Optical measurement system and optical measurement method

Abstract

One objective of the present invention is to provide a technique for measuring a sample by irradiating it with near-infrared light. Another objective of the present invention is to provide a technique for improving the signal-to-noise ratio of the measurement. [Solution] The optical measurement system 1 includes a first light source that generates near-infrared light, a silicon-based image sensor D, and an optical system including beam splitters BS1 and BS2 that split the light from the first light source into a first light and a second light. The optical system is configured to record a first hologram obtained by illuminating a sample S with the first light and modulating the resulting light with the second light, which is divergent light, using the image sensor.

Description

[Technical Field]

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

[0002] Technologies for inspecting defects that may occur in samples such as silicon wafers have existed for some time.

[0003] For example, Japanese Patent Publication No. 2011-033449 (Patent Document 1) discloses a technique for inspecting defects inside and on the front and back surfaces of a wafer using a transmission image obtained by irradiating the wafer with infrared light. Furthermore, apparatus for realizing wafer internal defect inspection using infrared light is known (see Non-Patent Document 1, etc.).

[0004] Furthermore, digital holography has been proposed and put into practical use as a method for measuring the shape of a sample with higher precision. Digital holography is a technique that measures the shape of a sample by observing interference fringes that are produced when a reference light and object light produced by illuminating the sample are superimposed, thereby obtaining the wavefront shape of the object light.

[0005] For example, International Publication No. 2012 / 005315 (Patent Document 2) discloses a configuration that can measure the shape of a sample by employing a reflective optical system. Also, International Publication No. 2020 / 045584 (Patent Document 3) discloses a configuration that uses a cube-type beam coupler and can easily realize recording of large numerical apertures and reflective illumination. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-033449 [Patent Document 2] International Publication No. 2012 / 005315 [Patent Document 3] International Publication No. 2020 / 045584 [Non-patent literature]

[0007] [Patent Document 1] TORAY, Wafer internal defect inspection system “INSPECTRA(R) IR” Series [online], [Accessed September 6, 2021], Internet<URL:https: / / www.toray-eng.com / tasmit / products / measuring / mea_020.html> [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The technology disclosed in the aforementioned Japanese Patent Publication No. 2011-033449 (Patent Document 1) employs a measurement method based on the difference in infrared light transmittance, making it difficult to detect defects on the order of nanometers. Similarly, the wafer internal defect inspection method (Non-Patent Document 1) also employs a measurement method based on the difference in infrared light transmittance, making it difficult to detect defects on the order of nanometers.

[0009] Furthermore, in known digital holography (see Patent Documents 2 and 3, etc.), it is difficult to increase the signal-to-noise ratio (SNR) when attempting to reconstruct an image by illuminating a sample with infrared light.

[0010] One objective of the present invention is to provide a technique for measuring a sample by irradiating it with near-infrared light. Another objective of the present invention is to provide a technique for improving the signal-to-noise ratio of the measurement. [Means for solving the problem]

[0011] An optical measurement system according to one aspect of the present invention includes a first light source that generates near-infrared light, a silicon-based image sensor, and an optical system including a beam splitter that splits the light from the first light source into a first beam and a second beam. The optical system is configured to record a first hologram obtained by illuminating a sample with the first beam and modulating the resulting light with a second beam, which is divergent light, using the image sensor.

[0012] The optical system may generate a first hologram from the transmitted light obtained by illuminating the sample with a first light. In the optical system, instead of the sample, a second hologram may be recorded from the transmitted light obtained by illuminating a substrate included in the sample that is not the object of measurement with the first light.

[0013] The optical system may generate a first hologram from the reflected light obtained by illuminating the sample with a first light. In the optical system, instead of the sample, a second hologram may be recorded from the reflected light obtained by illuminating a reference plane with the first light.

[0014] The optical measurement system may further include a second light source that generates visible light and a processing unit. The optical system may be interchangeable between a first configuration that generates a first hologram from transmitted light obtained by illuminating the sample with the first light and a second configuration that generates a first hologram from reflected light obtained by illuminating the sample with the first light. The processing unit may measure the internal structure of the sample based on the first hologram recorded when the first light source and the first configuration of the optical system are combined, and measure the surface shape of the sample based on the first hologram recorded when the second light source and the second configuration of the optical system are combined.

[0015] The optical system may be an off-axis holographic optical system. The optical system may include a limiting unit that restricts the size of the range over which the sample is illuminated by the first light, so that the component corresponding to the first light and components other than the component corresponding to the first light do not overlap in the spatial frequency domain of the hologram recorded by the image sensor.

[0016] In another aspect of the present invention, an optical measurement method is provided that uses an optical system including a beam splitter that splits light from a first light source that generates near-infrared light into a first light and a second light. The optical measurement method includes the steps of illuminating a sample with the first light and recording a first hologram obtained by modulating the resulting light with a second light, which is divergent light, using a silicon-based image sensor, and recording a second hologram obtained by modulating the first light with the second light using the image sensor in the absence of a sample.

[0017] An optical measurement system according to yet another aspect of the present invention includes a light source, an optical system including a beam splitter that splits light from the light source into a first beam and a second beam, an image sensor that records a hologram generated by the optical system, and a processing device that calculates the amplitude phase distribution on the sample surface, which is the surface of interest of the sample, based on a first hologram obtained by modulating the light obtained by illuminating the sample with the first beam with the second beam, and a second hologram obtained by modulating the first beam with the second beam when the sample is absent. The optical system includes a mechanism for changing the form of illumination by the first beam. The processing device is configured to calculate a composite amplitude phase distribution by integrating the amplitude phase distributions calculated for each form of illumination by the first beam while they are still complex numbers.

[0018] The mechanism may also be configured to change the angle at which the first light illuminates. The mechanism may also be configured to change the azimuth angle while keeping the incidence angle of the first light constant.

[0019] The optical system may include a limiting unit that restricts the size of the range over which the sample is illuminated by the first light, so that the component corresponding to the first light and components other than the component corresponding to the first light do not overlap in the spatial frequency domain of the hologram recorded by the image sensor.

[0020] The processing device may also provide a user interface screen that accepts a setting for the number of forms to be illuminated by the first light.

[0021] In yet another aspect of the present invention, an optical measurement method is provided that uses an optical system including a beam splitter that splits light from a light source into a first light and a second light. The optical measurement method includes the steps of: recording a first hologram obtained by illuminating a sample with the first light and modulating the resulting light with the second light using an image sensor; recording a second hologram obtained by modulating the first light with the second light using an image sensor when no sample is present; changing the mode of illumination with the first light; calculating the amplitude phase distribution on the sample surface, which is the surface of interest of the sample, based on the first hologram and the second hologram for each mode of illumination with the first light; and calculating a composite amplitude phase distribution by integrating the amplitude phase distributions calculated for each mode of illumination with the first light while they are still complex numbers. [Effects of the Invention]

[0022] According to one embodiment of the present invention, a technique can be realized in which a sample can be measured by illuminating it with near-infrared light. According to another embodiment of the present invention, a technique can be realized in which the signal-to-noise ratio of the measurement can be increased. [Brief explanation of the drawing]

[0023] [Figure 1] This is a schematic diagram showing an example configuration of an optical measurement system according to Embodiment 1. [Figure 2] This is a schematic diagram showing a detailed configuration example of the optical system for measurement in an optical measurement system according to Embodiment 1. [Figure 3] This figure illustrates the effects obtained by changing the form in which the illumination light is lit in an optical measurement system according to this embodiment. [Figure 4] This diagram illustrates the conditions under which object light and off-axis reference light are incident on the recording surface of an image sensor. [Figure 5] This figure illustrates the relationship between the sample and the off-axis reference light R in an optical measurement system according to this embodiment. [Figure 6]This figure illustrates the relationship between spatial frequency bands and off-axis holograms in an optical measurement system according to this embodiment. [Figure 7] This flowchart shows the processing procedure for a surface shape measurement method using an optical measurement system according to Embodiment 1. [Figure 8] This flowchart shows the processing procedure for measuring the internal structure using an optical measurement system according to Embodiment 1. [Figure 9] This is a schematic diagram showing an example configuration of an optical measurement system according to Embodiment 2. [Figure 10] This flowchart shows the processing procedure for a surface shape measurement method using an optical measurement system according to Embodiment 2. [Figure 11] This is a flowchart showing the processing procedure for measuring the internal structure using an optical measurement system according to Embodiment 2. [Figure 12] This is a schematic diagram showing an example of the hardware configuration of a processing unit included in an optical measurement system according to this embodiment. [Figure 13] This is a schematic diagram showing an example of the functional configuration of a processing unit included in an optical measurement system according to this embodiment. [Figure 14] This is a schematic diagram showing an example of a user interface screen provided in an optical measurement system according to this embodiment. [Figure 15] This figure shows an example of surface shape measurement using an optical measurement system according to this embodiment. [Figure 16] This figure shows an example of measuring the internal structure using an optical measurement system according to this embodiment. [Figure 17] This is a schematic diagram showing an example of a composite configuration of an optical measurement system according to this embodiment. [Modes for carrying out the invention]

[0024] Embodiments of the present invention will be described in detail with reference to the drawings. Note that identical or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

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

[0026] In the following description, an optical measurement system mainly employing an off-axis holography optical system will be described. In Embodiment 1, a transmission optical system will be exemplified, and in Embodiment 2, a reflection optical system will be exemplified. Note that "the present embodiment" may include Embodiment 1 and Embodiment 2.

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

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

[0029] The optical system shown in FIG. 1(A) corresponds to an optical system for recording an off-axis hologram I obtained by modulating an in-line reference light L serving as a recording reference with an off-axis reference light R. LR corresponding to.

[0030] The optical system shown in Figure 1(B) modulates the object light O obtained by illuminating a sample S with illumination light Q into an off-axis hologram I using an off-axis reference light R, which is divergent light. OR This corresponds to an optical system for recording the off-axis hologram I obtained by illuminating a sample S with illumination light Q. More specifically, the optical system shown in Figure 1(B) records the off-axis hologram I from the transmitted light. OR A first hologram (object light hologram) is generated. An illumination light profile is also acquired using the optical system shown in Figure 1(B). In this case, sample S is not placed.

[0031] The processing device 100 is an off-axis hologram I LR and Off-axis Hologram I OR Based on this, the surface shape and internal structure of sample S are measured.

[0032] Referring to Figure 1(A), the optical measurement system 1 is an off-axis hologram I LR The optical system for recording includes a light source 10, a beam expander BE, beam splitters BS1 and BS2, mirrors M1 and M2, an objective lens MO, a pinhole P, a lens L1, a mask A1, and an image sensor D.

[0033] The light source 10 is composed of a laser or the like and generates coherent light. In the optical measurement system according to this embodiment, the wavelength band of the light generated by the light source 10 may be varied depending on the measurement content (measurement of surface shape or measurement of internal structure).

[0034] More specifically, when measuring the surface shape of sample S, a light source 10 that emits visible light may be used. Specifically, a light source 10 that emits light having components in at least a portion of the wavelength range of 380 to 780 nm may be used. For example, a visible light source with a peak wavelength of 532 nm may be used.

[0035] On the other hand, when measuring the internal structure of sample S, a light source 10 that emits near-infrared light may be used. Specifically, a light source 10 that emits light having components in at least a portion of the wavelength range of 1000 to 1200 nm may be used. For example, a near-infrared light source with a peak wavelength of 1030 nm may be used.

[0036] In the optical measurement system according to this embodiment, the type of light source 10 can be arbitrarily changed.

[0037] Image sensor D records holograms generated by the optical system shown in Figures 1(A) and 1(B). Image sensor D is a general CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary MOS) image sensor. These image sensors are semiconductor integrated circuits consisting of electronic circuits formed on a silicon substrate. In other words, in the optical measurement system according to this embodiment, a silicon-based image sensor is used. Silicon-based image sensors have light-receiving sensitivity mainly in the visible light band, but also have light-receiving sensitivity in the near-infrared in addition to visible light.

[0038] The beam expander BE expands the cross-sectional diameter of the light from the light source 10 to a predetermined size. The beam splitter BS1 splits the light expanded by the beam expander BE into two. One of the beams split by the beam splitter BS1 corresponds to the in-line reference light L (first light), and the other corresponds to the off-axis reference light R (second light).

[0039] The inline reference light L is reflected by mirror M2 and guided to beam splitter BS2. Furthermore, the inline reference light L passes through the half mirror HM2 of beam splitter BS2 and is guided to image sensor D. An objective lens MO and a pinhole P are positioned between mirror M2 and beam splitter BS2. The inline reference light L is focused by objective lens MO and its cross-sectional diameter is narrowed by pinhole P. The pinhole P corresponds to the position of the point source of the inline reference light L. The objective lens MO and pinhole P realize the point source of the inline reference light L.

[0040] Meanwhile, the off-axis reference light R is reflected by mirror M1 and guided to beam splitter BS2. Furthermore, the off-axis reference light R is reflected by the half-mirror HM2 of beam splitter BS2 and guided to image sensor D. A mask A1 and lens L1 are positioned between mirror M1 and beam splitter BS2. After passing through mask A1, the off-axis reference light R is focused by lens L1, and the focal point FP1, where the light is focused, corresponds to the position of the point source of the off-axis reference light R.

[0041] Mask A1 has an aperture pattern SP1 in the region through which the off-axis reference light R passes. The image corresponding to the aperture pattern SP1 of mask A1 is formed on the image sensor D. The size of the aperture pattern SP1 of mask A1 is determined so that the off-axis reference light R that has passed through mask A1 does not illuminate the area beyond the surface of the beam splitter BS2 on the image sensor D side. By determining the size of the aperture pattern SP1 of mask A1 in this way, the generation of noise due to unwanted interference is suppressed.

[0042] Additionally, the off-axis reference light R is adjusted to allow the in-line reference light L to record as a hologram.

[0043] The in-line reference light L and the off-axis reference light R are superimposed by the beam splitter BS2, which is positioned in front of the image sensor D, via the optical path described above. In other words, the image sensor D modulates the in-line reference light L with the divergent off-axis reference light R to produce an off-axis hologram I. LR This is obtained.

[0044] The beam splitter BS2 is preferably configured in a cube shape to facilitate placement in front of the image sensor D. The point source of the inline reference light L and the point source of the off-axis reference light R are optically positioned in close proximity by the beam splitter BS2.

[0045] Referring to Figure 1(B), the optical measurement system 1 is an off-axis hologram I OR Instead of the mirror M2, objective lens MO, and pinhole P, the optical system for recording includes a measuring optical system 30.

[0046] The measuring optical system 30 includes a mechanism for changing the form in which the illumination light is emitted, and a mechanism for limiting the range of illumination. More specifically, the measuring optical system 30 includes a movable mirror MM, lenses L2, L31, L32, and a mask A2.

[0047] The sample S to be measured is placed between the measurement optical system 30 and the beam splitter BS2.

[0048] Furthermore, if the distance required by the measuring optical system 30 is longer than the distance required by the objective lens MO and pinhole P of the optical system shown in Figure 1(A), the beam splitter BS1 is positioned closer to the light source 10.

[0049] The light output from one side of the beam splitter BS1 is used as illumination light Q (first light) to illuminate the sample S.

[0050] The optical measurement system according to this embodiment has a mechanism for changing the form of illumination by the illumination light Q. As an example of such a mechanism, Figure 1(B) shows a movable mirror MM. More specifically, the movable mirror MM rotates to change the form of illumination of the illumination light Q. In this case, the change in the form of illumination of the illumination light Q means a change in the angle at which the illumination light Q is illuminating. Hereinafter, the angle at which the illumination light Q is illuminating will also be referred to as the "illumination angle".

[0051] On the other hand, the off-axis reference light R (second light) output from the other side of the beam splitter BS1 is guided to the image sensor D via the same optical path as in Figure 1(A).

[0052] The object light O obtained by illuminating the sample S with illumination light Q (i.e., the light transmitted through the sample S) is guided to the image sensor D through the half mirror HM2 of the beam splitter BS2. Between the movable mirror MM and the beam splitter BS2, lenses L3, mask A2, and lens L2 are arranged in that order.

[0053] The illumination light Q is focused by lens L3 and passes through mask A2. After passing through mask A2, the illumination light Q is further focused by lens L2 and imaged onto sample S.

[0054] Mask A2 corresponds to a limiting section that restricts the area in which the sample S is illuminated by illumination light Q to a predetermined range. As an example of a limiting section, a mask A2 may be used in which an aperture pattern SP2 corresponding to a predetermined range is formed on the shielding member. The illumination light Q passes through the region corresponding to the aperture pattern SP2.

[0055] The image of the aperture pattern SP2 on mask A2 passes through lens L2 and is imaged onto sample S. In other words, of the light illuminating mask A2, only the portion of the light corresponding to the aperture pattern SP2 passes through mask A2. This limits the range in which the illumination light Q that has passed through mask A2 illuminates sample S. By limiting the illumination range of illumination light Q, unwanted light can be reduced and measurement accuracy can be improved.

[0056] In the optical measurement system 1, the illumination range may vary depending on the thickness of the sample S. In such cases, the aperture pattern SP2 of the mask A2 may be changed, or the position of the lens L2 for imaging the illumination light Q onto the sample S may be changed as needed.

[0057] Furthermore, the configuration for illuminating mask A2 with illumination light Q is not limited to the configuration shown in Figure 1(B), but any configuration can be adopted.

[0058] Figure 2 is a schematic diagram showing a detailed configuration example of the measurement optical system 30 in the optical measurement system 1 according to Embodiment 1.

[0059] Referring to Figure 2(A), the illumination light Q passes through the movable mirror MM, lens L31, lens L32, mask A2, and lens L2 in that order, and is imaged onto the sample S. Lenses L31 and L32 constitute an imaging optical system 20, such as a 4f optical system.

[0060] Illumination light Q, incident on the movable mirror MM, is reflected in a direction corresponding to the angle (orientation) of the movable mirror MM and incident on the imaging optical system 20. The illumination light Q then propagates in the direction from which it was reflected by the movable mirror MM, passes through the aperture pattern SP2 of the mask A2, and is then imaged onto the sample S in the same shape as the aperture pattern SP2.

[0061] Figure 2(B) shows an example of an optical system when the illumination light Q illuminating the sample S is parallel light. More specifically, in the optical system shown in Figure 2(B), lenses L21 and L22 are placed in place of lens L2 in the optical system shown in Figure 2(A). Both lenses L21 and L22 are focusing lenses, and when combined, the illumination light Q that has passed through mask A2 illuminates the sample S while remaining parallel light.

[0062] The optical systems positioned before and after mask A2 are not limited to those shown in Figures 2(A) and 2(B). Any configuration is acceptable for the optical system positioned before mask A2, as long as it projects reflected light from the movable mirror MM so as to cover the aperture pattern SP2 of mask A2. Similarly, any configuration is acceptable for the optical system positioned after mask A2, as long as it can image the aperture pattern SP2 of mask A2 onto the sample S. The number and type of lenses can be arbitrarily designed as long as these requirements are met. Furthermore, the system can be implemented using any optical device, not just lenses.

[0063] Furthermore, if the movable mirror MM and mask A2 are positioned optically in close proximity, lenses L31 and L32 may be omitted.

[0064] (b2: Measurement process) Next, the basic process for measuring the shape of sample S in the optical measurement system 1 according to Embodiment 1 will be described. In the following description, the light-receiving surface of the image sensor D will be referred to as the "recording surface," and the intersection point of the recording surface and the central optical axis of the beam splitter BS2 will be referred to as the "origin." The optical axis direction will be defined as the z-axis, and the two axes perpendicular to the z-axis will be defined as the x-axis and y-axis, respectively. That is, the optical axis will be perpendicular to the recording surface of the image sensor D, and the x-axis and y-axis will be parallel to the recording surface of the image sensor D. The same applies to other embodiments.

[0065] The distribution of object light O, off-axis reference light R, and in-line reference light L on the recording surface of the image sensor D can be expressed by the following general equations (1) to (3).

[0066]

number

[0067] The in-line reference light L, object light O, and off-axis reference light R are lights with mutually coherent angular frequencies ω. The off-axis hologram I is recorded in the optical system shown in Figure 1(A).LR is calculated as in the following equation (4) as the light intensity of the combined light of the light expressed by equation (3) and the light expressed by equation (1). Also, the off-axis hologram I recorded in the optical system shown in Fig. 1(B) OR is calculated as in the following equation (5) as the light intensity of the combined light of the light expressed by equation (2) and the light expressed by equation (3).

[0068]

Equation

[0069] Note that the off-axis hologram I LR is invariant regardless of the state of the object light O, so it may be recorded only once.

[0070] In equations (4) and (5), the first term on the right side corresponds to the light intensity component of the object light O or the in-line reference light L, the second term on the right side corresponds to the light intensity component of the off-axis reference light R, the third term on the right side corresponds to the direct image component generated by modulating the object light O with the off-axis reference light R, and the fourth term on the right side corresponds to the conjugate image component.

[0071] When a band-pass filter is applied to equations (4) and (5) to extract the direct image component of the third term, the complex amplitude off-axis hologram J recording the in-line reference light L LR and the complex amplitude off-axis hologram J recording the object light O OR are calculated as in the following equations (6) and (7), respectively.

[0072]

Equation

[0073] Here, when equation (7) is divided by equation (6), the component of the off-axis reference light R is removed, and the complex amplitude in-line hologram J with respect to the in-line reference light L OL is calculated as in the following equation (8).

[0074]

number

[0075] The component of the inline reference light L is the complex amplitude inline hologram J shown in equation (8). OL This can be removed by multiplying it by an inline reference light L. The method for calculating the inline reference light L can be the method described in International Publication No. 2020 / 045584 (Patent Document 3). Through the above process, an object light hologram U as shown in equation (9) below is obtained.

[0076]

number

[0077] Here, if the object light hologram U contains frequency components that do not satisfy the sampling theorem, the following correction process is applied to generate a hologram that contains information capable of reproducing the state of the surface of interest (hereinafter also referred to as the "sample surface") located at a predetermined distance from the recording surface. Σ In addition, if the sampling theorem is satisfied, the object light hologram U is used as is for reproducing the object light hologram U. Σ Let's assume that.

[0078] As an example of correction processing, the number of sampling points constituting the image output from the image sensor D may be increased by interpolation before removing the inline reference light L. Alternatively, the pixel pitch of the image sensor D may be subdivided by applying the segmentation and superposition process disclosed in International Publication No. 2020 / 045584 (Patent Document 3). By using the segmentation and superposition process, the amount of computation can be reduced.

[0079] Regenerative object optical hologram U Σ By performing diffraction calculations using plane wave unfolding, the light wave distribution on any sample surface can be reconstructed. Reconstruction object light hologram U ΣThe hologram obtained by propagating it over a distance d (on the sample surface at a distance d from the recording surface) is U d Let's assume that.

[0080] The distance between the light-receiving surface (recording surface) of the image sensor D and the desired playback distance d is the distance of the M media (m=1,2,...,M) contained within that distance. m , refractive index n m Therefore, Hologram U d This can be generalized as shown in equation (10) below, where k in the equation zm It is calculated according to equation (11).

[0081]

number

[0082] Furthermore, if multiple media are present, the interface between the media is assumed to be parallel to the recording surface. Also, the transmission coefficient when incident from medium m to medium m+1 is given by T. m,m+1 (k x ,k y ) is expressed as. However, T M,M+1 (k x ,k y For ), we always consider it to be 1.

[0083] For example, if the signal propagates only through the air over a distance d, then M=1 and d1=d,n m = 1.

[0084] Furthermore, the transmission coefficient when incident from medium m to medium m+1 is wavenumber k x ,k y If it can be considered nearly uniform without depending on, then T m,m+1 You can simplify the calculation by assuming ≡1.

[0085] (b3: Mechanism for changing the form in which the illumination light is emitted) Next, we will explain the mechanism for changing the form in which the illumination light Q is lit.

[0086] The optical measurement system according to this embodiment changes the form in which the illumination light Q illuminates multiple off-axis holograms I OR The recording (which will be either an object light hologram or an illumination light hologram depending on the presence or absence of sample S) is performed. As a form of illumination for the illumination light Q, for example, an illumination angle may be used.

[0087] Figure 3 is a diagram illustrating the effects obtained by changing the illumination pattern of the illumination light Q in an optical measurement system according to this embodiment.

[0088] Referring to Figures 3(A) to (C), we assume the presence of object A on the sample surface and object B located away from the sample surface. Object A is the object to be reconstructed as an image, and object B is an object located outside the sample surface that causes scattering.

[0089] As shown in Figure 3(A), when illumination light Q is illuminating from a single direction (when the illumination angle is single), diffracted light generated by scattering at object B affects the sample surface (the focal position of the illumination light), degrading the quality of the reconstructed image.

[0090] Here, as shown in Figure 3(B), when the illumination angle is changed, the position of the image of object A on the sample surface does not change, while the position of the diffracted light produced by scattering from object B on the sample surface changes depending on the illumination angle.

[0091] Therefore, as shown in Figure 3(C), multiple images are reconstructed by changing the illumination angle, and these reconstructed images are added together. Through this summing of multiple images, object A, whose signal amplitude and phase are nearly identical among the multiple images, is emphasized, while the influence of object B becomes relatively smaller.

[0092] The illumination angle is changed in i ways (where i is an integer greater than or equal to 2) (Illumination light Q i ), multiple off-axis holograms I ORi Record the following. Off-axis hologram I ORi From regenerative object light hologram UΣi Each of these is calculated. Then, the regenerated object light hologram U Σi The light wave distribution obtained by propagating the plane wave to the sample surface (the propagation distance is the same) using plane wave unfolding is called the object light distribution U Si Let's assume that... Furthermore, illumination light Q i The resulting illumination light distribution Q on the sample surface Si The object light distribution U with complex amplitude Si By dividing by the amplitude phase distribution U on the sample surface, Pi Calculate.

[0093] Thus, the amplitude phase distribution U on the sample surface Pi This is calculated based on the object light hologram (first hologram) obtained by illuminating sample S with illumination light Q and modulating the object light O with off-axis reference light R, and the illumination light hologram (second hologram) obtained by modulating the illumination light Q with off-axis reference light R in the absence of sample S. Amplitude phase distribution U Pi is, illumination light Q i Phase distribution θ Qi The phase change amount Δθ caused by sample S. i This will be the sum of the added amounts.

[0094] Finally, according to equation (12) below, the amplitude phase distribution U is calculated for each illumination mode (illumination angle) with the illumination light. Pi By integrating them as complex numbers, the composite amplitude phase distribution U SA Calculate.

[0095]

number

[0096] As shown in equation (12) above, the amplitude phase distribution U PiBy integrating the complex numbers without converting them to intensity (absolute value), the information can be treated as directional, vector-like data. As a result, if the phase components outside the sample plane can be considered sufficiently random, they can be expected to cancel each other out and converge to the average value of zero. Consequently, the influence of diffracted light caused by scattering at object B can be suppressed. This improves the signal-to-noise ratio of the reconstructed image.

[0097] Note that the amplitude phase distribution U Pi When converted to intensity (absolute value) and then integrated, the intensity is always a positive value, meaning that the effect of diffracted light caused by scattering at object B remains.

[0098] To ensure that phase components other than those on the sample plane are sufficiently random, it is preferable to set a sufficiently large number of illumination patterns (e.g., illumination angles) for the illumination light Q. The signal-to-noise ratio (SNR) will be proportional to the square root of the number of illumination patterns for the illumination light Q (for example, if measurements are taken with four different illumination angles, the SNR will be twice as high as when measurements are taken with one illumination angle).

[0099] The range in which the illumination angle can be changed is optically determined by factors such as the size of the sample S, the resolution of the image sensor D, and the field of view of the image sensor D. The illumination angle will be changed within the optically permissible range. Here, changing the illumination angle means changing the azimuth angle while keeping the incident angle of the illumination light Q constant.

[0100] As will be discussed later, the number of times the lighting angle is changed is typically determined based on factors such as the required quality and the allowable processing time.

[0101] Furthermore, due to external disturbances, the regenerative object light hologram U ΣiIf a positional shift occurs in the coordinates of the image reconstructed from the sample, the phase resolution will not decrease, but the spatial resolution (on the xy plane) may decrease. In this case, it is preferable to correct the shift of the reconstructed image or sample S before integration. More specifically, the coordinates at which the phase interval between object light sources is maximized are calculated, and the shift of the reconstructed image or sample S is calculated based on these calculated coordinates. That is, the shift from the reference coordinates is calculated and corrected before the integration process is performed.

[0102] (b4: Mechanism to limit the area to be illuminated) Next, we will describe the mechanism for limiting the illuminated area.

[0103] In order to apply a bandpass filter to equations (5) and (4) and extract the direct image component of the third term, it is necessary to ensure that the direct image component does not overlap with the light intensity component and the conjugate image component in the spatial frequency band. Therefore, in this embodiment, the range of illumination light Q is limited by a limiting unit such as mask A2 to prevent image degradation due to overlap in the spatial frequency band.

[0104] By imaging the aperture pattern SP2 of mask A2, which is positioned at a distance from sample S, onto sample S, the spatial frequency bandwidth included in the interference fringes is appropriately controlled while maintaining the flexibility of the illumination method, thereby efficiently utilizing the spatial frequency bandwidth that the image sensor D can record.

[0105] In the optical measurement system 1, the mask A1 and lens L1 realize a point source of off-axis reference light R. The spatial frequency f of the interference fringes at any point on the recording surface is the incident angle θ of the object light O at that point. O and the incident angle θ of the off-axis reference light R R Using these, it can be expressed as shown in equation (13) below.

[0106]

number

[0107] Figure 4 illustrates the conditions in which object light O and off-axis reference light R are incident on the recording surface of the image sensor D. Figure 4(A) shows the case where the off-axis reference light R is a plane wave, and Figure 4(B) shows the case where the off-axis reference light R is a spherical wave.

[0108] Referring to Figure 4(A), when the off-axis reference light R is a plane wave, the angle between the object light O and the off-axis reference light R at any point on the recording surface of the image sensor D depends on the position on the recording surface of the image sensor D. For example, the angle α between the object light O and the off-axis reference light R at the upper edge of the recording surface of the image sensor D is significantly different from the angle β between them at the lower edge of the recording surface.

[0109] In contrast, referring to Figure 4(B), when the off-axis reference light R is a spherical wave, the angle between the object light O and the off-axis reference light R at a single point on the recording surface of the image sensor D is approximately the same, regardless of their position on the recording surface. For example, the angle α between the object light O and the off-axis reference light R at the upper edge of the recording surface of the image sensor D and the angle β at the lower edge of the recording surface are approximately the same.

[0110] In other words, by using a point source for the off-axis reference light R, the angle between the light ray originating from any point on the sample S (object light O) and the light ray originating from the point source of the off-axis reference light R can be made approximately constant at any point on the recording surface.

[0111] If we consider object light O as a collection of wave sources on the same z-plane as the point source of off-axis reference light R, then the position of the wave sources on that z-plane (x s ,y s ) and the corresponding spatial frequency (u s ,v s The relationship shown in equation (14) below approximately holds between ) and .

[0112]

number

[0113] z in the formulaL λ is the distance in the z-axis direction from the point source of the off-axis reference light R to the recording surface, and λ is the wavelength. Also, let u be the spatial frequency in the x-direction and v be the spatial frequency in the y-direction.

[0114] As shown in equation (14), the position of the wave source (object light O) on the z-plane and the spatial frequency (coordinates of the spectral components) are approximately linearly related. Therefore, by restricting the region in which the wave source (object light O) exists, the spread of the spatial frequency band of the direct image component can be controlled. This allows for efficient use of the spatial frequency band.

[0115] Here, the "region where the wave source exists" refers to the area where the sample S is illuminated. In other words, by optimizing the aperture pattern SP2 of mask A2, the illumination range is limited, thereby allowing for appropriate control of the spatial frequency band. Since mask A2 simply limits the area illuminating the sample S, it will not cause distortion in the reconstructed image as long as the complex amplitude of the object light O is recorded correctly.

[0116] Next, we will explain how to determine the size of the opening pattern SP2 of mask A2. As described above, the off-axis hologram I recorded in the optical system shown in Figure 1(B) OR This is calculated as shown in equation (5). In equation (5), the component necessary for image reconstruction is the direct image component of the third term, and the other terms are superimposed as noise components and therefore need to be removed by a bandpass filter.

[0117] Let the origin coordinates of image sensor D be (0,0,0), and the center coordinates of sample S be (0,0,z L )

[0118] Figure 5 is a diagram illustrating the relationship between the sample S and the off-axis reference light R in an optical measurement system according to this embodiment. Referring to Figure 5, the coordinates of the point source (focus point FP1) of the off-axis reference light R, when unfolded towards the sample S side with respect to the half mirror HM2 of the beam splitter BS2, are (x R ,y R ,z R =z L ) and assuming the illumination range of sample S is a rectangle with size a in the x direction and size b in the y direction, then for the direct image component of the third term, the bandwidth W in the u direction x and bandwidth W in the v direction y This can be approximately expressed as shown in equation (15) below, where the center frequency u in the u direction c and the center frequency v in the v direction c This can be approximately expressed as shown in equation (16) below.

[0119]

number

[0120] Furthermore, the bandwidth W in the u direction of the conjugate image component (term 4) x and bandwidth W in the v direction y This can also be expressed approximately as in equation (15) above. On the other hand, the center frequency u in the u direction of the conjugate image component (4th term) c and the center frequency v in the v direction c This is obtained by reversing the sign of equation (16) above.

[0121] Furthermore, the bandwidth of the combined light intensity component of the first and second terms will expand to twice the size of equation (15) around the origin.

[0122] The above relationship can be illustrated as shown in Figure 6. Figure 6 is a diagram illustrating the relationship between spatial frequency bands for off-axis holograms in an optical measurement system according to this embodiment. Figure 6(A) shows z=z in real space. LThe position of the off-axis reference light R and the illumination range of the sample S on the surface are shown. Figure 6(B) shows the spectrum obtained by the 2D Fourier transform of the hologram recorded on the recording surface (z=0).

[0123] Referring to Figure 6(A), in real space, sample S is (0,0,z L It exists with a size of a×b centered at the coordinates of (0,0,z). The point source of the off-axis reference light R is (0,0,z L From the coordinates of ), in the x direction x R and in the y direction R It is located at a distance of only that much.

[0124] Referring to Figure 6(B), in Fourier space (spatial frequency domain), the direct image component of the third term, which contains information about the object light O, has a bandwidth W. x ×W y The image spreads out to a certain size, and the center frequency of the direct image component is the coordinate (x) of the point source of the off-axis reference light. R ,y R It depends on the situation.

[0125] To extract only the third term (direct image component), which contains information about the object light O, from the Fourier space spectrum shown in Figure 6(B) using a bandpass filter, it is necessary to ensure that it does not overlap with the components of the other terms (first, second, and fourth terms).

[0126] On the other hand, since the spatial frequency bandwidth of image sensor D is finite, the center frequency u c and v c Making this component excessively large is also undesirable. Therefore, in order to efficiently utilize the spatial frequency band of the image sensor D, it is necessary to bring the component of the third term as close as possible to the limit where it does not overlap with the components of the other terms (first, second, and fourth terms).

[0127] To place each frequency band in close proximity, the spatial frequency bandwidth is limited to an appropriate range. Here, if the off-axis reference light is a divergent light (point source), the relationship in equation (5) above holds, and by limiting the illumination range of the illumination light Q, the spatial frequency bandwidth of each component can be limited to an appropriate range.

[0128] In this way, the size of the area in which the sample S is illuminated by the illumination light Q (i.e., the aperture pattern SP2 of the limiting mask A2) is determined so that the component corresponding to the illumination light Q (third term) and the components other than those corresponding to the illumination light Q (first and second terms) do not overlap in the Fourier space (spatial frequency domain) of the hologram recorded by the image sensor D.

[0129] By limiting the spatial frequency bandwidth of each component to an appropriate range, the spatial frequency bandwidth of the image sensor D can be utilized efficiently, and noise caused by overlapping spatial frequency bandwidths can be suppressed.

[0130] Although the application to off-axis holography optical systems has been described, the mask A2 mentioned above is also effective in other holographic optical systems that use divergent light (i.e., a point light source, or a light source that can be considered a point light source) as reference light, for example, when limiting the spatial frequency bandwidth of the direct image component to a range that can be recorded by the image sensor D.

[0131] The mask A2 used in the optical measurement system according to this embodiment may be externally similar to a field diaphragm used in an optical microscope. However, field diaphragms are used to suppress stray light caused by extraneous light (light outside the field of view) hitting the walls along the optical path. While field diaphragms can reduce the noise level, the amount of stray light suppressed is small, and unless the purpose is to detect very weak light, it does not pose a major problem even without taking proactive measures.

[0132] In contrast, limiting the illumination range in digital holography using divergent light as the reference light has the effect of limiting the spatial frequency bandwidth included in the interference fringes to a range that can be recorded by the image sensor D. Mask A2 used in the optical measurement system according to this embodiment is used for this purpose.

[0133] Thus, the mask A2 used in the optical measurement system according to this embodiment exhibits effects that are different from those of a field diaphragm used in an optical microscope.

[0134] In the above explanation, an example of a limiting element was described in which a mask A2 with an aperture pattern SP2 of a predetermined size is formed is used. However, the limiting element is not limited to this, and any optical element may be used to realize the limiting element.

[0135] For example, by using optical elements that can control the light transmittance, such as polarizing mirrors or liquid crystals, the size of the aperture pattern (the cross-sectional area through which illumination light passes) can be arbitrarily changed. By configuring the system to allow arbitrary changes in the size of the aperture pattern, it is possible to easily adapt to changes in the distance between the sample S and the image sensor D, or changes in the position of the off-axis reference light point source.

[0136] (b5: Illumination light profile) The optical measurement system according to this embodiment has a composite amplitude phase distribution U SA Calculations such as these require an illumination light profile.

[0137] For example, when measuring by sequentially replacing samples S, the distance from the recording surface to the sample surface may change. In this case, diffraction calculations can be used to calculate the illumination light profile at a different distance based on the illumination light profile at a certain distance from the recording surface. Therefore, it is not necessary to record the illumination light profile each time the distance from the recording surface to the sample surface changes.

[0138] If sample S includes a substrate that is not the target of measurement, the illumination light profile for the illumination light transmitted through the substrate can be calculated by performing propagation calculations in the medium using plane wave unfolding on the illumination light profile. In this case, if the approximate thickness and refractive index of the substrate are known, it is not necessary to prepare a sample of only the substrate (a sample separate from sample S, the target of measurement) and record its illumination light profile.

[0139] Using the illumination light profile transmitted through the substrate, layers other than the substrate of the sample S can be measured. Also, when recording can be performed only on the substrate, by recording the illumination light profile transmitted through the substrate with only the substrate placed, the propagation calculation in the medium of the substrate can be omitted.

[0140] (b6: Measurement of the surface shape of the sample) Next, a method for measuring the surface shape of the sample S using the optical measurement system 1 according to the first embodiment will be described. For measuring the surface shape of the sample S, the amount of phase change generated by the sample is used. In this case, it is preferable to use visible light as the illumination light Q.

[0141] In the optical measurement system according to the present embodiment, the phase distribution θ of the illumination light is obtained using the illumination light profile recorded in a state where the sample S is not placed. Q is subtracted from the phase distribution of the combined amplitude phase distribution U SA to calculate the amount of phase change Δθ i generated by the sample S.

[0142] In the optical measurement system 1 according to the first embodiment, the surface shape of the sample S is measured using the relational expression between the amount of phase change Δθ generated by the sample S and the thickness Δd of the sample S shown in the following equation (17).

[0143]

Equation

[0144] In the equation, k z1 is the wave number in the z direction in the sample S, k z2 is the wave number in the z direction in the medium where the sample S exists, δ is the phase correction term, and λ is the light source wavelength. The wave numbers k z1 and k z2 can be calculated according to the following equations (18) and (19), respectively.

[0145]

Equation

[0146] In the formula, n1 is the refractive index of the medium in which the sample S exists, and n2 is the refractive index of the sample S. For example, when the sample S exists in a vacuum, the refractive index n1 = 1.

[0147] The wave number k in the x direction in the formula x and the wave number k in the y direction y are the amounts of phase change per unit length in the x and y directions. Therefore, as in the following formulas (20) and (21), the phase distribution θ of the illumination light Q on the sample surface Q can be calculated by differentiating.

[0148]

Number

[0149] The phase correction term δ in formula (17) is used to correct the phase change due to the complex transmittance when the transmittance becomes a complex number due to reasons such as light absorption in the sample S. If the phase change due to the complex transmittance can be considered uniform throughout the sample S due to reasons such as the sample S being all of the same material, the phase correction term δ may be omitted.

[0150] When a displacement occurs in the coordinates of the point source of the illumination light due to disturbance, the illumination light Q i may be corrected by the parallel movement of the pixels on the image sensor D. The amount of parallel movement is typically determined such that the correlation between the object light distribution U S and the illumination light Q i becomes maximum.

[0151] When the shape of the wavefront of the illumination light is smooth, the amount of information may be reduced by a low-pass filter or polynomial approximation.

[0152] Figure 7 is a flowchart showing the processing procedure for measuring surface shape using the optical measurement system 1 according to Embodiment 1. In the processing procedure shown in Figure 7, a visible light source may be used as the light source 10.

[0153] Referring to Figure 7, first, the process of acquiring the inline reference light L is performed. More specifically, the optical system shown in Figure 1(A) is configured (step S2). Then, coherent light is generated from the light source 10, and the processing unit 100 modulates the inline reference light L recorded in the image sensor D with the off-axis reference light R to create an off-axis hologram I. LR The result is obtained (step S4). Steps S2 and S4 only need to be performed once unless the optical system related to the off-axis reference light R is changed. Also, the processing in steps S2 and S4 is to improve the accuracy of the reconstructed image, and depending on the required accuracy, the processing in steps S2 and S4 may be omitted.

[0154] Next, the process of acquiring the illumination light profile is executed. More specifically, the optical system shown in Figure 1(B) is configured (step S6). At this time, the system is maintained in a state where no sample S exists. A substrate with the same thickness as the substrate of sample S may be placed at the location where sample S would be placed (sample position), or nothing may be placed at the sample position. This state corresponds to the measurement reference.

[0155] Next, the movable mirror MM is driven to set the illumination angle to one of several illumination angles (step S8). Then, coherent light is generated from the light source 10, and the processing unit 100 records the illumination light hologram Q on the image sensor D. i Obtain (x,y) (second hologram) (step S10).

[0156] In this way, the processing unit 100 records a hologram obtained by modulating the light obtained by illuminating with illumination light Q with off-axis reference light R using the image sensor D, even when the sample S is not present. Alternatively, the processing unit 100 records a hologram obtained by illuminating only the substrate that is not the target of measurement and contained in the sample S with illumination light Q using the image sensor D.

[0157] The processing device 100 emits an illumination light hologram Q i Illumination light profile Q from (x,y) Σi Calculate (x,y) (Step S12).

[0158] The process in steps S8 to S12 is repeated a predetermined number of times (N) for each illumination angle (1 ≤ i ≤ N).

[0159] Next, a process is performed to acquire the amplitude phase distribution of sample S. More specifically, sample S is placed in its original position in the optical system shown in Figure 1(B) (step S14). Subsequently, the movable mirror MM is driven to set the illumination angle to one of several illumination angles (step S16). Then, coherent light is generated from the light source 10, and the processing unit 100 generates an object light hologram U, which is recorded in the image sensor D. i Get (x,y) (step S18).

[0160] Next, the processing unit 100 processes the object light hologram U i (x,y) to regenerate object light hologram U Σi (x,y) is calculated (step S20). Then, the processing device 100 generates the object light hologram U Σi (x,y) and the corresponding illumination light profile Q Σi The (x,y) signal is propagated to the sample surface by plane wave expansion, and the object light distribution U at the sample surface is determined. Si (x,y) and illumination light distribution Q Si (x,y) is calculated (step S22). Furthermore, the processing device 100 calculates the object light distribution U Si (x,y) corresponds to the illumination light distribution Q SiDivide by (x,y) to obtain the amplitude phase distribution U on the sample surface. Pi Calculate (x,y) (Step S24).

[0161] The process in steps S16 to S24 is repeated a predetermined number of times (N) for each illumination angle (1 ≤ i ≤ N).

[0162] Next, the processing device 100 calculates the surface shape of the sample S. More specifically, the processing device 100 calculates the amplitude phase distribution U Pi By integrating (x,y) as complex numbers, the composite amplitude phase distribution U SA Calculate (x,y) (Step S26).

[0163] Next, the processing device 100 processes the composite amplitude phase distribution U on the sample surface. SA The phase change amount Δθ(x,y) is calculated from the argument of (x,y) (step S28). Then, the processing device 100 calculates the thickness Δd(x,y) of the sample S using the phase change amount Δθ(x,y) (step S30). The relationship shown in equation (17) above is used to calculate the thickness Δd of the sample S.

[0164] Finally, the processing unit 100 collects the thickness Δd(x,y) at each coordinate of the sample surface to calculate the shape profile of the sample S (step S32).

[0165] The surface shape of sample S can be calculated through the above process. Furthermore, the refractive index and refractive index profile of sample S can also be measured. In this case, in step S30, the refractive index n2(x,y) of sample S is calculated, and in step S32, the refractive index profile of sample S is calculated by aggregating the refractive index n2(x,y) at each coordinate on the sample surface.

[0166] (b7: Measurement of the internal structure of the sample) Next, a method for measuring the internal structure of the sample S using the optical measurement system 1 according to Embodiment 1 will be described. For measuring the internal structure of the sample S, it is preferable to use near-infrared light as the illumination light Q. By using near-infrared light as the illumination light Q, the object light hologram U obtained by illuminating the sample S with the illumination light Q shows the internal structure of the sample S. By setting a sample plane at an arbitrary position with respect to the sample S (a position separated from the recording surface by an arbitrary distance), the internal structure of the sample S can be measured.

[0167] FIG. 8 is a flowchart showing the processing procedure of the method for measuring the internal structure using the optical measurement system 1 according to Embodiment 1. For the processing procedure shown in FIG. 8, a near-infrared light source may be used as the light source 10.

[0168] The procedure shown in the flowchart of FIG. 8 employs a process (step S34) of imaging the intensity distribution and / or phase distribution of the synthetic amplitude-phase distribution U(x,y) instead of the processes of steps S28 to S32 shown in the flowchart of FIG. 7. SA (x,y) is imaged.

[0169] That is, the processing device 100 calculates the synthetic amplitude-phase distribution U(x,y) by integrating the amplitude-phase distribution U(x,y) as a complex number (step S26), and visualizes the internal structure of the sample S by imaging the calculated synthetic amplitude-phase distribution U(x,y). Pi (x,y) by integrating it as a complex number to calculate the synthetic amplitude-phase distribution U(x,y) (step S26), and visualizes the internal structure of the sample S by imaging the calculated synthetic amplitude-phase distribution U(x,y). SA (x,y) and visualizes the internal structure of the sample S by imaging the calculated synthetic amplitude-phase distribution U(x,y). SA (x,y).

[0170] <C. Embodiment 2: Reflective Optical System> (c1: Optical System) FIG. 9 is a schematic diagram showing a configuration example of the optical measurement system 2 according to Embodiment 2. FIG. 9(A) shows the optical system when in-line reference light is recorded, and FIG. 9(B) shows the optical system when object light is recorded. The optical measurement system 2 can be configured with the optical systems shown in FIGS. 9(A) and 9(B).

[0171] The optical system shown in Figure 9(A) is the same as the optical system used when recording inline reference light in the optical measurement system 1 according to Embodiment 1 shown in Figure 1(A), so a detailed explanation will not be repeated.

[0172] The optical system shown in Figure 9(B) is an off-axis hologram I obtained by illuminating a sample S with illumination light Q and modulating the object light O with off-axis reference light R. OR This corresponds to an optical system for recording the off-axis hologram I obtained by illuminating the sample S with illumination light Q. More specifically, the optical system shown in Figure 9(B) records the off-axis hologram I obtained from the reflected light. OR A first hologram (object light hologram) is generated. An illumination light profile is also acquired using the optical system shown in Figure 9(B). In this case, a reference plane is placed in place of the sample S, as will be described later.

[0173] The optical system shown in Figure 9(B) differs from the optical system used when recording object light in the optical measurement system 1 according to Embodiment 1 shown in Figure 1(B) in that it has a different configuration for illuminating the sample S with illumination light Q. Therefore, the off-axis reference light R output from the other side of the beam splitter BS1 is guided to the image sensor D via the same optical path as in Figures 1(A), 1(B), and 9(A).

[0174] The light output from one side of the beam splitter BS1 is used as illumination light Q to illuminate the sample S.

[0175] More specifically, the illumination light Q, split by the beam splitter BS2, is reflected by the mirror M2, then passes through the measurement optical system 32, and is led back to the beam splitter BS2. The illumination light Q is further reflected by the half mirror HM2 of the beam splitter BS2 to illuminate the sample S. The object light O obtained by illuminating the sample S with the illumination light Q (i.e., the light reflected by the sample S) passes through the half mirror HM2 of the beam splitter BS2 and is led to the image sensor D.

[0176] The measurement optical system 32 includes a movable mirror MM, lens L3, mask A2, and lens L4. Similar to Embodiment 1, the illumination light Q reflected by the movable mirror MM is focused by lens L3 and passes through mask A2. The illumination light Q that has passed through mask A2 is further focused by lens L4 and images onto the sample S. That is, the image of the aperture pattern SP2 of mask A2 passes through lens L4 and images onto sample S. This limits the range in which the illumination light Q that has passed through mask A2 illuminates sample S. By limiting the illumination range of the illumination light Q, unwanted light can be reduced and measurement accuracy can be improved. In addition, the rotation of the movable mirror MM changes the shape in which the illumination light Q is illuminated.

[0177] In the optical measurement system 1, the illumination range may vary depending on the thickness of the sample S. In such cases, the aperture pattern SP2 of the mask A2 may be changed, or the position of the lens L2 for imaging the illumination light Q onto the sample S may be changed as needed.

[0178] Furthermore, if mirror M2 and mask A2 are positioned optically close together, lens L3 may be omitted.

[0179] (c2: Illumination light profile) Next, the illumination light profile in the optical measurement system 2 will be described. In the reflective optical system employed by the optical measurement system 2, a reference plane is placed at the position where the sample S should be placed (sample position), and the reflected light from this reference plane is used as the illumination light Q. The reference plane is preferably a flat surface, and for example, an optical flat can be used. That is, in the optical system shown in Figure 9(B), instead of the sample S, the illumination light profile is obtained from the reflected light obtained by illuminating the reference plane with illumination light Q.

[0180] By propagating the recorded illumination light Q, the illumination light distribution Q at different distances on the sample surface can be determined. SSince this can be calculated, it is not necessary to record the illumination light Q each time the distance from the recording surface changes, similar to Embodiment 1 (transmissive optical system). Furthermore, if a positional shift occurs in the coordinates of the point source of the illumination light due to disturbances, the illumination light Q may be corrected by parallel movement of the pixels on the image sensor D.

[0181] To remove shape errors contained in the reference plane, multiple illumination light profiles may be recorded while translating the reference plane in the x and y directions, and the average value of the recorded illumination light profiles may be used as the actual illumination light profile.

[0182] (c3: Measurement of the surface shape of the sample) Next, a method for measuring the surface shape of a sample S using the optical measurement system 2 according to Embodiment 2 will be described. The amount of phase change caused by the sample S is used to measure the surface shape of the sample S. In this case, it is preferable to use visible light as the illumination light Q.

[0183] The relationship between the phase change Δθ caused by sample S and the height Δh of sample S is given by equation (22) below.

[0184]

number

[0185] k in the formula x is the wavenumber in the x direction, and k y δ is the wavenumber in the y-direction, and δ is the phase correction term.

[0186] wave number k x and wavenumber k y This can be calculated according to equations (20) and (21) above. The phase correction term δ may also be omitted if the phase change due to complex reflectance can be considered uniform across the entire sample S, for example, if all the samples S are made of the same material.

[0187] Furthermore, when measuring the shape (in-plane profile) across the entire sample surface, an optical system that uses parallel light for illumination Q may be employed. If the illumination light Q is a spherical wave, a focus shift relative to the sample surface may be detected as a concave or convex false shape. Since such false shapes are caused by the illumination light being a spherical wave, it is preferable to employ an optical system that uses parallel light for illumination Q when measuring the shape (in-plane profile) across the entire sample surface.

[0188] Figure 10 is a flowchart showing the processing procedure for measuring surface shape using the optical measurement system 2 according to Embodiment 2. In the processing procedure shown in Figure 10, a visible light source may be used as the light source 10.

[0189] Referring to Figure 10, first, the process of acquiring the inline reference light L is performed. More specifically, the optical system shown in Figure 9(A) is configured (step S52). Then, coherent light is generated from the light source 10, and the processing unit 100 modulates the inline reference light L recorded in the image sensor D with the off-axis reference light R to create an off-axis hologram I. LR The result is obtained (step S54). Steps S52 and S54 only need to be performed once unless the optical system related to the off-axis reference light R is changed. Also, the processing in steps S2 and S4 is to improve the accuracy of the reconstructed image, and depending on the required accuracy, the processing in steps S2 and S4 may be omitted.

[0190] Next, the process of acquiring the illumination light profile is executed. More specifically, the optical system shown in Figure 9(B) is configured (step S56). At this time, the sample S is not placed, and a reference plane is placed where the sample S would be placed (sample position). This state corresponds to the measurement reference.

[0191] Subsequently, the movable mirror MM is driven to set it to any one of a plurality of illumination angles (step S58). Then, the coherent light is generated from the light source 10, and the processing device 100 records the illumination light hologram Q i (x,y) (the second hologram) is acquired (step S60).

[0192] The processing device 100 records the illumination light hologram Q i (x,y) to calculate the illumination light profile Q Σi (x,y) (step S62).

[0193] The processes of steps S58 to S62 are repeated the number (N) of predetermined illumination angles (1 ≤ i ≤ N).

[0194] Next, the process of acquiring the amplitude-phase distribution of the sample S is executed. More specifically, the sample S is placed at the original position of the optical system shown in Fig. 9(B) (step S64). Subsequently, the movable mirror MM is driven to set it to any one of a plurality of illumination angles (step S66). Then, the coherent light is generated from the light source 10, and the processing device 100 records the object light hologram U i (x,y) is acquired (step S68).

[0195] Subsequently, the processing device 100 records the object light hologram U i (x,y) to calculate the object light hologram U for reproduction Σi (x,y) Then, the processing device 100 records the object light hologram U for reproduction Σi (x,y) and the corresponding illumination light profile Q Σi (x,y) are propagated to the position of the sample surface by plane wave expansion, and the object light distribution U Si (x,y) and the illumination light distribution Q Si (x,y) on the sample surface are calculated (step S72). Further, the processing device 100 divides the object light distribution U Si (x,y) by the corresponding illumination light distribution Q Si (x,y) to obtain the amplitude-phase distribution U on the sample surfacePi Calculate (x,y) (Step S74).

[0196] The process in steps S66 to S74 is repeated a predetermined number of times (N) for each illumination angle (1 ≤ i ≤ N).

[0197] Next, the processing device 100 calculates the surface shape of the sample S. More specifically, the processing device 100 calculates the amplitude phase distribution U Pi By integrating (x,y) as complex numbers, the composite amplitude phase distribution U SA Calculate (x,y) (Step S76).

[0198] Next, the processing device 100 processes the composite amplitude phase distribution U on the sample surface. SA The phase change amount Δθ(x,y) is calculated from the argument of (x,y) (step S78). Then, the processing unit 100 calculates the height h(x,y) of the sample S using the phase change amount Δθ(x,y) (step S80). The relationship shown in equation (22) above is used to calculate the height h of the sample S.

[0199] Finally, the processing unit 100 collects the thickness Δd(x,y) at each coordinate of the sample surface to calculate the shape profile of the sample S (step S82).

[0200] The surface shape of sample S can be calculated through the above process. (c4: Measurement of the internal structure of the sample) For measuring the internal structure of sample S, it is preferable to use near-infrared light as the illumination light Q. By using near-infrared light as the illumination light Q, the object optical hologram U obtained by illuminating sample S with illumination light Q shows the internal structure of sample S. The internal structure of sample S can be measured by setting the sample surface at an arbitrary position relative to sample S (at an arbitrary distance from the recording surface).

[0201] FIG. 11 is a flowchart showing the processing procedure of the method for measuring the internal structure using the optical measurement system 2 according to Embodiment 2. In the processing procedure shown in FIG. 11, a near-infrared light source may be used as the light source 10.

[0202] The procedure shown in the flowchart of FIG. 11 employs the process of imaging the intensity distribution and / or phase distribution of the composite amplitude-phase distribution U SA (x, y) (step S84) instead of the processes of steps S78 to S82 shown in the flowchart of FIG. 10.

[0203] That is, the processing device 100 calculates the composite amplitude-phase distribution U Pi (x, y) by integrating the amplitude-phase distribution U SA (x, y) as a complex number (step S76), and visualizes the internal structure of the sample S by imaging the calculated composite amplitude-phase distribution U SA (x, y).

[0204] <D. Processing Device 100> (d1: Example of Hardware Configuration) FIG. 12 is a schematic diagram showing an example of the hardware configuration of the processing device 100 included in the optical measurement system according to the present embodiment. Referring to FIG. 12, the processing device 100 includes, as main hardware elements, a processor 102, a main memory 104, an input unit 106, a display unit 108, a storage 110, an interface 120, a network interface 122, and a media drive 124.

[0205] The processor 102 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), and it 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 DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory), and it functions as working memory for the processor 102 to execute programs.

[0206] The input unit 106 includes a keyboard and mouse, and accepts user input. The display unit 108 outputs the results of program execution by the processor 102 to the user.

[0207] The storage 110 consists of non-volatile memory such as a hard disk or flash memory, and stores various programs and data. More specifically, the storage 110 holds the operating system 112 (OS), the measurement program 114, the hologram data 116, and the measurement results 118.

[0208] The operating system 112 provides an environment for the processor 102 to execute programs. The measurement program 114 is executed by the processor 102 to realize an optical measurement method according to this embodiment. The hologram data 116 corresponds to the image data output from the image sensor D. The measurement result 118 includes the measurement result obtained by executing the measurement program 114.

[0209] Interface 120 mediates data transmission between the processing unit 100 and the image sensor D. Network interface 122 mediates data transmission between the processing unit 100 and an external server device.

[0210] The media drive 124 reads necessary data from a recording medium 126 (such as an optical disk) storing a program executed by the processor 102 and stores it in the storage 110. Note that the measurement program 114 and the like executed in the processing device 100 may be installed via the recording medium 126 or downloaded from a server device via the network interface 122 or the like.

[0211] The measurement program 114 may call necessary modules in a predetermined array at a predetermined timing among the program modules provided as part of the operating system 112 to execute processing. In such a case, the 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 incorporated in a part of another program.

[0212] 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 (such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit)).

[0213] The example of the hardware configuration of the processing device 100 is the same in other embodiments, so detailed description will not be repeated.

[0214] (d2: Functional configuration example) FIG. 13 is a schematic diagram showing a functional configuration example of the processing device 100 included in the optical measurement system according to the present embodiment. Each functional element shown in FIG. 13 may typically be realized by the processor 102 of the processing device 100 executing the measurement program 114. Note that appropriate hardware for realizing the functional configuration shown in FIG. 13 is selected according to each era.

[0215] Referring to Figure 13, the processing unit 100 includes, as its main functional elements, an off-axis hologram acquisition module 150, an illumination light hologram acquisition module 152, an object light hologram acquisition module 154, a hologram playback module 156, an amplitude phase distribution calculation module 158, an integration module 160, an object light phase calculation module 162, an object shape calculation module 164, an imaging module 166, and an illumination angle control module 168.

[0216] The off-axis hologram acquisition module 150, with the optical system configured for recording in-line reference light, records the hologram to be recorded on the image sensor D as an off-axis hologram I. LR Record it as such.

[0217] The illumination light hologram acquisition module 152, with its optical system configured for recording object light, records the illumination light hologram Q on the image sensor D. i Get (x, y).

[0218] The object light hologram acquisition module 154, with its optical system configured for recording object light, records the object light hologram U on the image sensor D. i Get (x, y).

[0219] Both the illumination light hologram acquisition module 152 and the object light hologram acquisition module 154 are configured to record the detection signal from the image sensor D, and one of them is activated depending on a status signal that is set manually or automatically.

[0220] The hologram playback module 156 receives the illumination light hologram Q acquired by the illumination light hologram acquisition module 152. i (x,y) to regenerate illumination light hologram (illumination light profile Q Σi The (x,y)) is calculated, and the object light hologram U acquired by the object light hologram acquisition module 154 is calculated. i (x,y) to regenerate object light hologram U ΣiCalculate (x,y).

[0221] The hologram playback module 156 uses illumination light profile Q Σi (x,y) and the object light hologram U for reproduction Σi The (x,y) signal is propagated to the sample surface by plane wave expansion, and the illumination light distribution Q on the sample surface is determined. Si (x,y) and object light distribution U Si Calculate (x,y).

[0222] The amplitude phase distribution calculation module 158 calculates the object light distribution U Si (x,y) corresponds to the illumination light distribution Q Si Divide by (x,y) to obtain the amplitude phase distribution U on the sample surface. Pi Calculate (x,y).

[0223] The integration module 160 uses an amplitude phase distribution U Pi By integrating these as complex numbers, the composite amplitude phase distribution U SA Calculate.

[0224] The object light phase calculation module 162 calculates the composite amplitude phase distribution U SA The phase change Δθ(x,y) is calculated from the argument of (x,y).

[0225] The object shape calculation module 164 uses the phase change amount Δθ(x,y) to calculate information that identifies the surface shape of sample S (such as thickness and refractive index). The object shape calculation module 164 outputs the calculation results as shape information of sample S.

[0226] The imaging module 166 uses a composite amplitude phase distribution U SA The intensity distribution and / or phase distribution of (x,y) are visualized.

[0227] The illumination angle control module 168 determines the type and number of illumination angles that the movable mirror MM should achieve, according to the settings. The illumination angle control module 168 works in conjunction with the hologram playback module 156 and other components to drive the movable mirror MM so that the desired illumination angles can be achieved.

[0228] (d3: User Interface) Next, an example of a user interface related to setting the illumination angle, which is implemented by the optical measurement system according to this embodiment, will be described.

[0229] Figure 14 is a schematic diagram showing an example of a user interface screen provided in an optical measurement system according to this embodiment. The user interface screen 170 shown in Figure 14 is typically displayed on the display unit 108 of the processing unit 100. That is, the processing unit 100 provides a user interface screen 170 that accepts the setting of the number of modes to be illuminated by illumination light Q (first light).

[0230] The user interface screen 170 includes an input field 172 for entering the number of illumination angles, a display field 174 showing the degree of improvement in the signal-to-noise ratio, and a display field 176 showing the time required for measurement.

[0231] The input field 172 accepts the setting of the number of illumination angles to be changed (i as described above). The processing unit 100 calculates the degree of improvement in the signal-to-noise ratio based on the set number of illumination angles and displays it in the display field 174, and also calculates the time required for measurement and displays it in the display field 176.

[0232] The user sets the number of illumination angles, taking into account the quality of the measurement results (S / N ratio) and the allowable cycle time, as displayed on the user interface screen 170. Alternatively, the system may suggest an appropriate number of illumination angles based on the input of the required quality and allowable cycle time.

[0233] The number of lighting angles may be set via a user interface screen 170, as shown in Figure 14.

[0234] <E. Measurement Example> Next, a measurement example by the optical measurement system according to this embodiment will be shown.

[0235] FIG. 15 is a diagram showing a measurement example of the surface shape by the optical measurement system according to this embodiment. In FIG. 15, an example of the amplitude-phase distribution of the surface (sample surface) of the USAF 1951 test target recorded using the optical measurement system 2 adopting the reflection optical system shown in FIG. 9 is shown. As the light source 10, a visible light source having a peak wavelength of 532 nm was used.

[0236] FIGS. 15(A) and 15(C) show the intensity distribution of the amplitude-phase distribution, and FIGS. 15(B) and 15(D) show the phase distribution of the amplitude-phase distribution.

[0237] FIGS. 15(A) and 15(B) show the amplitude-phase distribution U P1 recorded with a single illumination angle of the illumination light. On the other hand, FIGS. 15(C) and 15(D) show the amplitude-phase distribution (synthesized amplitude-phase distribution U SA ) recorded by changing the illumination angle of the illumination light to 500 types. That is, FIGS. 15(C) and 15(D) show the amplitude-phase distribution U Pi (i = 500) as described above, and an example of the synthesized amplitude-phase distribution U SA calculated by integrating the complex numbers.

[0238] In the measurement examples shown in FIGS. 15(A) and 15(B), it can be seen that the reproduced image is deteriorated due to the influence of the diffracted light contained in the illumination light. In particular, in the phase distribution of FIG. 15(B), the shape of the pattern contained in the test target is unclear.

[0239] On the other hand, by integrating a plurality of amplitude-phase distributions U Pi while keeping them as complex numbers, it can be seen that the influence of the diffracted light contained in the illumination light can be suppressed, and not only the shape of the pattern but also the dirt attached to the surface of the test target can be clearly visualized.

[0240] FIG. 16 is a diagram showing a measurement example of an internal structure state by the optical measurement system according to the present embodiment. FIG. 16 shows an example of the amplitude-phase distribution of a sample surface set at 600 μm from the surface of a silicon wafer recorded using the optical measurement system 1 employing the reflection optical system shown in FIG. 1. As the light source 10, a near-infrared light source having a peak wavelength of 1030 nm was used. Note that there are internal cracks on the sample surface.

[0241] In FIG. 16(A), the phase distribution of the amplitude-phase distribution U P1 recorded with a single illumination angle of the illumination light is shown. On the other hand, FIG. 16(B) shows the phase distribution of the amplitude-phase distribution (synthetic amplitude-phase distribution U SA ) recorded by changing the illumination angle of the illumination light to 32 types. That is, FIG. 16(B) shows an example of the synthetic amplitude-phase distribution U Pi calculated by integrating the amplitude-phase distributions U SA (i = 32) as complex numbers.

[0242] In the measurement example shown in FIG. 16(A), it can be seen that the reproduced image is deteriorated by the influence of spectral noise due to diffracted light contained in the illumination light. On the other hand, as shown in FIG. 16(B), by integrating a plurality of amplitude-phase distributions U Pi as complex numbers, the influence of spectral noise due to diffracted light contained in the illumination light can be suppressed, and it can be seen that not only the presence of cracks is clearly visualized, but also the shape of the cracks is clearly visualized.

[0243] As shown in FIGS. 15 and 16, by integrating a plurality of amplitude-phase distributions U Pi as complex numbers to calculate the synthetic amplitude-phase distribution U SA , noise can be reduced and the quality of the reproduced image can be improved.

[0244] <F. Composite Configuration> When assuming a silicon wafer as the sample S, in order to measure both the surface shape and the internal structure, a composite configuration combining a reflection-type optical measurement system 2 (see Fig. 9(B)) and a transmission-type optical measurement system 1 (see Fig. 1(B)) can be adopted.

[0245] Fig. 17 is a schematic diagram showing an example of the composite configuration of the optical measurement system according to the present embodiment. Referring to Fig. 17, the optical measurement system according to the present embodiment can be changed between a first configuration (see Fig. 17(B)) that generates an object light hologram (first hologram) from the transmitted light obtained by illuminating the sample S with the illumination light Q, and a second configuration (see Fig. 17(A)) that generates an object light hologram (first hologram) from the reflected light obtained by illuminating the sample S with the illumination light Q.

[0246] Referring to Fig. 17(A), since visible light does not pass through the silicon wafer, a visible light source is used as the light source 10 in the reflection-type optical measurement system 2 to measure the surface shape. That is, the processing device 100 measures the surface shape of the sample S based on the object light hologram recorded when combining the visible light source that generates visible light and Fig. 17(A).

[0247] Referring to Fig. 17(B), since near-infrared light passes through the silicon wafer, a near-infrared light source is used as the light source 10 in the transmission-type optical measurement system 1 to measure the internal structure. That is, the processing device 100 measures the internal structure of the sample S based on the object light hologram recorded when combining the near-infrared light source that generates near-infrared light and Fig. 17(B).

[0248] As shown in Fig. 17, the surface shape and the internal structure of the silicon wafer can be measured using the reflection-type optical measurement system 2 and the transmission-type optical measurement system 1.

[0249] <G. Other Embodiments> As described above, the off-axis hologram I LRThe process of obtaining it (the processes of steps S2 and S4 in FIGS. 7 and 8, and the processes of steps S52 and S54 in FIGS. 10 and 11) is for improving the accuracy of the reproduced image, and may be omitted when relatively high accuracy is not required.

[0250] Off-axis hologram I LR When not obtaining it, the calculation process according to the above formula (8) is not performed, and the complex amplitude off-axis hologram J shown in formula (7) OR may be directly used as the object light hologram U(x, y).

[0251] Alternatively, the complex amplitude off-axis hologram J shown in formula (7) OR may be used as the object light hologram U(x, y) after removing the component of the off-axis reference light R (=R0exp(iφ R ))). When removing the off-axis reference light R, the complex amplitude off-axis hologram J shown in formula (7) OR may be divided by the complex conjugate of the off-axis reference light R. The distribution of the off-axis reference light R can be obtained by a method such as calculating from the analytical solution of the spherical wave based on the physical arrangement of the point light source of the off-axis reference light R.

[0252] In addition, when not obtaining the off-axis hologram I LR in addition to the above formula (8), formulas (4), (6), and (9) are not used.

[0253] <H. Modified Example> The above-described optical system is an example, and any optically equivalent change can be made according to constraints such as required specifications and space. For example, a single lens may be changed to a compound lens, or any reflecting member may be used instead of the mirror.

[0254] Furthermore, while the above description illustrates an implementation example in which the processing device 100 performs calculation processing related to measurement on the surface shape and / or internal structure of the sample S, any implementation form can be adopted, and is not limited to this. For example, some or all of the processing performed by the processing device 100 may be performed using computing resources on the cloud.

[0255] Furthermore, although the above explanation mainly described the case of measuring a sample S such as a silicon wafer, the sample S to be measured is not limited. In other words, for the measurement of any sample S for which an improvement in the signal-to-noise ratio is required, the amplitude phase distribution U described above can be used. Pi By integrating them as complex numbers, the composite amplitude phase distribution U SA A process can be applied to calculate this.

[0256] <I.まとめ> The optical measurement system according to this embodiment allows the selection of near-infrared and visible light to illuminate the sample, depending on the type of sample and the purpose of measurement. Furthermore, by employing a silicon-based image sensor D, it has light-receiving sensitivity to both visible and near-infrared light, eliminating the need for replacement. By employing such a combination of light source and image sensor, the surface shape and internal structure of samples such as silicon wafers can be measured.

[0257] The optical measurement system according to this embodiment uses the phase information of object light to measure the surface shape and internal structure of a sample. Therefore, the depth resolution (resolution on the z-axis) is not limited by the depth of focus, and the sample can be measured on the order of nanometers. At this time, the internal structure of the sample can be observed with high resolution by diffraction calculations that take into account the refractive index of the medium. As a result, defects on the order of nanometers within the sample can also be detected.

[0258] The optical measurement system according to this embodiment can reconstruct an image at any distance from the light wave distribution obtained by digital holography, thus eliminating the need for a vertical scanning mechanism or the like.

[0259] The optical measurement system according to this embodiment calculates a composite amplitude-phase distribution by integrating the amplitude-phase distributions calculated for each illumination pattern (illumination angle) using the illumination light, while keeping them as complex numbers. By integrating the amplitude-phase distributions as complex numbers while varying the illumination pattern (illumination angle) using the illumination light, noise can be reduced and the signal-to-noise ratio (SNR) can be improved.

[0260] In the optical measuring device according to this embodiment, by limiting the range in which the sample is illuminated by illumination light to a predetermined range, overlap in Fourier space (spatial frequency domain) can be avoided between the component containing information about the object light, the light intensity component, and the conjugate light component. As a result, noise due to overlap between components can be suppressed, and more accurate measurements can be achieved.

[0261] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0262] 1,2 Optical measurement system, 10 Light source, 20 Imaging optical system, 30,32 Measurement optical system, 100 Processing unit, 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 Off-axis hologram acquisition module, 152 Illumination light hologram acquisition module, 154 Object light hologram acquisition module, 156 Hologram playback module, 158 Amplitude phase distribution calculation module, 160 Integration module, 162 Object light phase calculation module, 164 Object shape calculation module, 166 Imaging module, 168 Illumination angle control module, 170 User interface screen, 172 Input field, 174,176 Display area, A1, A2 Mask, BE Beam expander, BS1, BS2 Beam splitter, D Image sensor, L Inline reference light, L1, L2, L3, L4, L21, L22, L31, L32 Lens, M1 Mirror, MO Objective lens, P Pinhole, S Sample, SP1, SP2 Aperture pattern.

Claims

1. A first light source that emits near-infrared light, Silicon-based image sensors, The system includes an optical system that splits the light from the first light source into a first beam and a second beam, The optical system is configured such that the first hologram obtained by illuminating a sample with the first light is modulated with the second light, which is divergent light, and recorded by the image sensor.

2. The optical system generates the first hologram from the transmitted light obtained by illuminating the sample with the first light. The optical measurement system according to claim 1, wherein, in the optical system, a second hologram is recorded from transmitted light obtained by illuminating a substrate, which is not the object to be measured and is included in the sample, with the first light, instead of the sample itself.

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

4. The aforementioned optical measurement system is A second light source that generates visible light, Further equipped with a processing unit, The optical system can be switched between a first configuration that generates a first hologram from transmitted light obtained by illuminating the sample with the first light, and a second configuration that generates a first hologram from reflected light obtained by illuminating the sample with the first light. The aforementioned processing apparatus is The internal structure of the sample is measured based on the first hologram recorded when the first light source and the first configuration of the optical system are combined. The optical measurement system according to any one of claims 1 to 3, configured to measure the surface shape of the sample based on the first hologram recorded when the second light source and the second configuration of the optical system are combined.

5. The optical measurement system according to any one of claims 1 to 4, wherein the optical system is an off-axis holography optical system.

6. The optical system according to any one of claims 1 to 5, wherein the optical system includes a limiting unit that limits the size of the range in which the sample is illuminated by the first light so that, in the spatial frequency domain of the hologram recorded by the image sensor, the component corresponding to the first light and components other than the component corresponding to the first light do not overlap.

7. An optical measurement method using an optical system that includes a beam splitter that splits light from a first light source that generates near-infrared light into a first beam of light and a second beam of light, The steps include recording a first hologram obtained by illuminating a sample with the first light and modulating the resulting light with the second light, which is divergent light, using a silicon-based image sensor, An optical measurement method comprising the step of recording a second hologram obtained by modulating the first light with the second light using the image sensor, in the absence of the aforementioned sample.

8. Light source and An optical system including a beam splitter that splits the light from the light source into a first beam of light and a second beam of light, An image sensor that records a hologram generated by the optical system, The apparatus comprises a processing device that calculates the amplitude phase distribution on the sample surface, which is the surface of interest of the sample, based on a first hologram obtained by modulating the light obtained by illuminating the sample with the first light with the second light, and a second hologram obtained by modulating the first light with the second light when the sample is not present. The optical system includes a mechanism for changing the form of illumination with the first light, The processing device is configured to calculate a composite amplitude phase distribution by integrating the amplitude phase distributions calculated for each mode of illumination with the first light while they are still complex numbers, and is an optical measurement system.

9. The optical measurement system according to claim 8, wherein the mechanism changes the angle at which the first light is illuminated.

10. The optical measurement system according to claim 9, wherein the mechanism changes the azimuth angle while keeping the incidence angle of the first light constant.

11. The optical system according to any one of claims 8 to 10, wherein the optical system includes a limiting unit that limits the size of the range in which the sample is illuminated by the first light so that, in the spatial frequency domain of the hologram recorded by the image sensor, the component corresponding to the first light and components other than the component corresponding to the first light do not overlap.

12. The optical measurement system according to any one of claims 8 to 11, wherein the processing device provides a user interface screen for receiving a setting for the number of forms of illumination with the first light.

13. An optical measurement method using an optical system that includes a beam splitter that splits light from a light source into a first beam of light and a second beam of light, The steps include recording a first hologram obtained by illuminating a sample with the first light and modulating the resulting light with the second light using an image sensor, The steps include recording a second hologram obtained by modulating the first light with the second light using an image sensor, in the absence of the aforementioned sample, The steps include changing the form of illumination with the first light, For each mode of illumination with the first light, the step of calculating the amplitude phase distribution on the sample surface, which is the surface of interest of the sample, based on the first hologram and the second hologram, An optical measurement method comprising the step of calculating a composite amplitude phase distribution by integrating the amplitude phase distributions calculated for each of the forms of illumination with the first light while they are still complex numbers.

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