Optical measurement system and optical measurement method

Abstract

This optical measurement system comprises: a light source; a beam splitter for splitting light from the light source into first light and second light; a reflection unit for causing the first light that has passed through a sample to pass through the sample again; a combining unit for combining the first light and the second light reflected by the reflection unit; an image sensor that receives the light combined by the combining unit; and a processing unit that calculates a light wave distribution in the sample on the basis of a hologram obtained using the image sensor.

Description

Optical measurement system and optical measurement method

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

[0002] Digital holography has been proposed and put into practical use as a method for optically measuring the structure and shape of a sample. Digital holography is a technique for measuring a sample by obtaining the shape of the wavefront of the object light by observing the interference fringes that occur when a reference light and an object light generated by irradiating a sample with light are superimposed on each other.

[0003] For example, WO 2020 / 045584 (Patent Document 1) discloses an optical system using a cube beam combiner, which makes it easy to achieve large numerical aperture recording and reflective illumination.

[0004] International Publication No. 2020 / 045584 International Publication No. 2023 / 079741 International Publication No. 2022 / 138716

[0005] For example, in a sample having a uniform structure such as a film, there may occasionally be defects or foreign matter. One object of the present invention is to provide an optical measurement system and an optical measurement method suitable for measuring such samples.

[0006] (Configuration 1) An optical measurement system according to one aspect of the present invention includes a light source, a beam splitter for splitting light from the light source into first light and second light, a reflecting unit for transmitting the first light that has passed through a sample back through the sample, a superposition unit for superimposing the first light and the second light reflected by the reflecting unit, an image sensor onto which the light superimposed by the superposition unit is incident, and a processing unit for calculating the light wave distribution in the sample based on a hologram acquired by the image sensor.

[0007] (Configuration 2) In Configuration 1, the reflecting unit may be configured to reflect the first light from the beam splitter and guide it to the sample. The first light reflected by the reflecting unit and the first light after passing through the sample again may propagate on the same optical axis.

[0008] (Configuration 3) In Configuration 1, the second light may be configured to be irradiated from an oblique direction relative to the surface of the sample. The overlapping portion may be positioned in the propagation direction of the first light reflected by the reflecting portion.

[0009] (Configuration 4) In configuration 3, the processing unit may calculate an object light hologram based on a hologram acquired by the image sensor, calculate a complex amplitude distribution, which is the light wave distribution at the center of rotation of the sample, by performing diffraction calculation on the object light hologram, and perform coordinate transformation of the complex amplitude distribution according to the angle between the recording surface of the image sensor and the surface of the sample.

[0010] (Configuration 5) In Configuration 1, the reflecting unit may include a pair of mirrors arranged opposite each other with the sample in between. The second light may be configured to be irradiated obliquely onto the surface of the sample.

[0011] (Configuration 6) In configuration 5, the processing unit may calculate an object light hologram based on a hologram acquired by the image sensor, and perform diffraction calculations on the object light hologram to calculate a complex amplitude distribution, which is a light wave distribution, for each distance from the recording surface of the image sensor to the sample and the mirror image of the sample generated by the reflecting unit.

[0012] (Configuration 7) In configuration 6, the processing unit may perform coordinate transformation of the complex amplitude distribution calculated for each distance in accordance with the angle formed between the recording surface of the image sensor and the surface of the sample.

[0013] (Configuration 8) According to another aspect of the present invention, there is provided an optical measurement method using an optical system including a beam splitter that splits light from a light source into first light and second light, the optical measurement method including the steps of: using a reflecting unit to transmit the first light that has transmitted through a sample back through the sample; superimposing the first light and the second light reflected by the reflecting unit; obtaining a hologram from the superimposed light using an image sensor; and calculating a light wave distribution in the sample based on the obtained hologram.

[0014] According to an embodiment of the present invention, an optical measurement system and an optical measurement method suitable for measuring a sample having a uniform structure such as a film can be realized.

[0015] FIG. 1 is a schematic diagram showing an example configuration of an optical measurement system according to a first embodiment. FIG. 1 is a schematic diagram showing an optical configuration around the sample shown in FIG. 1 . FIG. 2 is a diagram for explaining a position of interest in the optical measurement system according to the first embodiment. FIG. 3 is a flowchart showing a measurement procedure by the optical measurement system according to the first embodiment. FIG. 3 is a schematic diagram showing an example configuration of an optical measurement system according to a second embodiment. FIG. 5 is a schematic diagram showing an optical configuration around the sample shown in FIG. 6. FIG. 7 is a diagram for explaining image reproduction processing in the optical measurement system according to the second embodiment. FIG. 8 is a flowchart showing a measurement procedure by the optical measurement system according to the second embodiment. FIG. 9 is a schematic diagram showing an example configuration of an optical measurement system according to a modification of the first embodiment. FIG. 10 is a schematic diagram showing an example configuration of an optical measurement system according to a third embodiment. FIG. 11 is a perspective view showing an example configuration of the optical measurement system according to the third embodiment. FIG. 12 is a diagram for explaining measurement processing in the optical measurement system according to the third embodiment. FIG. 13 is a flowchart showing a measurement procedure by the optical measurement system according to the third embodiment. FIG. 14 is a schematic diagram showing an example configuration of an optical measurement system according to another modification of the first embodiment. FIG. 15 is a schematic diagram showing an example hardware configuration of a processing device included in the optical measurement system according to the present embodiment. FIG. 16 is a schematic diagram showing an example functional configuration of a processing device included in the optical measurement system according to the present embodiment.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings, in which the same or corresponding parts are designated by the same reference numerals and will not be described repeatedly.

[0017] <A. Optical Measurement System> The optical measurement system according to this embodiment optically measures a sample. The optical measurement system according to this embodiment utilizes digital holography, which uses diverging light such as a point light source as reference light. The optical measurement system according to this embodiment has a lensless digital holography configuration, in which no lens is present between the sample and the image sensor.

[0018] The optical measurement system according to this embodiment measures a sample with a uniform structure, such as a film. Such samples occasionally contain defects or foreign matter, and the optical measurement system according to this embodiment is capable of measuring such defects and foreign matter. Because samples such as film are highly transparent, when light passes through the sample, the phase of the light is not significantly disturbed. This means that when the human eye views a distant object through the film, there is little distortion of the image seen at that distance.

[0019] Below, an example of a configuration suitable for measuring highly transparent samples such as films will be described.

[0020] B. First Embodiment (b1: Optical System) FIG. 1 is a schematic diagram showing an example of the configuration of an optical measurement system 1 according to a first embodiment.

[0021] Referring to FIG. 1 , the optical measurement system 1 includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M1, M2 and M3, focusing lenses L1 and L2, a mask A1, an image sensor D, and a processing device 100.

[0022] 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.

[0023] The beam splitter BS1 splits the light expanded by the beam expander BE into two beams. One beam split by the beam splitter BS1 corresponds to illumination light Q (first light) for illuminating the sample S, and the other beam corresponds to reference light R (second light). The beam splitter BS1 splits the light from the light source 10 into illumination light Q (first light) and reference light R (second light).

[0024] After being reflected by mirror M1, illumination light Q is collected by collecting lens L1 and enters beam splitter BS2. Illumination light Q is reflected by the half mirror of beam splitter BS2 and directed toward sample S. After transmitting through sample S, illumination light Q is reflected by fixed mirror RF1. Beam splitter BS2 is configured to reflect illumination light Q from beam splitter BS1 and direct it toward sample S.

[0025] The illumination light Q reflected by the fixed mirror RF1 passes through the sample S again and then re-enters the beam splitter BS2. The illumination light Q re-entering the beam splitter BS2 contains changes that occur due to passing through the sample S twice. The light obtained after the illumination light Q passes through the sample S twice is also referred to as "object light O" hereinafter.

[0026] The fixed mirror RF1 corresponds to a reflecting section for transmitting the illumination light Q (first light) that has passed through the sample S back through the sample S.

[0027] The reference light R is reflected sequentially by mirror M2 and mirror M3 and passes through mask A1. After passing through mask A1, the reference light R is focused by condenser lens L2 and enters beam splitter BS2. With respect to the reference light R, the focus point of condenser lens L2 corresponds to the position of the point light source. In other words, mask A1 and condenser lens L2 realize the point light source of the reference light R.

[0028] The object light O and the reference light R are superimposed by the half mirror of the beam splitter BS2. The beam splitter BS2 corresponds to a superimposing unit for superimposing the object light O (illumination light Q) and the reference light R reflected by the fixed mirror RF1.

[0029] The light beams (object light beam O and reference light beam R) superimposed by the beam splitter BS2 are incident on the image sensor D. The image sensor D generates a hologram I by modulating the object light beam O with the reference light beam R, which is a divergent light beam. ＯＲ is obtained.

[0030] Fig. 2 is a schematic diagram showing the optical configuration around the sample S shown in Fig. 1. The beam splitter BS2 may be configured in a cube shape to make it easier to form an optical path. In the optical configuration shown in Fig. 2, a condenser lens L1 is arranged corresponding to one surface of the beam splitter BS2. A point light source (condensing point FP1) of the reference light R is arranged corresponding to the surface opposite to the surface on which the condenser lens L1 is arranged.

[0031] An image sensor D is disposed on another surface of the beam splitter BS2. A sample S and a fixed mirror RF1 are disposed on the surface opposite to the surface on which the image sensor D is disposed.

[0032] In the optical system of the optical measurement system 1, the illumination light Q reflected by the beam splitter BS2 and the illumination light Q after passing through the sample S again propagate on the same optical axis.

[0033] The reference measurement in the optical measurement system 1 may be performed in the absence of the sample S. In the reference measurement, the illumination light Q also propagates along the same optical path as in Figures 1 and 2. That is, the illumination light Q reflected by the half mirror HM2 of the beam splitter BS2 is reflected by the fixed mirror RF1 and re-enters the beam splitter BS2.

[0034] Hereinafter, the state of measuring the sample S will also be referred to as sample measurement in comparison with the reference measurement.

[0035] The processing device 100 detects the hologram I captured by the image sensor D. ＯＲ Based on this, the light wave distribution in the sample S is calculated (reproduced).

[0036] (b2: Measurement Process) Next, a description will be given of the process of measuring the sample S in the optical measurement system 1 according to the embodiment 1. In the following description, the light receiving surface of the image sensor D is referred to as the "recording surface," and the intersection of the light receiving surface (recording surface) of the image sensor D and the central optical axis of the beam splitter BS2 is referred to as the "origin OP."

[0037] The optical axis direction is the z-axis, and the two axes perpendicular to the z-axis are the x-axis and y-axis. That is, 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. This also applies to other embodiments.

[0038] The light wave distributions 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).

[0039]

[0040] The object beam O and the reference beam R are mutually coherent beams of light having an angular frequency ω. For convenience of explanation, the coordinates (x, y) may be omitted as appropriate in the following equations.

[0041] The image sensor D records a hologram I in one shot. ＯＲ is calculated as the light intensity of the composite light of the light expressed by the formula (1) and the light expressed by the formula (2) by the following formula (3).

[0042]

[0043] By applying spatial frequency filtering to equation (3), the complex amplitude hologram J ＯＲ is calculated as in the following equation (4).

[0044]

[0045] Complex Amplitude Hologram J ＯＲ is the complex conjugate R of the light wave distribution of the reference light R ＊ (=R ０ exp(-iφ Ｒ )), the object beam hologram U is calculated as shown in the following equation (5).

[0046]

[0047] The object light hologram U shown in equation (5) corresponds to the light wave distribution of the object light O on the recording surface of the image sensor D minus the time term (−ωt). Therefore, by using a diffraction calculation that does not use approximations such as plane wave expansion, accurate image reconstruction without aberrations can be performed.

[0048] The light wave distribution of the reference light R can be obtained using, for example, the calibration process disclosed in International Publication No. 2023 / 079741 (Patent Document 2).

[0049] When 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. The size of the grating is preferably larger than the size of the image reproduced 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.

[0050] 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.

[0051] The complex amplitude distribution obtained by increasing the number of samples and superimposing them is used as a reconstruction object light hologram U Σ However, if there is no need to increase the number of samples or to superimpose, the object light hologram U can be used as the reconstruction object light hologram U as is. Σ Treat as.

[0052] Reconstruction object beam hologram U Σ is a hologram that contains information that can reconstruct the state of the sample surface. Σ By performing a diffraction calculation using a plane wave expansion for Σ The light wave distribution propagated by a distance d (on the sample surface that is a distance d away from the recording surface) is called the complex amplitude distribution U ｄ Let's say.

[0053] 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).

[0054]

[0055] When multiple media exist, the interface between the media is assumed to be parallel to the recording surface. The transmission coefficient when light is incident from medium m to medium m+1 is defined as T ｍ，ｍ＋１ (k ｘ , k ｙ ) where T Ｍ，Ｍ＋１ (k ｘ , k ｙ ) is always considered to be 1. For example, when propagating only through the air for a distance d, M = 1 and d １ = d, n ｍ =1.

[0056] The transmission coefficient when light enters medium m+1 is wave number k ｘ , k ｙ If it can be considered almost uniform without depending on T ｍ，ｍ＋１ The calculation may be simplified by setting ≡1.

[0057] 3 is a diagram for explaining a position of interest in optical measurement system 1 according to embodiment 1. Referring to FIG. 3, when viewed from the recording surface of image sensor D, sample S (second transmission), fixed mirror RF1, and sample S (first transmission) exist in this order.

[0058] By setting the sample S (second transmission) as the position of interest, the light wave distribution in the sample S can be reconstructed. In the optical measurement system 1 shown in FIGS. 1 and 2, the reconstruction object light hologram U Σ is expanded into a plane wave over the distance d from the image sensor D to the sample S (second transmission), the light wave distribution (complex amplitude distribution U ｄ ) is reproduced. The reproduced complex amplitude distribution U ｄBased on this, the presence or absence of defects or foreign matter in the sample S can be observed.

[0059] For example, the complex amplitude distribution U ｄ In this case, if a certain region exhibits a light wave distribution (phase distribution) different from that of other regions, it can be determined that a defect or foreign substance exists in that region.

[0060] More specifically, similarly to the above-mentioned formulas (3) to (5), the hologram I acquired by the image sensor D in the reference measurement is ＱＲ (x, y) to obtain the reference hologram U Ｑ The complex amplitude distribution U ｄ Similarly to the reconstruction of the reference hologram U Ｑ is expanded into a plane wave over the distance d from the image sensor D to the sample S (second transmission), the reference light wave distribution (complex amplitude distribution U Ｑｄ ) will be played.

[0061] A complex amplitude distribution U representing the wavefront of illumination light Q Ｑｄ The complex amplitude distribution U indicates the structure of the sample S based on ｄ The phase difference distribution (complex amplitude distribution U ｄ / Complex amplitude distribution U Ｑｄ ) indicates the amount of change due to the internal structure of the sample S. Regions showing characteristic changes in the phase difference distribution can be determined to be areas where defects, foreign matter, etc. are present.

[0062] In addition, when performing measurement processing using inline reference light rather than acquiring the light wave distribution of reference light R, it is sufficient to remove fixed mirror RF1 and adopt an optical system in which light focused by an objective lens or the like is introduced into beam splitter BS2 from the side of fixed mirror RF1.

[0063] (b3: Measurement Procedure) Fig. 4 is a flowchart showing the measurement procedure by optical measurement system 1 according to embodiment 1. It is assumed that a reference measurement has been performed in advance.

[0064] 4, a sample S is placed at a measurement position (step S2). A light source 10 generates coherent light, and a processing device 100 detects a hologram I to be recorded on an image sensor D. ＯＲ is acquired (step S4).

[0065] The processing device 100 processes the acquired hologram I ＯＲ and the light wave distribution of the reference beam R, the object beam hologram U is calculated (step S6). The processing device 100 applies necessary correction processing to the object beam hologram U to obtain the object beam hologram U for reconstruction. Σ (step S8). The processing device 100 calculates the reconstruction object beam hologram U Σ is propagated by a distance d by plane wave expansion, and the complex amplitude distribution U ｄ is calculated (step S10).

[0066] The processing device 100 calculates the complex amplitude distribution U ｄ (Step S12). The complex amplitude distribution U ｄ The output of the complex amplitude distribution U ｄ The phase distribution may be visualized (for example, by converting the phase difference into a color according to its magnitude).

[0067] By performing the above-described processing, defects, foreign matter, and the like contained in the sample S can be observed. In the optical measurement system 1 according to the first embodiment, a highly transparent sample S is the measurement target. The illumination light Q passes through the sample S twice, but if the sample S is highly transparent, it is thought that the wavefront of the illumination light Q will not be significantly disturbed by the first pass. As a result, sufficiently accurate measurements can be performed using the illumination light that has passed through the sample S once.

[0068] In the optical measurement system 1 according to the first embodiment, the illumination light Q, whose beam diameter has been narrowed by the condenser lens L1, passes through the sample S for the first time. This reduces the influence of the illumination light Q passing through the sample S on the wavefront (phase distribution) of the illumination light Q.

[0069] <C. Second Embodiment> In the first embodiment described above, an optical system in which illumination light Q is irradiated from a direction perpendicular to the surface of the sample S is exemplified, but illumination light Q may also be irradiated from an oblique direction onto the surface of the sample S.

[0070] 5 is a schematic diagram showing a configuration example of an optical measurement system 2 according to embodiment 2. Referring to FIG. 5, optical measurement system 2 includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M4, M5, M6, M7, and M8, condenser lenses L3 and L4, a mask A1, an image sensor D, and a processing device 100.

[0071] The light source 10, the beam expander BE, and the beam splitter BS1 are the same as those in the optical measurement system 1 shown in FIG.

[0072] One of the beams split by the beam splitter BS1 corresponds to illumination light Q (first light) for illuminating the sample S, and the other corresponds to reference light R (second light).

[0073] Illumination light Q is reflected by mirror M4, then focused by focusing lens L3, and passes through sample S. After passing through sample S, illumination light Q is reflected by fixed mirror RF2. Illumination light Q reflected by fixed mirror RF2 passes through sample S again, and then enters beam splitter BS2. Illumination light Q entering beam splitter BS2 is object light O that includes changes that occur by passing through sample S twice.

[0074] The fixed mirror RF2 corresponds to a reflecting section for transmitting the illumination light Q (first light) that has passed through the sample S back through the sample S.

[0075] The reference light R is reflected sequentially by mirrors M5, M6, and M7, and passes through the mask A1. The reference light R that passes through the aperture pattern SP1 of the mask A1 is focused by the condenser lens L4. The point of focus of the condenser lens L4 is located on the surface of mirror M8. The reference light R is reflected by mirror M8 and enters the beam splitter BS2. With respect to the reference light R, the point of focus of the condenser lens L4 (the surface of mirror M8) corresponds to the position of the point light source. In other words, the mask A1, the condenser lens L4, and the mirror M8 realize the point light source of the reference light R.

[0076] The object light O and the reference light R are superimposed by the half mirror of the beam splitter BS2. The beam splitter BS2 corresponds to a superimposing unit for superimposing the object light O (illumination light Q) and the reference light R reflected by the fixed mirror RF2.

[0077] The light beams (object light beam O and reference light beam R) superimposed by the beam splitter BS2 are incident on the image sensor D. The image sensor D generates a hologram I by modulating the object light beam O with the reference light beam R, which is a divergent light beam. ＯＲ is obtained.

[0078] Fig. 6 is a schematic diagram showing the optical configuration around the sample S shown in Fig. 5. The beam splitter BS2 may be configured in a cube shape to facilitate the formation of an optical path. In the optical configuration shown in Fig. 6, a focal point FP2 (mirror M8 shown in Fig. 5) is arranged corresponding to one surface of the beam splitter BS2.

[0079] An image sensor D is disposed on another surface of the beam splitter BS2. A sample S and a fixed mirror RF2 are disposed on the surface opposite to the surface on which the image sensor D is disposed.

[0080] The optical system of the optical measurement system 2 is configured so that the illumination light Q is irradiated from an oblique direction onto the surface of the sample S. The beam splitter BS2 is positioned in the propagation direction of the illumination light Q reflected by the fixed mirror RF2.

[0081] The reference measurement in the optical measurement system 2 may be performed in the absence of the sample S. In the reference measurement, the illumination light Q also propagates along the same optical path as in Figures 5 and 6. That is, the illumination light Q is reflected by the fixed mirror RF2 and enters the beam splitter BS2.

[0082] The processing device 100 detects a hologram (hologram I) acquired by the image sensor D. ＯＲ ) the light wave distribution in the sample S is calculated (reproduced).

[0083] In the optical measurement system 2 according to the second embodiment, the surface of the sample S is not parallel to the recording surface of the image sensor D. That is, the image of the sample S is incident on the recording surface of the image sensor D at an angle. Therefore, the complex amplitude distribution U ｄ You need to play it.

[0084] FIG. 7 is a diagram for illustrating the image reproduction process in optical measurement system 2 according to the second embodiment.

[0085] Referring to FIG. 7, first, the object beam hologram U Σ By expanding the complex amplitude distribution U ｄ is reproduced. The complex amplitude distribution U ｄ is the light wave distribution at the center of rotation of the sample S (position at a distance d).

[0086] Next, the complex amplitude distribution U ｄ That is, depending on the tilt angle, the complex amplitude distribution U ｄ The coordinate transformation is performed.

[0087] Complex amplitude distribution U ｄ The rotational transformation is the complex amplitude distribution U ｄ This includes extracting each component of the plane wave contained in the signal and rotating each component of the plane wave.

[0088] The reproduced complex amplitude distribution U ｄBy Fourier transforming (x, y), the spectrum F[U ｄ ](u, v) is calculated.

[0089] Spectrum F[U ｄ ](u, v) is the complex amplitude distribution U ｄ (x, y) represents a group of plane waves propagating in various directions. Here, the wave vector k of each plane wave is k = (k ｘ , k ｙ , k ｚ ) is the spectrum F[U ｄ ] and the wavelength λ of the light source according to equation (8).

[0090]

[0091] Thus, the spectrum F[U ｄ ] (u, v) to obtain the complex amplitude distribution U ｄ The wave vector k of each plane wave included in (x, y) is calculated.

[0092] Next, the spectrum F[U ｄ ] (u, v) according to the tilt angle. More specifically, a three-dimensional rotation matrix T Ｒ The wave vector k of the plane wave is transformed by the rotation of each plane wave. ｘ ', k ｙ ', k ｚ '), it is calculated according to equation (9).

[0093]

[0094] In this way, the three-dimensional rotation matrix T corresponding to the tilt angle to the wave vector k of each plane wave is Ｒ The three-dimensional rotation matrix T Ｒ can be determined, for example, according to the Rodriguez rotation formula.

[0095] By rotating the wave vector k, the spectrum F[U ｄ ] coordinates (u, v) are ｘ ' / 2π, k ｙ' / 2π). We can apply this coordinate transformation to all plane waves (spectrum F[U ｄ ] (u, v)) to obtain a new spectrum F[U Ｔ ](u, v) is calculated.

[0096] Thus, the spectrum F[U Ｔ ] (u, v) and the wave vector k′ after rotation of each plane wave, a spectrum F [U Ｔ ](u,v) is calculated.

[0097] Finally, the new spectrum F[U Ｔ ] is inverse Fourier transformed to obtain the complex amplitude distribution U Ｔ will be played.

[0098] In the optical measurement system 2 according to the second embodiment, the processing device 100 processes the hologram (hologram I) acquired by the image sensor D. ＯＲ ) based on which the object beam hologram U (or the reconstructed object beam hologram U Σ The processing device 100 calculates the object beam hologram U (or the reconstruction object beam hologram U Σ ) is calculated by diffraction calculation, the complex amplitude distribution U ｄ is calculated, and the complex amplitude distribution U ｄ This transforms the complex amplitude distribution U on the surface of the sample S. Ｔ will be played.

[0099] FIG. 8 is a flowchart showing a measurement procedure by optical measurement system 2 according to the second embodiment.

[0100] 8 differs from the flowchart shown in FIG. 4 in that it includes steps S14 to S20 instead of step S12. That is, the processing device 100 calculates the complex amplitude distribution U ｄ is Fourier transformed to obtain the spectrum F[U ｄ] (step S14). ｄ ] is multiplied by a three-dimensional rotation matrix to obtain the spectrum F[U Ｔ ] (step S16). The processing device 100 calculates the calculated spectrum F[U Ｔ ] is inverse Fourier transformed to obtain the complex amplitude distribution U Ｔ is calculated (step S18).

[0101] The processing device 100 calculates the complex amplitude distribution U Ｔ (Step S20). The complex amplitude distribution U Ｔ The output of the complex amplitude distribution U Ｔ The phase distribution may be visualized (for example, by converting the phase difference into a color according to its magnitude).

[0102] By the above-described processing, it is possible to observe defects, foreign matter, and the like contained in the sample S. Of the processing and measurement order for measuring the sample S in the optical measurement system 2 according to the second embodiment, detailed description of the content common to the first embodiment will not be repeated.

[0103] The optical measurement system 2 according to the second embodiment employs an optical system that irradiates the surface of the sample S with illumination light Q from an oblique direction, thereby reducing unnecessary reflected components and reducing noise caused by scattered light and unnecessary light.

[0104] D. Modifications of Embodiments 1 and 2 The optical measurement system 1 according to the first embodiment and the optical measurement system 2 according to the second embodiment described above employ an optical system in which the illumination light Q passes through the sample S twice. Therefore, if a relatively large defect or foreign matter is present in the area through which the illumination light Q passes through the sample S the first time, there is a possibility that part of the light passing through the sample S the second time will be dark. Therefore, the angle at which the illumination light Q is applied may be changed to reduce measurement noise.

[0105] FIG. 9 is a schematic diagram showing an example of the configuration of an optical measurement system 1A according to a modification of the first embodiment.

[0106] 9, optical measurement system 1A is different from optical measurement system 1 shown in FIG. 1 in that it includes a movable mirror MM and lenses L11 and L12 instead of mirror M1.

[0107] The movable mirror MM changes its angle with time with respect to the illumination light Q split by the beam splitter BS1. The illumination light Q reflected by the movable mirror MM passes through lenses L11 and L12 and then enters the beam splitter BS2. The lenses L11 and L12 form an imaging optical system such as a 4f optical system.

[0108] When the movable mirror MM and the condenser lens L1 are arranged optically close to each other, the lenses L11 and L12 may be omitted.

[0109] Rotation of the movable mirror MM changes the form of illumination of the illumination light Q. More specifically, the angle at which the illumination light Q is incident on the beam splitter BS2 changes over time. Hereinafter, the angle at which the illumination light Q is illuminated will also be referred to as the "illumination angle." By changing the illumination angle of the illumination light Q over time, the situation in which the illumination light Q passes through the sample S for the first time changes, so even if a relatively large defect or foreign matter is present in the sample S, it is possible to reduce the shadow of the defect or foreign matter cast by the illumination light Q.

[0110] The processing device 100 may average multiple results measured at different illumination angles.

[0111] By changing the illumination angle over time, it is possible to reduce measurement noise. Note that the optical measurement system 2 according to the second embodiment can also employ a modified configuration similar to that shown in FIG.

[0112] E. Third Embodiment Next, an example of an optical measurement system suitable for measuring a sample having a large area will be described. Below, an example of a configuration applicable to in-line measurement in a production line for a film or the like will be described.

[0113] Fig. 10 is a schematic diagram showing an example of the configuration of optical measurement system 3 according to the third embodiment. Fig. 11 is a perspective view showing an example of the configuration of optical measurement system 3 according to the third embodiment.

[0114] 10 and 11, the optical measurement system 3 includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M9 and M10, a focusing lens L5, a mask A1, an image sensor D, fixed mirrors RF3 and RF4, and a processing device 100.

[0115] The sample S is, for example, a film transported on a production line. Hereinafter, the direction in which the sample S is transported will also be referred to as the "transport direction," and the direction perpendicular to the transport direction on the surface of the sample S will also be referred to as the "width direction."

[0116] The light source 10, the beam expander BE, and the beam splitter BS1 are the same as those in the optical measurement system 1 shown in FIG.

[0117] One of the beams split by the beam splitter BS1 corresponds to illumination light Q (first light) for illuminating the sample S, and the other corresponds to reference light R (second light).

[0118] After being reflected by mirror M9, illumination light Q is incident on sample S, which is disposed between fixed mirror RF3 and fixed mirror RF4. After passing through sample S, illumination light Q is reflected by fixed mirror RF3. After being reflected by fixed mirror RF3, illumination light Q passes through sample S again and is then reflected by fixed mirror RF4. Illumination light Q is reflected multiple times between fixed mirror RF3 and fixed mirror RF4, passing through sample S multiple times. Finally, illumination light Q is incident on beam splitter BS2. Beam splitter BS2 corresponds to a superposition unit for superposing object light O (illumination light Q) and reference light R, which have been multiple-reflected by fixed mirror RF3 and fixed mirror RF4. Illumination light Q incident on beam splitter BS2 is object light O that includes changes that occur due to passing through sample S multiple times.

[0119] The fixed mirror RF3 and the fixed mirror RF4 correspond to a reflecting unit for transmitting the illumination light Q (first light) that has passed through the sample S back through the sample S. That is, the reflecting unit includes a pair of mirrors (fixed mirrors RF3, RF4) that are arranged opposite each other with the sample S interposed therebetween.

[0120] The reference light R is reflected by mirror M10 and passes through mask A1. After passing through mask A1, the reference light R is focused by condenser lens L5 and enters beam splitter BS2. With respect to the reference light R, the point of focus of condenser lens L5 corresponds to the position of the point light source. In other words, mask A1 and condenser lens L5 realize the point light source of the reference light R.

[0121] The optical system of the optical measurement system 3 is configured so that the illumination light Q is irradiated onto the surface of the sample S from an oblique direction.

[0122] The object light O and the reference light R are superimposed by the half mirror of the beam splitter BS2. The superimposed light (object light O and reference light R) by the beam splitter BS2 is incident on the image sensor D. The image sensor D displays a hologram I, which is the object light O modulated with the reference light R, which is a divergent light. ＯＲ is obtained.

[0123] FIG. 12 is a diagram for explaining the measurement process in optical measurement system 3 according to the third embodiment.

[0124] Referring to FIG. 12A, the illumination light Q adjusted to be P-polarized has a Brewster angle θ Ｂ The illumination light Q is incident on the sample S at a Brewster angle θ Ｂ By making the light incident on the sample S at this angle, noise due to reflected light from the sample S can be reduced.

[0125] 12(B) shows an example of the sample S and a mirror image of the sample S as viewed from the image sensor D, which are produced by the fixed mirror RF3 and the fixed mirror RF4. As shown in FIG. 12(B), the illumination light Q passes through the sample S at distances d1, d2, d3, d4, ... from the image sensor D. The distances d1, d2, d3, d4, ... correspond to the respective regions of the sample S in the width direction.

[0126] It should be noted that a point light source (focus point FP3) of the reference light R is arranged on an optical axis different from the optical axis along which the illumination light Q propagates.

[0127] The object beam hologram U for reproduction is generated by setting each of the distances d1, d2, d3, d4, . . . from the image sensor D as a target position. Σ By performing a diffraction calculation using a plane wave expansion for the above, the light wave distribution of each region present in the width direction of the sample S can be reconstructed. However, since the surface of the sample S or the surface of the mirror image of the sample S is not parallel to the recording surface of the image sensor D, the complex amplitude distribution U ｄ needs to be transformed into coordinates.

[0128] The processing device 100 detects a hologram (hologram I) acquired by the image sensor D. ＯＲ ), the light wave distribution in the sample S is calculated (reconstructed). More specifically, the processing device 100 sequentially changes the position of interest to generate a reconstruction object light hologram U Σ By repeating the diffraction calculation and coordinate transformation for , the light wave distribution of each region existing in the width direction of the sample S is reconstructed.

[0129] In this way, the processing device 100 processes the hologram (hologram I) acquired by the image sensor D. ＯＲ ) based on which the object beam hologram U (or the reconstructed object beam hologram U Σ The processing device 100 calculates the object beam hologram U (or the reconstruction object beam hologram U Σ ) is calculated by diffraction calculation, the complex amplitude distribution U ｄ The processing device 100 calculates a complex amplitude distribution U ｄ This transforms the complex amplitude distribution U on the surface of the sample S. Ｔ will be played.

[0130] In the reference measurement, an off-axis hologram is acquired in the absence of the sample S. The off-axis hologram acquired in the reference measurement contains information on the profile of the mirror shape.

[0131] Fig. 13 is a flowchart showing a measurement procedure by optical measurement system 3 according to embodiment 3. In the measurement procedure shown in Fig. 13, it is assumed that a reference measurement has been performed in advance.

[0132] 13, in a state where a sample S is present in the optical measurement system 3 (for example, the sample S is moving in the transport direction), the light source 10 generates coherent light (step S100). The processing device 100 processes the hologram I recorded on the image sensor D. ＯＲ is acquired (step S102).

[0133] The processing device 100 processes the acquired hologram I ＯＲ and the light wave distribution of the reference beam R, the object beam hologram U is calculated (step S104). The processing device 100 applies necessary correction processing to the object beam hologram U to obtain the object beam hologram U for reconstruction. Σ is calculated (step S106).

[0134] The processing device 100 selects one of a plurality of preset distances as a target position (step S108), and generates a reconstruction object beam hologram U Σ is propagated by a selected distance using a plane wave expansion to obtain the complex amplitude distribution U ｄ (Step S110). The processing device 100 calculates the calculated complex amplitude distribution U ｄ is Fourier transformed to obtain the spectrum F[U ｄ ] (step S112). ｄ ] is multiplied by a three-dimensional rotation matrix to obtain the spectrum F[U Ｔ ] (step S114). The processing device 100 calculates the calculated spectrum F[U Ｔ ] is subjected to an inverse Fourier transform to obtain the complex amplitude distribution U Ｔ is calculated (step S116).

[0135] The processing device 100 determines whether all of the plurality of preset distances have been selected as positions of interest (step S118). If there are any distances among the plurality of preset distances that have not been selected (NO in step S118), the processing from step S108 onwards is repeated.

[0136] If all of the predetermined distances have been selected as positions of interest (YES in step S118), the processing device 100 calculates the complex amplitude distribution U Ｔ (step S120), and the integrated complex amplitude distribution U Ｔ is output (step S122).

[0137] By the above-described processing, the presence or absence of defects or foreign matter can be observed in the width direction of the sample S. In addition, the complex amplitude distribution U Ｔ is calculated, it is also possible to identify areas in the sample S where defects or foreign matter exist.

[0138] <F. Limiting the Illumination Range> In order to improve measurement accuracy, the range of the sample S illuminated by the illumination light Q may be limited.

[0139] FIG. 14 is a schematic diagram showing an example of the configuration of an optical measurement system 1B according to another modification of the first embodiment.

[0140] 14, optical measurement system 1B is different from optical measurement system 1 shown in FIG. 1 in that it includes a mask A2 and condenser lenses L21 and L22 instead of condenser lens L1.

[0141] The illumination light Q is reflected by the mirror M1, then condensed by the condenser lens L21, and passes through the mask A2. The illumination light Q that has passed through the mask A2 is further condensed by the condenser lens L22 and directed to the sample S.

[0142] The mask A2 corresponds to a limiting unit that limits the spread of light obtained by illuminating the sample S with the illumination light Q to a predetermined range. As an example of the limiting unit, the mask A2 may have an aperture pattern SP2 formed on a shielding member that corresponds to the predetermined range. The illumination light Q passes through the area corresponding to the aperture pattern SP2.

[0143] Of the light illuminating the mask A2, only the light in the portion corresponding to the opening pattern SP2 passes through the mask A2. This makes it possible to limit the range in which the illumination light Q that has passed through the mask A2 illuminates the sample S. In this way, the mask A2 limits the range in which the illumination light Q illuminates the sample S to a predetermined range, thereby reducing unnecessary light and improving measurement accuracy.

[0144] The opening pattern SP2 of the mask A2 may be changed when it is necessary to set an optimum illumination range depending on the sample S. Alternatively, the position of the condenser lens L22 may be changed.

[0145] When the illumination range of the illumination light Q is limited, the measurement process disclosed in International Publication No. 2022 / 138716 (Patent Document 3) may be adopted.

[0146] The configuration of the restriction section shown in FIG. 14 can be similarly applied to other optical systems (FIGS. 5, 9, and 10).

[0147] <G. Processing device 100> (g1: Hardware configuration example) Fig. 15 is a schematic diagram showing an example of the hardware configuration of processing device 100 included in the optical measurement system according to the present embodiment. Referring to Fig. 15, 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.

[0148] The processor 102 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and reads one or more programs stored in the storage 110 into the main memory 104 and executes them. The main memory 104 is a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and functions as a working memory for the processor 102 to execute the programs.

[0149] The input unit 106 includes a keyboard, a mouse, etc., and receives operations from a user. The display unit 108 outputs results of program execution by the processor 102 to the user.

[0150] 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 holds an operating system (OS) 112, a measurement program 114, hologram data 116, and measurement results 118.

[0151] The operating system 112 provides an environment in which the processor 102 executes programs. The measurement program 114 is executed by the processor 102 to realize the optical measurement method according to the present embodiment. The hologram data 116 corresponds to the image data output from the image sensor D. The measurement results 118 include the measurement results obtained by executing the measurement program 114.

[0152] 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.

[0153] The media drive 124 reads necessary data from a recording medium 126 (e.g., an optical disk) that stores programs to be executed by the processor 102, and stores the necessary data in the storage 110. The measurement program 114 to be executed by the processing device 100 may be installed via the recording medium 126, or may be downloaded from a server device via the network interface 122.

[0154] The measurement program 114 may execute processing by calling necessary modules in a predetermined sequence at a predetermined timing among the program modules provided as part of the operating system 112. In such a case, a measurement program 114 that does not include such modules is also included in the technical scope of the present invention. The measurement program 114 may be provided as part of another program.

[0155] 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 (e.g., an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit)).

[0156] The hardware configuration example of the processing device 100 is similar to that of the other embodiments, and therefore detailed description thereof will not be repeated.

[0157] (g2: Functional Configuration Example) Fig. 16 is a schematic diagram showing an example of the functional configuration of processing device 100 included in the optical measurement system according to this embodiment. Typically, each functional element shown in Fig. 16 may be realized by processor 102 of processing device 100 executing measurement program 114. Note that the hardware that realizes the functional configuration shown in Fig. 16 is selected appropriately according to the times.

[0158] Referring to Figure 16, the processing device 100 includes, as its main functional elements, a reference light distribution acquisition module 150, a sample measurement module 152, an object light hologram calculation module 154, a hologram reproduction module 156, a tilt angle correction module 158, and an output module 160.

[0159] The reference light distribution acquisition module 150 acquires the light wave distribution of the reference light R. The sample measurement module 152 acquires the hologram I recorded on the image sensor D in sample measurement. ＯＲ Get.

[0160] The object beam hologram calculation module 154 calculates the hologram I ＯＲ and the light wave distribution of the reference light R, an object light hologram U is calculated.

[0161] The hologram reconstructing module 156 reconstructs the object beam hologram U from the object beam hologram U. Σ By calculating the complex amplitude distribution U at an arbitrary position of interest and performing a diffraction calculation using a plane wave expansion, ｄ Play.

[0162] The tilt angle correction module 158 calculates the complex amplitude distribution U ｄ The output module 160 performs a rotational transformation on the complex amplitude distribution U ｄ and / or the rotationally transformed complex amplitude distribution U Ｔ Output.

[0163] <H. Other Embodiments> The optical system described above is one example, and any optically equivalent modification can be made depending on the required specifications, space constraints, etc. For example, a single lens may be changed to a compound lens, or any reflective member may be used instead of a mirror.

[0164] In the above description, an implementation example in which the processing device 100 executes arithmetic processing related to the measurement of the sample S has been exemplified, but the present invention is not limited to this and any implementation form can be adopted. For example, a part or all of the processing performed by the processing device 100 may be performed using computing resources on the cloud.

[0165] <I. Summary> According to the optical measurement system according to the present embodiment, it is possible to measure the presence or absence of defects or foreign matter in a sample having a uniform structure such as a film.

[0166] 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.

[0167] 1, 1A, 1B, 2, 3 Optical measurement system, 10 Light source, 100 Processing device, 102 Processor, 104 Main memory, 106 Input unit, 108 Display unit, 110 Storage, 112 Operating system, 114 Measurement program, 116 Hologram data, 118 Measurement results, 120 Interface, 122 Network interface, 124 Media drive, 126 Recording medium, 150 Reference light distribution acquisition module, 152 Sample measurement module, 154 Object light hologram calculation module, 156 Hologram reproduction module, 158 Tilt angle correction module, 160 Output module, A1, A2 Mask, BE Beam expander, BS1, BS2 Beam splitter, D Image sensor, F Spectrum, FP1, FP2, FP3 Focus point, L1, L2, L3, L4, L5, L21, L22 Condenser lens, L11, L12 lenses, M1, M2, M3, M4, M5, M6, M7, M8, M9, M10 mirrors, O object light, Q illumination light, R reference light, RF1, RF2, RF3, RF4 fixed mirrors, S sample, SP1, SP2 aperture patterns.

Claims

1. An optical measurement system comprising: a light source; a beam splitter for splitting light from the light source into first light and second light; a reflecting unit for transmitting the first light that has passed through a sample back through the sample; a superimposing unit for superimposing the first light and the second light reflected by the reflecting unit; an image sensor onto which the light superimposed by the superimposing unit is incident; and a processing unit for calculating the light wave distribution in the sample based on a hologram acquired by the image sensor.

2. The optical measurement system according to claim 1, wherein the reflecting section is configured to reflect the first light from the beam splitter and guide it to the sample, and the first light reflected by the reflecting section and the first light after passing through the sample again propagate on the same optical axis.

3. The optical measurement system of claim 1, wherein the second light is configured to be irradiated from an oblique direction onto the surface of the sample, and the overlapping portion is positioned in the propagation direction of the first light reflected by the reflecting portion.

4. The optical measurement system of claim 3, wherein the processing unit calculates an object light hologram based on the hologram acquired by the image sensor, calculates a complex amplitude distribution, which is the light wave distribution at the center of rotation of the sample, by performing diffraction calculation on the object light hologram, and performs coordinate transformation on the complex amplitude distribution according to the angle between the recording surface of the image sensor and the surface of the sample.

5. The optical measurement system according to claim 1, wherein the reflecting section includes a pair of mirrors arranged opposite each other across the sample, and the second light is configured to be irradiated from an oblique direction onto the surface of the sample.

6. The optical measurement system of claim 5, wherein the processing unit calculates an object light hologram based on the hologram acquired by the image sensor, and calculates a complex amplitude distribution, which is a light wave distribution, for each distance from the recording surface of the image sensor to the sample and the mirror image of the sample generated by the reflecting unit by performing diffraction calculations on the object light hologram.

7. The optical measurement system according to claim 6, wherein the processing unit performs coordinate transformation of the complex amplitude distribution calculated for each distance in accordance with the angle formed between the recording surface of the image sensor and the surface of the sample.

8. An optical measurement method using an optical system including a beam splitter that splits light from a light source into a first light and a second light, comprising the steps of: using a reflecting unit to transmit the first light that has passed through a sample back through the sample; superimposing the first light and the second light reflected by the reflecting unit; using an image sensor to obtain a hologram from the superimposed light; and calculating the light wave distribution in the sample based on the obtained hologram.

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