Optical measuring system, optical measuring method, and measurement program

Abstract

This optical measuring system includes: a light source for generating coherent light; a first beam splitter for splitting the coherent light from the light source into first light and second light; an image sensor for recording a hologram generated by modulating, with the second light, light obtained by illuminating a sample with the first light; and a processing device. The second light is divergent light. The processing device executes: processing for calculating, on the basis of a first hologram, which is the hologram recorded by the image sensor, a second hologram showing an image at a position separated from the image sensor by a predetermined distance; and processing for calculating, on the basis of the second hologram, a third hologram showing an image on an inclined surface set with an inclination with respect to a recording surface of the image sensor. The processing for calculating the third hologram includes a coordinate transformation corresponding to the angle of the inclined surface.

Description

Optical measurement system, optical measurement method, and measurement program

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

[0002] Digital holography has been proposed and put into practical use as a method for measuring the shape of a sample with higher accuracy.

[0003] WO 2022 / 137560 (Patent Document 1) and WO 2022 / 138716 (Patent Document 2) disclose optical measurement systems that can suppress noise and achieve more accurate measurements.

[0004] WO 2020 / 045584 (Patent Document 3) discloses a configuration that uses a cube beam combiner and can easily achieve large numerical aperture recording and reflective illumination.

[0005] International Publication No. WO 2022 / 137560 International Publication No. WO 2022 / 138716 International Publication No. WO 2020 / 045584

[0006] The sample surface is not necessarily parallel to the recording surface of the image sensor, and there may be a need to measure an arbitrary surface within the sample.

[0007] One object of the present invention is to provide a novel mechanism capable of reproducing an image on an inclined plane set at an angle with respect to the recording surface of an image sensor.

[0008] According to one aspect of the present invention, an optical measurement system includes a light source that generates coherent light, a first beam splitter that splits the coherent light from the light source into first light and second light, an image sensor that records a hologram by modulating light obtained by illuminating a sample with the first light with the second light, and a processing device. The second light is divergent light. The processing device performs the following steps: calculating a second hologram that represents an image at a position a predetermined distance from the image sensor based on the first hologram recorded by the image sensor; and calculating a third hologram that represents an image on an inclined plane that is set at an angle with respect to the recording surface of the image sensor based on the second hologram. The optical measurement system provides an optical measurement system in which the processing for calculating the third hologram includes coordinate transformation according to the angle of the inclined plane.

[0009] The coordinate transformation according to the angle of the inclined surface may include a process for calculating a first spectrum by Fourier transforming the second hologram, a process for calculating the wave vector of each plane wave included in the second hologram from the first spectrum, a process for calculating the rotated wave vector of each plane wave by multiplying the wave vector of each plane wave by a three-dimensional rotation matrix corresponding to the angle of the inclined surface, and a process for calculating a second spectrum showing an image on the inclined surface based on the first spectrum and the rotated wave vector of each plane wave.

[0010] The processing device may perform processing to provide a user interface screen including an object for accepting settings for the inclined plane.

[0011] The user interface screen may further include an object for accepting a designation of a predetermined distance.

[0012] The processing device may further perform processing for outputting at least one of a shape profile and a refractive index profile of the inclined surface as a measurement result based on the third hologram.

[0013] The optical measurement system may further include a second beam splitter for modulating light obtained by illuminating the sample with the first light with the second light, a lens for focusing the second light, a lens holding barrel for holding the lens, and an inclination member for positioning the central axis of the lens holding barrel at a predetermined inclination relative to the central optical axis of the second beam splitter.

[0014] The optical measurement system may further include a second beam splitter for modulating light obtained by illuminating the sample with the first light with the second light, a first lens for focusing the first light, which is arranged on the opposite side of the sample from the second beam splitter, a second lens for focusing the first light, which is arranged on the same side of the sample as the second beam splitter, and an optical element for switching whether the first light is directed to the first lens or the second lens.

[0015] According to another aspect of the present invention, there is provided an optical measurement method using an optical measurement device. The optical measurement device includes a light source that generates coherent light, a first beam splitter that splits the coherent light from the light source into first light and second light, and an image sensor that records a hologram generated by illuminating a sample with the first light and modulating the light obtained with the second light. The second light is diverging light. The optical measurement method includes the steps of: calculating a second hologram representing an image at a position a predetermined distance from the image sensor based on the first hologram recorded by the image sensor; and calculating a third hologram representing an image on an inclined plane set at an angle with respect to the recording surface of the image sensor based on the second hologram. The step of calculating the third hologram includes coordinate transformation according to the angle of the inclined plane.

[0016] According to yet another aspect of the present invention, there is provided a measurement program executed on a computer connected to an optical measurement device. The optical measurement device includes a light source that generates coherent light, a first beam splitter that splits the coherent light from the light source into first light and second light, and an image sensor that records a hologram generated by illuminating a sample with the first light and modulating the light obtained with the second light. The second light is diverging light. The measurement program causes the computer to perform the following steps: calculating a second hologram that represents an image at a position a predetermined distance from the image sensor based on the first hologram that is a hologram recorded by the image sensor; and calculating a third hologram that represents an image on an inclined plane that is set at an angle with respect to the recording surface of the image sensor based on the second hologram. The step of calculating the third hologram includes coordinate transformation according to the angle of the inclined plane.

[0017] According to an embodiment of the present invention, it is possible to reproduce an image on an inclined plane that is set at an inclination relative to the recording surface of the image sensor.

[0018] FIG. 13 is a schematic diagram showing an example of the configuration of an optical measurement system according to the present embodiment. FIG. 14 is a schematic diagram showing an example of the configuration of an optical measurement device according to the present embodiment. FIG. 15 is a schematic diagram showing an example of the configuration of a processing device according to the present embodiment. FIG. 16 is a schematic diagram showing an example of a sample arranged at an angle with respect to the recording surface of an image sensor. FIG. 17 is a schematic diagram showing an example of a user interface screen provided by the processing device according to the present embodiment. FIG. 18 is a schematic diagram showing another example of the user interface screen provided by the processing device according to the present embodiment. FIG. 19 is a flowchart showing an example of the processing procedure for measuring a sample using the optical measurement system according to the present embodiment. FIG. 19 is a diagram showing an example of a measurement of a sample tilted by 45° in the X-axis direction. FIG. 19 is a diagram showing an example of a measurement of a sample tilted by 80° in the X-axis direction. FIG. 19 is a cross-sectional view showing an example of the configuration for irradiating off-axis reference light in the optical measurement device according to the present embodiment. FIG. 19 is a perspective view showing an example of the configuration for irradiating off-axis reference light in the optical measurement device according to the present embodiment. FIG. 19 is a cross-sectional view showing an example of the configuration of the tilting member shown in FIG. 12. FIG. 19 is a diagram showing an example of a transmission optical system configured in the optical measurement device according to the present embodiment. FIG. 19 is a diagram showing an example of a reflective optical system configured in the optical measurement device according to the present embodiment.

[0019] 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.

[0020] <A. Configuration Example of Optical Measurement System 1> First, a configuration example of the optical measurement system 1 according to the present embodiment will be described.

[0021] 1 is a schematic diagram showing an example of the configuration of an optical measurement system 1 according to the present embodiment. Referring to FIG. 1, the optical measurement system 1 includes an optical measurement device 10 and a processing device 100.

[0022] The sample S is placed at a predetermined position in the optical measurement device 10. An example of the configuration of the member on which the sample S is placed will be described later.

[0023] The optical measurement device 10 utilizes digital holography that uses diverging light as a reference light. The optical measurement device 10 employs an example of a lensless digital holography configuration in which no lens exists between the sample and the image sensor.

[0024] The processing device 100 executes an optical measurement method using the optical measurement device 10. The processing device 100 issues an instruction to start measurement to the optical measurement device 10 in response to a user operation or the like, processes measurement data from the optical measurement device 10, and outputs the measurement results of the sample.

[0025] <B. Configuration Example of Optical Measuring Device 10> Next, a configuration example of optical measuring device 10 included in optical measuring system 1 according to the present embodiment will be described.

[0026] FIG. 2 is a schematic diagram showing an example configuration of an optical measurement device 10 according to the present embodiment. Referring to FIG. 2, optical measurement device 10 includes an optical system for recording a hologram generated by modulating object light O, obtained by illuminating a sample S with illumination light Q, with reference light R, which is divergent light. When the hologram is generated, reference light R is irradiated off-axis. Therefore, reference light R can also be referred to as off-axis reference light. The recorded hologram can also be referred to as an off-axis hologram.

[0027] The optical measurement device 10 includes a light source 20, a beam expander BE, and a beam splitter BS1.

[0028] The light source 20 is configured with a laser or the like and generates coherent light. When measuring the surface shape of the sample S, a light source 20 that generates visible light may be used. Specifically, a light source 20 that generates light having components in at least a part of the wavelength range of 380 to 780 nm may be used. For example, a visible light source having a peak wavelength at 532 nm may be used.

[0029] When measuring the internal structure of the sample S, a light source 20 that emits near-infrared light may be used. Specifically, a light source 20 that emits light having components in at least a part of the wavelength range of 1000 to 1200 nm may be used. For example, a near-infrared light source having a peak wavelength at 1030 nm may be used.

[0030] The wavelength band of the coherent light generated by the light source 20 can be appropriately designed depending on the measurement content, etc.

[0031] The beam expander BE expands the cross-sectional diameter of the coherent light emitted by the light source 20 to a predetermined size. The beam splitter BS1 splits the coherent light expanded by the beam expander BE into two beams.

[0032] One of the beams split by the beam splitter BS1 is used as illumination light Q, and the other is used as reference light R. The beam splitter BS1 (corresponding to a first beam splitter) splits the coherent light from the light source 20 into illumination light Q (first light) and reference light R (second light).

[0033] One of the beams split by the beam splitter BS1 (illumination light Q) is guided to the measurement optical system 30. The other beam split by the beam splitter BS1 (reference light R) passes through a mirror M2 and a mask A2 and is guided to a lens L2. The lens L2 focuses the reference light R.

[0034] The optical measurement device 10 includes a half mirror HM2 onto which object light O obtained by illuminating a sample S with illumination light Q from a measurement optical system 30 and reference light R from a lens L1 are incident, and an image sensor D arranged in correspondence with the half mirror HM2.

[0035] The image sensor D records a hologram generated by the half mirror HM2. That is, the image sensor D records a hologram generated by modulating the object light O obtained by illuminating the sample S with the illumination light Q using the reference light R. The image sensor D can be, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary MOS) image sensor. The image sensor D has a light receiving sensitivity according to the wavelength components contained in the coherent light generated by the light source 20.

[0036] The measurement optical system 30 adjusts the illumination light Q so as to generate a hologram with less noise. More specifically, the measurement optical system 30 includes at least one of a mechanism for changing the illumination form of the illumination light Q and a mechanism for limiting the illumination range of the illumination light Q.

[0037] More specifically, the measurement optical system 30 includes a movable mirror MM, lenses L11, L12, and L2, and a mask A1.

[0038] The movable mirror MM corresponds to at least a part of a mechanism that changes the illumination form of the illumination light Q. The relative relationship between the reflecting surface of the movable mirror MM and the direction in which the illumination light Q from the beam splitter BS1 is incident is variable. In other words, the angle at which the illumination light Q is irradiated is changed by rotating the movable mirror MM. Hereinafter, the angle at which the illumination light Q is irradiated is also referred to as the "illumination angle."

[0039] The illumination light Q is reflected by the movable mirror MM and then passes through the lenses L11 and L12, which form an imaging optical system.

[0040] The illumination light Q passes through lenses L11 and L12 and then through a mask A1. The mask A1 limits the range of illumination of the sample S with the illumination light Q to a predetermined range. In other words, the mask A1 corresponds to at least a part of a mechanism for limiting the illumination range of the illumination light Q.

[0041] The mask A1 may include an aperture pattern SP1. The aperture pattern SP1 is a shielding member having a window formed therein corresponding to a predetermined range. After passing through the aperture pattern SP1, the illumination light Q is condensed by a lens L2 and then imaged onto the sample S. The illumination light Q passes only through the window of the aperture pattern SP1. Therefore, of the illumination light Q illuminating the mask A2, the light illuminating the sample S is limited to a range corresponding to the window of the aperture pattern SP1. In this way, by limiting the illumination range of the illumination light Q, unnecessary light can be reduced and measurement accuracy can be improved.

[0042] Object light O (i.e., light transmitted through the sample S) obtained by illuminating the sample S with illumination light Q passes through the half mirror HM2 of the beam splitter BS2 and is guided to the image sensor D.

[0043] The illumination range of the illumination light Q may vary depending on the thickness of the sample S. When the illumination range of the illumination light Q varies, the position or shape of the aperture pattern SP1 may be changed, or the position of the lens L2 may be changed.

[0044] When the movable mirror MM and the mask A2 are arranged optically close to each other, the lenses L11 and L12 may be omitted.

[0045] On the other hand, the reference light R from the beam splitter BS1 is reflected by the mirror M3 and then passes through the mask A2. The mask A2 may include an aperture pattern SP2. The aperture pattern SP2 is a shielding member in which a window portion corresponding to a predetermined range is formed. The image of the reference light R after passing through the aperture pattern SP2 is focused by the lens L3. The position where the reference light R is focused (focus point FP2) corresponds to the position of the point source of the off-axis reference light. In other words, it can be considered that the point source of the off-axis reference light exists at the focus point FP2. The off-axis reference light is reference light from a point source at the focus point FP2.

[0046] The reference light R passes through the lens L3, is reflected by the half mirror HM2 of the beam splitter BS2, and then forms an image on the image sensor D.

[0047] Beam splitter BS2 (corresponding to a second beam splitter) modulates object light O, obtained by illuminating sample S with illumination light Q, with reference light R. The size of aperture pattern SP2 is determined so that reference light R does not illuminate an area beyond the surface of beam splitter BS2 on the image sensor D side. By appropriately determining the size of aperture pattern SP2, it is possible to suppress the generation of noise due to unnecessary interference.

[0048] <C. Configuration Example of Processing Device 100> Next, a configuration example of processing device 100 included in optical measurement system 1 according to the present embodiment will be described.

[0049] 3 is a schematic diagram showing an example of the configuration of a processing device 100 according to the present embodiment. Referring to FIG. 3, processing device 100 is an example of a computer, and includes one or more processors 102, a main memory device 104, an input unit 106, a display unit 108, an auxiliary memory device 110, an interface 120, a network interface 122, and a media drive 124.

[0050] The one or more processors 102 include, for example, an arithmetic circuit that executes processing according to computer-readable instructions. The one or more processors 102 load one or more programs stored in the auxiliary storage device 110 into the main storage device 104 and execute them. The one or more processors 102 may be multi-core processors or multi-processors.

[0051] In this specification, the term "processor" includes at least a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), and a DRP (Dynamically Reconfigurable Processor).

[0052] The main memory device 104 is made up of volatile memory such as a dynamic random access memory (DRAM) or a static random access memory (SRAM), and functions as a working memory for one or more processors 102 to execute programs.

[0053] The auxiliary storage device 110 is, for example, a nonvolatile memory such as a hard disk or flash memory, and stores various programs and data. For example, the auxiliary storage device 110 stores an operating system 112 (OS), a measurement program 114, hologram data 116, and measurement results 118.

[0054] As used herein, the term “memory” encompasses at least primary memory 104 and secondary memory 110 .

[0055] The operating system 112 provides an environment in which one or more processors 102 execute programs. The measurement program 114 is executed by one or more processors 102 to realize the optical measurement method according to this embodiment, etc. The measurement program 114 is executed by the processing device 100, which is an example of a computer, to cause the processing device 100 to execute the optical measurement method using the optical measurement device 10.

[0056] 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.

[0057] The input unit 106 includes a keyboard, a mouse, etc., and receives operations from a user. The display unit 108 outputs to the user the results of program execution by one or more processors 102. The display unit 108 displays a user interface screen, as will be described later.

[0058] The interface 120 mediates data transmission between the processing device 100 and the optical measurement device 10 .

[0059] The network interface 122 mediates data transmission between the processing device 100 and an external server device.

[0060] The media drive 124 reads necessary data from a recording medium 126 (e.g., an optical disk) that stores programs and the like to be executed by one or more processors 102, and stores the data in the auxiliary storage device 110. The measurement program 114 and the like to be executed by the processing device 100 may be installed via the recording medium 126 or the like, or may be downloaded from a server device via the network interface 122 or the like.

[0061] The measurement program 114 may call and use necessary modules at a predetermined timing from among the program modules provided as part of the operating system 112. Therefore, even a measurement program 114 that does not include some of the modules necessary for the processing of the present invention is included in the technical scope of the present invention. The measurement program 114 may be provided as part of another program.

[0062] <D. Measurement Processing Example> Next, an example of measurement processing of sample S using optical measurement system 1 according to the present embodiment will be described.

[0063] 2 , the light-receiving surface of the image sensor D is referred to as the recording surface 40, and the intersection of the recording surface 40 and the central optical axis of the beam splitter BS2 is referred to as the origin 42. The central optical axis of the beam splitter BS2 is referred to as the Z axis, and two axes perpendicular to the Z axis are referred to as the X axis and the Y axis, respectively. The central optical axis of the beam splitter BS2 is perpendicular to the recording surface 40. The X axis and the Y axis are parallel to the recording surface 40.

[0064] In the optical measurement system 1, it is possible to reconstruct the light wave distribution on a plane (hereinafter also referred to as the "sample plane") that is a distance d away from the recording plane 40 in the Z-axis direction. A hologram containing information necessary for reconstructing the light wave distribution on the sample plane is called a reconstruction object beam hologram U. Σ It is called.

[0065] The processing device 100 detects the object beam hologram U for reproduction recorded by the image sensor D.Σ (x, y) (or object beam hologram U(x, y)) (corresponding to the first hologram) is used to generate a hologram U(x, y) that shows an image at a position a predetermined distance d away from the image sensor D. ｄ A process is performed to calculate (x, y) (corresponding to the second hologram).

[0066] More specifically, the reconstruction object beam hologram U Σ By performing diffraction calculations using plane wave expansion for (x, y), the light wave distribution at any sample surface can be reconstructed. For example, when measuring the surface shape of sample S, the sample surface (i.e., distance d) is set near the surface of sample S. When measuring the internal structure of sample S, the sample surface (i.e., distance d) is set at a position corresponding to the interior of sample S.

[0067] The object beam hologram U for reconstruction is obtained by plane wave expansion. Σ (x, y) is propagated over a distance d and the result is a hologram U ｄ (x, y). Hologram U ｄ (x, y) indicates the image (light wave distribution of the object light O) on the sample surface that is a distance d away from the recording surface 40 in the Z-axis direction.

[0068] Here, it is assumed that there are M media between the recording surface 40 and the sample surface. When there are multiple media, it is assumed that the boundary surfaces between the media are parallel to the recording surface 40.

[0069] The distance (thickness) of each medium in the Z-axis direction is d ｍ (m = 1, 2, ..., M), the refractive index is n ｍ (m=1, 2, ..., M), the hologram U ｄ can be generalized as in equation (1).

[0070]

[0071] In equation (1), F means Fourier transform, and F －１ means the inverse Fourier transform. ｘ , k ｙ is the wave number. ｍ，ｍ＋１ (k ｘ , kｙ ) is the transmission coefficient when light enters the (m+1)th medium from the mth medium. Ｍ，Ｍ＋１ (k ｘ , k ｙ ) = 1. Also, the transmission coefficient when light enters the (m+1)th medium from the mth medium is the wave number k ｘ , k ｙ If it can be considered almost uniform without depending on T ｍ，ｍ＋１ (k ｘ , k ｙ )≡1 to simplify the calculation.

[0072] For example, the reconstruction object beam hologram U Σ When (x, y) is propagated only through the air by a distance d, the number of media M = 1, and the distance d １ = d, refractive index n ｍ =1.

[0073] If the object beam hologram U(x, y) (the hologram recorded by the image sensor D) generated by modulating the object beam O with the reference beam R satisfies the sampling theorem, the object beam hologram U can be directly converted into a reconstruction object beam hologram U Σ It can be (x, y).

[0074] If the object beam hologram U contains frequency components that do not satisfy the sampling theorem, the number of pixels in the image output by the image sensor D may be increased by interpolation. Alternatively, the pixel pitch of the image sensor D may be subdivided by applying the division and superposition process disclosed in International Publication No. 2020 / 045584 (Patent Document 3).

[0075] The optical measurement system 1 according to this embodiment can also measure a sample S that is placed at an angle with respect to the recording surface 40 of the image sensor D.

[0076] 4 is a schematic diagram showing an example of a sample S that is placed at an angle relative to the recording surface 40 of the image sensor D. As shown in FIG. 4, the optical measurement system 1 can measure the sample S even when the surface of the sample S is not in relation to the recording surface 40.

[0077] The process of reproducing an image on a surface that is not parallel to the recording surface 40 of the image sensor D (hereinafter referred to as an "inclined surface" in contrast to the above-mentioned "sample surface") will be described.

[0078] The processing device 100 processes the hologram U ｄ Based on (x, y) (corresponding to the second hologram), a hologram U is generated, which shows an image on an inclined plane set with an inclination relative to the recording surface 40 of the image sensor D. Ｔ (x, y) (corresponding to the third hologram). As will be described later, the hologram U Ｔ The process of calculating (x, y) includes coordinate transformation according to the angle of the tilted surface.

[0079] The calculation of the image on the tilted plane is ｄ Calculation of hologram U ｄ and rotating each component of the plane wave by the angle of the inclined surface.

[0080] As described above, by the diffraction calculation according to the formula (1), the hologram U at the distance d from the origin 42 of the recording surface 40 to the sample surface along the Z axis is obtained. ｄ (x, y) is calculated. Then, the hologram U ｄ Using (x, y), a coordinate transformation is performed according to the angle of the inclined surface, as will be described in detail below.

[0081] First, the calculated hologram U ｄ (x, y) is Fourier transformed to obtain the spectrum F[U ｄ ](u,v) (corresponding to the first spectrum) is calculated.

[0082] Spectrum F[U ｄ ](u, v) is the hologram 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 (2).

[0083]

[0084] Thus, the spectrum F[U ｄ ] (u, v) to the hologram U ｄ The wave vector k of each plane wave contained in (x, y) is calculated.

[0085] Next, the spectrum F[U ｄ ] (u, v) is rotated according to the angle of the inclined surface. 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 (3).

[0086]

[0087] In this way, the three-dimensional rotation matrix T corresponding to the angle of the tilted surface 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.

[0088] By rotating the wave vector k, the spectrum F[U ｄ ] coordinates (u, v) are ｘ ' / 2π, k ｙ ' / 2π). This coordinate transformation is applied to all plane waves (spectrum F[U ｄ ] (u, v)) to obtain a new spectrum F[U Ｔ ](u,v) is calculated.

[0089] 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) (corresponding to the second spectrum) is then calculated.

[0090] Finally, the calculated new spectrum F[U Ｔ ] is inverse Fourier transformed to obtain the image U Ｔ will be played.

[0091] The three-dimensional rotation matrix T of the equation (3) Ｒ may be determined in response to user input via a user interface as described below.

[0092] <E. Example of User Interface Screen> Next, an example of a user interface screen for accepting a designation of image reproduction will be described.

[0093] FIG. 5 is a schematic diagram showing an example of a user interface screen provided by processing device 100 according to the present embodiment.

[0094] 5A , user interface screen 150 includes operation object 151 that accepts designation of distance d from recording surface 40 to the sample surface (inclined surface), and operation objects 152 and 153 that accept designation of the angle of inclination (inclined surface) relative to the sample surface. Operation object 152 accepts designation of an azimuth angle. Operation object 153 accepts designation of an inclination angle.

[0095] Referring to FIG. 5B, the azimuth angle θ determined in response to the user's operation on the operation object 152 is １ indicates the direction in which the sample surface 50 is tilted. The tilt angle θ is determined in response to a user operation on the operation object 153. ２ indicates the inclination of the sample surface 50 relative to a plane parallel to the recording surface 40.

[0096] Here, the unit vector (N ｘ , N ｙ , N ｚ ) is introduced. ｘ , N ｙ , N ｚ ) may be the same as the coordinate system that defines the wave vector k, or may be based on any coordinate system defined on the user interface screen.

[0097] three-dimensional rotation matrix TＲ is a unit vector (N ｘ , N ｙ , N ｚ ) and the azimuth angle θ shown in FIG. １ and tilt angle θ ２ Using this, it is expressed as in equation (4).

[0098]

[0099] In addition, the unit vector (N ｘ , N ｙ , N ｚ ) is made to coincide with the coordinate system that defines the wave vector k, the rotation axis will exist on the XY plane. Therefore, for rotation according to the specified azimuth angle and tilt angle, N ｚ = 0. As a result, equation (4) can be simplified to equation (5).

[0100]

[0101] FIG. 6 is a schematic diagram showing another example of a user interface screen provided by processing device 100 according to the present embodiment.

[0102] Referring to Figure 6 (A), the user interface screen 160 includes an operation object 161 that accepts specification of the distance d from the recording surface 40 to the sample surface (inclined surface), an operation object 162 that accepts specification of the inclination angle of the sample surface in the X-axis direction (rotation angle around the Y-axis), and an operation object 163 that accepts specification of the inclination angle of the sample surface in the Y-axis direction (rotation angle around the X-axis).

[0103] Referring to FIG. 6B, the tilt angle θ determined in response to the user's operation on the operation object 162 is ｘ indicates the angle by which the sample surface 50 is tilted in the X-axis direction. The tilt angle θ is determined in response to a user operation on the operation object 163. ｙ indicates the angle at which the sample surface 50 is tilted in the Y-axis direction. A vector r indicating the tilt direction is expressed by equation (6).

[0104]

[0105] Using the vector r, the azimuth angle θ１ and tilt angle θ ２ is calculated according to equation (7). In equation (7), arg is a function for obtaining the argument of a complex number.

[0106]

[0107] The azimuth angle θ calculated according to equation (7) １ and tilt angle θ ２ By substituting into the above equation (4) or (5), the three-dimensional rotation matrix T Ｒ is calculated.

[0108] 7 is a schematic diagram showing yet another example of a user interface screen provided by processing device 100 according to the present embodiment. Referring to Fig. 7, user interface screen 170 includes operation object 171 for accepting designation of distance d from recording surface 40 to the sample surface (inclined surface), and two-dimensional map 172.

[0109] In the two-dimensional map 172, a point 173 on the two-dimensional coordinate system indicates the direction (azimuth angle) and angle (tilt angle) of tilting the sample surface 50. The origin of the two-dimensional map 172 means that both the azimuth angle and the tilt angle are zero. The coordinate orientation of the point 173 on the two-dimensional map 172 is determined by the azimuth angle 174 (azimuth angle θ １ ), and the distance 175 from the origin is the inclination angle θ ２ Shows.

[0110] Although a display area for displaying the two-dimensional map 172 is required, the user can specify the azimuth angle and tilt angle more intuitively. Note that the three-dimensional rotation matrix T Ｒ is the same as the above-mentioned equation (4).

[0111] Furthermore, the angles (azimuth and tilt angles) of the sample surface (inclined surface) may be automatically detected, in which case the optimal values ​​of the azimuth and tilt angles (and distance) are determined based on, for example, the degree of focus of the reconstructed image.

[0112] As shown in Figures 5 to 7, the processing device 100 provides user interface screens 150, 160, and 170 including objects for accepting inclined surface settings (operation objects 152 and 153 in Figure 5, operation objects 162 and 163 in Figure 6, and two-dimensional map 172 in Figure 7).

[0113] As shown in Figures 5 to 7, user interface screens 150, 160, and 170 may include objects for accepting the specification of a predetermined distance d (operation object 151 in Figure 5, operation object 161 in Figure 6, and operation object 171 in Figure 7).

[0114] <F. Measurement Processing Procedure> Next, an example of a measurement processing procedure for the sample S using the optical measurement system 1 according to the present embodiment will be described.

[0115] 8 is a flowchart showing an example of a processing procedure for measuring the sample S using the optical measurement system 1 according to the present embodiment. The processing shown in FIG. 8 may be realized by one or more processors of the processing device 100 executing the measurement program 114.

[0116] The processing device 100 generates an illumination light hologram Q by generating a hologram by generating coherent light from a light source 20 without a sample S being placed therein and recording the hologram with an image sensor D. Σ (x, y) is stored in advance.

[0117] 8, processing device 100 acquires an object beam hologram U(x, y) by recording a hologram generated by generating coherent light from light source 20 with image sensor D while sample S is placed at a predetermined position (step S2). For simplicity of explanation, the acquired object beam hologram U(x, y) is referred to as a reconstruction object beam hologram U(x, y). Σ It is assumed that the coordinates are treated as (x, y).

[0118] The processing device 100 acquires the distance d to the sample surface designated by the user (step S4). For example, the user designates the distance d on the user interface screens shown in the above-mentioned FIGS.

[0119] The processing device 100 performs plane wave expansion to generate a reconstruction object beam hologram U Σ (x, y) is propagated by a distance d to produce a hologram U ｄ (x, y) is calculated (step S6). Plane wave expansion is performed according to the above equation (1).

[0120] Similarly, the processing device 100 calculates the illumination light hologram Q by plane wave expansion. Σ (x, y) is propagated by a distance d to produce a hologram Q ｄ (x, y) is calculated (step S8). Plane wave expansion is performed according to the above equation (1).

[0121] The processing device 100 acquires the inclined surface designation specified by the user (step S10), and calculates a three-dimensional rotation matrix T Ｒ (Step S12) For example, the user specifies the tilt plane (azimuth angle, tilt angle, etc.) on the user interface screens shown in the above-mentioned FIGS.

[0122] The processing device 100 calculates the hologram U ｄ (x, y) is Fourier transformed to obtain the spectrum F[U ｄ ](u, v) (step S14). ｄ ] (step S16). The processing device 100 calculates the wave vector k of each plane wave from the three-dimensional rotation matrix T Ｒ The wave number vector k of each plane wave is rotated according to the inclined plane using the above formula (step S18). ｄ ] (u, v) and the wave vector k′ of each plane wave, a spectrum F [U Ｔ ](u, v) (step S20). Ｔ ](u, v) is inverse Fourier transformed to obtain a hologram U Ｔ (x, y) is calculated (step S22).

[0123] Similarly, the processing device 100 calculates the hologram Q calculated in step S8. ｄ (x, y) is Fourier transformed to obtain the spectrum F[Q ｄ ](u, v) (step S24). The processing device 100 calculates the spectrum F[Q ｄ ] (step S26). The processing device 100 calculates the wave vector k of each plane wave from the three-dimensional rotation matrix T Ｒ The wave number vector k of each plane wave is rotated according to the inclined plane using the above formula (step S28). ｄ ] (u, v) and the wave vector k′ of each plane wave, a spectrum F[Q Ｔ ](u, v) (step S30). The processing device 100 calculates the spectrum F[Q Ｔ ] (u, v) is inverse Fourier transformed to obtain a hologram Q Ｔ (x, y) is calculated (step S32).

[0124] Next, the processing device 100 processes the hologram U Ｔ (x, y) is hologram Q Ｔ Divide by (x, y) to get the amplitude and phase distribution on the sample surface. Ｔ (x, y) is calculated (step S34).

[0125] The processing device 100 Ｔ Based on (x, y), the measurement result of the sample S is output (step S36).

[0126] The measurement results are, for example, amplitude and phase distribution UP Ｔ The measurement result may be a shape profile of the sample surface (or inclined surface) obtained by aggregating thicknesses at each coordinate calculated from the amount of movement change Δθ(x, y) of (x, y). The measurement result may be a refractive index profile of the sample surface (or inclined surface). The measurement result may be an intensity distribution or phase distribution of the sample surface (or inclined surface).

[0127] In this way, the processing device 100 processes the hologram UＴ Based on (x, y), at least one of a shape profile and a refractive index profile on the sample surface (inclined surface) may be output as a measurement result.

[0128] The processing device 100 may repeat the processes of steps S2 to S36 at a predetermined interval, or may execute the processes of steps S2 to S36 again when the distance d or the inclined surface designated by the user is changed. Furthermore, when the inclined surface designated by the user is changed, the processing device 100 may execute the processes of steps S10 to S36 again.

[0129] When the illumination form of the illumination light Q is changed using the movable mirror MM, the illumination form of the illumination light Q is changed to generate a plurality of object light holograms U. ｉ (x, y) may be acquired. In this case, multiple object beam holograms U ｉ The amplitude and phase distribution UP calculated for each of (x, y) Ｔｉ By accumulating (x, y) as complex numbers, the composite amplitude and phase distribution is increased. ＴＳＡ (x, y) is calculated. ＴＳＡ Based on (x, y), the measurement result of the sample S is output.

[0130] The above-described steps S14 to S22 and steps S24 to S32 may be performed in any order. Ｔ (x, y) and the hologram Q Ｔ The processes for calculating (x, y) may be performed one after the other, or may be performed in parallel.

[0131] <G. Measurement Example> Next, a measurement example of sample S placed at an angle with respect to recording surface 40 using optical measurement system 1 according to this embodiment will be shown.

[0132] First, image reconstruction when the tilt angle is relatively small will be illustrated. Fig. 9 shows a measurement example of a sample S tilted by 45° in the X-axis direction. Fig. 9(A) shows an example of an image reconstructed without the above-mentioned coordinate transformation, and Fig. 9(B) shows an example of an image reconstructed after the above-mentioned coordinate transformation.

[0133] Referring to Figure 9(A), in the image reproduced without coordinate transformation, good focus is obtained near the center in the left-right direction, but it can be seen that the image becomes less focused as you go to both sides in the left-right direction.

[0134] In contrast to this, referring to FIG. 9B, in the image reconstructed after the coordinate transformation, a good focus state is achieved over the entire surface.

[0135] In this way, by performing the coordinate transformation according to this embodiment, it is possible to reproduce with higher accuracy an image on a sample surface (inclined surface) that is not parallel to the recording surface 40 .

[0136] Next, image reconstruction when the tilt angle is large will be illustrated. Fig. 10 shows a measurement example of a sample S tilted by 80° in the X-axis direction. Fig. 10(A) shows an example of an image reconstructed without the above-mentioned coordinate transformation, and Fig. 10(B) shows an example of an image reconstructed after the above-mentioned coordinate transformation.

[0137] Referring to FIG. 10(A), it can be seen that in the image reproduced without coordinate transformation, a good focus state is obtained in a small area near the center in the left-right direction, but the other areas are out of focus.

[0138] In contrast to this, referring to FIG. 9B, in the image reconstructed after the coordinate transformation, a good focus state is achieved over the entire surface.

[0139] In this way, by performing the coordinate transformation according to this embodiment, it is possible to reproduce with higher accuracy an image on a sample surface (inclined surface) that is not parallel to the recording surface 40 .

[0140] <H. Off-Axis Reference Light> Next, an example of a configuration for irradiating off-axis reference light in the optical measurement device 10 will be described.

[0141] 11 is a cross-sectional view showing an example of a configuration for irradiating off-axis reference light in optical measurement device 10 according to this embodiment. Fig. 11 shows a cross-sectional structure centered around beam splitter BS2.

[0142] 11 , the optical measurement device 10 includes a base 70 and a beam splitter BS2 disposed in an opening formed in the base 70. A sample S is disposed at a position above the beam splitter BS2 on the paper surface. Object light obtained by illuminating the sample S with illumination light Q from above the paper surface is incident on the beam splitter BS2. A lens holding barrel 74 and an image sensor D are positioned at predetermined positions by a holding member 72.

[0143] The lens holding barrel 74 holds the lens L3. The lens L3 is disposed inside the lens holding barrel 74. The reference light R from the left side of the drawing is collected by the lens L3 disposed inside the lens holding barrel 74 and then enters the beam splitter BS2.

[0144] The lens holding barrel 74 is arranged to have a non-zero angle with respect to the axial direction of the beam splitter BS2, so that the reference beam R is irradiated off-axis.

[0145] 12 is a perspective view showing an example of a configuration for irradiating off-axis reference light in optical measurement device 10 according to this embodiment, as seen from the image sensor D side.

[0146] 12, a recording unit 78, which integrates a beam splitter BS2 and an image sensor D, is disposed on the side of the base 70 opposite to the side on which the sample S is disposed. A lens holding barrel 74 is disposed on the side of the recording unit 78 via an inclined member 76.

[0147] The tilting member 76 is disposed between the side surface of the image sensor D and the end surface of the lens holding cylinder 74. The surface of the tilting member 76 that comes into contact with the side surface of the image sensor D and the surface of the tilting member 76 that comes into contact with the end surface of the lens holding cylinder 74 are not parallel to each other, but are tilted at a predetermined angle.

[0148] Fig. 13 is a cross-sectional view showing an example of the configuration of the inclined member 76 shown in Fig. 12. Note that the cross-sectional view shown in Fig. 13 is drawn to make the structural features easier to understand, and does not necessarily represent the actual size.

[0149] 11 and 13 , the tilting member 76 includes a surface 760 that contacts the image sensor D and a surface 762 that contacts the end face of the lens holding barrel 74. The surface 762 is formed in a tilted state with respect to the surface 760. The tilt of the surface 762 with respect to the surface 760 is determined according to the angle at which the reference light R is irradiated off-axis. The tilting member 76 is formed with an opening 764 through which the reference light R passes.

[0150] In this way, the tilting member 76 positions the central axis Ax2 of the lens holding barrel 74 at a predetermined tilt with respect to the central optical axis Ax1 of the beam splitter BS2. By connecting the image sensor D and the lens holding barrel 74 via the tilting member 76, off-axis reference light can be easily achieved with high precision.

[0151] <I. Configuration in which the transmissive optical system and the reflective optical system can be switched freely> Next, an example of a configuration in which the transmissive optical system and the reflective optical system can be switched freely will be described.

[0152] Depending on the material of the sample S, it may be preferable to perform measurement using a reflective optical system rather than the transmissive optical system shown in Fig. 2. In a transmissive optical system, the object light O is generated when the illumination light Q passes through the sample S. In a reflective optical system, the object light O is generated when the illumination light Q is reflected by the sample S.

[0153] The optical measurement device 10 of the optical measurement system 1 according to the present embodiment may employ a configuration that allows for free switching between a transmissive optical system and a reflective optical system. An example of a configuration that allows for switching between a transmissive optical system and a reflective optical system will be described below.

[0154] Fig. 14 is a diagram showing an example of a transmission type optical system configured by optical measurement device 10 according to the present embodiment. Fig. 15 is a diagram showing an example of a reflection type optical system configured by optical measurement device 10 according to the present embodiment.

[0155] 14 and 15, the optical measurement device 10 includes a detachable mirror M10. When the mirror M10 is placed in a predetermined position, a transmission optical system as shown in Fig. 14 is formed. When the mirror M10 is removed, a reflection optical system as shown in Fig. 15 is formed.

[0156] In the transmission optical system shown in Figure 14, illumination light Q from beam splitter BS1 is reflected by movable mirror MM and mirror M10, respectively, and passes through lenses L11 and L12. After passing through lenses L11 and L12 and mask A1, illumination light Q is reflected by mirror M12. After being reflected by mirror M12, illumination light Q is collected by lens L2 and forms an image on sample S. Illumination light Q passes through sample S to become object light O, which is then imaged on image sensor D.

[0157] The lens L2 is disposed on the opposite side of the sample S from the beam splitter BS2. The lens L2 collects the illumination light Q, and therefore the object light O generated when the illumination light Q passes through the sample S is incident on the beam splitter BS2.

[0158] In the reflective optical system shown in Figure 15, illumination light Q from beam splitter BS1 is reflected by movable mirror MM and, since there is no movable mirror MM, is incident on lenses L11' and L12'. After being reflected by lenses L11' and L12' and mirror M14, illumination light Q passes through mask A1'. After passing through mask A1', illumination light Q is collected by lens L2' and incident on beam splitter BS2. Illumination light Q is reflected by beam splitter BS2 toward sample S and forms an image on sample S. Illumination light Q becomes object light O when reflected by sample S, and object light O forms an image on image sensor D.

[0159] Lens L2' is disposed on the same side as beam splitter BS2 with respect to sample S. Lens L2' focuses illumination light Q, and object light O resulting from the reflection of illumination light Q on sample S is incident on beam splitter BS2.

[0160] The mirror M10 corresponds to an optical member for switching whether to guide the illumination light Q to the lens L2 or the lens L2′. Note that, instead of the mirror M10, for example, an optical element that can switch between reflection and transmission in accordance with an external signal may be used.

[0161] 14 and 15, reference light R from beam splitter BS1 is reflected by mirror M3 and then passes through mask A2. After passing through mask A2, reference light R is collected by lens L3 and enters beam splitter BS2. The optical system that causes reference light R to enter beam splitter BS2 may employ lens holding barrel 74 and tilting member 76 shown in FIGS. 11 to 13.

[0162] <J. Modifications> 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.

[0163] In the above-described configuration example, the processing device 100 executes the arithmetic processing related to the measurement of the sample S, but, for example, some or all of the arithmetic processing related to the measurement may be executed using computing resources on the cloud.

[0164] K. Summary The optical measurement system according to this embodiment can reconstruct an image of a sample surface that is any distance away from the recording surface of the image sensor, and can also reconstruct an image of a sample surface that has any tilt with respect to the recording surface of the image sensor. In this way, regardless of the shape of the sample or how the sample is positioned, it is possible to reconstruct an image of the target surface.

[0165] 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.

[0166] 1 Optical measurement system, 10 Optical measurement device, 20 Light source, 30 Measurement optical system, 40 Recording surface, 42 Origin, 50 Sample surface, 70 Base, 72 Holding member, 74 Lens holding barrel, 76 Inclination member, 78 Recording unit, 100 Processing device, 102 Processor, 104 Main memory device, 106 Input unit, 108 Display unit, 110 Auxiliary memory device, 112 Operating system, 114 Measurement program, 116 Hologram data, 118 Measurement results, 120 Interface, 122 Network interface, 124 Media drive, 126 Recording medium, 150, 160, 170 User interface screen, 151, 152, 153, 161, 162, 163, 171 Operation object, 172 Two-dimensional map, 173 Point, 174 Azimuth angle, 175 Distance, 760, 762 Surface, 764 Aperture, A1, A2 Mask, BE Beam expander, BS1, BS2 Beam splitter, D Image sensor, FP2 Focus point, L1, L2, L3, L11, L12 Lens, M3, M10, M12, M14 Mirror, MM Movable mirror, O Object light, R Reference light, S Sample, SP1, SP2 Aperture pattern.

Claims

1. A light source that generates coherent light, A first beam splitter that splits the coherent light from the light source into a first beam and a second beam, An image sensor for recording a hologram generated by illuminating a sample with the first light and modulating the resulting light with the second light, Equipped with a processing device, The second light is divergent light, The aforementioned processing apparatus is A process for calculating a second hologram, which shows an image at a predetermined distance from the image sensor, based on a first hologram, which is a hologram recorded by the image sensor; Based on the second hologram, a process is performed to calculate a third hologram showing an image on an inclined surface set with an inclination relative to the recording surface of the image sensor. The process for calculating the third hologram includes an optical measurement system that includes a coordinate transformation according to the angle of the inclined surface.

2. The coordinate transformation corresponding to the angle of the inclined surface is, A process for calculating the first spectrum by performing a Fourier transform on the second hologram, A process for calculating the wave vector of each plane wave contained in the second hologram from the first spectrum, A process for calculating the rotated wave vector of each plane wave by multiplying the wave vector of each plane wave by a three-dimensional rotation matrix corresponding to the angle of the inclined surface, The optical measurement system according to claim 1, further comprising a process for calculating a second spectrum showing an image on the inclined surface based on the first spectrum and the rotated wave vectors of each plane wave.

3. The optical measurement system according to claim 1, wherein the processing apparatus performs processing to provide a user interface screen that includes an object for receiving the setting of the inclined surface.

4. The optical measurement system according to claim 3, wherein the user interface screen further includes an object for receiving the specification of a predetermined distance.

5. The optical measurement system according to any one of claims 1 to 4, wherein the processing apparatus further performs processing to output at least one of the shape profile and refractive index profile of the inclined surface as a measurement result based on the third hologram.

6. A second beam splitter for modulating the light obtained by illuminating the sample with the first light with the second light, The second lens for focusing light, A lens holder cylinder for holding the aforementioned lens, The optical measurement system according to any one of claims 1 to 4, further comprising an inclined member for positioning the central axis of the lens holding cylinder at a predetermined inclination with respect to the central optical axis of the second beam splitter.

7. A second beam splitter for modulating the light obtained by illuminating the sample with the first light with the second light, With respect to the sample, a first lens for focusing the first light is positioned on the opposite side from the second beam splitter, With respect to the aforementioned sample, a second lens for focusing the first light is positioned on the same side as the second beam splitter, The optical measuring system according to any one of claims 1 to 4, further comprising an optical member for switching which of the first light is directed to the first lens and the second lens.

8. An optical measurement method using an optical measuring device, The optical measuring device is, A light source that generates coherent light, A first beam splitter that splits the coherent light from the light source into a first beam and a second beam, The system includes an image sensor for recording a hologram generated by illuminating a sample with the first light and modulating the resulting light with the second light, The second light is divergent light, The aforementioned optical measurement method is A step of calculating a second hologram showing an image at a predetermined distance from the image sensor, based on a first hologram which is a hologram recorded by the image sensor, The process includes the step of calculating a third hologram based on the second hologram, which shows an image on an inclined surface set to be tilted with respect to the recording surface of the image sensor, The third step of calculating the hologram is an optical measurement method that includes a coordinate transformation according to the angle of the inclined surface.

9. A measurement program executed on a computer connected to an optical measuring device, The optical measuring device is, A light source that generates coherent light, A first beam splitter that splits the coherent light from the light source into a first beam and a second beam, The system includes an image sensor for recording a hologram generated by illuminating a sample with the first light and modulating the resulting light with the second light, The second light is divergent light, The measurement program is programmed to the computer, A step of calculating a second hologram showing an image at a predetermined distance from the image sensor, based on a first hologram which is a hologram recorded by the image sensor, The process involves performing the following steps: calculating a third hologram based on the second hologram, which shows an image on an inclined surface set to be tilted with respect to the recording surface of the image sensor; The third step of calculating the hologram is a measurement program that includes a coordinate transformation according to the angle of the inclined surface.

Images