Optical measurement system and optical measurement method

Abstract

There is a demand for measuring devices that can more accurately measure the surface shape of samples. [Solution] The optical measurement system includes a light source, an optical system that illuminates a sample using light from the light source and records the wavefront of the reflected light from the sample, and a processing unit that calculates the surface shape of the sample based on the wavefront information of the reflected light. The incident angle of the light illuminating the sample is set based on a first complex amplitude reflection coefficient based on the light reflected at the surface of the sample and a second complex amplitude reflection coefficient based on the light reflected elsewhere than the surface of the sample.

Description

[Technical Field]

[0001] The present invention relates to an optical measurement system and an optical measurement method for measuring surface shape. [Background technology]

[0002] The following prior art methods are known for measuring the surface shape of a sample. Japanese Patent Publication No. 2009-145774 (Patent Document 1) discloses a scanning laser microscope that is inexpensive, highly accurate, and capable of measuring height information at high speed.

[0003] Japanese Patent Publication No. 2018-146391 (Patent Document 2) discloses a surface shape measuring device that can improve the accuracy of surface shape measurement by appropriately selecting the objective lens and adjusting the light intensity when measuring the surface shape of a surface to be measured.

[0004] Japanese Patent Publication No. 2012-168001 (Patent Document 3) discloses a configuration that uses a contact-type probe to stably control the contact force and perform highly accurate shape measurement even on steeply inclined surfaces that are nearly vertical. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-145774 [Patent Document 2] Japanese Patent Publication No. 2018-146391 [Patent Document 3] Japanese Patent Publication No. 2012-168001 [Patent Document 4] International Publication No. 2023 / 079741 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In both the method disclosed in Japanese Patent Publication No. 2009-145774 (Patent Document 1) and the method disclosed in Japanese Patent Publication No. 2018-146391 (Patent Document 2), if the reflective component on the back surface of the sample is stronger than the reflective component on the front surface of the sample, the surface shape of the sample cannot be measured correctly.

[0007] Furthermore, the method disclosed in Japanese Patent Publication No. 2012-168001 (Patent Document 3) is a contact-type measurement method, which may damage the sample. In addition, since this method is a linear measurement, it takes time to perform the measurement.

[0008] There is a demand for measuring devices that can more accurately measure the surface shape of samples. [Means for solving the problem]

[0009] (Configuration 1) The optical measurement system according to this embodiment includes a light source, an optical system that illuminates a sample using light from the light source and records the wavefront of the reflected light from the sample, and a processing unit that calculates the surface shape of the sample based on the wavefront information of the reflected light. The incident angle of the light illuminating the sample is set based on a first complex amplitude reflection coefficient based on the light reflected at the surface of the sample and a second complex amplitude reflection coefficient based on the light reflected from areas other than the surface of the sample.

[0010] (Configuration 2) In Configuration 1, the optical system may include an image sensor into which reflected light is incident, and an optical fiber for superimposing the reflected light and the light from the light source on the light-receiving surface of the image sensor.

[0011] (Configuration 3) In Configuration 1 or 2, the sample may be positioned such that the direction of the cross-sectional shape to be measured is perpendicular to the direction of the light illuminating the sample.

[0012] (Configuration 4) In any of Configurations 1 to 3, the optical measurement system may further include a lens that converts light from a light source into parallel light. The converted parallel light may be incident on the sample.

[0013] (Configuration 5) In any of Configurations 1 to 3, the optical measurement system may further include a pinhole through which light from the light source passes. Divergent light passing through the pinhole may be incident on the sample.

[0014] (Configuration 6) In any of Configurations 1 to 5, the processing unit may extract information on bright and dark lines of interference fringes that appear in the hologram produced by the superposition of light, which is recorded by the image sensor, and calculate the surface shape of the sample.

[0015] (Configuration 7) In any of Configurations 1 to 6, the processing unit may calculate the surface shape of the sample using a correction amount based on the magnitude of the complex amplitude reflection coefficient of the sample, the magnitude of the first complex amplitude reflection coefficient, and the magnitude of the second complex amplitude reflection coefficient.

[0016] (Configuration 8) The optical measurement system according to this embodiment includes a light source, an optical system that illuminates a sample using light from the light source and records the wavefront of the reflected light from the sample, and a processing unit that calculates the surface shape of the sample based on the information of the wavefront of the reflected light. The incident angle of the light illuminating the sample is set to exceed the inverse cosine of the value obtained by dividing half the wavelength of the light from the light source by the variation range of the surface shape of the sample.

[0017] (Configuration 9) An optical measurement method according to this embodiment includes the steps of illuminating a sample with light from a light source, recording the wavefront of the reflected light from the sample, and calculating the surface shape of the sample based on the wavefront information of the reflected light. The incident angle of the light illuminating the sample is set based on a first complex amplitude reflection coefficient based on the light reflected at the surface of the sample and a second complex amplitude reflection coefficient based on the light reflected elsewhere than the surface of the sample. [Effects of the Invention]

[0018] One embodiment of the present invention provides a measuring device that can more accurately measure the surface shape of a sample. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing an example of the basic configuration of an optical measurement system according to this embodiment. [Figure 2] This is a schematic diagram showing an example configuration of an optical measurement system according to this embodiment. [Figure 3] This is a schematic diagram showing an example configuration of an information processing device according to this embodiment. [Figure 4] This flowchart shows an example of the processing procedure for measuring a sample using the optical measurement system according to this embodiment. [Figure 5] This diagram illustrates the behavior of light waves incident on a sample with a film structure. [Figure 6] This figure shows the case where the error in the angular displacement is maximum. [Figure 7] This figure shows an example of measurement when a relatively small incidence angle is set. [Figure 8] This figure shows an example of measurement when a relatively large incidence angle is set. [Figure 9] This figure illustrates the high-resolution axis and low-resolution axis in an optical measurement system according to this embodiment. [Figure 10] This is a schematic diagram showing another basic configuration example of an optical measurement system according to this embodiment. [Figure 11] This figure shows an example of the relationship between the phase of the complex amplitude reflection coefficient of the surface reflection and the phase of the complex amplitude reflection coefficient of the multiple reflections. [Figure 12] This diagram illustrates the phase shift caused by the complex amplitude reflection coefficient of multiple reflected light. [Figure 13] This figure shows an example of measurement of a sample with a rough surface. [Modes for carrying out the invention]

[0020] 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.

[0021] <Example configuration of optical measurement system> First, an example configuration of the optical measurement system according to the present embodiment will be described.

[0022] FIG. 1 is a schematic diagram showing an example of the basic configuration of the optical measurement system according to the present embodiment. Referring to FIG. 1, the optical measurement system includes an optical system for illuminating a sample S with light from a light source and recording the wavefront of reflected light 4 from the sample S.

[0023] The wavefront sensor 10 acquires the plane distribution of light amplitude and phase as wavefront information. The wavefront sensor 10 outputs information on the recorded wavefront of the reflected light 4.

[0024] The optical measurement system includes a processing unit (for example, the information processing apparatus 100 shown in FIG. 3) that calculates the surface shape of the sample S based on the wavefront information of the reflected light 4. For example, the processing unit calculates the surface shape and the like of the sample S based on the plane distribution of light amplitude and phase acquired by the wavefront sensor 10. The surface shape of the sample S measured by the optical measurement system may be the shape of the outermost surface of the sample S (hereinafter also referred to as "topmost surface").

[0025] Incident angle θ of illumination light 2 i is selected to be a relatively large angle. For example, the incident angle θ of illumination light 2 i may be set to 70 degrees or more and less than 90 degrees. Incident angle θ i may be set to 75 degrees or more and less than 90 degrees. The incident angle θi may be set to 80 degrees or more and less than 90 degrees. The incident angle θ of illumination light 2 i will be described later.

[0026] The optical system that records the wavefront of the reflected light 4 from the sample S may employ any method such as holography, interference fringe analysis, or Shack-Hartmann wavefront sensor.

[0027] Figure 2 is a schematic diagram showing an example configuration of the optical measurement system 1 according to this embodiment. The configuration example shown in Figure 2 is one implementation example of the basic configuration example shown in Figure 1.

[0028] Figure 2 illustrates the case of measuring a disc-shaped sample S. Figure 2(A) shows a top view of the optical system of the optical measurement system 1, and Figure 2(B) shows a side view of the optical system of the optical measurement system 1.

[0029] Figure 2 shows an example of an implementation of an optical system for recording wavefronts, using the principle of off-axis holography. That is, the optical measurement system 1 shown in Figure 2 includes an optical system that follows off-axis holography.

[0030] The optical measurement system 1 includes an image sensor 20, a light source 22, optical fibers 24, 28, and 30, a coupler 26, and a lens 32 as an optical system for recording wavefronts. The optical measurement system 1 also includes an information processing device 100 (see Figure 3).

[0031] The light source 22 generates illumination light Q and reference light R. The light source 22 may be an coherent light source such as a laser.

[0032] The optical fiber 24 optically connects the light source 22 and the coupler 26. The coupler 26 branches the light from the light source 22 that is input through the optical fiber 24. Optical fibers 24, 28, and 30 may all be single-mode fibers.

[0033] One of the light beams, split by the coupler 26, is emitted from the fiber end 29 of the optical fiber 28. The light emitted from the fiber end 29 of the optical fiber 28 is converted (or collimated) by the lens 32 into parallel light of a predetermined diameter. The lens 32 converts the light from the light source 22 into parallel light. The parallel light converted by the lens 32 is used as illumination light Q. The illumination light Q has an incident angle θ iThe sample S is illuminated by being incident on the sample S. Object light O generated by reflection of illumination light Q from the sample S is incident on the image sensor 20.

[0034] The other beam split by the coupler 26 is emitted from the fiber end 31 of the optical fiber 30. The light emitted from the fiber end 31 of the optical fiber 30 is used as reference light R. The reference light R emitted from the fiber end 31 of the optical fiber 30 is incident on the image sensor 20. Since the light emitted from the fiber end 31 of the optical fiber 30 is directly used as the reference light R, the fiber end 31 can be regarded as a point light source for the reference light R.

[0035] The object light O and the reference light R are superimposed on a light-receiving surface of the image sensor 20 (hereinafter also referred to as a "recording surface"). In this way, the optical fiber 30 (or the fiber end 31) superimposes the object light O, which is reflected light from the sample S, and the reference light R, which is light from the light source 22, on the recording surface of the image sensor 20. The optical axis of the object light O does not coincide with the optical axis of the reference light R.

[0036] Since the object light O and the reference light R have coherence, interference fringes are generated on the recording surface of the image sensor 20. The interference fringes generated on the recording surface of the image sensor 20 reflect the surface shape of the sample S illuminated by the illumination light Q. Image information indicating the interference fringes recorded by the image sensor 20 is output to the information processing apparatus 100.

[0037] The information processing apparatus 100 analyzes interference fringes obtained by superimposing the object light O and the reference light R, and acquires the planar distribution of the amplitude and phase of light.

[0038] <B.Configuration Example of Information Processing Apparatus 100> Next, a configuration example of the information processing apparatus 100 included in the optical measurement system 1 according to the present embodiment will be described.

[0039] Figure 3 is a schematic diagram showing an example configuration of an information processing device 100 according to this embodiment. Referring to Figure 3, the information processing device 100 is an example of a computer and includes one or more processors 102, memory 104, input unit 106, display unit 108, storage 110, interface 120, network interface 122, and media drive 124.

[0040] One or more processors 102 include, for example, arithmetic circuits that perform processing according to computer-readable instructions. One or more processors 102 read one or more programs stored in storage 110 into memory 104 and execute them. One or more processors 102 may be multi-core processors or multi-processors.

[0041] In this specification, the term "processor" includes, at a minimum, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), and a DRP (Dynamically Reconfigurable Processor).

[0042] Memory 104 consists of volatile memory such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory), and functions as working memory for one or more processors 102 to execute programs.

[0043] The storage 110 consists of non-volatile memory such as a hard disk or flash memory, and stores various programs and data. For example, the storage 110 stores the operating system 112 (OS), the measurement program 114, the interference fringe image data 116, and the measurement results 118.

[0044] In this specification, the term “memory” includes at least the memory 104 and the storage 110.

[0045] The operating system 112 provides an environment in which one or more processors 102 execute programs. The measurement program 114 is executed by one or more processors 102 to realize an optical measurement method according to this embodiment. The measurement program 114 is executed by an information processing device 100, which is an example of a computer, to cause the information processing device 100 to execute the optical measurement method according to this embodiment. The measurement program 114 may be a collection of multiple programs.

[0046] The interference fringe image data 116 includes information recorded by the image sensor 20. The measurement result 118 includes measurement results (e.g., surface shape of sample S) obtained by executing the measurement program 114.

[0047] The input unit 106 includes, for example, a keyboard or mouse, and accepts user input.

[0048] The display unit 108 outputs to the user the results of program execution by one or more processors 102.

[0049] Interface 120 is responsible for data transmission, for example, to acquire information from the image sensor 20.

[0050] The network interface 122 is responsible for data transmission between, for example, the information processing device 100 and an external server device.

[0051] The media drive 124 reads necessary programs and data from the recording medium 126 (e.g., an optical disk, etc.) and stores them in the storage 110 or the like. The measurement program 114 executed in the information processing apparatus 100 may be installed via the recording medium 126 or the like, or may be downloaded from a server apparatus via the network interface 122 or the like.

[0052] The measurement program 114 may call and use a necessary module at a predetermined timing from among program modules provided as part of the operating system 112. Therefore, even the measurement program 114 that does not include some of the modules required for the processing according to the present invention is included in the technical scope of the present invention. The measurement program 114 may be provided by being incorporated into a part of another program.

[0053] <C. Surface Shape Measurement Processing> Next, surface shape measurement processing in the optical measurement system 1 according to the present embodiment will be described. In the following description, the direction perpendicular to the recording surface is defined as the z-axis, and the two axes orthogonal to the z-axis are defined as the x-axis and the y-axis, respectively. That is, the x-axis and the y-axis are parallel to the recording surface. For example, the intersection of the recording surface and the central optical axis of the object light O is set as the "origin" (x=0, y=0, z=0). Any point on the recording surface may be used as the origin. For simplification of description, the description of coordinates (x,y) may be appropriately omitted in the following formulas.

[0054] The object light O and the reference light R are lights having mutually coherent angular frequency ω. The planar distributions of the object light O and the reference light R are represented by the general formulas shown in the following formulas (1) and (2).

[0055] [Mathematical Formula]

[0056] In the optical system shown in FIG. 2, an off-axis hologram I recorded on the recording surface of the image sensor 20 OR is expressed as the light intensity of the combined light of the light expressed by formula (1) and the light expressed by formula (2), as shown in the following formula (3).

[0057]

Math.

[0058] In formula (3), the first term on the right-hand side corresponds to the light intensity component of the object beam O, the second term on the right-hand side corresponds to the light intensity component of the reference beam R, the third term on the right-hand side corresponds to the direct image component generated by modulating the object beam O with the reference beam R, and the fourth term on the right-hand side corresponds to the conjugate image component.

[0059] In the optical system shown in FIG. 2, the incident direction of the reference beam R is arranged to be inclined with respect to the incident direction of the object beam O. Therefore, when discrete Fourier transform is performed on the off-axis hologram I OR , a spectrum in which the third term on the right-hand side is separated from other terms can be obtained. By applying frequency filtering to the obtained spectrum, the direct image component of the third term is extracted.

[0060] By applying discrete Fourier transform and frequency filtering, a complex amplitude off-axis hologram J recording the object beam O shown in formula (4) OR (x,y) is obtained.

[0061]

Math.

[0062] The distribution of the reference beam R is expressed as an analytical solution of a spherical wave shown in formula (5) based on, for example, the coordinates (x R , y R , z R ) of a known point light source and the wave number k (=2π / λ, λ: wavelength) of the point light source.

[0063]

Math.

[0064] From equations (4) and (5), the object light hologram U(x,y) is expressed as in equation (6). Here, * represents the complex conjugate.

[0065]

number

[0066] The object light hologram U(x,y) in equation (6) corresponds to the surface distribution of the amplitude and phase of the object light O on the recording surface of the image sensor 20.

[0067] To calculate the complex amplitude reflection coefficient r of a sample from an object light hologram U(x,y), the illumination light hologram U(x,y) is used based on the information of the illumination light Q. Q We need to obtain (x,y). Illumination light hologram U Q (x,y) can be calculated by placing a reference surface with a known complex amplitude reflection coefficient in place of the sample S, and basing the calculation on the reflected light from the reference surface. The reference surface may be formed on a substrate. The object on which the reference surface is formed is also called the reference.

[0068] In equations (1) to (6) above, replace the object light O produced when the illumination light Q is reflected by the sample S with the reference reflected illumination light Q produced when the illumination light Q is reflected by the reference surface. ref By applying this, the reference reflective illumination light hologram U Qref (x,y) is obtained. Reference reflected illumination light hologram U Qref (x,y) includes information calculated from the reference surface. Illumination light hologram U Q (x,y) is the known complex amplitude reflection coefficient r of the reference surface. ref Using this, it can be expressed as in equation (7).

[0069]

number

[0070] Note that, when the planar distribution Q(x,y) of illumination light Q can be represented by an analytical solution, an analytical solution may be used to obtain the illumination light hologram U Q (x,y) instead of performing reference measurement using a reference surface. Specifically, the planar distribution r(x,y) of the complex amplitude reflectance of the sample can be expressed by formula (8) using the object light hologram U(x,y) and the illumination light hologram U Q (x,y).

[0071]

Mathem.

[0072] When only reflection from the outermost surface of the sample S is recorded, the surface profile h(x,y) of the sample S is expressed by formula (9) using the planar distribution r(x,y) of the complex amplitude reflectance.

[0073]

Mathem.

[0074] Here, λ is the wavelength of the light source, and θ i is the incident angle to the sample S, and arg is a function that calculates the argument (phase) of a complex number. Since arg is a multivalued function, phase connection processing or the like for determining the value may be performed as necessary.

[0075] Note that, in an optical system with a small numerical aperture, high coordinate accuracy of the point light source of the reference light R is not particularly required; however, when coordinate accuracy is required, for example, the method disclosed in International Publication No. WO 2023 / 079741 (Patent Document 4) may be used.

[0076] <D. Procedure of Measurement Processing> Next, an example of the procedure of measurement processing for a sample S using the optical measurement system 1 according to the present embodiment will be described.

[0077] Figure 4 is a flowchart showing an example of the processing procedure for measuring a sample S using the optical measurement system 1 according to this embodiment. Figure 4(A) shows an example of the processing procedure for reference measurement, and Figure 4(B) shows an example of the processing procedure for sample measurement. The order in which the reference measurement shown in Figure 4(A) and the sample measurement shown in Figure 4(B) are performed does not matter.

[0078] Referring to Figure 4(A), the optical system of the optical measurement system 1 is configured (step S2). In the configured optical system, a reference surface with a known complex amplitude reflection coefficient is placed at the position where the sample S is to be placed (step S4).

[0079] The reference surface is illuminated with illumination light Q generated by the light source 22 (step S6), and the reference reflected illumination light Q is also emitted from the reference surface. ref Off-axis hologram I, in which the reference light R is superimposed. QrefR (x,y) is recorded by the image sensor 20 (step S8). That is, in step S8, the wavefront of the reflected light from the reference surface is recorded.

[0080] The information processing device 100 displays an off-axis hologram I recorded by the image sensor 20. QrefR The discrete Fourier transform is performed on the reference reflected illumination light Q (step S10). The information processing device 100 applies frequency filtering to the spectrum obtained by the discrete Fourier transform, thereby obtaining the reference reflected illumination light Q ref A complex amplitude off-axis hologram J recorded QrefR Calculate (x,y) (Step S12).

[0081] The information processing device 100 acquires the surface distribution R(x,y) of the reference light R (step S14). For example, the surface distribution R(x,y) of the reference light R may be the analytical solution of the spherical wave shown in equation (5) above. The information processing device 100 then acquires the complex amplitude off-axis hologram J QrefR Based on (x,y) and the complex conjugate of the surface distribution R(x,y) of the reference light R, the reference reflected illumination light hologram U QrefCalculate (x,y) (Step S16).

[0082] The information processing device 100 uses a reference reflective illumination light hologram U Qref (x,y) and the known complex amplitude reflection coefficient r of the reference surface ref Using this, the illumination light hologram U Q The coordinates (x,y) are calculated (step S18). Then the process ends.

[0083] As mentioned above, if the surface distribution Q(x,y) of the illumination light Q can be expressed by an analytical solution, the reference measurement shown in Figure 4(A) can be omitted.

[0084] Referring to Figure 4(B), the optical system of the optical measurement system 1 is configured (step S20). If the optical system of the optical measurement system 1 has already been configured, the process in step S20 is omitted. The sample S is placed in the configured optical system (step S22).

[0085] The sample S is illuminated by the illumination light Q generated by the light source 22 (step S24), and the object light O, which is the reflected light from the sample S, and the reference light R are superimposed to form an off-axis hologram I. OR (x,y) is recorded by the image sensor 20 (step S26). That is, in step S26, the wavefront of the reflected light from the sample S is recorded.

[0086] The information processing device 100 displays an off-axis hologram I recorded by the image sensor 20. OR The discrete Fourier transform of (x,y) is performed (step S28). The information processing device 100 applies frequency filtering to the spectrum obtained by the discrete Fourier transform to record the object light O as a complex amplitude off-axis hologram J. OR Calculate (x,y) (Step S30).

[0087] The information processing apparatus 100 acquires the plane distribution R(x,y) of the reference light R (step S32). For example, the plane distribution R(x,y) of the reference light R may be an analytical solution of a spherical wave shown in the above formula (5). Note that if the plane distribution R(x,y) of the reference light R has already been calculated, the process of step S32 is omitted. The information processing apparatus 100 obtains a complex amplitude off-axis hologram J OR (x,y) and the conjugate complex number of the plane distribution R(x,y) of the reference light R, and calculates an object light hologram U(x,y) (step S34).

[0088] The information processing apparatus 100 obtains the object light hologram U(x,y) and an illumination light hologram U Q (x,y), and calculates the plane distribution r(x,y) of the complex amplitude reflection coefficient of the sample S (step S36). The information processing apparatus 100 calculates the plane distribution of the argument of the plane distribution r(x,y) of the complex amplitude reflection coefficient of the sample S (step S38), and calculates the surface shape h(x,y) of the sample S based on the calculated plane distribution of the argument, the cosine of the incident angle θ i and the wavelength λ of the light source (step S40). Then, the process ends.

[0089] <E. Setting of Incident Angle> Next, the behavior of the complex amplitude reflection coefficient r in a sample having a film structure will be described.

[0090] FIG. 5 is a diagram for explaining the behavior of a light wave incident on a sample having a film structure. Referring to FIG. 5, multiple reflection can occur when light is incident on a sample having a film structure.

[0091] Complex amplitude E i light wave is incident on a sample having a film structure, and a m-th order reflected light with complex amplitude E rm (where m is an integer of 1 or greater) is generated. The complex amplitude reflection coefficient r is expressed as the sum of the reflection on the outermost surface and other multiple reflection components, as shown in formula (10).

[0092]

Mathematics

[0093] Here, E r1 / E i Let r1 be the complex amplitude reflection coefficient of the surface reflected light, and Σ(E rm / E i ) the complex amplitude reflection coefficient r of the multiple reflected light rem Therefore, the complex amplitude reflection coefficient r can be expressed as shown in equation (11).

[0094]

number

[0095] The complex amplitude reflection coefficient r1 of the surface-reflected light is based on the light reflected from the surface (or outermost surface) of sample S, and the complex amplitude reflection coefficient r of the multiple reflections rem This is based on multiple beams of light reflected from surfaces other than the surface (or outermost surface) of sample S.

[0096] For example, in a sample where a transparent film is formed on a highly reflective surface, the magnitude of the complex amplitude reflection coefficient |r1| of the transparent film is equal to the magnitude of the complex amplitude reflection coefficient |r rem It can become smaller. In this case, r rem The components of this substance may be measured as part of the surface morphology of the sample.

[0097] In the optical measurement system 1 according to this embodiment, the incident angle θ of the illumination light Q is determined based on the complex amplitude reflection coefficient of the transparent film and the complex amplitude reflection coefficient of the multiple reflected light. i This is set. For example, the magnitude of the complex amplitude reflection coefficient |r1| of the transparent film is set to the magnitude of the complex amplitude reflection coefficient |r rem |To make it larger, the incident angle θ of the illumination light Q θ i The incident angle θ of the illumination light Q may be set. i The magnitude of the complex amplitude reflection coefficient r1 of the surface reflected light is equal to the complex amplitude reflection coefficient r of the multiple reflected light. rem It may be set to be larger than the size of [the object].

[0098] Furthermore, since the measurement accuracy is determined based on the relationship between the reflection from the outermost surface and the other multiple reflection components, the magnitude of the complex amplitude reflection coefficient r1 of the outermost surface reflection and the complex amplitude reflection coefficient r of the multiple reflections are determined according to the required measurement accuracy. rem The relationship with the size can be set as appropriate. For example, |r1|>α×|r rem (For example, 0.8 < α < 1 is also acceptable.)

[0099] Incident angle θ i The value of the complex amplitude reflection coefficient r1 of the surface reflected light, which is necessary for setting this, can be calculated using Fresnel's equation.

[0100] Specifically, when light is incident from a medium with refractive index n0 to a medium with refractive index n1, the angle of incidence θ i When light is incident on it, the S polarization reflection coefficient r 01s and P polarization reflection coefficient r 01p These are expressed as equations (12) and (13), respectively, according to Fresnel's equations.

[0101]

number

[0102] Here, θ t This is the angle of refraction when light is incident from a medium with refractive index n0 to a medium with refractive index n1, and is calculated from Snell's law shown in equation (14).

[0103]

number

[0104] By using equations (12) to (14), the S polarization reflection coefficient r 01s and P polarization reflection coefficient r 01p From this, the complex amplitude reflection coefficient r1 of the surface reflected light can be calculated.

[0105] The complex amplitude reflection coefficient r of a sample, calculated according to Fresnel's equation, is given by the incident angle θ. iAs the magnitude increases, the magnitude of the complex amplitude reflection coefficient |r1| of the surface reflection also approaches 1. The remaining component of the sample's complex amplitude reflection coefficient r is the complex amplitude reflection coefficient r of the multiple reflections. rem Since this corresponds to the angle of incidence θ i To increase the amount of the complex amplitude reflection coefficient r1 of the surface reflected light, rem It can be made larger.

[0106] Complex amplitude reflection coefficient r rem The value of is generally calculated using the multiple reflection formula. However, the film structure of the sample is unknown, and the complex amplitude reflection coefficient r rem If the value cannot be calculated, the maximum value in the absence of permeable components and membrane absorption is taken as |r rem | 2 =1-|r1| 2 It can be estimated as follows: |r1| 2 The incidence angle θ such that it exceeds 50% i You may set it to this.

[0107] Furthermore, |r1| is |r rem |To make it larger, the angle of incidence θ i Even if you set r rem The component of this cannot be zero. The complex amplitude reflection coefficient r of the multiple reflected light. rem The maximum error that the component of gives to the argument of r1 (see equation (9)) is given by r1 and r rem This can be estimated by assuming the case where the angle of the sum of the two values ​​deviates the most. In other words, the influence on the measurement result of the surface shape h(x,y) of sample S can be evaluated based on the maximum deviation in the angle of the sum.

[0108] Figure 6 shows the case where the error in the angular displacement is maximum. Refer to Figure 6, in the complex plane, r1 and r rem The sum of these is the vector representing r1 and r rem This corresponds to the composite vector of the vectors that represent r1 and r rem The tip of the vector representing the sum of and is centered at the tip of the vector representing r1, with radius |r rem It lies on the circumference of the circle |.

[0109] between r1 and r rem the argument of the sum has the largest deviation, as shown in FIG. 6, between r1 and r rem when the straight line passing through the origin for the vector representing the sum is tangent to the circumference. Therefore, for the surface shape h(x,y) of the sample, the maximum influence exerted by the r rem component on h err is expressed by formula (15) below.

[0110]

Math

[0111] According to formula (15), when the incident angle θ i is increased, the influence of r rem on the measurement result can be reduced, while the error caused to the measurement result by the coefficient 1 / cosθ i also increases. Further, if δ is the in-sample-plane resolution when the illumination light Q is incident perpendicularly, the in-sample-plane resolution in the direction in which the illumination light Q is tilted is degraded to δ / cosθ i . Therefore, the upper limit of the incident angle θ i may be determined based on the required resolution and allowable error.

[0112] <F. Measurement Example> Next, an example of measurement of sample S by the optical measurement system 1 according to the present embodiment will be described. In the following measurement example, the sample S is a mirror surface to which transparent ink is adhered.

[0113] FIG. 7 is a diagram showing a measurement example when a relatively small incident angle is set. FIG. 8 is a diagram showing a measurement example when a relatively large incident angle is set.

[0114] Specifically, as a comparative example, FIG. 7 shows a measurement example in the optical measurement system 1 shown in FIG. 2 when the incident angle θ i is set to 5.1 degrees. FIG. 8 shows, in the optical measurement system 1 shown in FIG. 2, when the incident angle θ ishows an example of measurement when set to 80.2 degrees. The incident angle θ of 80.2 degrees i satisfies the condition that the magnitude of the complex amplitude reflection coefficient |r1| of the outermost reflected light is greater than the magnitude of the complex amplitude reflection coefficient |r rem | of the multiple reflected light.

[0115] FIG. 7(A) shows an image visualizing the plane distribution of the calculated surface shape h(x,y) of sample S. FIG. 7(B) shows the cross-sectional shape (or profile) of the portion indicated by the arrow in the image shown in FIG. 7(A). In the measurement example shown in FIG. 7, the shape of the ink adhered to the mirror surface should exhibit a convex shape, but it is erroneously measured as a concave shape due to the influence of interference between the ink surface and the mirror surface.

[0116] FIG. 8(A) shows an image visualizing the plane distribution of the calculated surface shape h(x,y) of sample S. FIG. 8(B) shows the cross-sectional shape of the portion indicated by the arrow in the image shown in FIG. 8(A). In the measurement example shown in FIG. 8, it can be seen that the reflection component on the ink surface is correctly extracted, and the original convex shape is measured.

[0117] As described above, according to the optical measurement system 1 according to the present embodiment, even for a transparent object existing on a highly reflective surface, the shape of the outermost surface of the object can be correctly measured.

[0118] <G. Wavefront Diffraction Calculation and Focusing on Inclined Surfaces> The above-mentioned object light hologram U(x,y) is an off-axis hologram I recorded by the image sensor 20 OR calculated based on (x,y). Therefore, the object light hologram U(x,y) represents the distribution on the recording surface of the image sensor 20. The distribution on the sample surface may be calculated from the object light hologram U(x,y). For calculation of the distribution on the sample surface, for example, a diffraction calculation method can be used.

[0119] As an example, when the angular spectrum method (plane wave expansion) is used, the object light hologram U on a surface separated by an arbitrary distance d according to formulas (16) and (17) d and the illumination light hologram U Qd can be calculated respectively.

[0120]

Math

[0121] Instead of the object light hologram U and the illumination light hologram U Q , the object light hologram U d and the illumination light hologram U Qd are used to execute the processing of steps S36 to S40 shown in Fig. 4B.

[0122] By calculating the distribution on the sample surface, the measurement accuracy of the surface shape h(x,y) can be further improved.

[0123] Furthermore, since the incident angle θ of the illumination light Q i is relatively large, the sample surface is greatly inclined with respect to the wavefront expansion direction (z-axis direction). The object light hologram U d and the illumination light hologram U Qd each hologram may be subjected to wavefront rotation processing so as to be focused on the inclined sample surface.

[0124] Specifically, the object light hologram U d (x,y) is Fourier-transformed to calculate the spectrum F[U d (u,v). The spectrum F[U d (u,v) represents a group of plane waves propagating in various directions included in the hologram U d (x,y).

[0125] Here, the wave number vector k=(k x ,k y ,k z ) is the spectrum F[U dThe coordinates u and v of the ] and the wavelength λ of the light source are determined according to equation (18).

[0126]

number

[0127] Thus, the spectrum F[U d Hologram U from ](u,v) d The wave vector k of each plane wave contained in (x,y) is calculated.

[0128] Next, the spectrum F[U d A process is executed to rotate each plane wave contained in ](u,v) according to the angle of the tilted sample surface. More specifically, a three-dimensional rotation matrix T corresponding to the angle of the sample surface is generated. R The wave vector k of the plane wave is transformed. The wave vector k' of each plane wave after rotation is k'=(k x ',k y ',k z If we assume '), it is calculated according to equation (19).

[0129]

number

[0130] Thus, the wave vector k of each plane wave corresponds to a three-dimensional rotation matrix T corresponding to the angle of the sample plane. R The process of multiplying by the three-dimensional rotation matrix T is executed to calculate the wave vector k' of each plane wave after rotation. R This can be determined, for example, according to Rodrigues' rotation formula.

[0131] By rotating the wave vector k, the spectrum F[U] corresponding to each component of the plane wave is obtained. d The coordinates (u,v) of ] are equal to the coordinates (k x ' / 2π,k y ' / 2π) is moved. Apply this coordinate transformation to all plane waves (spectrum F[U d(all coordinates included in (u,v)), a new spectrum F[U T (u,v) is calculated.

[0132] Finally, by performing inverse Fourier transform on the calculated new spectrum F[U T , an object light hologram U on the inclined sample surface dT is calculated.

[0133] For the illumination light hologram U Qd (x,y), the illumination light hologram U on the inclined sample surface is obtained through the same calculation QdT is calculated.

[0134] Instead of the object light hologram U and the illumination light hologram U Q , the illumination light hologram U Qd (x,y) and the illumination light hologram U Qd are used to execute the processing of steps S36 to S40 shown in FIG. 4(B).

[0135] As described above, by performing wavefront rotation processing on the hologram, the measurement accuracy of the surface shape h(x,y) on the inclined sample surface can be further improved.

[0136] <H. Sample Arrangement Method> In the optical system of the optical measurement system according to the present embodiment, a relatively large incident angle θ i is selected, so the in-plane resolution differs between the direction in which the illumination light is inclined and the direction orthogonal to said direction.

[0137] FIG. 9 is a diagram for explaining the high-resolution axis and low-resolution axis in the optical measurement system 1 according to the present embodiment. Referring to FIG. 9, when the optical system of the optical measurement system 1 is viewed from above, the in-sample-plane resolution in the direction in which the illumination light Q is incident is lower than the in-sample-plane resolution in the direction orthogonal to said direction (which can also be referred to as, for example, the irradiation width of the illumination light Q).

[0138] In FIG. 9, an axis with relatively low in-sample-plane resolution is referred to as a low-resolution axis, and an axis with relatively high in-sample-plane resolution is referred to as a high-resolution axis. Let δ be the in-sample-plane resolution when the illumination light Q is normally incident, then the in-sample-plane resolution δ in the direction in which the illumination light Q is tilted θi is δ θi =δ / cosθ i .

[0139] When it is desired to measure the cross-sectional shape of a sample in consideration of such a difference in in-sample-plane resolution, the sample may be placed such that the cross-sectional direction of the measurement object coincides with the high-resolution axis. That is, the sample may be placed such that the direction of the measured cross-sectional shape is orthogonal to the irradiation direction (or the tilt direction) of the illumination light Q that illuminates the sample S.

[0140] For example, when it is desired to measure the cross-sectional shape of an edge portion of a sample, the direction of the cross-sectional shape can be made to coincide with the high-resolution axis by tilting the illumination light in the tangential direction of the edge of the sample from the normal incidence state.

[0141] <I. Modified Example of Incident Light> In the basic configuration example of the optical measurement system according to the present embodiment shown in FIG. 1, the illumination light 2 is parallel light having a predetermined diameter. The illumination light 2 does not have to be parallel light. For example, divergent light can also be used as the illumination light 2.

[0142] FIG. 10 is a schematic diagram showing another basic configuration example of the optical measurement system according to the present embodiment. In the optical measurement system shown in FIG. 10, the illumination light 2 is incident on the sample S after passing through the pinhole 6. Therefore, the illumination light 2 that illuminates the sample S is divergent light. That is, divergent light that has passed through the pinhole 6 is incident on the sample S.

[0143] Note that the pinhole 6 may be omitted, and light emitted from the fiber end of an optical fiber may be directly used as the illumination light 2 as it is.

[0144] By employing an optical system including a pinhole 6, or an optical system that directly uses light emitted from a fiber end as illumination light 2, noise components superimposed on the illumination light 2 can be reduced.

[0145] In the optical system shown in Fig. 10, the incident angle θ i varies depending on the position of the sample surface, so the incident angle θ i is not a constant value, and calculation using the incident angle θ i (x,y) for each coordinate of the sample S is required.

[0146] However, if θ i can be regarded as sufficiently constant for the required measurement accuracy, approximate calculation may be performed with the incident angle θ i set as a constant value.

[0147] <J. Method using information of bright fringes and dark fringes of interference fringes> As described above, the maximum influence exerted by the component of the complex amplitude reflection coefficient r rem on the sample surface profile h(x,y), denoted as h err , is calculated by equation (15). When the incident angle θ i is increased, the coefficient including the incident angle θ i (1 / cosθ i ) increases, so the measurement sensitivity for the surface profile h(x,y) decreases. That is, there is a limit to reducing errors only by setting the incident angle θ i .

[0148] Therefore, by referring to not only the phase information of the complex amplitude reflection coefficient r of the sample but also the amplitude information, the measurement accuracy can be further improved.

[0149] Fig. 11 is a diagram showing an example of the relationship between the phase of the complex amplitude reflection coefficient r1 of the outermost surface reflected light and the phase of the complex amplitude reflection coefficient r rem of multiple reflected light. Fig. 11(A) shows the case where r1 and r rem are in phase, and Fig. 11(B) shows the case where r1 and r rem are in opposite phase.

[0150] As shown in FIG. 11(A), r1 and r rem are in the same phase, and as shown in FIG. 11(B), r1 and r rem are in opposite phases, no error caused by the phase difference occurs. Here, when r1 and r rem are in the same phase, r1 and r rem the amplitude of the complex amplitude reflection coefficient r of the sample, which is the sum of rem and [[r]], is maximized when r1 and r are in opposite phases, the amplitude of the complex amplitude reflection coefficient r of the sample is minimized.

[0151] That is, when the ratio of the amplitude component of r1 to the amplitude component of r rem can be regarded as substantially constant, for the complex amplitude reflection coefficient r of the sample which is the sum of r1 and r rem , it can be considered that no error caused by the phase difference exists at the position where the amplitude is maximum or the position where the amplitude is minimum. This means that if the position is at the bright and dark lines of the interference fringes appearing in the hologram, it can be considered that there is no error caused by the phase difference.

[0152] As described above, by extracting information on the bright lines and dark lines of interference fringes appearing in the hologram recorded by the image sensor 20 and calculating the surface shape of the sample, the error shown in the above formula (15) is eliminated, and the measurement accuracy can be further improved. For example, off-axis hologram I OR information on bright lines and dark lines of interference fringes appearing therein is extracted to generate a noise-removed off-axis hologram, and the surface shape h(x,y) of the sample S may be calculated based on the noise-removed off-axis hologram.

[0153] <K. Correction Method Based on Magnitude of Complex Amplitude Reflection Coefficient> Next, for intermediate data that are neither in-phase nor opposite-phase, the complex amplitude reflection coefficient r rem a method for correcting the phase shift caused by [[the above]] will be described.

[0154] More specifically, the magnitude |r| of the complex amplitude reflection coefficient of the sample, the magnitude |r1| of the complex amplitude reflection coefficient, and the magnitude |r of the complex amplitude reflection coefficientrem The surface shape of the sample may be calculated using a correction amount based on |. Note that the magnitude of the complex amplitude reflection coefficient of the sample is |r|, the magnitude of the complex amplitude reflection coefficient is |r1|, and the magnitude of the complex amplitude reflection coefficient is |r rem Assume that the required precision is obtained.

[0155] Figure 12 shows the complex amplitude reflection coefficient r of the multiple reflected light. rem This diagram illustrates the phase shift caused by the above.

[0156] Refer to Figure 12, the complex amplitude reflection coefficient r rem The phase shift amount φ from r1 of the complex amplitude reflection coefficient caused by err is, r rem The phase of φ rem Then, it can be expressed by equation (20) below. Here, r rem Phase φ rem |r|, |r1| and |r rem It is calculated using equation (21) with |.

[0157]

number

[0158] However, equation (21) alone does not give the phase φ rem Since the sign cannot be determined, the phase φ is determined based on prior information about the sample's characteristics, as well as information such as how the value changes when polarization, incident angle, wavelength, etc. are changed. rem Determine the sign.

[0159] Ultimately, the phase shift φ from the complex amplitude reflection coefficient r1 of the surface reflection is err Using this, the corrected surface shape h(x,y) can be calculated by equation (22) below.

[0160]

number

[0161] In the method using information of bright fringes and dark fringes of interference fringes described above, the number of effective sampling points on the sample surface decreases, and there is a possibility that the in-plane resolution of the sample is reduced. Also, depending on the sample, clear bright fringes and dark fringes may not be generated.

[0162] In contrast, by using a method of correcting the phase shift caused by the complex amplitude reflection coefficient r rem using intermediate data, multiple reflection components can be removed and measurement accuracy can be further improved.

[0163] <L.Sample having a rough surface> In the optical measurement system 1 according to the present embodiment, the surface shape of a sample S having a rough surface can be measured.

[0164] As shown in the above formula (9), the surface shape h(x,y) of the sample S is calculated by obtaining the argument of the complex amplitude reflection coefficient. However, if the variation range of the argument exceeds 2π, the value of the arg function in formula (9) cannot be determined, and thus the surface shape h(x,y) of the sample S cannot be determined.

[0165] Here, the phase φ of the complex amplitude reflection coefficient r of the sample S with respect to the surface shape h(x,y) is represented by the following formula (23).

[0166]

Mathematical Expression

[0167] The surface shape h(x,y) is multiplied by a term of cosθ i , and therefore the amount of change in phase φ can be reduced as the incident angle θ i increases. That is, within the range of the height h included in the surface shape h(x,y) (the range from the minimum value h min to the maximum value h max ), the incident angle θ iBy setting this, the surface shape of a sample S with a rough surface can be measured. In other words, even a sample with undulations in height can be measured accurately. This condition is expressed by equation (24) below. Rearranging equation (24), the incident angle θ i As a condition, we obtain equation (25).

[0168]

number

[0169] In other words, the angle of incidence θ i This is the half-wavelength (λ / 2) of the light source that corresponds to the variation range (h) of the surface shape (or height from the measurement reference surface) of the sample S. max -h min The value may also be set to exceed the inverse cosine (arccosine) of the value obtained by dividing by (i.e., the quotient). Furthermore, if the value obtained by dividing the half wavelength (λ / 2) of the light emitted by the light source 22 by the variation range of the surface shape of the sample S exceeds 1, any incident angle θ i However, the phase difference φ does not exceed 2π, so the incident angle θ i This can be set arbitrarily.

[0170] The incident angle θ as described above i By setting this parameter, the surface curvature of sample S can be measured. Furthermore, the surface shape can be measured for any sample, not just those with a transparent film formed on a highly reflective surface.

[0171] Figure 13 shows an example of measurement of a sample with a rough surface. Figure 13 shows a measurement example using the optical measurement system 1 shown in Figure 2, where a metal surface with a surface shape variation range of approximately 2 μm was measured as sample S. In Figure 13, a laser with a wavelength of 638 nm was used as the light source 22. In this case, according to equation (25) above, the incident angle θ i It is calculated that this needs to be greater than approximately 80.822. Figure 13 shows the incident angle θ. i This shows an example of a measurement when the temperature is set to 81 degrees.

[0172] Fig. 13(A) shows an image visualizing the plane distribution of the calculated surface shape h(x,y) of the sample S. Fig. 13(B) shows the cross-sectional shape (or profile) of the portion indicated by the arrow in the image shown in Fig. 13(A).

[0173] In the measurement example shown in Fig. 13, it can be seen that a streak shape of about 2 μm can be measured. As described above, the incident angle θ of the illumination light Q i is set appropriately, whereby even the shape of a rough surface that is difficult to measure when the illumination light Q is vertically incident can be correctly measured.

[0174] <M. Variations> The optical system described above is an example, and any optically equivalent modifications can be made according to constraints such as required specifications and space. Further, the plurality of processes and functions described above can be arbitrarily combined.

[0175] In the optical measurement system described above, as an implementation example, an optical system using the principle of off-axis holography is illustrated, but any optical system may be used for implementation as long as it can acquire the plane distribution of the amplitude and phase of light.

[0176] The processing content of each step constituting the above flowchart is illustrative, and the processing of a plurality of steps may be combined into the processing of one step, or the processing of one step may be decomposed into the processing of a plurality of steps. The processing procedure shown in the above flowchart is an example, and the execution order of processing may be changed as appropriate.

[0177] In the configuration example described above, the information processing apparatus 100 executes arithmetic processing related to the measurement of the sample S, but for example, part or all of the arithmetic processing related to measurement may be executed using computing resources on the cloud.

[0178] <N. Summary> The optical measurement system according to this embodiment can measure the shape of the outermost surface of a sample non-contact, even when, for example, a transparent film is formed on a surface with high reflectivity. For example, the optical measurement system according to this embodiment can measure the incident angle θ of the illumination light. i By setting the angle to a relatively large value and employing a measurement algorithm based on wavefront information, the effects of multiple reflections within the sample are reduced. This makes it possible, for example, to measure the shape of the film structure of a sample with nanometer resolution.

[0179] The optical measurement system according to this embodiment can measure the surface shape of a sample without contact, thus avoiding damage to the sample. Furthermore, because the optical measurement system according to this embodiment performs surface measurement, it can perform measurements at a higher speed compared to line measurement.

[0180] 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]

[0181] 1 Optical measurement system, 2,Q Illumination light, 4 Reflected light, 6 Pinhole, 10 Wavefront sensor, 20 Image sensor, 22 Light source, 24,28,30 Optical fiber, 26 Coupler, 29,31 Fiber end, 32 Lens, 100 Information processing unit, 102 Processor, 104 Memory, 106 Input unit, 108 Display unit, 110 Storage, 112 Operating system, 114 Measurement program, 116 Interference fringe image data, 118 Measurement results, 120 Interface, 122 Network interface, 124 Media drive, 126 Recording medium, R Reference light, S Sample.

Claims

1. Light source and An optical system that illuminates a sample using light from the aforementioned light source and records the wavefront of the reflected light from the sample, The system includes a processing unit that calculates the surface shape of the sample based on the wavefront information of the reflected light, An optical measurement system in which the angle of incidence of light illuminating the sample is set based on a first complex amplitude reflection coefficient based on light reflected from the surface of the sample and a second complex amplitude reflection coefficient based on light reflected from surfaces other than the surface of the sample.

2. The optical system described above is The image sensor into which the reflected light is incident, The optical measurement system according to claim 1, further comprising an optical fiber for superimposing the reflected light and the light from the light source on the light-receiving surface of the image sensor.

3. The optical measurement system according to claim 1, wherein the sample is positioned such that the direction of the cross-sectional shape to be measured is perpendicular to the direction of irradiation of light illuminating the sample.

4. The system further includes a lens that converts light from the aforementioned light source into parallel light, The optical measurement system according to any one of claims 1 to 3, wherein the converted parallel light is incident on the sample.

5. The system further comprises a pinhole through which light from the aforementioned light source passes, The optical measurement system according to any one of claims 1 to 3, wherein divergent light passing through the pinhole is incident on the sample.

6. The optical measurement system according to claim 2, wherein the processing unit extracts information on bright and dark lines of interference fringes appearing in a hologram produced by the superposition of light, recorded by the image sensor, and calculates the surface shape of the sample.

7. The optical measurement system according to any one of claims 1 to 3, wherein the processing unit calculates the surface shape of the sample using a correction amount based on the magnitude of the complex amplitude reflection coefficient of the sample, the magnitude of the first complex amplitude reflection coefficient, and the magnitude of the second complex amplitude reflection coefficient.

8. Light source and An optical system that illuminates a sample using light from the aforementioned light source and records the wavefront of the reflected light from the sample, The system includes a processing unit that calculates the surface shape of the sample based on the wavefront information of the reflected light, An optical measurement system in which the angle of incidence of light illuminating the sample is set to exceed the inverse cosine of the value obtained by dividing half the wavelength of light from the light source by the variation range of the surface shape of the sample.

9. The steps include illuminating the sample with light from a light source, The steps include recording the wavefront of the reflected light from the aforementioned sample, The process includes the step of calculating the surface shape of the sample based on the wavefront information of the reflected light, An optical measurement method in which the angle of incidence of light illuminating the sample is set based on a first complex amplitude reflection coefficient based on light reflected from the surface of the sample and a second complex amplitude reflection coefficient based on light reflected from surfaces other than the surface of the sample.

Images