S can be measured. A field limiting mask FA may be arranged near the sample S as needed. By arranging the field limiting mask FA, noise can be suppressed.

[0191] Referring to FIG. 14(B), the calibration process in the optical measurement system 1D is performed using a transmissive optical system, similar to FIGS. 2 and 12(B). More specifically, the profile generation unit 30 including the calibration unit 20 is arranged on the optical path of the illumination light Q after removing the sample S. The calibration process is the same as the above-described process.

[0192] (h5: Modification 5) In the above description, the configuration using the light source 10 that generates coherent light in a specific wavelength band has been mainly described, but a light source 10 that generates coherent light in a plurality of wavelength bands may be used instead. For example, by generating coherent light in wavelength bands corresponding to red (R), green (G), and blue (B) respectively, and adopting an image sensor D having light reception sensitivity for each color, holograms of each color can be recorded.

[0193] Also, by adopting a polarization image sensor as the image sensor D, a polarization hologram can be recorded.

[0194] <I. Advantages> The optical measurement system according to this embodiment employs a lensless digital holography configuration in which no imaging optical system such as a lens exists between the sample and the image sensor, so errors such as aberrations do not occur in the object light obtained by illuminating the sample with illumination light.

[0195] The optical measurement system according to this embodiment acquires information on the light wave distribution of the reference light (for example, the complex conjugate R of the light wave distribution of the reference light R) through a calibration process. * ) is acquired in advance. The optical measurement system calculates an object light hologram based on a hologram generated by modulating the object light obtained by illuminating the sample with illumination light using reference light and information on the light wave distribution of the reference light, thereby making it possible to subsequently calculate or measure the shape (light wave amplitude and phase) of any position on the sample.

[0196] The optical measurement system according to this embodiment can calculate information about the light wave distribution of the reference light by illuminating a known light wave distribution from a known arrangement position (coordinates) instead of the object light. Therefore, there is no need to accurately adjust the in-line spherical wave light to the in-line axis, and adjustment does not require much effort.

[0197] The optical measurement system according to this embodiment can calculate information about the light wave distribution of the reference light by parameter fitting by illuminating a known light wave distribution from multiple positions (coordinates) instead of the object light. Therefore, there is no need to accurately adjust the inline spherical wave light to the inline axis, and adjustment does not require much effort. In addition, accurate information about the light wave distribution of the reference light can be calculated even if the exact position at which the known light wave distribution is illuminated is not known.

[0198] 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]

[0199] 1, 1A, 1B, 1C, 1D optical measurement system, 10 light source, 20 calibration unit, 30, 30A, 30B, 30C, 30D profile generation unit, 31, 33, 34 light shielding Plate, 32, 36 Pinhole, 35, 37, L1, L2, L3, L4 Condenser lens, 38 Objective lens, 100 processing device, 102 processor, 104 main memory, 106 input unit, 108 display unit, 110 storage, 111 operating system, 112 measurement program, 113 calibration program, 114 calibration information, 115 hologram data, 116 measurement results, 120 interface, 122 network interface, 124 media drive, 126 recording medium, A1 field of view mask, BE beam expander, BS1, BS2 beam splitter, D image sensor, FA field of view limiting mask, FP1 focusing point, M1, M2, M3, M4, M5, M6 mirrors, O object light, Q illumination light, R reference light, S sample, SP1, SP2 apertures.

Claims

1. configuring an optical system for recording a hologram generated by illuminating a sample with illumination light and modulating the resulting object light with a reference light coherent with the illumination light; a calibration unit including an optical system that generates a known light wave distribution, disposed on an optical path of the illumination light in the absence of the sample; recording a first hologram generated when the calibration unit generates a light wave distribution; an optical measurement method comprising a step of calculating information on the light wave distribution of the reference light based on information indicating the placement position of the calibration unit, the known light wave distribution, and the first hologram.

2. the calibration unit is configured to spatially move the generated light wave distribution; The optical measurement method includes: moving the generated light wave distribution to a plurality of positions different from the position where the first hologram was recorded, and recording a plurality of second holograms generated at the plurality of positions; calculating a wavefront aberration from a spectrum calculated from a known light wave distribution and a spectrum calculated from light wave distributions corresponding to the plurality of second holograms; The optical measurement method according to claim 1 , further comprising the step of adjusting information indicating a placement position of the calibration unit so as to minimize the wavefront aberration.

3. applying spatial frequency filtering to each of the plurality of second holograms, and calculating a plurality of object beam holograms corresponding to the plurality of second holograms, based on a filtering result and information on the light wave distribution of the reference beam; 3. The optical measurement method according to claim 2, further comprising the step of calculating a plurality of light wave distributions corresponding to the plurality of second holograms by correcting the plurality of object light holograms based on the known light wave distributions.

4. The step of calculating the wavefront aberration includes: calculating a phase difference distribution spectrum, which is a phase difference distribution between a spectrum calculated from the known light wave distribution and a spectrum calculated from the light wave distribution corresponding to the second hologram; 4. The optical measurement method according to claim 2, further comprising the step of calculating a root mean square error of an average value of the entire phase difference distribution spectrum.

5. recording a third hologram generated by modulating the object beam obtained by illuminating the sample with the illumination beam using the reference beam; The optical measurement method according to any one of claims 1 to 4, further comprising a step of applying spatial frequency filtering to the third hologram and calculating an object light hologram based on a filtering result and information on the light wave distribution of the reference light.

6. 6. The optical measurement method according to claim 1, wherein the information on the light wave distribution of the reference light includes a complex conjugate of the light wave distribution of the reference light.

7. configuring an optical system for recording a hologram generated by illuminating a sample with illumination light and modulating the resulting object light with a reference light coherent with the illumination light; acquiring information about the light wave distribution of the reference light in the optical system; recording a hologram generated by modulating an object beam obtained by illuminating a sample with an illumination beam using a reference beam coherent with the illumination beam; applying spatial frequency filtering to the hologram, and calculating an object beam hologram based on the filtering result and information on the light wave distribution of the reference beam.

8. 8. The optical measurement method according to claim 7, wherein the information on the light wave distribution of the reference light is calculated in advance based on a hologram recorded when a calibration unit including an optical system that generates a known light wave distribution is placed on the optical path of the illumination light in the absence of the sample, information indicating the placement position of the calibration unit, and the known light wave distribution.

9. a light source that generates coherent light; a beam splitter that generates illumination light and reference light from the coherent light from the light source; an optical system for recording a hologram generated by modulating object light obtained by illuminating a sample with illumination light and a reference light coherent with the illumination light using an image sensor; a processing device having a storage unit for storing information on the light wave distribution of the reference light in the optical system, The processing device applies spatial frequency filtering to the hologram recorded by the image sensor, and calculates an object beam hologram based on the filtering result and information on the light wave distribution of the reference beam.

10. 10. The optical measurement system of claim 9, wherein the information on the light wave distribution of the reference light is calculated in advance based on a hologram recorded when a calibration unit including an optical system that generates a known light wave distribution is placed on the optical path of the illumination light in the absence of the sample, information indicating the placement position of the calibration unit, and the known light wave distribution.

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