Optical Measurement Methods and Systems

Abstract

The optical measurement method includes the following steps: constructing an optical system for recording a reference light coherent with the illumination light and modulating the object light illuminating the sample with the illumination light to generate a holographic projection; configuring a correction unit, which includes an optical system that generates a known light wave distribution, along the optical path of the illumination light in the absence of a sample; recording the first holographic projection generated when the correction unit generates a light wave distribution; and calculating information about the light wave distribution of the reference light based on information indicating the placement position of the correction unit, the known light wave distribution, and the first holographic projection.

Description

Technical Field

[0001] This invention relates to an optical measurement method and system utilizing digital holography. Prior Technology

[0002] Digital holography has been proposed and put into practical use as a method for measuring the shape of samples with high precision. Digital holography is a technique that observes the interference fringes produced by superimposing reference light and illumination light onto a sample, thereby obtaining the shape of the wavefront of the object light to measure the shape of the sample. Typically, the following prior technologies exist.

[0003] U.S. Patent No. 6,411,406 (Patent Document 1) discloses a method for reconstructing holographic images, etc.

[0004] International Publication No. 2013 / 047709 (Patent Document 2) discloses a practical digital holographic photography method that performs both reflection and transmission modes.

[0005] International Publication No. 2011 / 089820 (Patent Document 3) discloses a method for creating a holographic projection on a complex amplitude line, etc.

[0006] International Publication No. 2012 / 005315 (Patent Document 4) discloses a method for creating a high-resolution image for playing an image obtained by using a complex amplitude online holographic projection of a tiny subject obtained by using online spherical wave light, thereby improving the resolution of the image.

[0007] International Publication No. 2020 / 045584 (Patent Document 5) discloses a holographic imaging device whose performance is improved by considering the influence of the refractive index of the cubic beam combiner constituting the optical system. More specifically, for spherical waves emitted from the focusing point of a spherical wave reference light on a line, the refractive index of the beam combiner is considered to perform light propagation calculations including the propagation within the beam combiner, thereby generating a holographic projection of the line reference light representing the light waves in the holographic projection plane. [Preliminary Technology Documents] [Patent Literature]

[0008] [Patent Document 1] US 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

[0009] [The problem the invention aims to solve]

[0010] The method disclosed in U.S. Patent No. 6,411,406 (Patent Document 1) has the problem that it is impossible to obtain a more accurate object light due to the superposition of conjugate images.

[0011] The method disclosed in International Publication No. 2013 / 047709 (Patent Document 2) uses an imaging optical system. Therefore, there is a problem that aberrations are generated in the imaging optical system, making it impossible to accurately record the three-dimensional distribution.

[0012] International Publication No. 2011 / 089820 (Patent Document 3) states that the determination of the reference light is incomplete, which leads to distortion of the recorded object's light data.

[0013] International Publication No. 2012 / 005315 (Patent Document 4) and International Publication No. 2020 / 045584 (Patent Document 5) present the problem that the axis of the spherical wave light on the line must be correctly adjusted, and the adjustment requires time.

[0014] This invention provides a technique for measuring samples with higher accuracy by continuously reducing the adjustment time. [Methods used to solve problems]

[0015] An optical measurement method according to a certain aspect of the present invention includes: the steps of constructing an optical system for recording an object light obtained by modulating the illumination light on a sample by an illumination light and a coherent reference light to generate a holographic projection; in the absence of a sample, configuring a correction unit comprising an optical system that generates a known light wave distribution along the optical path of the illumination light; and recording a first holographic projection generated in the state where the correction unit generates a light wave distribution; and calculating information on the light wave distribution of the reference light based on information indicating the configuration position of the correction unit, the known light wave distribution, and the first holographic projection.

[0016] The correction unit can be constructed such that the generated light wave distribution can be spatially moved. The optical measurement method may also include: the steps of moving the generated light wave distribution to a plurality of positions different from the position of the first holographic projection, and simultaneously recording multiple second holographic projections at these multiple positions; the steps of calculating wavefront aberration from the spectrum calculated from the known light wave distribution and the spectrum calculated from the light wave distribution corresponding to the multiple second holographic projections; and the steps of adjusting information representing the configuration position of the correction unit to minimize wavefront aberration.

[0017] The optical measurement method may also include: applying spatial frequency filtering to each of the complex second holographic projections, and calculating the complex object light holographic projections corresponding to the complex second holographic projections based on the filtering result and information on the light wave distribution of the reference light; and correcting the complex object light holographic projections based on the known light wave distribution, thereby calculating the complex light wave distribution corresponding to the complex second holographic projections.

[0018] The steps for calculating wavefront aberration may also include: calculating the phase difference distribution spectrum, which is the spectrum calculated from the known light wave distribution and the spectrum calculated from the light wave distribution corresponding to the second holographic projection; and calculating the error by taking the root mean square of the average value of the entire phase difference distribution spectrum.

[0019] The optical measurement method may also include: the steps of recording the object light obtained by illuminating the sample with reference light and modulating it with illumination light to generate a third holographic projection; and the steps of applying spatial frequency filtering to the third holographic projection and calculating the object light holographic projection based on the filtering result and information on the light wave distribution of the reference light.

[0020] Information on the wave distribution of the reference light may also include the conjugate complex number of the wave distribution of the reference light. According to another aspect of the present invention, an optical measurement method includes: the steps of constructing an optical system for recording a reference light coherent with the illumination light, modulating object light obtained by illuminating a sample with the illumination light, and generating a holographic projection; the steps of obtaining information on the wave distribution of the reference light in the optical system; the steps of recording a reference light coherent with the illumination light, modulating object light obtained by illuminating a sample with the illumination light, and generating a holographic projection; and the steps of applying spatial frequency filtering to the holographic projection, and calculating the holographic projection of the object light based on the filtering result and information on the wave distribution of the reference light.

[0021] Based on the information of the light wave distribution, it can also be calculated in advance in the absence of a sample, by configuring a correction unit containing an optical system that generates a known light wave distribution on the optical path of the illumination light, recording the holographic projection, the information indicating the configuration position of the correction unit, and the known light wave distribution.

[0022] An optical measurement system according to another aspect of the present invention includes: a light source that generates coherent light; a beam splitter that generates illumination light and a reference light from the coherent light from the light source; an optical system for generating a holographic projection by recording, with an image detector, an object light obtained by modulating the illumination light on a sample using a reference light coherent with the illumination light; and 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 holographic projection recorded by the image detector and calculates the object light holographic projection based on the filtering result and the information on the light wave distribution of the reference light.

[0023] Based on the information of the light wave distribution, it can also be calculated in advance, in the absence of a sample, by configuring a correction unit containing an optical system that generates a known light wave distribution on the optical path of the illumination light, recording the holographic projection, information indicating the configuration position of the correction unit, and the known light wave distribution. [Invention Benefits]

[0024] When implemented according to the present invention, adjustment time can be continuously reduced, and samples can be measured with higher accuracy. Simple Explanation of the Diagram

[0025] Figure 1 is a schematic diagram showing a construction example (for measurement processing) of the optical measurement system of this embodiment. Figure 2 is a schematic diagram showing a construction example (calibration process) of the optical measurement system of this embodiment. Figure 3 is a schematic diagram showing an example of the structure of the contour generation unit of the optical measurement system of this embodiment. Figure 4 is a schematic diagram showing an example of the hardware structure of the processing device included in the optical measurement system of this embodiment. Figure 5 is a flowchart illustrating the measurement process performed in the optical measurement system of this embodiment. Figure 6 is a flowchart illustrating the calibration process performed in the optical measurement system of this embodiment. Figure 7 is a flowchart illustrating another process of the calibration process performed in the optical measurement system of this embodiment. FIG. 8 is a diagram showing a measurement example in an initial stage of calibration processing of the optical measurement system of the present embodiment. FIG. 9 is a diagram showing a measurement example after the calibration processing of the optical measurement system of the present embodiment. FIG. 10 is a diagram showing a measurement example of a sample by the optical measurement system of the present embodiment. FIG. 11 is a schematic diagram showing a structural example of the optical measurement system according to Modification 1 of the present embodiment. FIG. 12 is a schematic diagram showing a structural example of the optical measurement system according to Modification 2 of the present embodiment. FIG. 13 is a schematic diagram showing a structural example of the optical measurement system according to Modification 3 of the present embodiment. FIG. 14 is a schematic diagram showing a structural example of the optical measurement system according to Modification 4 of the present embodiment. Embodiment

[0026] [Mode for Carrying Out the Invention]

[0027] The embodiments of the present invention will be described in detail while referring to the drawings. Moreover, the same or corresponding parts in the drawings are given the same reference numerals, and the description thereof will not be repeated.

[0028] <A. Structural Example of Optical Measurement System> The optical measurement system of the present embodiment uses digital holography that uses divergent light from a point light source as reference light. The optical measurement system of the present embodiment adopts a lensless digital holography structure in which there is no lens between the sample and the image detector.

[0029] FIG. 1 is a schematic diagram showing a structural example (for measurement processing) of the optical measurement system 1 of the present embodiment. By using the structural example shown in FIG. 1, the light wave distribution representing the shape of the sample is recorded. More specifically, the optical system shown in FIG. 1 corresponds to an optical system for recording the object light O illuminated by the illumination light Q modulated by the reference light R arranged off-axis to generate the holographic projection I OR.

[0030] Referring to FIG. 1, the optical measurement system 1 includes a light source 10, a beam expander BE, beam splitters BS1, BS2, mirrors M1, M2, a field mask A1, condenser lenses L1, L2, and an image detector D.

[0031] The light source 10 is composed of a laser or the like to generate coherent light. The beam expander BE enlarges the cross-sectional diameter of the light from the light source 10 to a predetermined size.

[0032] The beam splitter BS1 splits the light into two beams, which are then amplified by the beam expander BE. One beam (the light on the reflecting side of beam splitter BS1) corresponds to the illumination light Q, and the other beam (the light on the transmitting side of beam splitter BS1) corresponds to the off-axis reference light R. Therefore, the illumination light Q and the reference light R are coherent. In this way, beam splitter BS1 generates the illumination light Q and the reference light R from the coherent light from light source 10.

[0033] The illumination light Q, after being reflected by the mirror M1 to change its propagation direction, passes through the field of view cover A1.

[0034] A field of view hood A1 limits the range of illumination of the sample S by the illumination light Q to a predetermined range. As an example of a limiting component, a field of view hood A1 with an opening SP1 corresponding to the predetermined range can also be used as a light-shielding member. The illumination light Q passes through the area corresponding to the opening SP1.

[0035] The image of the opening SP1 of the field of view A1 is imaged onto the sample S through the light-collecting lens L1. That is, only the portion of the light corresponding to the opening SP1 that illuminates the field of view A1 passes through the field of view A1. In this way, the range of the illumination light Q after passing through the field of view A1 that illuminates the sample S can be limited.

[0036] The range of the illumination sample S is determined such that repetition in the Fourier space (spatial frequency domain) can be avoided between the components containing information about the object light O, the light intensity components, and the conjugate light components. By limiting the illumination range of this illumination light Q, noise caused by repetition between components can be suppressed, thereby achieving higher accuracy in measurement. However, the field of view mask A1 can also be omitted.

[0037] Illumination light Q passes through sample S, and object light O is generated. Object light O passes through the semi-reflective mirror HM2 of beam splitter BS2 and is incident on image detector D.

[0038] Furthermore, the reference light R, after being reflected by the mirror M2 to change its propagation direction, is collected by the light-collecting lens L2. The light-collecting point FP1 caused by the light-collecting lens L2 corresponds to the position of a point light source. That is, the reference light R, which is positioned off-axis, can be regarded as light illuminated by a point light source. Finally, the reference light R is reflected by the semi-reflective mirror HM2 and enters the image detector D.

[0039] In this way, the object light O obtained by illuminating the sample S with illumination light Q in the semi-reflective mirror HM2 is modulated by the reference light R placed off-axis. The holographic projection I OR generated by the modulation is recorded by the image detector D.

[0040] The processing device 100 uses the holographic projection I OR recorded by the image detector D and the correction information 114, which includes the conjugate complex number R* of the light wave distribution of the reference light R obtained by correction, to calculate the information necessary for playing the image of the sample S.

[0041] Figure 1 shows a construction example of a cube-shaped beam splitter BS2. However, for the purpose of increasing the number of openings and ensuring the operating distance, the refractive index of the beam splitter BS2 can also be relatively increased, or the shape of the deformed cube can be any other arbitrary shape.

[0042] A beam splitter used for recording holographic projection I OR can take any shape, as long as the boundary surface of the interface between different media is considered a plane. For example, a plate-shaped beam splitter can be used instead of a cube.

[0043] Furthermore, the beam splitter BS2 can be tilted relative to the wavefront of the object's light. This tilting can suppress stray light. Also, although the example shown is of a configuration in which the beam splitter BS2 is held and the sample S and the image detector D are arranged facing each other, a configuration in which the beam splitter BS2 is held and the light-collecting lens L2 and the image detector D are arranged facing each other can also be used.

[0044] Figure 2 is a schematic diagram showing a construction example (calibration process) of the optical measurement system 1 of this embodiment. The optical measurement system 1 shown in Figure 2, in the construction shown in Figure 1, has a calibration unit 20 installed instead of the sample S, field of view cover A1, and light-collecting lens L1. Furthermore, the construction of the reference light R (reflector M2 and light-collecting lens L2) is maintained as in Figure 1.

[0045] Using the construction example shown in Figure 2, a correction holographic projection I PiR is recorded. The correction holographic projection I PiR is a set of holographic projections generated by modulating a known light wave distribution P(x,y,z) to a complex position by parallel shifting it. The reference light R is positioned off-axis.

[0046] In this patent specification, the term "known light wave distribution" means a specific light wave distribution with the required accuracy for the requested measurement performance. Therefore, the light wave distribution generated by the holographic projection I PiR used for calibration only needs to be approximately represented with the necessary accuracy, and it may not be possible to describe it completely without error. However, the light wave distribution itself is not altered by parallel shifts.

[0047] The holographic projection I PiR for recording correction differs from the structures disclosed in Patent Documents 4 and 5 above, as it does not require proper adjustment of the axis of the spherical wave light on the line. The processing of image playback using the holographic projection I PiR for correction will be described later.

[0048] The correction unit 20 includes a contour generation unit 30 and a field-of-view limiting mask FA. The contour generation unit 30 is an optical system that generates a known light wave distribution. In this way, when the sample S is not present, a correction unit 20 containing the optical system (contour generation unit 30) that generates a known light wave distribution is arranged on the optical path of the illumination light Q.

[0049] The contour generation unit 30 is constructed in a way that allows the generated light wave distribution to move spatially. More specifically, the contour generation unit 30 can also have the function of allowing the light wave distribution to move (relocate) in parallel along the x-axis, y-axis, and z-axis directions, respectively. The illumination light Q, which is split by the beam splitter BS1, is reflected by the reflector M1, and after its propagation direction is changed, it enters the contour generation unit 30, thereby generating a known light wave distribution P that can be moved spatially.

[0050] The field-of-view limiting mask FA has an opening SP2 corresponding to the field of view that can be recorded by the image detector D. Moreover, the position of the field-of-view limiting mask FA is fixed. The light wave distribution P generated by the contour generation unit 30 can be translated in the x-axis direction, y-axis direction, and z-axis direction respectively, but the opening SP2 of the field-of-view limiting mask FA is designed not to block the light wave distribution P generated by the contour generation unit 30. That is, the light wave distribution P is translated within the range that can pass through the opening SP2 of the field-of-view limiting mask FA. However, the field-of-view limiting mask FA can also be omitted.

[0051] <B. Structural Example of the Contour Generation Unit 30> Next, a structural example of the contour generation unit 30 of the calibration unit 20 will be described. As described above, any optical system can be adopted for the contour generation unit 30 as long as it can generate a known light wave distribution. Several typical structural examples of the contour generation unit 30 will be described.

[0052] FIG. 3 is a schematic diagram showing a structural example of the contour generation unit 30 of the optical measurement system 1 of the present embodiment. The optical systems shown in FIGS. 3(A) to 3(D) all generate a known light wave distribution P when the illumination light Q as a plane wave is incident.

[0053] The contour generation unit 30A shown in FIG. 3(A) is an optical system using a pinhole and includes a light shielding plate 31 that can be translated in three axes respectively. 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.

[0054] The contour 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 can be translated in three axes respectively. The light shielding plates 33 and 34 are connected to each other and move in parallel as a unit. 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 after passing through the light shielding plate 34. The beam diameter of the illumination light Q is set to a sufficient light quantity that can pass through the condenser lens 35 and the pinhole 36.

[0055] The contour 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 contour generation unit 30C includes a light-shielding plate 31 that can be translated in parallel on 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 that can sufficiently illuminate the range including the condenser lens 37.

[0056] The contour 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 contour generation unit 30D includes a light-shielding plate 31 that can be translated in parallel on 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 that can sufficiently illuminate the range including the objective lens 38.

[0057] Moreover, it is not limited to the structural examples shown in FIGS. 3(A) to 3(D), and any optical system that can generate a known light wave distribution can be adopted.

[0058] <C. Measurement Processing> Next, the measurement processing of the sample S performed by the optical measurement system 1 will be described. In the following description, the light-receiving surface of the image detector D is taken as the "recording surface", and the intersection of the recording surface and the central optical axis of the beam splitter BS2 is taken as the "origin". The optical axis direction is taken as the z-axis, and the two axes orthogonal to the z-axis are taken as the x-axis and the y-axis, respectively. That is, the optical axis is perpendicular to the recording surface of the image detector D, and the x-axis and the y-axis are parallel to the recording surface of the image detector D.

[0059] Also, the surface of interest that is only at a predetermined distance away from the recording surface is called the "sample surface". In the optical system shown in FIG. 1, the light wave distributions of the object light O and the reference light R recorded by the image detector D can be expressed by the general formulas as shown in the following formulas (1) and (2).

[0060]

[0061] Moreover, the object light O and the reference light R arranged off-axis have an angular frequency ω and are coherent with each other. For the sake of convenience in explanation, the coordinates (x, y) are sometimes appropriately omitted in the following formulas.

[0062] The image detector D uses the holographic projection I OR recorded in a single shot, and its light intensity is calculated as the light intensity of the composite light represented by formula (1) and formula (2) as shown in the following formula (3).

[0063]

[0064] Spatial frequency filtering is applied to Equation (3), thereby the complex amplitude holographic projection JOR is calculated as shown in Equation (4).

[0065]

[0066] The complex amplitude holographic projection JOR is divided by the conjugate complex number R* (=R Oexp(-iϕ R)) of the light wave distribution of the reference light R obtained by the correction process. In this way, the object light holographic projection U is calculated as follows (5).

[0067]

[0068] The object light holographic projection U shown in Equation (5) is equivalent to the light wave distribution of the object light O in the recording plane of the image detector D, excluding the time term (-ωt). Therefore, by using a diffraction calculation without an approximation called plane wave expansion, aberration-free and accurate image playback can be achieved.

[0069] Furthermore, when the object's holographic projection U contains frequency components that do not satisfy the standardization theorem, interpolation can be used to increase the sampling number (number of pixels) of the complex amplitude holographic projection JOR before dividing by the conjugate complex number R* of the light wave distribution of the reference light R. Alternatively, after increasing the sampling number, the increased complex amplitude holographic projection JOR can be divided into a lattice structure, and the lattices can be superimposed to reduce the size of the complex amplitude holographic projection JOR. Moreover, the size of the lattice is preferably larger than the size of the image projected from the holographic projection. This increase in sampling number and superposition can suppress the increase in computational load.

[0070] Alternatively, the properties of Fourier transform can be utilized to achieve a process equivalent to increasing and superimposing the number of sampling points on the Fourier spectrum.

[0071] The complex amplitude distribution obtained by increasing and superimposing the number of samples is used as the optical holographic projection UΣ of the object for playback. However, when it is not necessary to increase and superimpose the number of samples, the optical holographic projection U is treated as the optical holographic projection UΣ of the object for playback as is.

[0072] The object holographic projection UΣ is a holographic projection containing information about the state of the playable sample surface.

[0073] Next, the calculation of diffraction within the medium and the playback of the image on the inclined surface will be explained. For the holographic projection UΣ of the object to be played, diffraction calculations are performed using plane wave expansion, thereby enabling the playback of light wave distributions within any sample surface. The light wave distribution that propagates only a distance d (from the recording surface to the sample surface only a distance d away) from the holographic projection UΣ of the object to be played is taken as the complex amplitude distribution Ud.

[0074] If we take the distances of M media (m=1,2,…,M) contained in the recording surface of the image detector D up to the distance d to be played as dm, and the refractive index as nm, the complex amplitude distribution Ud can be generalized as follows: Equation (6). However, kzm in the equation is calculated according to Equation (7).

[0075]

[0076] Furthermore, when multiple media are present, the boundary surfaces between the media are considered parallel to the recording surface. Also, the transmission coefficient when incident from medium m to medium m+1 is expressed as T m,m+1(kx,ky). However, for TM,M+1(kx,ky), it is always considered to be 1.

[0077] For example, when propagating only a distance d in the air, at M=1, it becomes d 1=d, nm=1.

[0078] Furthermore, when the transmission coefficients from medium m to medium m+1 are not dependent on wavenumbers kx and ky, but are considered to be almost equal, they can also be represented as Tm,m+1≡1 to simplify calculations.

[0079] Moreover, when the boundary surface between media does not coincide with the light wave surface, the coordinate system is rotated and transformed so that the light wave surface coincides with the boundary surface. In this case, the boundary surface between media may also be non-parallel with respect to the recording surface. The operation of rotation and transformation can be performed on the spatial frequency spectrum. In accordance with the following formulas (8) and (9), the light wave surface in the medium with the Fourier-transformed refractive index n is calculated, whereby the spatial frequency vector ν = (u, v, w) in the coordinates (u, v) of the spatial frequency spectrum is obtained.

[0080]

[0081] In accordance with the following formula (10), the spatial frequency vector ν is rotationally transformed using the rotation transformation matrix A that defines the rotation to the new coordinate system, whereby the new spatial frequency vector (u’, v’, w’) is obtained.

[0082]

[0083] The coordinates u’ and v’ of the calculated spatial frequency vector correspond to the coordinates of the rotationally transformed spatial frequency spectrum. By performing the operation of rotation and transformation as described above on all the data of the wave surface in front of the boundary surface, the spatial frequency spectrum of the wave surface behind the boundary surface can be calculated.

[0084] Moreover, it can also be used to play the image of the inclined plane. By performing an inverse Fourier transform on the spatial frequency spectrum of the rotationally transformed wave surface, the light wave distribution in the rotationally transformed plane can be calculated.

[0085] The light wave distribution obtained as the result of the diffraction calculation becomes the complex amplitude distribution Ud of the object light. Therefore, the complex amplitude distribution Ud can be visualized by any calculation process. For example, by extracting the amplitude component from the complex amplitude distribution Ud and imaging it, an image equivalent to the bright field of an optical microscope can be obtained.

[0086] <D. Calibration Process> Next, the calibration process using the structural example shown in FIG. 2 will be described. In the calibration process, the 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 conjugate complex number R* of the light wave distribution of the reference light R.

[0087] In the construction example shown in Figure 2, the known light wave distribution P generated by the correction unit 20 is moved parallel to any offset coordinate (x pi, y pi, z pi) (i=0~N-1), thereby generating the light wave distribution Pi (i=0~N-1). For example, as shown in Figures 3(A) to 3(D), the light wave distribution Pi can be generated by arbitrarily moving the contour generation unit 30 in one or more of the x-axis, y-axis, and z-axis directions (that is, by configuring the optical unit that generates the light wave distribution P at any offset coordinate).

[0088] The light wave distribution Pi is the known light wave distribution P that is moved parallel to each axis direction. Therefore, the light wave distribution Pi in the recording plane (z=0) of the image detector D, using the known light wave distribution P in the recording plane (z=0) of the image detector D and the offset coordinates (xpi, ypi, zpi), can be expressed as the following formula (11).

[0089]

[0090] The correction holographic projection I PiR recorded by the image detector D can be expressed as shown in the following formula (12). The third term of the filtering formula (12) is used to calculate the complex amplitude holographic projection J PiR, which can be calculated as shown in the following formula (13).

[0091]

[0092] If the offset coordinates (x pi, y pi, z pi) are known, the conjugate complex number R * (=R 0exp(-iϕ R)) of the light wave distribution of the reference light R can be calculated as follows (14).

[0093]

[0094] In this case, the complex conjugate R* of the light wave distribution of the reference light R can be calculated from the light wave distribution P0 corresponding to an offset coordinate (x p0, y p0, z p0). The contour generation unit 30 does not need to have the function of moving the known light wave distribution P parallel to the complex position in advance.

[0095] In addition, when the offset coordinates are unknown, or when the required accuracy of the offset coordinates cannot be obtained, the following parameter fitting is used to determine the conjugate complex number R* of the light wave distribution of the reference light R.

[0096] More specifically, appropriate initial values ​​are set as offset coordinates (x p0, y p0, z p0) corresponding to the light wave distribution P 0 of number i=0. The initial values ​​are determined taking into account the optical positional relationship of the correction unit 20. For any number i, the object light holographic projection U i is expressed as follows using the conjugate complex number R* of the light wave distribution of the reference light R shown in formula (14), as shown in formula (15).

[0097]

[0098] At this point, for all numbers i (i=0~N-1), the following formula (16) must hold true.

[0099]

[0100] In the case where i=0, it is obvious that the relation of formula (16) holds. In the case where i≠0, if the conjugate complex number R* of the light wave distribution of the reference light R shown in formula (14) is correctly calculated, formula (16) can be transformed into formula (17), so the relation of formula (16) holds.

[0101]

[0102] That is, for all numbers i (i=0~N-1), when the relationship of formula (16) does not hold, it means that the conjugate complex number R* of the light wave distribution of the reference light R has not been calculated correctly. The reason why the conjugate complex number R* of the light wave distribution of the reference light R has not been calculated correctly is that the offset coordinates (x p0, y p0, z p0) are incorrect, and the offset coordinates (x p0, y p0, z p0) must be adjusted to the correct values.

[0103] Before adjusting the offset coordinates (x p0, y p0, z p0), it is best to first correct the light wave distribution calculated by the self-calibrating holographic projection I PiR.

[0104] More specifically, for each number i = 1 to N-1, the light wave distribution Pi is corrected so that the light wave distribution of the image projected from the object's holographic projection Ui is consistent with the known light wave distribution P in the recording plane. The corrected light wave distribution is called the corrected light wave distribution Pi'.

[0105] From formulas (11) and (15) to (17), the relationship shown in formula (18) below holds. However, it is assumed that the conjugate complex number R* of the light wave distribution of the reference light R has not been correctly calculated. In this state, as shown in formula (19) below, the object light holographic projection Ui is corrected on the x-axis, y-axis, and z-axis respectively to be consistent with the known light wave distribution P, thereby determining the corrected light wave distribution Pi'.

[0106]

[0107] The adjustments in the x-axis and y-axis directions are achieved by offsetting the object pixel group of the image detector D corresponding to the object's optical holographic projection Ui(x,y). The correction in the z-axis direction (focal position) is achieved by diffraction calculations performed using the plane wave expansion shown in Equation (6). That is, the correction in the z-axis direction is achieved by changing the distance at which the image is played when performing diffraction calculations on the object's optical holographic projection Ui recorded by the image detector D.

[0108] Furthermore, when the light wave distribution Pi (i=1~N-1) passes through a medium such as a semi-reflecting mirror, it is best to apply the same processing to the diffraction calculation within the medium and the image playback of the tilted surface.

[0109] Thus, for numbers i=1~N-1, the corrected light wave distribution P i' is calculated.

[0110] Finally, the processing of the conjugate complex R* of the light wave distribution of the reference light R is performed. Specifically, for all numbers i (i=0~N-1), the known light wave distribution P and the corrected light wave distribution Pi' are Fourier transformed respectively to calculate the spectrum F[P] and the spectrum F[Pi']. Moreover, the phase difference distribution spectrum Wi(u,v) (=arg(F[Pi'] / F[P])) representing the phase difference distribution between the spectrum F[P] and the spectrum F[Pi'] is calculated. Here, arg() is a function to calculate the complex deflection angle (phase).

[0111] Furthermore, in the phase difference distribution spectrum Wi(u,v), for the parts with phase discontinuities (gap) caused by the influence of phase periodicity, it is best to process them as continuous phases.

[0112] Using the phase difference distribution spectrum Wi(u,v), the wavefront aberration Wi_err can be calculated as shown in the following formula (20). The wavefront aberration Wi_err is calculated by taking the average value Wave of the entire phase difference distribution spectrum Wi as the true value and the root mean square of the true value as the error.

[0113]

[0114] Here, the average value Wave is the average value of the phase difference distribution spectrum Wi(u,v), and the area of ​​the integral phase difference distribution spectrum Wi(u,v) in the Sw system. The integral range is the portion of the phase difference distribution spectrum Wi(u,v) in which there is valid data, and it is common in the calculation of wavefront aberration Wi_err and the average value Wave.

[0115] Furthermore, the narrow definition of "wavefront aberration" refers to the wavefront aberration Wi_err multiplied by λ / 2π (λ wavelength). Therefore, Wi_err × λ / 2π can also be called wavefront aberration. However, λ / 2π is a fixed coefficient, so for the following treatment, the form after omitting λ / 2π as a coefficient will be explained. However, in the measurement examples shown in Figures 8 and 9 below, the narrow definition of wavefront aberration is used for evaluation.

[0116] When the light wave distribution is played back based on the conjugate complex number R* of the correct reference light R, the wavefront aberration Wi_err system becomes 0. However, when there is an error in the conjugate complex number R* of the light wave distribution of the reference light R, distortion occurs in the wavefront phase, therefore, the wavefront aberration Wi_err system does not become 0.

[0117] Therefore, the offset coordinates (x p0, y p0, z p0) are adjusted to minimize the sum of the absolute values ​​of the wavefront aberrations Wi_err for all numbers i (i = 0 to N-1) (= Σ Wi_err). For parameter fitting, a general optimization algorithm can be used.

[0118] Moreover, the more the number of generated light wave distributions Pi, the more reliable the parameter fitting can be improved. Also, the light wave distribution Pi is preferably set without deviation over the entire field of view that can be recorded by the image detector D.

[0119] <E. Processing Device 100> Next, a hardware configuration example of the processing device 100 included in the optical measurement system 1 will be described.

[0120] FIG. 4 is a schematic diagram showing a hardware configuration example of the processing device 100 included in the optical measurement system 1 of the present embodiment. Referring to FIG. 4, the processing device 100, as a main hardware component, includes a processor 102, a main memory 104, an input unit 106, a display unit 108, a storage unit 110, an interface 120, a network interface 122, and a media drive 124.

[0121] Typically, the processor 102 is a computing 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 unit 110 into the main memory 104 to execute them. The main memory 104 is a volatile memory called DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory), and functions as a working memory for the processor 102 to execute programs.

[0122] The input unit 106 includes a keyboard, a mouse, etc., and accepts operations from the user. The display unit 108 outputs the execution results of programs performed by the processor 102, etc., to the user.

[0123] The storage unit 110 is composed of non-volatile memories such as a hard disk and a flash memory, and stores various programs, data, etc. More specifically, the storage unit 110 stores an operating system 111 (OS: Operating System), a measurement program 112, a calibration program 113, calibration information 114, holographic projection data 115, and measurement results 116.

[0124] Operating system 111 provides an environment for processor 102 to execute programs. Measurement program 112, executed by processor 102, performs measurement processing in accordance with this embodiment. Calibration program 113, executed by processor 102, performs calibration processing in accordance with this embodiment. Calibration information 114 consists of parameters determined by the calibration processing and referenced in the measurement processing. Holographic projection data 115 is equivalent to image data output from image detector D. Measurement result 116 includes the measurement results obtained from executing measurement program 112.

[0125] In this way, the storage unit 110 stores information (correction information 114) on the light wave distribution of the reference light R in the optical system shown in Figures 1 and 2.

[0126] Interface 120 mediates data transmission between processing device 100 and image detector D. Network interface 122 mediates data transmission between processing device 100 and external server device.

[0127] The media drive 124 reads necessary data from the recording medium 126 (e.g., CD-ROM) containing the program executed by the processor 102 and stores it in the storage unit 110. Furthermore, the measurement program 112 and / or calibration program 113 executed in the processing device 100 can also be installed via the recording medium 126 or downloaded from the server via the network interface 122.

[0128] Measurement program 112 and / or calibration program 113 may also be part of the operating system 111, provided as a program module, in which necessary modules are called up in a predetermined arrangement at predetermined times to perform processing. In this case, measurement program 112 and / or calibration program 113 that do not include this module are also included within the technical scope of the present invention. Measurement program 112 and / or calibration program 113 may also be incorporated into other programs and provided.

[0129] Furthermore, all or part of the functions provided by the processor 102 of the processing device 100 can be implemented by hard-wired logic circuits (such as FPGA (Field-Programmable Gate Array) or ASIC (Application Specific Integrated Circuit)).

[0130] For ease of explanation, FIG. 4 shows a structural example of the processing device 100 that can perform measurement processing and calibration processing. However, it can also be one that can only perform one of the measurement processing and calibration processing. For example, before the factory shipment of the optical measurement system 1, the calibration processing is executed, and the conjugate complex number R* of the optical wave distribution of the reference light R is determined in advance. Therefore, after the factory shipment, sometimes the calibration processing does not need to be executed, and only the measurement processing is executed. In this case, a processing device that can execute the calibration processing and a processing device that can execute the measurement processing can also be prepared separately.

[0131] <F. Processing Procedure> Next, the measurement processing and calibration processing executed in the optical measurement system 1 will be described.

[0132] (f1: Measurement Processing) FIG. 5 is a flowchart showing the processing procedure of the measurement processing executed in the optical measurement system 1 of the present embodiment. In the measurement processing shown in FIG. 5, the conjugate complex number R* of the information on the optical wave distribution of the reference light R in the optical systems shown in FIGS. 1 and 2 is obtained in advance by some method. The steps executed by the processing device 100 shown in FIG. 5 are typically implemented by the processor 102 of the processing device 100 by executing the measurement program 112.

[0133] Referring to FIG. 5, the optical system shown in FIG. 1 is configured, and the sample S is arranged at the same time (step S100). Moreover, coherent light is generated from the light source 10, and the processing device 100 records the holographic projection IOR with the image detector D (step S102). In this way, the processing of recording the holographic projection IOR (the third holographic projection) generated by modulating the object light O illuminated on the sample S with the reference light R by the illumination light Q is executed.

[0134] The processing device 100 calculates the complex amplitude holographic projection JOR by applying spatial frequency filtering to the recorded holographic projection IOR (step S104) (refer to the above formula (4)). Next, the processing device 100 calculates the object light holographic projection U by dividing the calculated complex amplitude holographic projection JOR by the conjugate complex number R* of the optical wave distribution of the reference light R (step S106) (refer to the above formula (5)). In this way, the processing of applying spatial frequency filtering to the holographic projection IOR (the third holographic projection) and calculating the object light holographic projection U based on the filtering result and the conjugate complex number R* of the optical wave distribution of the reference light R (the information on the optical wave distribution of the reference light R) is executed.

[0135] Furthermore, the processing device 100 can also perform processing to increase and superimpose the number of sampling points for the object's optical holographic projection U, thereby calculating the object's optical holographic projection UΣ for playback. When the processing to increase and superimpose the number of sampling points is omitted, the object's optical holographic projection U is processed as is as the object's optical holographic projection UΣ for playback.

[0136] The processing device 100 calculates the total image projection UΣ of the object light for playback by diffraction calculation up to the sample surface, and thereby calculates the complex amplitude distribution Ud (step S108) (refer to formulas (6) and (7) above). Furthermore, the processing device 100 uses part or all of the information of the calculated complex amplitude distribution Ud to generate a measurement result (step S110). For example, from the complex amplitude distribution Ud, the amplitude component is extracted and imaged, thereby generating an image equivalent to a bright field of view of an optical microscope.

[0137] The processing steps S102 to S110 shown in Figure 5 are performed for each sample S. Furthermore, the holographic projections I and OR corresponding to the complex number of samples S can be recorded beforehand, and the processing to generate the measurement results can be performed afterwards.

[0138] (f2: Correction processing) Figure 6 is a flowchart illustrating the calibration process performed in the optical measurement system 1 of this embodiment. The calibration process shown in Figure 6 is the process when a known light wave distribution P and the correct offset coordinates can be obtained. The steps executed by the processing device 100 shown in Figure 6 are typically implemented by the processor 102 of the processing device 100 by executing the calibration program 113.

[0139] Referring to Figure 6, the optical system shown in Figure 2 is configured, and the correction unit 20 is configured (step S200). At this time, the offset coordinates (x p0, y p0, z p0) of the correction unit 20 are correctly set (step S202). In this way, the processing of configuring an optical system (optical measurement system 1 shown in Figures 1 and 2) for recording the object light O obtained by modulating the illumination light Q to illuminate the sample S with reference light R, and the processing of configuring the correction unit 20, which includes an optical system (contour generation unit 30) that generates a known light wave distribution P, on the optical path of the illumination light Q when the sample S is not present, is performed.

[0140] Furthermore, coherent light is generated from the light source 10, and the processing device 100 records the correction holographic projection I P0R with the image detector D (step S204). In this way, the processing of the correction holographic projection I P0R (first holographic projection) generated by the recording correction unit 20 in the state of generating light wave distribution P0 is performed.

[0141] The processing device 100 calculates the light wave distribution P0 using the known light wave distribution P and offset coordinates (x p0, y p0, z p0) (step S206) (refer to formula (11) above). Using the calculated light wave distribution P0 and the recorded correction holographic projection I P0R, it calculates the conjugate complex number R* of the light wave distribution of the reference light R (step S208) (refer to formula (14) above). In this way, the processing system calculates the conjugate complex number R* of the light wave distribution information of the reference light R based on the information (offset coordinates) indicating the configuration position of the correction unit 20, the known light wave distribution P, and the correction holographic projection I P0R (first holographic projection).

[0142] Furthermore, the processing device 100 outputs correction information 114 (step S210) including the conjugate complex number R* of the calculated light wave distribution of the reference light R. The correction processing then concludes.

[0143] Figure 7 is a flowchart illustrating another processing procedure of the calibration process performed in the optical measurement system 1 of this embodiment. The calibration process shown in Figure 7 is the process when the correct offset coordinates cannot be obtained. The steps performed by the processing device 100 shown in Figure 7 are typically implemented by the processor 102 of the processing device 100 executing the calibration program 113.

[0144] Referring to Figure 7, the optical system shown in Figure 2 is configured, and the correction unit 20 is configured (step S250). In this way, the processing of configuring an optical system (optical measurement system 1 shown in Figures 1 and 2) for recording the object light O obtained by modulating the illumination light Q to illuminate the sample S with reference light R and generating a holographic projection, and the processing of configuring the correction unit 20, which includes an optical system (contour generation unit 30) that generates a known light wave distribution P, on the optical path of the illumination light Q in the absence of the sample S, are performed.

[0145] Next, the parallel movement of the contour generation unit 30 and the recording of N correction holographic projections I PiR are performed. More specifically, the correction unit 20 is set to the offset coordinates (x pi, y pi, z pi) corresponding to the number i (step S252). Furthermore, coherent light is generated from the light source 10, and the processing device 100 records the correction holographic projections I PiR using the image detector D (step S254). In steps S252 and S254, the number i is repeated from 0 to N-1.

[0146] In this way, the processing of the correction holographic projection I P0R (first holographic projection) generated by the correction unit 20 in the state of generating light wave distribution P0 is performed. Furthermore, the processing of moving the light wave distribution generated by the correction unit 20 to a complex position (offset coordinates (x p0, y p0, z p0)) different from the position where the correction holographic projection I P0R (first holographic projection) is recorded (offset coordinates (x p0, y p0, z p0)) and simultaneously recording a complex number of correction holographic projections I PiR (complex second holographic projections) at the complex positions is performed.

[0147] Next, the processing system temporarily calculates the complex conjugate R* of the light wave distribution of the reference light R. More specifically, an appropriate initial value is set as the offset coordinate (x p0, y p0, z p0) corresponding to the light wave distribution P 0 with number i=0 (step S256). Furthermore, the processing device 100 calculates the light wave distribution P 0 using the known light wave distribution P and the initial value of the offset coordinate (x p0, y p0, z p0) (step S258) (refer to the above formula (11)), and uses the calculated light wave distribution P 0 and the recorded correction holographic projection I P0R to temporarily calculate the complex conjugate R* of the light wave distribution of the reference light R (step S260) (refer to the above formula (14)).

[0148] In this way, the processing system is executed to calculate the conjugate complex number R* of the light wave distribution information of the reference light R based on the information representing the configuration position of the correction unit 20 (initial value of the offset coordinate), the known light wave distribution P, and the correction holographic projection I P0R (first holographic projection).

[0149] Next, the processing system for correcting the light wave distribution is performed. More specifically, the processing device 100 applies spatial frequency filtering to the recorded correction holographic projection I PiR and calculates the complex amplitude holographic projection J PiR (step S262) (refer to formula (4) above). Next, the processing device 100 divides the calculated complex amplitude holographic projection J PiR by the current conjugate complex number R*, thereby calculating the object light holographic projection Ui (step S264) (refer to formulas (6) and (7) above). In this way, the processing system for calculating the complex object light holographic projection Ui corresponding to the complex correction holographic projection I PiR is performed based on the filtering result and the conjugate complex number R* (information on the light wave distribution of the reference light R) for each of the complex correction holographic projections I PiR.

[0150] Next, the processing device 100 determines the light wave distribution Pi based on the self-calculated object light holographic projection Ui (step S266). Furthermore, the processing device 100 corrects the object light holographic projection Ui to make it consistent with the known light wave distribution P, thereby calculating the corrected light wave distribution Pi' (step S268) (refer to the above formulas (18) and (19)). In this way, the processing device 100 corrects multiple object light holographic projections Ui based on the known light wave distribution P, thereby calculating multiple corrected light wave distributions Pi' corresponding to multiple correction holographic projections I PiR.

[0151] Next, the processing device 100 calculates the wavefront aberration from the spectrum calculated from the known light wave distribution P and the spectrum calculated from the corrected light wave distribution Pi' corresponding to the complex correction holographic projection I PiR (the second complex holographic projection).

[0152] More specifically, the processing device 100 performs Fourier transforms on the known light wave distribution P and the corrected light wave distribution Pi', respectively, and calculates the spectrum F[P] and the spectrum F[Pi'] (step S270). Furthermore, the processing device 100 calculates the phase difference distribution spectrum Wi(u,v) (=arg(F[Pi'] / F[P])) representing the phase difference distribution between the spectrum F[P] and the spectrum F[Pi'] (step S272). Thus, the processing device 100 calculates the phase difference distribution spectrum Wi(u,v) as the phase difference distribution between the spectrum F[P] calculated from the known light wave distribution P and the spectrum F[Pi'] calculated from the corrected light wave distribution Pi' corresponding to the correction holographic projection I PiR (second holographic projection).

[0153] Finally, the processing device 100 calculates the wavefront aberration Wi_err using the calculated phase difference distribution spectrum Wi(u, v) (step S274). As shown in the above formula (20), the processing device 100 calculates the root mean square of the average Wave of the entire phase difference distribution spectrum Wi as an error in the calculation process of the wavefront aberration Wi_err.

[0154] The processes of steps S262 to S274 are repeated with the number i ranging from 1 to N - 1. Next, the processing device 100 adjusts the values of the offset coordinates (xp0, yp0, zp0) of the correction unit 20 (information indicating the arrangement position) to minimize the wavefront aberration Wi_err.

[0155] More specifically, the processing device 100 calculates the sum of the wavefront aberrations Wi_err calculated in step S274 (= ΣWi_err) (step S276), and determines whether the sum of the calculated wavefront aberrations Wi_err satisfies the convergence condition (step S278). The convergence condition may, for example, also include the case where the sum of the wavefront aberrations Wi_err is less than or equal to a predetermined value.

[0156] If the sum of the wavefront aberrations Wi_err does not satisfy the convergence condition (NO in step S278), the processing device 100 changes the values of the offset coordinates (xp0, yp0, zp0) (step S280) and repeats the processes below step S260.

[0157] If the sum of the wavefront aberrations Wi_err satisfies the convergence condition (YES in step S278), the processing device 100 outputs the correction information 114 including the current conjugate complex number R* (step S282). Moreover, the correction process ends.

[0158] <G. Measurement Example> Next, a measurement example performed by the optical measurement system of this embodiment is shown. The following measurement example is for explaining the improvement in accuracy achieved by using the correction unit 20 to determine the conjugate complex number R* of the light wave distribution of the reference light R.

[0159] First, the optical system shown in Figure 2 is constructed. The wavelength of the light source 10 is set to 532 nm, and the optical system with a recording aperture number NA = 0.5 is constructed. Furthermore, the light wave distribution Pi (i = 0 ~ N-1) generated by the correction unit 20 is recorded. In the measurement examples shown in Figures 8 and 9, the light wave distribution Pi is recorded at 11 locations (N = 11; i = 0 ~ 10).

[0160] As described above, the light wave distribution Pi is a known light wave distribution P that moves parallel to each other along the x-axis, y-axis, and z-axis within the field of view of the image detector D. The known light wave distribution P uses a point light source.

[0161] As the offset coordinates (x p0, y p0, z p0) corresponding to the light wave distribution P 0, an initial value is set considering the optical positional relationship of the correction unit 20 to determine the initial value. Using the set initial value, the conjugate complex number R* of the light wave distribution of the reference light R is calculated.

[0162] Figure 8 is a measurement example showing the initial stage of the calibration process of the optical measurement system 1 of this embodiment. Figure 8(A) shows the amplitude distribution near the spotting point of the projected object's optical holographic projection U1 using the initial value of the offset coordinates. Figure 8(B) shows the distribution of the calculated wavefront aberration W1_err using the amplitude distribution near the spotting point of the object's optical holographic projection U1. The wavefront aberration W1_err after using the initial value of the offset coordinates is 2.924λ.

[0163] The initial value of the offset coordinates does not accurately reflect the optical positional relationship of the correction unit 20. Therefore, the conjugate complex number R* of the light wave distribution of the reference light R is also incorrect. As a result, as shown in Figure 8(A), the light-gathering point (the point of the Airy disk) is not a point but has jagged edges. Furthermore, as shown in Figure 8(B), a large wavefront aberration is also produced in the object's optical holographic projection U1.

[0164] Next, following the above process, the offset coordinates (x p0, y p0, z p0) are adjusted to minimize the sum of wavefront aberrations. Using the adjusted offset coordinates (x p0, y p0, z p0), the conjugate complex number R* of the light wave distribution of the reference light R is calculated.

[0165] Figure 9 shows a measurement example after the calibration processing of the optical measurement system 1 of this embodiment. Figure 9(A) shows the amplitude distribution near the spotting point of the object's holographic projection U1 using the adjusted offset coordinates. Figure 9(B) shows the distribution of the calculated wavefront aberration W1_err using the amplitude distribution near the spotting point of the object's holographic projection U1. The wavefront aberration W1_err after using the initial value of the offset coordinates is 0.023λ. As shown in Figure 9(A), by correctly determining the conjugate complex number R* of the light wave distribution of the reference light R, a spotting point (the point of the Airy disk) is formed on the object's holographic projection U1. As shown in Figure 9(B), no obvious wavefront aberration is observed.

[0166] Generally, a wavefront aberration of 0.07λ or less is considered diffraction-limited, and the wavefront aberration Wi_err is 0.023λ, thus possessing sufficient imaging performance. Furthermore, when the wavefront aberration is calculated for numbers i=2~10, the wavefront aberration Wi_err becomes 0.07λ or less for all played images, extending across the entire field of view, thus exhibiting diffraction-limited imaging performance.

[0167] Figure 10 is a diagram showing a measurement example of a sample taken by the optical measurement system 1 of this embodiment. Figure 10 shows a playback image of a sample (USAF 1951 resolution test target) recorded by the optical measurement system 1 shown in Figure 1 using a holographic projection I OR.

[0168] Figures 10(A1) and 10(A2) show the playback image after using the initial values ​​of the offset coordinates. Figure 10(A1) shows the overall image of the resolution test target, and Figure 10(A2) shows a partial enlarged view of the resolution test target.

[0169] In the playback images shown in Figures 10(A1) and 10(A2), there is significant distortion, and the circuit lines in group 9 of the resolution test target cannot be fully decomposed.

[0170] Figures 10(B1) and 10(B2) show the playback image using the adjusted offset coordinates. Figure 10(B1) shows the overall image of the resolution test target, and Figure 10(B2) shows a partial enlarged view of the resolution test target.

[0171] In the playback image shown in FIG. 10(B1), no significant distortion occurs. Also, in FIG. 10(B2), it can be seen that the line (width 0.548 μm) of the 9-6 circuit of the test target shown by the rectangular frame line can be decomposed into three lines, and performance equivalent to the theoretical resolution of 0.532 μm determined by the optical system can be obtained.

[0172] In this way, by the calibration process as described above, the conjugate complex number R* of the optical wave distribution of the reference light R is correctly determined, whereby the sample can be measured with high precision.

[0173] <H. Modified Example> In FIGS. 1 and 2, an example structure of the optical measurement system 1 using a transmissive optical system is illustrated. However, it is not limited to this structure example and can be variously modified as follows.

[0174] (h1: Modified Example 1) As Modified Example 1 of this embodiment, a structure example in which the reference light is arranged near the sample will be described.

[0175] FIG. 11 is a schematic diagram showing a structure example of the optical measurement system 1A according to Modified Example 1 of this embodiment. In FIG. 11(A), a structure example for the measurement process is shown, and in FIG. 11(B), a structure example for the calibration process is shown.

[0176] Referring to FIG. 11(A), in the optical measurement system 1A, a mirror M3 is arranged instead of the half-reflection mirror HM2. The mirror M3 is arranged outside the range irradiated by the sample S and the object light O. The reference light R is reflected by the mirror M4 to change its propagation direction and is guided to the mirror M3. The reference light R is also reflected by the mirror M3 and guided to the light-receiving surface of the image detector D. That is, in the light-receiving surface of the image detector D, the object light O obtained by illuminating the sample S with the illumination light Q is modulated by the reference light R.

[0177] In this way, when there is no need to ensure the operating distance, the mirror M3 can be used instead of the half-reflection mirror HM2. The mirror M3 can be any one of a plane mirror, a convex mirror, and a concave mirror.

[0178] Referring to FIG. 11(B), in the optical measurement system 1A, the contour generation unit 30 including the calibration unit 20 is arranged in the form of replacing the field mask A1 and the condenser lens L1 of the illumination optical system. The calibration process is the same as the above-described process.

[0179] (h2: Variation Example 2) This is a variation of the present embodiment, with the lighting optical system omitted.

[0180] Figure 12 is a schematic diagram showing a construction example of the optical measurement system 1B according to Modification 2 of this embodiment. Figure 12(A) shows a construction example for measurement processing, and Figure 12(B) shows a construction example for calibration processing.

[0181] Referring to Figure 12(A), in the optical measurement system 1B, the field-of-view limiting hood FA is positioned near the sample S. By using this field-of-view limiting hood FA, the illumination optical system can be simplified or omitted. Figure 12(A) shows a construction example after omitting the combined optical system (field-of-view hood A1 and light-collecting lens L1), which corresponds to the illumination optical system.

[0182] Furthermore, the optical system illuminating the sample S with the illumination light Q can be arbitrary, as long as interference can be maintained between the illumination light Q and the reference light R. For example, the illumination light Q can be incident at an angle, or the illumination light Q can be diffused.

[0183] Referring to Figure 12(B), the optical measurement system 1B includes a contour generation unit 30 comprising a correction unit 20, which is positioned on the optical path of the illumination light Q after the sample S is removed. Furthermore, the illumination optical system is omitted; therefore, it is not necessary to remove the illumination optical system when configuring the correction unit 20. The correction process is the same as described above.

[0184] (h3: Variation Example 3) This section describes a variation of the present embodiment, specifically a construction example employing a reflective optical system.

[0185] Figure 13 is a schematic diagram showing a construction example of the optical measurement system 1C according to the modified example 3 of this embodiment. Figure 13(A) shows a construction example for measurement processing, and Figure 13(B) shows a construction example for calibration processing.

[0186] Referring to Figure 13(A), in the optical measurement system 1C, the illumination light Q, after being split by the beam splitter BS1, is reflected by mirrors M1 and M5 respectively. After its propagation direction is changed, it passes through the light-collecting lens L3, the field of view cover A1, and the light-collecting lens L4, and is guided to the semi-reflective mirror HM2. Moreover, the illumination light Q, reflected by the semi-reflective mirror HM2, illuminates the sample S. The object light O obtained by illuminating the sample S with the illumination light Q (that is, the light reflected by the sample S) passes through the semi-reflective mirror HM2 and is incident on the image detector D.

[0187] Additionally, the reference light R is reflected by mirror M2, changing its propagation direction, and then collected by light-collecting lens L2. The light-collecting point FP1 formed by light-collecting lens L2 corresponds to the position of a point light source. Finally, the reference light R is reflected by semi-reflective mirror HM2 and incident on the image detector D.

[0188] Referring to Figure 13(B), the calibration process in the optical measurement system 1C is performed using a transmission-type optical system, similar to that in Figures 2 and 12(B). More specifically, the contour generation unit 30, which includes the calibration unit 20, is positioned on the optical path of the illumination light Q after the sample S is removed. The calibration process is the same as described above.

[0189] (h4: Variation Example 4) This is a variation of the present embodiment, specifically example 4, which is applicable to the construction of measuring scattered light from sample S.

[0190] Figure 14 is a schematic diagram showing a construction example of an optical measurement system 1D according to a modified example 4 of this embodiment. Figure 14(A) shows a construction example for measurement processing, and Figure 14(B) shows a construction example for calibration processing.

[0191] Referring to Figure 14(A), in the optical measurement system 1D, the illumination light Q, after being split by the beam splitter BS1, is reflected by the mirror M6, and after its propagation direction is changed, it illuminates the sample S. The scattered light generated by the illumination light Q illuminating the sample S is incident on the image detector D as the object light O.

[0192] In the optical measurement system 1D, the scattered light generated by the sample S can be measured. Furthermore, a field-of-view limiting mask FA can be configured near the sample S as needed. By configuring the field-of-view limiting mask FA, noise can be suppressed.

[0193] Referring to FIG. 14(B), the calibration process in the optical measurement system 1D is carried out in the same manner as in FIGS. 2 and 12(B), and it is performed using a transmissive optical system. More specifically, the contour generation unit 30 including the calibration unit 20 is disposed 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.

[0194] (h5: Variant 5) In the above description, although the structure using the light source 10 that generates coherent light of a specific wavelength band has been mainly described, a light source 10 that generates coherent light of a plurality of wavelength bands can also be used. For example, coherent light corresponding to each of red (R), green (G), and blue (B) wavelength bands is generated, and an image detector D having light reception sensitivity for each color is used. Thereby, holographic projection of each color can be recorded.

[0195] Further, when the image detector D is a polarization image detector, polarization holographic projection can be recorded.

[0196] <I. Advantages> The optical measurement system of this embodiment adopts a lensless digital holography structure in which there is no imaging optical system such as a lens between the sample and the image detector. Therefore, no errors such as aberration occur in the object light obtained by illuminating the sample with the illumination light.

[0197] The optical measurement system of this embodiment obtains information on the light wave distribution of the reference light (for example, the conjugate complex number R * of the light wave distribution of the reference light R) in advance by the calibration process. The optical measurement system modulates the object light obtained by illuminating the sample with the illumination light using the reference light, and calculates the object light holographic projection based on the generated holographic projection and the information on the light wave distribution of the reference light. Thereby, the shape (light wave amplitude and phase, etc.) of an arbitrary position of the sample can be calculated or measured afterwards.

[0198] The optical measurement system of this embodiment illuminates a known light wave distribution from a known arrangement position (coordinates) instead of the object light, thereby calculating the information on the light wave distribution of the reference light. Therefore, it is not necessary to correctly adjust the on-axis of the on-line spherical light wave to the line, and there is no need for adjustment time.

[0199] The optical measurement system of the present embodiment, which replaces the object light, illuminates the known light wave distribution from the configuration position (coordinates) of the complex number, whereby information of the light wave distribution of the reference light can be calculated by parameter fitting. Therefore, there is no need to properly adjust the spherical wave light on the line to the axis on the line, and no time for adjustment is required. Moreover, information on the light wave distribution of the correct reference light can be calculated even if the configuration position of the light wave distribution known to the illumination is not known correctly.

[0200] The embodiment of the present disclosure must be thought of as exemplifying at the point in its entirety, not as limiting. The scope of the present invention is not expressed by the foregoing explanation, but in order to express it by the scope of the applied patent, it intends to include all changes in meaning and scope equal to the scope of the applied patent.

[0201] 1,1A,1B,1C,1D: Optical measurement system 10: Light source 20: Calibration unit 30, 30A, 30B, 30C, 30D: profile generation section 31,33,34: Visor 32, 36: pinhole 35, 37, L1, L2, L3, L4: light-collecting lenses 38: Object lens 100: Processing device 102: Processor 104: Main memory 106: Input Department 108: Display Department 110: Storage body 111: Operating System 112: Measurement program 113: Calibration program 114: Calibration information 115: Holographic projection data 116: Measurement results 120: Interface 122: Web interface 124: Media Drive 126: Recording media A1: Vision cover BE: beam extender BS1, BS2: beam splitter D: Image detector FA: Vision limit cover FP1: Concentration point M1, M2, M3, M4, M5, M6: Reflectors O: Object light Q: Illumination light R: Reference light S: Sample SP1, SP2: Openings

Claims

1. An optical measurement method, comprising: The steps include: constructing an optical system for recording a reference light coherent with the illumination light, modulating the object light obtained by illuminating a sample with the illumination light, and generating a holographic projection; configuring a correction unit, comprising an optical system that generates a known light wave distribution, along the optical path of the illumination light in a state where the sample is absent; recording the first holographic projection generated by the correction unit in a state where a light wave distribution is generated; and calculating information about the light wave distribution of the reference light based on information indicating the placement position of the correction unit, the known light wave distribution, and the first holographic projection.

2. The optical measurement method of claim 1, wherein the correction unit is configured to allow the generated light wave distribution to be spatially shifted, the optical measurement method further includes: The steps include: moving the generated light wave distribution to a plurality of positions different from the position recorded after the first holographic projection, and simultaneously recording a plurality of second holographic projections at the plurality of positions; calculating wavefront aberration from the spectrum calculated from the known light wave distribution and the spectrum calculated from the light wave distribution corresponding to the plurality of second holographic projections; and adjusting the information representing the configuration position of the correction unit to minimize the wavefront aberration.

3. The optical measurement method as described in claim 2, further comprising: The steps include: applying spatial frequency filtering to each of the complex second holographic projections; calculating the complex object light holographic projections corresponding to the complex second holographic projections based on the filtering result and the information of the light wave distribution of the reference light; and correcting the complex object light holographic projections based on the known light wave distribution, and calculating the complex light wave distribution corresponding to the complex second holographic projections.

4. The optical measurement method as described in claim 2, wherein it includes: The steps to calculate the wavefront aberration; The steps include: calculating the spectrum calculated from the known light wave distribution and the spectrum calculated from the light wave distribution corresponding to the second holographic projection as a phase difference distribution spectrum; and calculating the root mean square of the entire phase difference distribution spectrum with respect to the average value as the error.

5. The optical measurement method of any one of claims 1 to 4, further comprising: The steps of recording the third holographic projection generated by modulating the object light obtained by illuminating the sample with the illumination light using the reference light; And the steps of applying spatial frequency filtering to the third holographic projection, and calculating the object's optical holographic projection based on the filtering result and the information of the light wave distribution of the reference light.

6. An optical measurement method as described in any of claims 1 to 4, wherein the information on the light wave distribution of the reference light includes the conjugate complex number of the light wave distribution of the reference light.

7. An optical measurement method, comprising: The steps include: constructing an optical system for recording a holographic projection generated by modulating the object light illuminating a sample with a reference light coherent with the illumination light; obtaining information on the light wave distribution of the reference light in the optical system; recording the holographic projection generated by modulating the object light illuminating a sample with a reference light coherent with the illumination light; and applying spatial frequency filtering to the holographic projection and calculating the object light holographic projection based on the filtering result and the information on the light wave distribution of the reference light. The information on the light wave distribution of the reference light is calculated in advance based on the holographic projection, information indicating the placement position of the correction unit, and the known light wave distribution. The holographic projection is recorded when, in the absence of the sample, a correction unit comprising an optical system that generates a known light wave distribution is arranged along the optical path of the illumination light.

8. An optical measurement system, comprising: A light source generates coherent light; a beam splitter generates illumination light and a reference light from the coherent light from the light source; an optical system is used to record, with an image detector, a reference light coherent with the illumination light, and modulate the object light obtained by illuminating the sample with the illumination light to generate a holographic projection; and 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 holographic projection recorded by the image detector and calculates the object light holographic projection based on the filtering result and the information on the light wave distribution of the reference light. The information on the light wave distribution of the reference light is calculated in advance based on the holographic projection, information indicating the placement position of the correction unit, and the known light wave distribution. The holographic projection is recorded when the sample is absent, and a correction unit containing an optical system that generates a known light wave distribution is arranged on the optical path of the illumination light.

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