Method for constructing spectral library, method and device for measuring optical critical dimension

Abstract

The present invention provides a method for constructing a spectral library, a method and device for measuring an optical critical dimension, relating to the technical field of optical critical dimension measurement. The method includes: respectively obtaining first-class spectral library data of at least three periods of a periodically variable structure; in the case where there is a linear difference in the spectra of the first-class spectral library data of the at least three periods, determining second-class spectral library data respectively corresponding to the remaining periods of the periodically variable structure according to the first-class spectral library data; and integrating the first-class spectral library data and the second-class spectral library data to construct a spectral library. By modeling the structures corresponding to at least three periods of the periodically variable structure to obtain the first-class spectral library data and fitting to obtain the second-class spectral library data of the structures corresponding to the remaining periods, the present invention reduces the number of modeling times required in the process of constructing the spectral library in OCD measurement, thereby reducing the construction time of the spectral library and improving the construction efficiency of the spectral library.

Description

Technical Field

[0001] The present invention relates to the technical field of optical critical dimension measurement, and particularly to a method for constructing a spectral library, a method for measuring an optical critical dimension, and an apparatus therefor. Background Art

[0002] After light waves are reflected and scattered by an object, the polarization state will change, thereby carrying a lot of characteristic information of the object. By studying the change in polarization of light waves before and after passing through the object, the polarization characteristics of the object can be obtained, and then information such as the structural morphology of the object can be obtained. Traditional optical critical dimension measurement obtains the theoretical spectral library by modeling the spectra of the periodic structures in the measured area, so as to obtain the three-dimensional parameters of the structure.

[0003] In the current measurement method, spectral libraries corresponding to different periodic structures need to be constructed separately for the matching process during measurement, with high construction costs and long required time. Summary of the Invention

[0004] The present invention provides a method for constructing a spectral library, a method for measuring an optical critical dimension, and an apparatus therefor, to solve the defect of high cost and long time in constructing a spectral library in the prior art, and to realize an efficient method for constructing a spectral library.

[0005] The present invention provides a method for constructing a spectral library, including:

[0006] Obtaining first-class spectral library data for at least three periods of a periodically variable structure respectively;

[0007] In the case where there is a linear difference in the spectra of the first-class spectral library data for the at least three periods, determining second-class spectral library data corresponding one by one to the remaining periods of the periodically variable structure according to the first-class spectral library data;

[0008] Integrating the first-class spectral library data and the second-class spectral library data to construct a spectral library.

[0009] According to the method for constructing a spectral library provided by the present invention, the periodically variable structure is a structure in a semiconductor process flow where the critical dimension and / or the pitch change.

[0010] According to the method for constructing a spectral library provided by the present invention, the critical dimension includes sub-critical dimensions of the periodically variable structure in several directions, and when the critical dimension changes, the sub-critical dimensions in at least one direction change;

[0011] The pitch includes sub-pitches of the periodically variable structure in several directions, and when the pitch changes, the sub-pitches in at least one direction change.

[0012] A method for constructing a spectral library provided by the present invention, the step of respectively obtaining the first type of spectral library data for at least three periods of the periodically variable structure specifically includes:

[0013] For each of the at least three periods, obtain the first theoretical spectrum of each period;

[0014] Obtain the first period value and the first structural parameter of each period as the first index parameter;

[0015] After establishing an index between the first theoretical spectrum and the first index parameter of each period, it is determined as the first type of spectral data of each period.

[0016] A method for constructing a spectral library provided by the present invention, the step of obtaining the first theoretical spectrum of each period specifically includes:

[0017] Perform rigorous coupled-wave analysis on the periodically variable structure in each period to obtain the first theoretical spectrum of each period.

[0018] A method for constructing a spectral library provided by the present invention, the step of fitting and determining the second type of spectral library data corresponding to the remaining periods of the periodically variable structure respectively according to the first type of spectral library data specifically includes:

[0019] Construct a model of the periodically variable structure based on the first theoretical spectrum of each period in the at least three periods, and determine the second theoretical spectra corresponding to the remaining periods of the periodically variable structure respectively based on the model of the periodically variable structure;

[0020] Parse each of the second theoretical spectra to obtain the second theoretical period value and the second theoretical structural parameter corresponding to each of the second theoretical spectra;

[0021] Correct the second theoretical period value and the second theoretical structural parameter to obtain the second period value and the second structural parameter corresponding to the second theoretical spectrum as the second index parameter;

[0022] After establishing an index between the second theoretical spectrum and the second index parameter of each period in the remaining periods of the periodically variable structure, it is determined as the second type of spectral library data.

[0023] A method for constructing a spectral library provided by the present invention, the step of correcting the second theoretical period value and the second theoretical structural parameter to obtain the second period value and the second structural parameter corresponding to the second theoretical spectrum as the second index parameter specifically includes:

[0024] Obtain the first theoretical period value and the first theoretical structural parameter of each period in the at least three periods;

[0025] Calculate a first period difference between the first theoretical period value and the first period value, and a first structure difference between the first theoretical structure parameter and the first structure parameter;

[0026] Fit the first period difference to obtain a second period difference for each period in the remaining periods of the period-variable structure, and fit the first structure difference to obtain a second structure difference for each period in the remaining periods of the period-variable structure;

[0027] Determine the second period value according to the second theoretical period value and the second period difference, and determine the second structure parameter according to the second theoretical structure parameter and the second structure difference.

[0028] The present invention also provides a method for measuring an optical critical dimension, including:

[0029] Obtain an outgoing Mueller spectrum of a period structure to be measured;

[0030] Match the outgoing Mueller spectrum in a spectral library constructed by the method for constructing any one of the above spectral libraries to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum;

[0031] Use the index parameter obtained by indexing the matching spectrum as the measurement parameter of the period structure to be measured.

[0032] The present invention also provides a device for constructing a spectral library, including:

[0033] A first acquisition module for respectively acquiring first-class spectral library data of at least three periods of a period-variable structure;

[0034] A second acquisition module for determining second-class spectral library data corresponding one by one to the remaining periods of the period-variable structure according to the first-class spectral library data when there is a linear difference in the spectra of the first-class spectral library data of the at least three periods;

[0035] A construction module for integrating the first-class spectral library data and the second-class spectral library data to construct a spectral library.

[0036] The present invention also provides a device for measuring an optical critical dimension, including:

[0037] A receiving module for obtaining an outgoing Mueller spectrum of a period structure to be measured;

[0038] A matching module for matching the outgoing Mueller spectrum in a spectral library constructed by the method for constructing any one of the above spectral libraries to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum;

[0039] A determination module, configured to use the index parameters obtained by matching the spectral indexes as the measurement parameters of the to-be-measured periodic structure.

[0040] The present invention further provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the method for constructing a spectral library as described in any one of the above is implemented.

[0041] The present invention further provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the method for constructing a spectral library as described in any one of the above is implemented.

[0042] The present invention further provides a computer program product, including a computer program. When the computer program is executed by a processor, the method for constructing a spectral library as described in any one of the above is implemented.

[0043] The method for constructing a spectral library, the method and device for measuring an optical critical dimension provided by the present invention obtain first-class spectral library data by modeling the structures corresponding to at least three periods of a periodically variable structure, fit the first-class spectral data to obtain second-class spectral library data of the structures corresponding to other periods of the periodically variable structure in the process requirements, and integrate the first-class spectral library data and the second-class spectral library data to construct a spectral library, reducing the number of modeling times required in the process of constructing the spectral library in OCD measurement, thereby reducing the construction time of the spectral library and improving the construction efficiency of the spectral library. In addition, an unexpected effect is that the critical dimensions of the structures corresponding to all periods of the periodically variable structure can be measured by using a constructed spectral library. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 is a schematic flowchart of the method for constructing a spectral library provided by the present invention;

[0046] Figure 2 is a schematic diagram of a periodically variable structure in the method for constructing a spectral library provided by the present invention;

[0047] Figure 3 is a schematic diagram of the structures of at least three periods of the periodically variable structure selected in the method for constructing a spectral library provided by the present invention;

[0048] Figure 4In (a), it is the theoretical spectral amplitude diagram mainly used to show the periodically variable structure with unchanged CD and changed space in the method for constructing the spectral library provided by the present invention;

[0049] Figure 4 In (b), it is the theoretical spectral phase diagram mainly used to show the periodically variable structure with unchanged CD and changed space in the method for constructing the spectral library provided by the present invention;

[0050] Figure 5 In (a), it is the theoretical spectral amplitude diagram mainly used to show the periodically variable structure with unchanged space and changed CD in the method for constructing the spectral library provided by the present invention;

[0051] Figure 5 In (b), it is the theoretical spectral phase diagram mainly used to show the periodically variable structure with unchanged space and changed CD in the method for constructing the spectral library provided by the present invention;

[0052] Figure 6 It is a schematic diagram mainly used to show the periodically variable structure with CD and space in multiple directions in the method for constructing the spectral library provided by the present invention;

[0053] Figure 7 It is a schematic diagram mainly used to show the technological process and its period involved in the semiconductor process in the method for constructing the spectral library provided by the present invention;

[0054] Figure 8 It is a schematic flow diagram of the method for measuring the optical critical dimension provided by the present invention;

[0055] Figure 9 It is a schematic structural diagram of the device for constructing the spectral library provided by the present invention;

[0056] Figure 10 It is a schematic structural diagram of the device for measuring the optical critical dimension provided by the present invention;

[0057] Figure 11 It is a schematic structural diagram of the electronic device provided by the present invention. Detailed implementation manners

[0058] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts fall within the scope of protection of the present invention.

[0059] The following will introduce the method for constructing the spectral library of the present invention in conjunction with Figures 1 to 5 as followsFigure 1 As shown in the figure, it includes:

[0060] Step 101: Obtain the first type of spectral library data for at least three periods of the variable-period structure respectively;

[0061] The variable-period structure is a structure whose period (pitch) changes in the semiconductor manufacturing process.

[0062] Optionally, for example, a structure with a fixed CD (Critical Dimension) and a changing space (the distance between two unit structures), or a structure with a changing CD and a fixed space. Among them, a variable-period structure with a fixed CD and a changing space is as shown in Figure 2 the figure.

[0063] Since the constructed spectral library is used to measure the critical dimensions of periodic structures in the production process, therefore, according to the process requirements of the periodic structures to be measured in the semiconductor manufacturing process, multiple periodic structures covering the process requirements can be pre-designed.

[0064] For example, for a fixed CD, in the process requirements of the semiconductor manufacturing process, there are 7 different spaces, that is, there are 7 different periods of the variable-period structure in the process requirements.

[0065] Determine at least three periods among all the periods of the variable-period structure, and obtain the first type of spectral library data of the variable-period structure in these three periods.

[0066] In a specific embodiment, referring to Figure 3 , corresponding to the variable-period structure with the above-mentioned 7 different periods, select the maximum period (period 3), the minimum period (period 1), and an intermediate period (period 2) required by its manufacturing process, and model the periodic structures corresponding to the selected three periods respectively to obtain the first type of spectral library data corresponding to the three periods respectively.

[0067] It can be understood that the first type of spectral library data represents the spectral library data obtained by modeling. The first type of spectral data for each period includes the theoretical spectrum of this period, as well as the period value and structural parameters corresponding to this period.

[0068] In other feasible embodiments, if the number of periods required by the variable-period structure manufacturing process is large, more periods can also be correspondingly selected and modeled.

[0069] Step 102: In the case where there is a linear difference in the spectra of the first type of spectral library data for the at least three periods, determine the second type of spectral library data corresponding to the remaining periods of the variable-period structure respectively one by one according to the first type of spectral library data;

[0070] Further, determine whether there are linear differences in the spectra of the first-class spectral library data for at least three periods. If so, the second-class spectral library data for the remaining periods of the variable-period structure can be determined based on the first-class spectral library data.

[0071] In a specific embodiment, Figure 4 Figures (a) and (b) in [reference] are schematic diagrams of theoretical spectra obtained by modeling three different periods of a variable-period structure. Among them, the CD of the variable-period structure is a fixed value of 40 nm, and the space is changed to 70 nm, 80 nm, and 90 nm respectively.

[0072] It can be seen that when the CD of the variable-period structure is fixed and the space is changed, the spectral amplitude increases by approximately 0.2 for each 10 nm increase in space at wavelengths from 400 to 440 nm; the spectral amplitude increases by approximately 0.05 for each 10 nm increase in space at wavelengths from 600 to 900 nm. The spectral phase decreases by approximately 0.125 for each 10 nm increase in space at wavelengths from 420 to 460 nm, and decreases by approximately 0.1 for each 10 nm increase in space at wavelengths from 540 to 680 nm.

[0073] Figure 5 Figures (a) and (b) in [reference] are schematic diagrams of theoretical spectra obtained by modeling three different periods of a variable-period structure. Among them, the space of the variable-period structure is a fixed value of 80 nm, and the CD is changed to 30 nm, 40 nm, and 50 nm respectively.

[0074] It can be seen that when the space of the variable-period structure is fixed and the CD is changed, the position of the spectral amplitude peak shifts by approximately 40 nm in wavelength for each 10 nm increase in CD at wavelengths from 300 to 540 nm; the spectral amplitude decreases by approximately 0.15 for each 10 nm increase in CD at wavelengths from 660 to 900 nm. The spectral phase valley shifts by approximately 40 nm in wavelength for each 10 nm increase in CD at wavelengths from 380 to 540 nm, and the spectral phase value decreases by approximately 0.4 for each 10 nm increase in CD at wavelengths from 540 to 640 nm.

[0075] That is to say, when there is a linear relationship between the spectral amplitude and the spectral phase with the change of the period at at least one wavelength in the spectral amplitude and spectral phase diagrams of at least three periods, it can be considered that there are linear differences in the spectra of the first-class spectral data of at least three periods.

[0076] For a structure with variable period, since the spectra with different periods have obvious linear differences, it is considered that the theoretical spectra of other periods of the structure with variable period can be determined by at least three known theoretical spectra, so that the corresponding structural parameters can be obtained by analyzing the theoretical spectra of other periods, and then the second type of spectral library data corresponding to other periods can be obtained.

[0077] It can be understood that the second type of spectral library data represents the spectral library data obtained by fitting. The second type of spectral library data includes the theoretical spectra, period values, and structural parameter values obtained by fitting for each period.

[0078] Step 103: Integrate the first type of spectral library data and the second type of spectral library data to construct a spectral library.

[0079] Integrate the first type of spectral library data obtained by modeling and the second type of spectral library data obtained by fitting, and put them into the same spectral library, then a spectral library for OCD measurement (Optical Critical Dimension Metrology) can be constructed.

[0080] It should be particularly noted that at this time, the spectral library constructed contains the spectral library data corresponding to all periods of the structure with variable period in the process requirements. Therefore, in the production process, through the constructed spectral library, it is possible to match the outgoing spectra of all periods of the structure with variable period and obtain the measurement results of each period of the structure with variable period.

[0081] In the method for constructing the spectral library of the present invention, the first type of spectral library data is obtained by modeling the structures corresponding to at least three periods of the structure with variable period, the second type of spectral library data corresponding to the structures of other periods of the structure with variable period in the process requirements is obtained by fitting based on the first type of spectral data, and the first type of spectral library data and the second type of spectral library data are integrated to construct a spectral library, which reduces the number of modeling times required in the process of constructing the spectral library in OCD measurement, thereby reducing the construction time of the spectral library and improving the construction efficiency of the spectral library. In addition, an unexpected effect is that through the constructed spectral library, it is possible to measure the critical dimensions of the structures corresponding to all periods of the structure with variable period.

[0082] In the method for constructing the spectral library of the present invention, the structure with variable period is a structure in the semiconductor process flow where the critical dimension and / or pitch changes.

[0083] In the case where the structure with variable period is a structure with period change in one direction, as Figure 2 shown, specifically, it is a structure in the semiconductor process flow where the CD remains unchanged and the space changes, or the CD changes and the space remains unchanged.

[0084] In the case where the periodically variable structure is a structure that varies periodically in multiple directions, as Figure 6 shown, there are CDs and spaces in two directions, the X-axis and the Y-axis, and it can also be a structure in which the CDs and spaces in one direction change while the CDs and spaces in the remaining directions remain unchanged.

[0085] Among them, some typical semiconductor process flows specifically include gate etching (Poly Etch), sidewall deposition (OSW Dep), shallow trench etching (STI Etch), copper planarization of the metal layer (Metal Cu CMP), and typical periods in these processes are as Figure 7 shown.

[0086] In the method for constructing the spectral library of the present invention, the critical dimensions include sub-critical dimensions of the periodically variable structure in several directions. When the critical dimensions change, the sub-critical dimensions in at least one direction change;

[0087] The pitches include sub-pitches of the periodically variable structure in several directions. When the pitches change, the sub-pitches in at least one direction change.

[0088] Specifically, as Figure 6 shown, in the case where a pattern feature includes a sub-critical dimension CD2 and a sub-pitch space2 in the X-axis direction, and a sub-critical dimension CD1 and a sub-pitch space1 in the Y-axis direction, when CD1 and / or CD2 change and space1 and space2 remain unchanged, or when space1 and / or space2 change and CD1 and CD2 remain unchanged, it can also be recognized as a periodically variable structure.

[0089] Meanwhile, if the CDs and spaces in one direction change simultaneously, for example, CD1 and space1 change while CD2 and space2 remain unchanged, or CD2 and space2 change while CD1 and space1 remain unchanged, it can also be recognized as a periodically variable structure.

[0090] In the method for constructing the spectral library of the present invention, the step of respectively obtaining first-class spectral library data of at least three periods of the periodically variable structure specifically includes:

[0091] For each of the at least three periods, obtaining the first theoretical spectrum of each period;

[0092] The first-class spectral library data includes at least the theoretical spectrum for matching with the outgoing spectrum and the structural parameters corresponding to each theoretical spectrum.

[0093] Therefore, for at least three selected periods, first, their first theoretical spectra are obtained respectively through conventional modeling means. It can be understood that the first theoretical spectra represent the actual spectral data obtained by modeling, including at least spectral amplitude and spectral phase.

[0094] Obtain the first period value and the first structural parameter of each of the above-mentioned periods as the first index parameter;

[0095] Furthermore, for at least three selected periods, obtain the first period value and the first structural parameter corresponding to the structure of each period as the first index parameter.

[0096] Among them, the first period value represents the structural period parameter corresponding to the structure of each selected period, including the CD of a pattern feature (poly) and the space between two pattern features; the first structural parameter represents the three-dimensional parameters of the structure of each selected period, such as line width, height, and angle, etc., which are determined according to the specific structure of the period-variable structure.

[0097] Specifically, through physical property characterization and analysis, directly obtain the first period value and the first structural parameter corresponding to the structure of each period.

[0098] After establishing an index between the first theoretical spectrum and the first index parameter of each of the above-mentioned periods, it is determined as the first type of spectral data of each of the above-mentioned periods.

[0099] Establish an index between the first theoretical spectrum and the first index parameter of each period, so that during the OCD measurement process, according to the matched theoretical spectrum, the first index data matched with the theoretical spectrum can be found according to its index.

[0100] It can be understood that the first index data represents the data obtained by querying according to the index, that is, the period value and the structural parameter corresponding to the theoretical spectrum.

[0101] The first index parameter X is expressed as X = (P 0 , X 1 , X 2 , ……, X n ). In the formula, P 0 represents the first period value, and X n represents the nth first structural parameter.

[0102] In the method for constructing the spectral library of the present invention, the step of obtaining the first theoretical spectrum of each of the above-mentioned periods specifically includes:

[0103] Perform rigorous coupled-wave analysis on the period-variable structure in each of the above-mentioned periods to obtain the first theoretical spectrum of each of the above-mentioned periods.

[0104] Rigorous Coupled-Wave Analysis (RCWA) is a numerical method used to calculate the propagation of light waves in periodic structures by considering the propagation and reflection of electromagnetic waves as the superposition of coupled waves propagating in the periodic structure.

[0105] Specifically, according to the structures corresponding to at least three periods selected, define the geometric shape, material parameters, and periodic characteristics of the structure corresponding to each period. Then, perform simulations on the structure. Based on the Fourier modal method, RCWA decomposes the periodic structure into multiple spatial harmonic components, and these components interact with each other through the coupled-wave equation.

[0106] Then, by solving the coupled-wave equation, analyze the propagation characteristics of electromagnetic waves in the periodic structure, and obtain the first theoretical spectrum of each period according to the simulation results.

[0107] In the method for constructing the spectral library of the present invention, the step of determining the second spectral library data corresponding to the remaining periods of the variable-period structure one by one according to the first type of spectral library data specifically includes:

[0108] Construct a model of the variable-period structure based on the first theoretical spectrum of each period in the at least three periods, and determine the second theoretical spectra corresponding to the remaining periods of the variable-period structure one by one based on the model of the variable-period structure;

[0109] To determine the second spectral library data based on the first spectral library data of at least three periods obtained through modeling, it is first necessary to determine the second theoretical spectra corresponding to the remaining periods of the variable-period structure.

[0110] It can be understood that although relatively accurate theoretical spectral data can be obtained through the RCWA method, the steps of the RCWA method are relatively cumbersome. If the structure of each period of the variable-period structure is modeled through the RCWA method to obtain its theoretical spectral data, the time required to construct the spectral library is relatively long.

[0111] Therefore, in the present invention, the second theoretical spectra of each period in the remaining periods are obtained by fitting the first theoretical spectra of each period in at least three periods.

[0112] Specifically, first, construct a model of the variable-period structure based on the fitting of the first theoretical spectra of each period in at least three periods, and then generate the second theoretical spectra of each period in the remaining periods of the variable-period structure based on the constructed model.

[0113] Analyze each of the second theoretical spectra to obtain the second theoretical period value and the second theoretical structure parameters corresponding to each of the second theoretical spectra;

[0114] In a feasible implementation manner, the physical property characterization analysis can be directly performed on the structures corresponding to the remaining periods of the period-variable structure to obtain the second period value and the second structure parameter corresponding to each period therein.

[0115] However, in order to further improve the construction speed of the spectral library, the present invention determines the second period value and the second structure parameter by analyzing the second theoretical spectrum.

[0116] Specifically, for the second theoretical spectrum corresponding to each period in the remaining periods, since the incident spectrum can be determined in advance according to the spectrum of the incident light used in OCD measurement, taking the second theoretical spectrum as the outgoing spectrum, the Mueller matrix is constructed based on the incident spectrum and the second theoretical spectrum as follows:

[0117] ;

[0118] In the formula, S n,IN represents the incident loss light amount, S n,OUT represents the outgoing loss light amount, n is 0, 1, 2 or 3, S 0 represents the total light intensity, S 1 represents the sum of the horizontal and disposal polarization components, S 2 represents the difference between the 45° and 135° polarization components, S 3 represents the difference between the right-handed and left-handed circular polarization components; M ij represents the contribution of the i th Stokes parameter of the matrix to the j th Stokes parameter, for example, M 21 represents S 0,IN 's contribution to S 1,OUT .

[0119] By analyzing the matrix elements of the Mueller matrix, the theoretical parameters of the structure corresponding to the Mueller matrix can be obtained, that is, based on the second theoretical spectrum corresponding to each period in the remaining periods, the second theoretical period value and the second theoretical structure parameter corresponding to each period in the remaining periods can be analyzed and obtained.

[0120] Correct the second theoretical period value and the second theoretical structure parameter to obtain the second period value and the second structure parameter corresponding to the second theoretical spectrum as the second index parameter;

[0121] It should be noted that since the structural parameters obtained by analyzing the Mueller matrix are theoretical values, and there is a certain difference between them and the actual values obtained by physical property characterization analysis. Therefore, after obtaining the second theoretical period value and the second theoretical structural parameters corresponding to each period in the remaining periods, it is necessary to correct the above theoretical values to obtain the second period value and the second structural parameters representing the actual values as the second index parameters finally stored in the spectral library.

[0122] In a feasible implementation manner, it is possible to obtain the difference between the theoretical period value data and the theoretical structural value data corresponding to each period in at least three periods and the first period value and the first structural parameter obtained by physical property characterization analysis, and correct the second theoretical period value and the second theoretical structural parameter based on the difference.

[0123] After establishing an index between the second theoretical spectrum and the second index parameter for each period in the remaining periods of the period-variable structure, it is determined as the second type of spectral library data.

[0124] After establishing an index between the second theoretical spectrum and the second index parameter corresponding to each period in the remaining periods of the period-variable structure, it is determined as one piece of the second type of spectral library data corresponding to that period.

[0125] In the present invention, by fitting the first theoretical spectra of at least three periods with a linear relationship, the second theoretical spectra of the remaining periods of the period-variable structure are obtained, and the second period value and the second structural parameter are obtained as the second index parameters based on the second theoretical period value and the second theoretical structural parameter obtained by analyzing the second theoretical spectra. That is, based on the modeling data of at least three periods, the spectral library data of the remaining periods of the period-variable structure are fitted, thereby effectively improving the construction speed of the spectral library for OCD measurement.

[0126] In the method for constructing the spectral library of the present invention, the step of correcting the second theoretical period value and the second theoretical structural parameter to obtain the second period value and the second structural parameter corresponding to the second theoretical spectrum as the second index parameter specifically includes:

[0127] Obtain the first theoretical period value and the first theoretical structural parameter of each of the at least three periods;

[0128] In order to correct the second theoretical period value and the second theoretical structural parameter more accurately, the present invention corrects the second theoretical period value and the second theoretical structural parameter based on the difference between the first period value and the first structural parameter and their corresponding theoretical values.

[0129] Therefore, in order to obtain the above difference, it is first necessary to determine the theoretical values corresponding to each first period value and the first structural parameter.

[0130] Optionally, for the structure of each of at least three selected periods, record the incident spectrum respectively S in1 、 S in2 ,……, S inn ,where n represents the number of selected periods. After the incident light acts on the structure of the corresponding period, the outgoing Mueller spectrum of the structure of each selected period is obtained through an ellipsometer S OUT1 、 S OUT2 ,……, S OUTn 。

[0131] For each of the above periods, based on the recorded incident spectrum and the collected outgoing Mueller spectrum information, construct and analyze the matrix elements of the Mueller matrix to obtain the first theoretical period value and the first theoretical structural parameter corresponding to each period, in the same way as obtaining the second theoretical period value and the second theoretical structural parameter, so it will not be elaborated here

[0132] Calculate the first period difference between the first theoretical period value and the first period value, and the first structure difference between the first theoretical structural parameter and the first structural parameter

[0133] Fit the first period difference to obtain the second period difference of each period in the remaining periods of the period-variable structure, and fit the first structure difference to obtain the second structure difference of each period in the remaining periods of the period-variable structure

[0134] Calculate the first period difference between the first theoretical period value and the first period value respectively, and the first structure difference between each first theoretical structural parameter and its corresponding first structural parameter

[0135] In a feasible implementation, the first index parameter X = (P 0真实 ,X 1真实 ,X 2真实 ,X 3真实 ,X 4真实 )is obtained through physical property characterization analysis, where P 0真实 represents the first period value, X n真实 represents the first structural parameter, and the theoretical structural parameter X 理论 = (P 0理论 ,X 1理论 ,X 2理论 ,X 3理论 ,X 4理论 )obtained by analyzing the Mueller matrix, where P 0理论 represents the second theoretical period value, X n理论represent the second structural parameter and put the theoretical structural parameter X 理论 into a separate preliminary spectral library. At the same time, put the determined first theoretical spectrum, second theoretical spectrum, second theoretical period value, and second theoretical structural parameter into the preliminary spectral library as well.

[0136] Calculate P 0真实 and P 0理论 to obtain the first period difference therebetween. Calculate the first structural difference between each structural parameter X n真实 and X n理论 respectively. In this embodiment, four first structural differences are correspondingly obtained.

[0137] Perform fitting on the first period differences corresponding to at least three obtained periods to obtain the second period differences corresponding to all the remaining periods; for each first structural difference, perform fitting respectively based on the first structural difference of this item corresponding to at least three periods to obtain the second structural difference of this item corresponding to all the remaining periods.

[0138] Determine the second period value according to the second theoretical period value and the second period difference, and determine the second structural parameter according to the second theoretical structural parameter and the second structural difference.

[0139] In the same way as obtaining the same first period difference, calculate the second period value through the second theoretical period value and the second period difference.

[0140] For example, when the first period difference is the first theoretical period value minus the first period value, the second period value is the second theoretical period value minus the second period difference; when the first period difference is the first period value minus the first theoretical period value, the second period value is the second theoretical period value plus the second period difference.

[0141] The method for determining the second structural parameter based on the second theoretical structural parameter and the second structural difference is the same as it, so it will not be elaborated here.

[0142] In a feasible embodiment, correspondingly supplement the fitted second period differences and each second structural difference into the pre-constructed preliminary spectral library, and update the second theoretical period value and the second theoretical structural parameter stored in the preliminary spectral library, then it can be updated to the second period value and the second structural parameter, that is, the constructed spectral library is obtained by updating the preliminary spectral library.

[0143] The present invention obtains the first theoretical spectra of at least three periods of a variable-period structure, fits them to obtain the second theoretical spectra of the remaining periods of the variable-period structure, fits the differences between the theoretical structure parameters and the actual structure parameters of at least three periods, corrects the theoretical structure parameters obtained by analyzing the second theoretical spectra to obtain the second period value and the second structure parameters, thereby realizing the fitting of the second theoretical spectral library data of the remaining periods based on the first theoretical spectral library data of at least three periods, effectively reducing the time required to separately model the structure of each period to form a spectral library, and improving the construction speed of the spectral library.

[0144] The present invention also provides a method for measuring an optical critical dimension, as Figure 8 shown, including:

[0145] Step 801, obtaining the outgoing Mueller spectrum of the to-be-measured periodic structure;

[0146] Through an ellipsometer or other spectral measurement device, obtain the outgoing Mueller spectrum after the incident light acts on the to-be-measured periodic structure.

[0147] Wherein, the to-be-measured periodic structure is a variable-period structure, that is, a structure in which CD and / or space change in the semiconductor manufacturing process.

[0148] Step 802, matching the outgoing Mueller spectrum in the spectral library constructed by the spectral library construction method described in each of the above methods to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum;

[0149] Match the obtained outgoing Mueller spectrum in the pre-constructed spectral library.

[0150] Specifically, the spectral library pre-constructed by each of the above methods contains the spectral library data of all periods of the variable-period structure corresponding to the to-be-measured periodic structure.

[0151] Match the outgoing Mueller spectrum of the to-be-measured periodic structure with the first theoretical spectrum and the second theoretical spectrum in the spectral library to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum.

[0152] In this embodiment, the method of spectral matching is not limited, as long as the matching spectrum corresponding to the outgoing Mueller spectrum can be quickly obtained.

[0153] Step 803, using the index parameters indexed by the matching spectrum as the measurement parameters of the to-be-measured periodic structure.

[0154] According to the obtained matching spectrum, index the corresponding index parameters, where the index parameters include the period value and various structure parameters of the matching spectrum, and use them as the measurement parameters of the to-be-measured periodic structure, that is, obtain the measurement result of the optical critical dimension measurement.

[0155] Through the pre-constructed spectral library model, when measuring a periodically variable structure, the pre-constructed spectral library can be used to measure the period value and structural parameters of the structure of the periodically variable structure at any of its periods. Unexpectedly, the construction time of the spectral library required for measurement is reduced, thereby reducing the total time required for measurement and improving the efficiency of optical critical dimension measurement.

[0156] The construction device of the spectral library provided by the present invention will be described below. The construction device of the spectral library described below can be correspondingly referred to the construction method of the spectral library described above.

[0157] As Figure 9 shown, the construction device of the spectral library includes a first acquisition module 901, a second acquisition module 902, and a construction module 903:

[0158] The first acquisition module 901 is configured to respectively acquire first-class spectral library data of at least three periods of the periodically variable structure;

[0159] The periodically variable structure is a structure whose period (pitch) changes in the semiconductor manufacturing process.

[0160] Optionally, for example, a structure with a fixed CD (Critical Dimension) and a changing space (the distance between two unit structures), or a structure with a changing CD and a fixed space. Among them, a periodically variable structure with a fixed CD and a changing space is as Figure 2 shown.

[0161] Since the constructed spectral library is used to measure the critical dimensions of the periodic structure in the production process, therefore, according to the process requirements of the periodic structure to be measured in the semiconductor manufacturing process, multiple periodic structures covering the process requirements can be pre-designed.

[0162] For example, for a fixed CD, in the process requirements of the semiconductor manufacturing process, there are 7 different spaces, that is, there are 7 different periods of the periodically variable structure in the process requirements.

[0163] Determine at least three periods among all the periods of the periodically variable structure, and acquire the first-class spectral library data of the periodically variable structure at these three periods.

[0164] In a specific embodiment, referring to Figure 3, corresponding to the above-mentioned period-variable structure with 7 different periods, select the maximum period (Period 1), the minimum period (Period 3), and an intermediate period (Period 2) required for its manufacturing process, and model the period structures corresponding to the selected three periods respectively to obtain the first-class spectral library data corresponding to the three periods respectively.

[0165] It can be understood that the first-class spectral library data represents the spectral library data obtained by modeling. The first-class spectral data of each period includes the theoretical spectrum of that period, as well as the period value and structural parameters corresponding to that period.

[0166] In other feasible embodiments, if the number of periods required for the manufacturing process of the period-variable structure is large, more periods can also be correspondingly selected and modeled.

[0167] The second acquisition module 902 is configured to, in the case where there are linear differences in the spectra of the first-class spectral library data of the at least three periods, determine the second-class spectral library data corresponding to the remaining periods of the period-variable structure respectively according to the first-class spectral library data;

[0168] Furthermore, determine whether there are linear differences in the spectra in the first-class spectral library data of the at least three periods obtained. If so, the second-class spectral library data of the remaining periods of the period-variable structure can be determined based on the first-class spectral library data.

[0169] In a specific embodiment, Figure 4 Figures (a) and (b) in are schematic diagrams of the theoretical spectra obtained by modeling three different periods of the period-variable structure. Among them, the CD of the period-variable structure is a fixed value of 40 nm, and the space is changed to 70 nm, 80 nm, and 90 nm respectively.

[0170] It can be seen that when the period-variable structure has a fixed CD and a changed space, its spectral amplitude increases by approximately 0.2 for each 10 nm increase in space at wavelengths from 400 to 440 nm; the spectral amplitude increases by approximately 0.05 for each 10 nm increase in space at wavelengths from 600 to 900 nm. The spectral phase decreases by approximately 0.125 for each 10 nm increase in space at wavelengths from 420 to 460 nm, and the phase value decreases by approximately 0.1 for each 10 nm increase in space at wavelengths from 540 to 680 nm.

[0171] Figure 5 Figures (a) and (b) in are schematic diagrams of the theoretical spectra obtained by modeling three different periods of the period-variable structure. Among them, the space of the period-variable structure is a fixed value of 80 nm, and the CD is changed to 30 nm, 40 nm, and 50 nm respectively.

[0172] It can be seen that for the period-variable structure, when the space is fixed and the CD is changed, the spectral amplitude at wavelengths from 300 to 540 nm shifts the peak position by approximately 40 nm in wavelength for every 10 nm increase in CD; the spectral amplitude at wavelengths from 660 to 900 nm decreases by approximately 0.15 for every 10 nm increase in CD; the spectral phase at wavelengths from 380 to 540 nm shifts the valley position by approximately 40 nm in wavelength for every 10 nm increase in CD, and at wavelengths from 540 to 640 nm, the phase value decreases by approximately 0.4 for every 10 nm increase in CD.

[0173] That is to say, when there is a linear relationship between the spectral amplitude and the spectral phase with the change of the period at least at one wavelength in the spectral amplitude and spectral phase diagrams of at least three periods, it can be considered that there is a linear difference in the spectra of the first-class spectral data of at least three periods.

[0174] For the period-variable structure, since the spectra with the change of the period have obvious linear differences, it is considered that the theoretical spectra of other periods of the period-variable structure can be determined by at least three known theoretical spectra, so that the corresponding structural parameters can be analyzed from the theoretical spectra of other periods, and then the second-class spectral library data corresponding to other periods can be obtained.

[0175] It can be understood that the second-class spectral library data represents the spectral library data obtained by fitting. The second-class spectral library data includes the theoretical spectra obtained by fitting for each period, the period values, and the structural parameter values.

[0176] The building block 903 is used to construct a spectral library by integrating the first-class spectral library data and the second-class spectral library data.

[0177] Integrate the first-class spectral library data obtained by modeling and the second-class spectral library data obtained by fitting, and put them into the same spectral library, then a spectral library for OCD measurement can be constructed.

[0178] It should be particularly noted that the spectral library constructed at this time contains the spectral library data corresponding to all periods of the period-variable structure in the process requirements. Therefore, in the production process, the spectral library constructed can match the outgoing spectra of all periods of the period-variable structure to obtain the measurement results of each period of the period-variable structure.

[0179] The present invention obtains the first type of spectral library data by modeling the structures corresponding to at least three periods of a period-variable structure, fits the second type of spectral library data of the structures corresponding to other periods of the period-variable structure in the process requirements based on the first type of spectral data, and integrates the first type of spectral library data and the second type of spectral library data to construct a spectral library, reducing the number of modeling times required in the process of constructing the spectral library in OCD measurement, thereby reducing the construction time of the spectral library and improving the construction efficiency of the spectral library. In addition, an unexpected effect is that the critical dimension measurement of the structures corresponding to all periods of the period-variable structure can be realized through a completed spectral library.

[0180] The optical critical dimension measurement device provided by the present invention will be described below. The optical critical dimension measurement device described below can be correspondingly referred to the optical critical dimension measurement method described above.

[0181] As Figure 10 shown, the optical critical dimension measurement device includes a receiving module 1001, a matching module 1002, and a determining module 1003:

[0182] The receiving module 1001 is configured to obtain the outgoing Mueller spectrum of the period structure to be measured;

[0183] Through an ellipsometer or other spectral measurement device, obtain the outgoing Mueller spectrum after the incident light acts on the period structure to be measured.

[0184] Among them, the period structure to be measured is a period-variable structure, that is, a structure in which CD and / or space change in the semiconductor manufacturing process.

[0185] The matching module 1002 is configured to match the outgoing Mueller spectrum in the spectral library constructed by the spectral library construction method described in the above methods to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum;

[0186] Match the obtained outgoing Mueller spectrum in the pre-constructed spectral library.

[0187] Specifically, the spectral library pre-constructed by the above methods includes the spectral library data of all periods of the period-variable structure corresponding to the period structure to be measured.

[0188] Match the outgoing Mueller spectrum of the period structure to be measured with the first theoretical spectrum and the second theoretical spectrum in the spectral library to obtain a matching spectrum with the highest similarity to the outgoing Mueller spectrum.

[0189] In this embodiment, the method of spectral matching is not limited, and as long as the matching spectrum corresponding to the outgoing Mueller spectrum can be quickly obtained.

[0190] A determination module 1003 is configured to use the index parameters obtained by matching the spectral indices as the measurement parameters of the to-be-measured periodic structure.

[0191] Based on the obtained matching spectral indices, corresponding index parameters are obtained, where the index parameters include the period value of the matching spectrum and various structural parameters, and these are used as the measurement parameters of the to-be-measured periodic structure, that is, the measurement result of the optical critical dimension measurement is obtained.

[0192] Through the pre-constructed spectral library model, when the present invention realizes the measurement of a periodically variable structure, the pre-constructed spectral library can be used to measure the period value and structural parameters of the structure of the periodically variable structure at any of its periods. An unexpected effect is that it reduces the construction time of the spectral library required for measurement, thereby reducing the total time required for measurement and improving the efficiency of optical critical dimension measurement.

[0193] Figure 11 An example of the physical structure diagram of an electronic device is shown as Figure 11 shown. The electronic device may include: a processor 1110, a communication interface 1120, a memory 1130, and a communication bus 1140. Among them, the processor 1110, the communication interface 1120, and the memory 1130 complete mutual communication through the communication bus 1140. The processor 1110 can call the logical instructions in the memory 1130 to execute the method for constructing the spectral library, and the method includes: respectively obtaining the first type of spectral library data of at least three periods of the periodically variable structure; fitting and determining the second type of spectral library data corresponding to the remaining periods of the periodically variable structure according to the first type of spectral library data; integrating the first type of spectral library data and the second type of spectral library data to construct a spectral library.

[0194] In addition, when the logical instructions in the above-mentioned memory 1130 are implemented in the form of software functional units and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0195] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the method for constructing a spectral library provided by each of the above methods. The method includes: respectively obtaining first-class spectral library data of at least three periods of a periodically variable structure; fitting and determining second-class spectral library data respectively corresponding to the remaining periods of the periodically variable structure according to the first-class spectral library data; and integrating the first-class spectral library data and the second-class spectral library data to construct a spectral library.

[0196] In another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the method for constructing a spectral library provided by each of the above methods. The method includes: respectively obtaining first-class spectral library data of at least three periods of a periodically variable structure; fitting and determining second-class spectral library data respectively corresponding to the remaining periods of the periodically variable structure according to the first-class spectral library data; and integrating the first-class spectral library data and the second-class spectral library data to construct a spectral library.

[0197] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0198] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the above technical solutions, in essence, or the part that contributes to the prior art can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0199] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for constructing a spectral library, characterized in that: include: Acquire first-type spectral library data of at least three periods of periodic variable structures respectively, wherein the periodic variable structures are structures in which critical dimensions and / or spacings are changed in a semiconductor process flow; In the case that there are linear differences in the spectra of the at least three periods of the first type of spectrum library data, determining the second type of spectrum library data corresponding to the remaining periods of the periodic variable structure according to the first type of spectrum library data; Integrating the first type of spectral library data and the second type of spectral library data to construct a spectral library; The step of determining the second type of spectral library data corresponding to the remaining periods of the periodic variable structure according to the first type of spectral library data specifically includes: Building a model of the periodic variable structure based on a first theoretical spectrum of each period of the at least three periods, and determining second theoretical spectra corresponding to the remaining periods of the periodic variable structure based on the model of the periodic variable structure, wherein the first theoretical spectrum represents actual spectral data obtained by modeling; Analyze each of the second theoretical spectra respectively to obtain a second theoretical period value and a second theoretical structure parameter corresponding to each of the second theoretical spectra; Correcting the second theoretical period value and the second theoretical structure parameter to obtain a second period value and a second structure parameter corresponding to the second theoretical spectrum as a second index parameter; After establishing an index between the second theoretical spectrum of each period in the remaining periods of the periodic variable structure and the second index parameter, the spectrum is determined as the second type of spectrum library data.

2. The method for constructing a spectral library according to claim 1, characterized in that: The critical dimension includes sub-critical dimensions of the periodically variable structure in several directions, and when the critical dimension changes, the sub-critical dimension in at least one direction changes; The pitch includes sub-pitch of the periodically variable structure in several directions, and when the pitch changes, the sub-pitch in at least one direction changes.

3. The method for constructing a spectral library according to claim 1, characterized in that: The step of respectively acquiring first-type spectral library data of at least three periods of the periodic variable structure specifically includes: For each period of the at least three periods, obtaining a first theoretical spectrum of each period; Acquire a first period value and a first structure parameter of each period as a first index parameter; After establishing an index between the first theoretical spectrum of each period and the first index parameter, the first type of spectrum data of each period is determined.

4. The method for constructing a spectral library according to claim 3, characterized in that: The step of obtaining the first theoretical spectrum of each period specifically includes: A rigorous coupled wave analysis is performed on the periodic variable structure in each period to obtain a first theoretical spectrum of each period.

5. The method for constructing a spectral library according to claim 3, characterized in that: The step of correcting the second theoretical period value and the second theoretical structure parameter to obtain the second period value and the second structure parameter corresponding to the second theoretical spectrum as the second index parameter specifically includes: Acquire a first theoretical cycle value and a first theoretical structure parameter of each cycle in the at least three cycles; Calculating a first period difference between the first theoretical period value and the first period value, and a first structure difference between the first theoretical structure parameter and the first structure parameter; Fitting the first period difference to obtain a second period difference of each period in the remaining periods of the period-variable structure, and fitting the first structure difference to obtain a second structure difference of each period in the remaining periods of the period-variable structure; The second period value is determined according to the second theoretical period value and the second period difference value, and the second structural parameter is determined according to the second theoretical structural parameter and the second structural difference value.

6. A method for measuring an optical critical dimension, characterized in that: include: Obtain the outgoing Mueller spectrum of the periodic structure to be measured; Matching the output Mueller spectrum in a spectral library constructed by the spectral library construction method according to any one of claims 1 to 5 to obtain a matching spectrum with the highest similarity to the output Mueller spectrum; The index parameters obtained by matching the spectrum index are used as measurement parameters of the periodic structure to be measured.

7. A device for constructing a spectral library, characterized in that: include: A first acquisition module is used to respectively acquire first-type spectral library data of at least three periods of a periodically variable structure, wherein the periodically variable structure is a structure in which a critical dimension and / or a spacing in a semiconductor process flow is changed; A second acquisition module is used to determine, when there are linear differences in the spectra of the at least three periods of the first-type spectrum library data, the second-type spectrum library data corresponding to the remaining periods of the periodic variable structure according to the first-type spectrum library data; A construction module, used for integrating the first type of spectral library data and the second type of spectral library data to construct a spectral library; The second acquisition module is specifically used to construct a model of the periodic variable structure based on the first theoretical spectrum of each period in the at least three periods, and determine second theoretical spectra corresponding to the remaining periods of the periodic variable structure based on the model of the periodic variable structure, wherein the first theoretical spectrum represents actual spectral data acquired by modeling; Analyze each of the second theoretical spectra respectively to obtain a second theoretical period value and a second theoretical structure parameter corresponding to each of the second theoretical spectra; Correcting the second theoretical period value and the second theoretical structure parameter to obtain a second period value and a second structure parameter corresponding to the second theoretical spectrum as a second index parameter; After establishing an index between the second theoretical spectrum of each period in the remaining periods of the periodic variable structure and the second index parameter, the spectrum is determined as the second type of spectrum library data.

8. An optical critical dimension measuring device, characterized in that: include: A receiving module, used for obtaining an outgoing Mueller spectrum of the periodic structure to be measured; A matching module, used for matching the output Mueller spectrum in a spectrum library constructed by the spectrum library construction method according to any one of claims 1 to 5, to obtain a matching spectrum with the highest similarity to the output Mueller spectrum; The determination module is used to use the index parameters obtained by matching the spectrum index as the measurement parameters of the periodic structure to be measured.

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