Optical measurement methods

Abstract

The present invention provides an optical measurement method, which includes: obtaining a measurement spectrum of a sample to be measured; performing smooth filtering on the measurement spectrum to obtain a high-frequency spectrum; establishing a variable substitution function relationship for the variable vacuum wavelength in the measurement spectrum based on the optical performance parameters of the sample to be measured to obtain a substitution variable; performing a reduction process on the high-frequency spectrum based on the substitution variable to obtain a target high-frequency signal; performing a Fourier transform on the target high-frequency signal to obtain a Fourier space spectrum; and performing peak search on the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured. The present invention improves the accuracy of the optical parameters of the sample to be measured by directly determining the parameter value corresponding to the maximum peak of the Fourier space spectrum and obtaining the parameter to be measured of the sample to be measured based on the parameter value.

Description

Technical Field

[0001] The present invention relates to the field of data analysis of precision optical measurement equipment, and in particular to an optical measurement method. Background Art

[0002] The measurement of optical parameters such as film thickness and optical critical dimensions (OCD) is widely used in the semiconductor and biomedical industries. The primary purpose of optical measurement is to obtain information such as film thickness, structure width, sidewall angle, and other critical dimensions, as well as optical constants. In the semiconductor manufacturing industry, fast measurement speeds, accurate results, and repeatability are often required.

[0003] The current method for measuring optical parameters such as thin film thickness and OCD is to obtain spectral data such as the sample's reflectivity, transmittance, ellipsometer parameters, and Mueller spectrum through equipment such as film thickness meters and ellipsometers. A theoretical spectral library is created based on the initial values of the parameters to be measured, and the initial values of the parameters to be determined are obtained through a certain algorithm (searching the spectral library based on the parameters to be determined, parsing the spectral data, etc.). The mean squared error (MSE) between the simulated spectrum and the experimental spectrum is usually calculated. When the mean squared error is minimized, the value of the parameter to be determined on the theoretical spectrum is the desired result.

[0004] However, when the film thickness to be measured exceeds 20 microns and the critical dimension aspect ratio exceeds 5 microns, high-frequency oscillations begin to appear in the spectrum, making it increasingly difficult to match the experimental spectrum using regression or library search methods. The main reasons are: 1. Due to the presence of multiple local minima, spectral fitting methods are highly dependent on the initial values. If the initial values deviate significantly (for example, by more than 50 nm), the mean squared error (MSE) between the theoretical spectrum created based on these initial values and the experimental spectrum will be large. 2. Due to the presence of high-frequency oscillations in the spectrum, the regression process often requires extensive trial and error, resulting in a long regression time. Although library search methods can be used to speed up the process, the accuracy requirements for library creation become increasingly stringent as the thickness increases, resulting in excessively large library files. 3. When the experimental spectrum contains certain errors, using the mean square error (MSE) as the best match criterion does not yield the true value.

[0005] Therefore, the present invention proposes an optical measurement method to improve the accuracy of measuring optical parameters such as film thickness and OCD. Summary of the Invention

[0006] The embodiment of the present invention provides an optical measurement method to improve the accuracy of measuring optical parameters such as film thickness and OCD.

[0007] The present invention provides an optical measurement method, comprising: S1, obtaining a measurement spectrum of a sample to be measured , is the vacuum wavelength of the incident light, and the is a variable; S2, the measured spectrum Perform smooth filtering to obtain the measured spectrum High frequency spectrum in S3, based on the optical performance parameters of the sample to be measured on the measured spectrum The vacuum wavelength Establish variable replacement function relationship to obtain replacement variables ; S4, based on the replacement variable , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal that presents a single periodic oscillation with the measured parameter of the sample to be measured ; S5, the target high frequency signal Performing Fourier transform to obtain a Fourier space spectrum; S6, searching for peaks in the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured.

[0008] The beneficial effect is that the optical measurement method provided by the present invention does not need to adopt linear regression or library search, and directly measures the target high-frequency signal. By performing Fourier transform to obtain the Fourier space spectrum and determining the parameter value corresponding to the maximum peak of the Fourier space spectrum, the measured parameters of the sample to be measured can be obtained according to the parameter value, thereby improving the measurement efficiency and accuracy of the optical parameters of the sample to be measured.

[0009] Optionally, the target high frequency signal Performing Fourier transform, including: Perform zero padding at the end to compensate for the target high frequency signal after zero padding Perform Fourier transform. Its beneficial effect is that: by End zero padding can improve the resolution of Fourier space and thus improve the measurement accuracy of optical parameters.

[0010] Optionally, the measured spectrum includes any one of an ellipsometric spectrum, a reflectivity spectrum, a transmittance spectrum, and a Mueller spectrum. The beneficial effect is that the present invention is applicable to various types of spectra and has a wide range of applications.

[0011] Optionally, the sample to be tested comprises N layers of thin films, where N is a positive integer. The beneficial effect is that the present invention is applicable to measuring parameters of a sample to be tested comprising multiple layers of thin films.

[0012] Further optionally, the replacement variable The N replacement variables corresponding to each film layer of the sample to be tested are included. , the replacement variable The functional relationship is established based on the refractive index of each thin film layer of the sample to be tested to obtain, , subscript Represents the order of the layers corresponding to each film, is a natural number less than or equal to N, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index of a thin film layer is defined in descending order, with the first thin film layer being the topmost thin film layer in the sample to be measured. This method has the beneficial effect of using parameters related to the film's own properties and corresponding functional relationships to set substitution variables, resulting in more accurate measurement results and improved efficiency in subsequent calculations.

[0013] Optionally, the measured spectrum Reflectance spectrum , the reflectance spectrum With the vacuum wavelength The parameters to be measured of each layer of the film of the sample to be measured satisfy the following relationship: ,in, i 、 j are all non-negative integers less than or equal to N, For the The thickness of the film to be measured, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index in a thin film.

[0014] Further optionally, the measurement spectrum Perform smooth filtering to obtain the measured spectrum High frequency spectrum in , including: the reflectance spectrum Perform smooth filtering to obtain the reflectivity spectrum High frequency spectrum in , .

[0015] Still further optionally, the replacement variable based on , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal that presents a single periodic oscillation with the measured parameter of the sample to be measured , including: based on each of the replacement variables , for the reflectance spectrum High frequency spectrum in Perform reduction processing to obtain the value of each replacement variable The corresponding The thickness of the film to be measured The target high-frequency signal presents a single periodic oscillation , .

[0016] Further optionally, the target high frequency signal Performing Fourier transform to obtain Fourier space spectrum, including: dividing the target high frequency signal Perform Fourier transform to obtain the Fourier space spectrum corresponding to each layer of the film , ,in is the Fourier space independent variable, is the Dirac function, The thickness to be measured The Fourier transform amplitude of a single periodic signal is presented, is the interference function of other periodic signals after Fourier transform.

[0017] Further optionally, the peak search is performed on the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured, including: the Fourier space spectrum corresponding to each layer of the film Peak search is performed, wherein the parameter value corresponding to the maximum peak is the measurement result of the thickness of the corresponding layer of the film to be measured in the sample to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of an embodiment of an optical measurement method provided by the present invention;

[0019] Figure 2 A schematic diagram of the structure of a sample to be tested provided by the present invention;

[0020] Figure 3 A schematic diagram of reflection of a sample to be tested in a vacuum provided by the present invention;

[0021] Figure 4 A schematic diagram of an embodiment of the present invention for measuring the film thickness of a sample A to be measured;

[0022] Figure 5 A schematic diagram of an embodiment of the present invention for measuring the film thickness of a sample B to be measured;

[0023] Figure 6 A schematic diagram of an embodiment of the present invention for measuring the film thickness of a sample C to be measured;

[0024] Figure 7 This is a schematic diagram of an embodiment of the present invention for measuring the film thickness of a sample D to be measured. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application are described below in conjunction with the accompanying drawings. The terms used in the following embodiments are for the purpose of describing specific embodiments only and are not intended to limit the present application. As used in the specification and claims of this application, the singular expressions "a," "the," "the," "the," and "the" are intended to include expressions such as "one or more," unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, "at least one" and "one or more" refer to one or more (including two). The term "and / or" is used to describe an association relationship between associated objects, indicating that three possible relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0026] References to "one embodiment" or "some embodiments" etc. described in this specification mean that the specific features, structures or characteristics described in conjunction with the embodiment are included in one or more embodiments of the present application. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. appearing in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in another way. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in another way. The term "connected" includes direct and indirect connections, unless otherwise stated. "First" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

[0027] In the embodiments of this application, words such as "exemplarily" or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplarily" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplarily" or "for example" is intended to present the relevant concepts in a concrete manner.

[0028] The present invention provides an optical measurement method, the process of which is as follows: Figure 1 Shown, including:

[0029] S1: Obtain the measurement spectrum of the sample to be tested , is the vacuum wavelength of the incident light, and the is a variable;

[0030] S2: Measure the spectrum Perform smooth filtering to obtain the measured spectrum High frequency spectrum in ;

[0031] S3: Based on the optical performance parameters of the sample to be measured, the measured spectrum The vacuum wavelength Establish variable replacement function relationship to obtain replacement variables ;

[0032] S4: Based on the replacement variables , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal that presents a single periodic oscillation with the measured parameter of the sample to be measured ;

[0033] S5: The target high frequency signal Perform Fourier transform to obtain Fourier space spectrum;

[0034] S6: Peak search is performed on the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured.

[0035] The optical measurement method provided by the present invention is to measure the measured spectrum based on the optical performance parameters of the sample to be measured. The vacuum wavelength Establish variable replacement function relationship to obtain replacement variables , can eliminate the problem of Fourier space peak shift and broadening caused by the change of material properties with vacuum wavelength λ. No need to use linear regression or library search, directly through the target high frequency signal By performing Fourier transform to obtain the Fourier space spectrum and determining the parameter value corresponding to the maximum peak of the Fourier space spectrum, the measured parameters of the sample to be measured can be obtained, thereby improving the measurement efficiency and accuracy of the optical parameters of the sample to be measured.

[0036] In a possible embodiment, the target high-frequency signal Performing Fourier transform, including: Perform zero padding at the end to compensate for the target high frequency signal after zero padding Perform Fourier transform. End zero padding can improve the resolution of Fourier space and thus improve the measurement accuracy of optical parameters.

[0037] In another possible embodiment, the measured spectrum includes any one of an ellipsometric spectrum, a reflectivity spectrum, a transmittance spectrum, and a Mueller spectrum. The present invention is applicable to various types of spectra and has a wide range of applications.

[0038] In another possible embodiment, the sample to be tested comprises N thin film layers, where N is a positive integer. The present invention is applicable to measuring parameters of a sample to be tested comprising multiple films. Optionally, N is greater than or equal to 1 and less than or equal to 5. The present invention can be used to measure the thickness of any film layer from the first to the fifth film layer on the sample to be tested. The first film layer is the film farthest from the base layer of the sample to be tested, and the first to fifth films are progressively closer to the base layer.

[0039] In one possible embodiment, the replacement variable The N replacement variables corresponding to each film layer of the sample to be tested are included. , the replacement variable The functional relationship is established based on the refractive index of each thin film layer of the sample to be tested to obtain, , subscript Represents the order of the layers corresponding to each film, is a natural number less than or equal to N, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index of a thin film layer is defined in descending order, with layer 1 being the topmost layer in the sample being measured. By using parameters related to the film's properties and corresponding functional relationships to set substitution variables, more accurate measurement results can be obtained and the efficiency of subsequent calculations can be improved.

[0040] In another possible embodiment, the measured spectrum Reflectance spectrum , the reflectance spectrum With the vacuum wavelength The parameters to be measured of each layer of the film of the sample to be measured satisfy the following relationship: ,in, i 、 j are all non-negative integers less than or equal to N, For the The thickness of the film to be measured, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index in a thin film.

[0041] In another possible embodiment, the measurement spectrum Perform smooth filtering to obtain the measured spectrum High frequency spectrum in , including: the reflectance spectrum Perform smooth filtering to obtain the reflectivity spectrum High frequency spectrum in , .

[0042] In another possible embodiment, the replacement variable , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal that presents a single periodic oscillation with the measured parameter of the sample to be measured , including: based on each of the replacement variables , for the reflectance spectrum High frequency spectrum in Perform reduction processing to obtain the value of each replacement variable The corresponding The thickness of the film to be measured The target high-frequency signal presents a single periodic oscillation , .

[0043] In a possible embodiment, the target high-frequency signal Performing Fourier transform to obtain Fourier space spectrum, including: dividing the target high frequency signal Perform Fourier transform to obtain the Fourier space spectrum corresponding to each layer of the film , ,in is the Fourier space independent variable, is the Dirac function, The thickness to be measured The Fourier transform amplitude of a single periodic signal is presented, is the interference function of other periodic signals after Fourier transform.

[0044] In a possible embodiment, the peak search of the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured, includes: searching the Fourier space spectrum corresponding to each layer of the film Peak search is performed, wherein the parameter value corresponding to the maximum peak is the measurement result of the thickness of the corresponding layer of the film to be measured in the sample to be measured.

[0045] In order to introduce the invention content of this application in more detail, examples are given here.

[0046] In a possible embodiment, the sample to be tested includes two layers of membrane, the specific structure is as follows Figure 2 As shown, the order of the film layers is defined from top to bottom, the first film layer is the top film layer in the sample to be tested, Film thickness About 20um~40um, Film thickness About 10um~30um. When the measured spectrum Reflectance spectrum , and the incident light beam is on the first film The incident angle is , through the incident angle , the refractive index in vacuum , the first layer of film Refractive index and the second membrane Refractive index get, , ;in, The incident light beam is on the first film and the second membrane The incident angle formed on the contact surface, The incident light beam is on the second film The incident angle formed on the contact surface of the substrate is the reflection diagram of the sample to be measured in vacuum, as shown in Figure 3 According to the Fresnel formula and ignoring multi-level reflection, the reflectivity spectrum is obtained The first approximation reflection coefficient , ,in, , is 1 or 2, The incident light beam is The film and the +1 film interface incident angle, The incident light is Refractive index in thin films; The incident light beam in vacuum and The reflection coefficient formed at the interface of film contact, The incident light beam is Membrane and The reflection coefficient formed at the interface of the film contact, The incident beam is The reflection coefficient formed at the interface between the film and the substrate. Vacuum, membrane, The refractive indices of the film and substrate are: 、 、 and ; Obtain the reflectivity spectrum according to the first-order approximation reflectance coefficient , , and in this formula, the first three terms contribute to low-frequency signals, while the last three terms containing film thickness information contribute to high-frequency signals. In order to improve the calculation sensitivity, the reflectivity spectrum Perform smooth filtering to obtain the reflectivity spectrum The high frequency part of the vacuum wavelength is constrained by the inherent properties of the thin film material of the sample to be tested. , to get the signal , Because the signal It is composed of three cosine functions superimposed on each other. When the refractive index of the material is constant, When is the independent variable, the reflectivity is expressed as 、 、 The three frequency signals are superimposed (among which, The first The real part of the refractive index of the layer material), the above three frequencies are due to and 、 and 、 and Interference is formed, and the reflectivity After Fourier transform, the frequency in Fourier space will be equal to the above three values ( 、 、 ) has a peak, and the rest of the frequencies are zero. But usually It is not a constant, but changes with the wavelength, resulting in peaks near the three frequencies mentioned above, and the highest peak position shifts, and the thicker the thickness, the more obvious the shift. At this time, the conventional method of calculating the thickness by Fourier transform of wave number to find the maximum peak position cannot accurately calculate the film thickness. To solve this problem, set , According to the The wavelength of the layer material properties is constrained and the signal Perform Fourier transform to obtain the Fourier space spectrum , ,in is the Dirac function, The thickness to be measured The Fourier transform amplitude of a single periodic signal is presented, is the interference function after Fourier transformation of other periodic signals. The Fourier space spectrum corresponding to each layer of the film is Peak search is performed, wherein the parameter value corresponding to the maximum peak is the measurement result of the thickness of the corresponding layer of the film to be measured in the sample to be measured. To account for the peaks introduced by other frequency signals, the refractive index of the first film is used as the independent variable. For example, the Fourier space spectrum of the first layer of film on the sample to be tested is , ;Apart from Beyond the peak, and There are peaks at , but these peaks change as the refractive index changes with wavelength, i.e. is not a constant, so the peak position will be broadened to a certain extent, resulting in a decrease in peak height and no highest peak will be formed. The secondary peak formed when the wavelength is greater than 1000nm does not affect the highest peak. Similarly, similar conclusions can be obtained for other films. Therefore, the measured thickness can be obtained by directly searching for the highest peak. Furthermore, because the wider the spectral independent variable range, the higher the resolution of the Fourier space, the high-frequency part has been removed before the Fourier transform in this step. The end zero padding is performed to improve the resolution of Fourier space.

[0047] In this embodiment, the incident angle of the incident light beam to the sample to be measured is and the wavelength of the incident light beam are both variable quantities, so in order to improve the feasibility of this solution, two methods can be used. The first method is to The first method is to use a fixed angle, but different wavelength light sources can be used to measure the optical parameters of the sample to be measured. Since this method does not require moving the light source and the probe, the measurement speed is relatively faster. The second method is to use a fixed wavelength and measure the optical parameters of the sample to be measured by changing the incident angle of the light beam. This method will not be affected by the dependence of the refractive index of the material on the wavelength. As long as the refractive index of the material at the wavelength used is known, the measurement results will be more accurate.

[0048] In a possible embodiment, the measured spectrum The corresponding film thickness is greater than or equal to 1000nm. The greater the thickness of the corresponding film, the more accurate the measurement method provided by the present invention. Greater than or equal to 1000nm. The larger the value, the more accurate the measurement method provided by the present invention.

[0049] The measured spectrum is filtered by at least one of a median filter, a finite length unit impulse response filter, a smoothing filter (Savitzky-Golay), or an empirical mode decomposition high-pass filter. Perform smooth filtering. Optionally, the median filter method, the finite length unit impulse response filter, and the Savitzky-Golay window size are 10-500.

[0050] In order to illustrate the effectiveness of the method, the present invention took four groups of test samples, namely test sample A, test sample B, test sample C and test sample D. The test sample A includes two layers of membrane and a base layer, which are 、 , a base layer; and said The thickness is 40 、 The thickness is 20 The sample B to be tested includes two layers of membrane and a base layer, which are 、 , a base layer; and said The thickness is 30 、 The thickness is 20 The sample C to be tested includes two layers of membrane and a base layer, which are 、 , a base layer; and said The thickness is 40 、 The thickness is 10 The sample D to be tested includes two layers of membrane and a base layer, which are 、 , a base layer; and said The thickness is 30 、 The thickness is 10 .

[0051] Figure 4 The reflectance spectrum of the sample A to be tested is shown. Figure 4 a in the figure is the reflectivity spectrum of each layer of film obtained by simulation calculation, which shows that the reflectivity varies with wavelength. Figure 4 b in the patent method is used to decompose the spectrum into high-frequency and low-frequency parts, where the solid line in b represents the high-frequency part of the spectrum and the dotted line in b represents the low-frequency part of the spectrum. When the membrane Figure 4 The c in the code is the first layer. After the refractive index of the film is reduced to wavelength, the high frequency part is Fourier transformed and the result is obtained. Figure 4 The horizontal coordinate position of the highest peak in c is 40 , that is, the measured The film thickness is the same as the initial setting. When the membrane Figure 4 The d in the figure is the use of the second layer After the refractive index of the film is reduced to wavelength, the high frequency part is Fourier transformed and the result is obtained. Figure 4 The horizontal coordinate position of the highest peak in d is 20 , that is, the measured The film thickness is the same as the initial setting.

[0052] Figure 5 The reflectance spectrum of the sample B to be tested is shown. Figure 5 a in the figure is the reflectivity spectrum of each layer of film obtained by simulation calculation, which shows that the reflectivity varies with wavelength. Figure 5 b in the patent method is used to decompose the spectrum into high-frequency and low-frequency parts, where the solid line in b represents the high-frequency part of the spectrum and the dotted line in b represents the low-frequency part of the spectrum. When the membrane Figure 5 The c in the figure is the result of Fourier transform of the high frequency part after wavelength reduction using the refractive index of the first Si film, and the result is Figure 5 The horizontal coordinate position of the highest peak in c is 40 , that is, the measured The film thickness is the same as the initial setting. When the membrane Figure 5 The d in the figure is the use of the second layer After the refractive index of the film is reduced to wavelength, the high frequency part is Fourier transformed and the result is obtained. Figure 5 The horizontal coordinate position of the highest peak in d is 20 , that is, the measured The film thickness is the same as the initial setting.

[0053] Figure 6 The reflectance spectrum of the sample C to be tested is shown. Figure 6 a in the figure is the reflectivity spectrum of each layer of film obtained by simulation calculation, which shows that the reflectivity varies with wavelength. Figure 6 b in the patent method is used to decompose the spectrum into high-frequency and low-frequency parts, where the solid line in b represents the high-frequency part of the spectrum and the dotted line in b represents the low-frequency part of the spectrum. When the membrane Figure 6 The c in the figure is the result of Fourier transform of the high frequency part after wavelength reduction using the refractive index of the first Si film, and the result is Figure 6 The horizontal coordinate position of the highest peak in c is 40 , that is, the measured The film thickness is the same as the initial setting. When the membrane Figure 6 The d in the figure is the use of the second layer After the refractive index of the film is reduced to wavelength, the high frequency part is Fourier transformed and the result is obtained. Figure 6 The horizontal coordinate position of the highest peak in d is 20 , that is, the measured The film thickness is the same as the initial setting.

[0054] Figure 7 The reflectance spectrum of the sample D to be tested is shown. Figure 7 a in the figure is the reflectivity spectrum of each layer of film obtained by simulation calculation, which shows that the reflectivity varies with wavelength. Figure 7 b in the patent method is used to decompose the spectrum into high-frequency and low-frequency parts, where the solid line in b represents the high-frequency part of the spectrum and the dotted line in b represents the low-frequency part of the spectrum. When the membrane Figure 7 The c in the figure is the result of Fourier transform of the high frequency part after wavelength reduction using the refractive index of the first Si film, and the result is Figure 7 The horizontal coordinate position of the highest peak in c is 40 , that is, the measured The film thickness is the same as the initial setting. When the membrane Figure 7 The d in the figure is the use of the second layer After the refractive index of the film is reduced to wavelength, the high frequency part is Fourier transformed and the result is obtained. Figure 7 The horizontal coordinate position of the highest peak in d is 20 , that is, the measured The film thickness is the same as the initial setting.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An optical measurement method, characterized in that: include: S1. Obtain the measurement spectrum of the sample to be tested , is the vacuum wavelength of the incident light, and the is a variable; S2, measuring the spectrum Perform smooth filtering to obtain the measured spectrum High-frequency spectrum in ; S3, the measurement spectrum based on the optical performance parameters of the sample to be measured The vacuum wavelength Establish variable replacement function relationship to obtain replacement variables , the replacement variable The N replacement variables corresponding to each film layer of the sample to be tested are included. , the replacement variable Acquired by establishing the functional relationship based on the refractive index of each thin film layer of the sample to be tested; S4, based on the replacement variable , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal corresponding to the measured parameter of the sample to be tested and presenting a single periodic oscillation ; S5, the target high frequency signal Perform Fourier transform to obtain Fourier space spectrum; S6. Peak search is performed on the Fourier space spectrum, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured.

2. The optical measurement method according to claim 1, wherein: The target high frequency signal Perform Fourier transforms, including: The target high frequency signal Perform zero padding at the end to compensate for the target high frequency signal after zero padding Perform a Fourier transform.

3. The optical measurement method according to claim 1, wherein: The measured spectrum includes any one of an ellipsometric spectrum, a reflectivity spectrum, a transmittance spectrum, and a Mueller spectrum.

4. The optical measurement method according to claim 1, wherein: The sample to be tested includes N layers of thin films, where N is a positive integer.

5. The optical measurement method according to claim 4, characterized in that: , subscript Represents the order of the layers corresponding to each film, is a natural number less than or equal to N, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index of the thin film is defined in order from top to bottom, and the first thin film is the topmost thin film in the sample to be tested.

6. The optical measurement method according to claim 5, characterized in that: The measured spectrum Reflectance spectrum , the reflectance spectrum With the vacuum wavelength The parameters to be measured of each layer of the film of the sample to be measured satisfy the following relationship: ,in, i 、 j are all non-negative integers less than or equal to N, For the The thickness of the film to be measured, The incident light beam is The film and the +1 film interface incident angle, The incident light is The refractive index in a thin film.

7. The optical measurement method according to claim 6, characterized in that: The measured spectrum Perform smooth filtering to obtain the measured spectrum High-frequency spectrum in , including: the reflectance spectrum Perform smooth filtering to obtain the reflectivity spectrum High-frequency spectrum in , .

8. The optical measurement method according to claim 7, characterized in that: The replacement variable , for the high frequency spectrum Perform reduction processing to obtain a target high-frequency signal that presents a single periodic oscillation with the measured parameter of the sample to be measured , including: based on each of the replacement variables , for the reflectance spectrum High-frequency spectrum in Perform reduction processing to obtain the same value as each of the replacement variables The corresponding The thickness of the film to be measured The target high-frequency signal presents a single periodic oscillation , .

9. The optical measurement method according to claim 8, characterized in that: The target high frequency signal Performing Fourier transform to obtain Fourier space spectrum, including: dividing the target high frequency signal Perform Fourier transform to obtain the Fourier space spectrum corresponding to each layer of the film , ,in is the Fourier space independent variable, is the Dirac function, The thickness to be measured The Fourier transform amplitude of a single periodic signal is presented, is the interference function of other periodic signals after Fourier transform.

10. The optical measurement method according to claim 9, characterized in that: The peak search of the Fourier space spectrum is performed, wherein the parameter value corresponding to the maximum peak is the measurement result of the parameter to be measured of the sample to be measured, including: the Fourier space spectrum corresponding to each layer of the film Peak search is performed, wherein the parameter value corresponding to the maximum peak is the measurement result of the thickness of the corresponding layer of the film to be measured in the sample to be measured.

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