A global calibration method for an optical measurement system

Abstract

The application provides a global calibration method of an optical measurement system, various system models of different installation modes are designed for the possible forward and reverse installation of a compound wave plate, correct global system parameters and the current installation mode of the optical measurement system are solved through iteration of the different system models, and then the parameters of a sample to be measured can be solved through iteration, and the global calibration of the optical measurement system parameters can also be realized for the case of reverse installation of the wave plate, and the robustness of the global calibration of the optical measurement system is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical measurement system, more particularly, to a global calibration method of optical measurement system. BACKGROUND

[0002] In the semiconductor industry, the measurement of optical critical dimension (OCD) and the measurement of fine structure film thickness are directly related to the precision and yield of the production sample. Optical measurement systems such as ellipsometer are widely used in semiconductor process monitoring due to their non-contact, non-destructive, fast, high-precision and other advantages.

[0003] The basic configuration of the ellipsometer includes (): Figure 2 ): light source 1, polarizer 2, first rotating motor 3, polarizing compound wave plate 4, sample to be measured 5, analyzing compound wave plate 6, second rotating motor 7, analyzer 8 and spectrometer 9. The basic principle of the global system calibration and measurement of the ellipsometer is as follows:

[0004] 1. Natural light passes through the polarizer and (rotating) wave plate to obtain polarized light;

[0005] 2. The new polarized light obtained by the reflection or transmission of the standard sample material;

[0006] 3. The new polarized light passes through the (rotating) wave plate of the analyzing arm and the analyzer to obtain the changed light intensity information;

[0007] 4. The measurement light intensity change information is processed to obtain the global system parameters.

[0008] 5. The light intensity information of the sample to be measured is measured, and the Fourier transform of the measurement light intensity is obtained.

[0009] 6. The sample parameters are calculated by using the global system parameters and the Fourier coefficients of the sample to be measured.

[0010] In the fourth step, the Fourier transform of the measurement light intensity information is performed to obtain the measured Fourier coefficients. Through the system model of the polarizing compound wave plate and the analyzing compound wave plate in normal installation, the global system parameters of the optical measurement system are iteratively solved. When the polarizing compound wave plate or the analyzing compound wave plate is reversed, the global system parameters of the optical measurement system solved by this method are inaccurate. SUMMARY

[0011] The present application provides a global calibration method of optical measurement system to solve the technical problems in the prior art, comprising:

[0012] Obtaining the full-band light intensity information of the standard sample in the optical measurement system, performing Fourier transform on the light intensity information, and calculating the measured Fourier coefficients of the standard sample;

[0013] According to the measured Fourier coefficient and the theoretical Fourier coefficient calculated by a plurality of system models corresponding to different installation modes of the compound wave plate in the optical measurement system, global system parameters of the optical measurement system are iteratively solved, and the current installation mode of the optical measurement system is determined.

[0014] Full-band light intensity information of the sample to be measured in the optical measurement system is acquired, and the light intensity information is subjected to Fourier transform to calculate a measured Fourier coefficient of the sample to be measured.

[0015] According to the measured Fourier coefficient of the sample to be measured and the global system parameters, a system model corresponding to the current installation mode of the optical measurement system is used to iteratively solve sample parameters.

[0016] The global calibration method of the optical measurement system provided by the application is capable of designing system models of various installation modes in view of the possible forward and reverse installation of the compound wave plate, iteratively solving correct global system parameters and the current installation mode of the optical measurement system, and further iteratively solving sample parameters. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Fig. 1 is a structural schematic diagram of an optical measurement system;

[0018] Figure 2 Fig. 2 is a flowchart of a global calibration method of an optical measurement system provided by the application;

[0019] In the drawings, the names of optical devices represented by the respective reference numerals include:

[0020] 1, light source, 2, polarizer, 3, rotary motor, 4, polarizing compound wave plate, 5, sample to be measured, 6, analyzing compound wave plate, 7, second rotary motor, 8, analyzer, 9, spectrometer. DETAILED DESCRIPTION

[0021] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application. In addition, the technical features in each embodiment or in a single embodiment provided by the present application can be combined with each other at will to form a feasible technical solution, and the combination is not restricted by the sequence of steps and / or the mode of structural composition, but should be based on the fact that the technical solution can be realized by those skilled in the art. When the combination of technical solutions appears to be contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the present application.

[0022] Figure 2 A flow chart of a global calibration method of an optical measurement system provided by the present application is shown in FIG. 1, and the method comprises the following steps. Figure 2

[0023] S1, obtaining full-band light intensity information of a standard sample in the optical measurement system, and performing Fourier transform on the light intensity information to calculate measured Fourier coefficients of the standard sample.

[0024] The full-band light intensity change information of the standard sample can be obtained by using a spectrometer or other measuring equipment, and the Fourier coefficients can be calculated by Fourier transform on the light intensity information, which are referred to as the measured Fourier coefficients of the standard sample.

[0025] S2, iteratively solving global system parameters of the optical measurement system according to the measured Fourier coefficients and theoretical Fourier coefficients calculated by a plurality of system models corresponding to different installation modes of a compound wave plate in the optical measurement system, and determining a current installation mode of the optical measurement system.

[0026] It can be understood that the compound wave plate in the optical measurement system includes a polarizing compound wave plate and an analyzing compound wave plate. When the compound wave plate in the optical measurement system is installed, the polarizing compound wave plate and the analyzing compound wave plate can be reversely installed. At this time, it is undoubtedly inaccurate to solve the global system parameters of the optical measurement system based on the system models of the polarizing compound wave plate and the analyzing compound wave plate in the normal installation mode. Therefore, different system models corresponding to different installation modes of the polarizing compound wave plate and the analyzing compound wave plate are designed.

[0027] ​The different installation modes of the compound wave plate in the optical measurement system include a polarizing compound wave plate positive installation-a detecting compound wave plate positive installation, a polarizing compound wave plate positive installation-a detecting compound wave plate reverse installation, a polarizing compound wave plate reverse installation-a detecting compound wave plate positive installation, and a polarizing compound wave plate reverse installation-a detecting compound wave plate reverse installation. Corresponding system models are respectively designed for the four different installation modes.

[0028] When the polarizing compound wave plate positive installation-a detecting compound wave plate positive installation, the system model is:

[0029] S out =[M A R(A+ρ2)]×[R(-ω2t+C2+θ2)M(δ2)R(ω2t+C2+θ2)]×Ms×[R(-ω1t-C1-θ1+ρ1)M(δ1)R(ω1t+C1+θ1-ρ1)]×[R(-P+ρ1)M P ]×S in (1);

[0030] The system parameters ρ1, θ1 and δ1 have the following relationship with the global system parameters of the polarizing compound wave plate model:

[0031]

[0032] The system parameters ρ2, θ2 and δ2 have the following relationship with the global system parameters of the detecting compound wave plate model:

[0033]

[0034] When the polarizing compound wave plate reverse installation-a detecting compound wave plate reverse installation, the system model is:

[0035] S out =[M A R(A+ρ2)]×[R(-ω2t+C2+θ2-ρ2)M(δ2)R(ω2t-C2-θ2+ρ2)]×Ms×[R(-ω1t+C1+θ1)M(δ1)R(ω1t-C1-θ1)]×[R(-P+ρ1)M P ]×S in (4);

[0036] The system parameters ρ1, θ1 and δ1 have the following relationship with the global system parameters of the polarizing compound wave plate model:

[0037]

[0038] The system parameters ρ2, θ2 and δ2 have the following relationship with the global system parameters of the detecting compound wave plate model:

[0039]

[0040] When the polarizing compound wave plate is positive and the analyzing compound wave plate is negative, the system model is:

[0041] S out = [M A R(A + p2)] x [R(-ω2t + C2+ θ2- p2)M(δ2)R(ω2t - C2- θ2+ p2)] x Ms x [R(-ω1t - C1- θ1+ p1)M(δ1)R(ω1t + C1+ θ1- p1)] x [R(-P + p1)M P ] x S in (7) ;

[0042] The system parameters p1, θ1, δ1 and the global system parameters of the polarizing compound wave plate model have the following relationship:

[0043]

[0044] The system parameters p2, θ2, δ2 and the global system parameters of the analyzing compound wave plate model have the following relationship:

[0045]

[0046] When the polarizing compound wave plate is negative and the analyzing compound wave plate is positive, the system model is:

[0047] S out = [M A R(A + p2)] x [R(-ω2t - C2- θ2)M(δ2)R(ω2t + C2+ θ2)] x Ms x [R(-ω1t + C1+ θ1)M(δ1)R(ω1t - C1- θ1)] x [R(-P + p1)M P ] x S in (10) ;

[0048] The system parameters p1, θ1, δ1 and the global system parameters of the polarizing compound wave plate model have the following relationship:

[0049]

[0050] The system parameters p2, θ2, δ2 and the global system parameters of the analyzing compound wave plate model have the following relationship:

[0051]

[0052] Wherein, M s is the measurement sample parameter, M P , M ALet M(δ1) and M(δ2) be the Mueller matrices of the polarizer arm and analyzer arm, respectively; ρ1 and ρ2 be the optical rotation angles of the polarizer composite waveplate 1 and analyzer composite waveplate 2; θ1 and θ2 be the optical axis azimuth angles of the polarizer composite waveplate 1 and analyzer composite waveplate 2; ω1 and ω2 be the rotational speeds of motor 1 and motor 2; M(δ1) and M(δ2) be the Mueller matrices of the phase delay of the polarizer composite waveplate and analyzer composite waveplate; R is the rotation matrix; P, A, C1, and C2 are the initial azimuth angles of the polarizer, analyzer, polarizer composite waveplate, and analyzer composite waveplate, respectively; and S is the initial azimuth angle of the polarizer, analyzer, polarizer composite waveplate, and analyzer composite waveplate. in Let wvl be the Stokes vector of normalized natural light, and λ be the wavelength. i Let be the center wavelength of the i-th waveplate in the composite waveplate model. Let M be the angle between the optical axes of the (i+1)th waveplate and the first waveplate in the composite waveplate model. wp is the equivalent Mueller matrix of the composite waveplate.

[0053] As an example, the global system parameters of the optical measurement system are iteratively solved based on the measured Fourier coefficients and the theoretical Fourier coefficients calculated by multiple system models corresponding to different installation methods of the composite waveplate in the optical measurement system. This includes: determining a set of global system parameters for each system model corresponding to each installation method of the composite waveplate, calculating the corresponding theoretical light intensity information based on the system model, performing a Fourier transform on the theoretical light intensity information to obtain the theoretical Fourier coefficients; and iteratively calculating the theoretical Fourier coefficients by continuously adjusting the global system parameters until the calculated theoretical Fourier coefficients are close to the measured Fourier coefficients of the standard sample, thereby obtaining the global system parameters of the optical measurement system.

[0054] Understandably, corresponding system models were designed for the four possible installation methods of the composite waveplate. Iterative solutions were then performed based on each system model to obtain the corresponding global system parameters. The specific iterative solution process is as follows: other parameters are known, while the global system parameters are unknown. The global system parameters include the center wavelength of the analyzer composite waveplate, the azimuth angle of the optical axis of the analyzer composite waveplate, the center wavelength of the polarizing composite waveplate, the azimuth angle of the optical axis of the polarizing composite waveplate, the initial azimuth angle of the analyzer composite waveplate, the initial azimuth angle of the polarizing composite waveplate, and the initial azimuth angle of the polarizer.

[0055] Determine an initial set of global system parameters, specifically including the center wavelengths λ1, λ2...λ of the polarization composite waveplate model. n Angle of optical axis The global system parameters of the polarization composite waveplate model are the center wavelengths λ1, λ2...λ. m Angle of optical axis The initial azimuth angles C2, A of the analyzing compound wave plate and the analyzing plate, the initial azimuth angles C1 of the polarizing compound wave plate and the polarizing plate, and A and P are used to calculate corresponding theoretical light intensity information based on the system model. The theoretical light intensity information is subjected to Fourier transform to obtain theoretical Fourier coefficients. The global system parameters of the optical measurement system are obtained by continuously adjusting the global system parameters and iteratively calculating the theoretical Fourier coefficients until the calculated theoretical Fourier coefficients are close to the measured Fourier coefficients of the standard sample. The fitting iteration method includes but is not limited to Levenberg-Marquardt method, Newton method, gradient descent method, and conjugate gradient method.

[0056] The difference between the theoretical Fourier coefficients and the measured Fourier coefficients of the standard sample can be determined by calculating the difference between the theoretical Fourier coefficients and the measured Fourier coefficients of the standard sample.

[0057] Based on the system model corresponding to each installation mode, the same iterative solution method is used to obtain the global system parameters, and four sets of global system parameters are obtained, wherein only one set of global system parameters is the correct global system parameters corresponding to the current installation mode.

[0058] The specific method for determining the correct global system parameters is that, for the global system parameters obtained by the four system models, the correct global system parameters and the current installation mode of the optical measurement system are determined by the mean square error MSE threshold method or the goodness of fit GOF threshold method or the difference ratio threshold method of the fitting parameters of the compound wave plate and the design parameters.

[0059] Specifically, the correct global system parameters are determined by the mean square error MSE threshold method or the goodness of fit GOF threshold method or the difference ratio threshold method of the fitting parameters of the compound wave plate and the design parameters, including: obtaining the theoretical Fourier system iteratively solved by the four system models, calculating the mean square error MSE between the theoretical Fourier coefficients and the measured Fourier coefficients of the standard sample, and determining the global system parameters corresponding to the minimum mean square error MSE as the correct global system parameters; or, obtaining the difference ratio between the theoretical system parameters of the compound wave plate and the design parameters iteratively solved by the four system models, determining the global system parameters corresponding to the minimum difference ratio as the correct global system parameters, and determining the system model and the global system parameters corresponding to the current installation mode of the optical measurement system.

[0060] S3, obtaining the full-band light intensity information of the sample to be measured in the optical measurement system, and performing Fourier transform on the light intensity information to calculate the measured Fourier coefficients of the sample to be measured.

[0061] It can be understood that the full-band light intensity variation information of the sample to be measured can be obtained by using a measuring device such as a spectrometer, and the Fourier coefficients, referred to as the measured Fourier coefficients of the sample to be measured, can be calculated by Fourier transform of the light intensity information.

[0062] S4, according to the measured Fourier coefficients of the sample to be measured and the global system parameters, the system model corresponding to the current installation mode of the optical measurement system is used to iteratively solve the sample to be measured parameters.

[0063] As an embodiment, according to the measured Fourier coefficients of the sample to be measured and the global system parameters, the system model corresponding to the current installation mode of the optical measurement system is used to iteratively solve the sample to be measured parameters, including: according to the determined global system parameters, the initial sample to be measured parameters are determined, the theoretical light intensity information is calculated by using the system model corresponding to the current installation mode of the optical measurement system, and the Fourier transform of the theoretical light intensity information is performed to obtain the theoretical Fourier coefficients; the sample to be measured parameters are continuously adjusted, the corresponding theoretical Fourier coefficients are calculated by using the system model, until the calculated theoretical Fourier coefficients are close to the measured Fourier coefficients of the sample to be measured, and the sample to be measured parameters Ms are obtained.

[0064] It can be understood that the global system parameters of the optical measurement system are solved in step S2, and the current installation mode of the optical measurement system and the system model are solved, the sample to be measured parameters Ms are adjusted based on the system model, the theoretical light intensity information is solved, and then the Fourier transform of the theoretical light intensity information is performed to obtain the corresponding Fourier coefficients. By continuously adjusting the sample to be measured parameters Ms, the corresponding theoretical Fourier coefficients are calculated, until the solved theoretical Fourier coefficients are close to the measured Fourier coefficients of the sample to be measured, and the sample to be measured parameters Ms are obtained, wherein the single-sided sample parameters are the Mueller matrix spectrum of the sample to be measured.

[0065] The optical measurement system global calibration method provided by the embodiment of the application can solve the problem that the correct global system parameters and the current installation mode of the optical measurement system cannot be solved when the composite wave plate is reversely installed, and can iteratively solve the parameters of the sample to be measured, so that the global calibration of the optical measurement system parameters can be realized even when the wave plate is reversely installed, and the robustness of the global calibration of the optical measurement system is increased.

[0066] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0067] Those skilled in the art will appreciate that embodiments of the present application can be devised for a variety of applications. It is intended that the present application be limited only by the scope of the appended claims, and it is intended that various modifications and alterations made by those skilled in the art be considered as within the scope of the present application. The embodiments of the present application will be described with reference to the attached drawings, wherein:

[0068] The present application is described in reference to the drawings using a flowchart and / or a block diagram of the method, apparatus (system) and computer program product according to embodiments of the application. It will be understood that each block of the flowchart and / or block diagram, and combinations of blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0069] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0070] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0071] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments by those skilled in the art once they learn of the basic inventive concepts. Therefore, the appended claims are intended to cover all such modifications and variations as fall within the scope of the present application.

[0072] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method of global calibration of an optical measurement system, characterized in that, The application relates to an optical measurement system and a parameter measurement method thereof. The application comprises the following steps: acquiring full-waveband light intensity information of a standard sample in an optical measurement system, performing Fourier transform on the light intensity information, and calculating measured Fourier coefficients of the standard sample; According to the measured Fourier coefficients and theoretical Fourier coefficients calculated through a plurality of system models corresponding to different installation modes of a composite wave plate in the optical measurement system, global system parameters of the optical measurement system are iteratively solved, and a current installation mode of the optical measurement system is determined; Acquiring full-waveband light intensity information of a sample to be measured in the optical measurement system, performing Fourier transform on the light intensity information, and calculating measured Fourier coefficients of the sample to be measured; According to the measured Fourier coefficients of the sample to be measured and the global system parameters, the sample to be measured parameters are iteratively solved through a system model corresponding to the current installation mode of the optical measurement system; the composite wave plate in the optical measurement system comprises a polarizing composite wave plate and an analyzing composite wave plate; different installation modes of the composite wave plate in the optical measurement system comprise polarizing composite wave plate positive-analyzing composite wave plate positive, polarizing composite wave plate positive-analyzing composite wave plate negative, polarizing composite wave plate negative-analyzing composite wave plate positive and polarizing composite wave plate negative-analyzing composite wave plate negative.

2. The method of global calibration of an optical measurement system according to claim 1, characterized in that, When the polarizing composite wave plate positive-analyzing composite wave plate positive, the system model is as follows: （1）； System parameters , , The global system parameters of the polarizing compound wave plate model have the following relationships: （2）； System parameters , , The global system parameters of the model of the polarizing and the compensating waveplates have the following relations （3）； When the polarizing composite wave plate negative-analyzing composite wave plate negative, the system model is as follows: （4）； System parameters , , The global system parameters of the polarizing compound wave plate model have the following relationships: （5）； System parameters , , The global system parameters of the model of the polarizing and the compensating waveplates have the following relations: （6）； When the polarizing composite wave plate positive-analyzing composite wave plate negative, the system model is as follows: （7）； System parameters , , The global system parameters of the polarizing compound wave plate model have the following relationships: （8）； System parameters , , The global system parameters of the model of the polarizing and the analyzing wave plate have the following relations: （9）； When the polarizing composite wave plate negative-analyzing composite wave plate positive, the system model is as follows: （10）； System parameters , , The global system parameters of the polarizing compound waveplate model have the following relationships: （11）； System parameters , , The global system parameters of the model of the polarizing and the analyzing wave plate have the following relations: （12）； wherein, is a parameter of a sample, is a polarizer Mueller matrix of a polarizing arm and an analyzing arm, is an optical rotation angle of a polarizing compound wave plate and an analyzing compound wave plate, is an optical axis azimuth angle of a polarizing compound wave plate and an analyzing compound wave plate, is a rotational speed of a first motor and a second motor, and is a phase retardation Mueller matrix of a polarizing compound wave plate and an analyzing compound wave plate, R is a rotation matrix, P, A, C 1、 C2 is an initial azimuth angle of a polarizer, an analyzer, a polarizing compound wave plate, and an analyzing compound wave plate, is a normalized natural light Stokes vector, wvl is a wavelength, is a center wavelength of an i-th wave plate of a compound wave plate model, is an optical axis included angle of an i+1-th wave plate and a first wave plate of a compound wave plate model, is an equivalent Mueller matrix of a compound wave plate.

3. The method of global calibration of an optical measurement system according to claim 2, characterized in that, The method comprises the following steps: For the system model corresponding to each installation mode of the composite wave plate, a group of global system parameters are determined, and corresponding theoretical light intensity information is calculated based on the system model; the theoretical light intensity information is subjected to Fourier transform to obtain theoretical Fourier coefficients; By continuously adjusting the global system parameters, the theoretical Fourier coefficients are iteratively calculated until the calculated theoretical Fourier coefficients are close to the measured Fourier coefficients of the standard sample, and the global system parameters of the optical measurement system are obtained.

4. The method of global calibration of an optical measurement system according to claim 3, characterized in that, The method comprises the following steps: For the global system parameters iteratively solved through the four system models, correct global system parameters and a current installation mode of the optical measurement system are determined through a mean square error (MSE) threshold mode, a goodness of fit (GOF) threshold mode or a difference proportion threshold mode of fitting parameters of the composite wave plate and design parameters.

5. The method of global calibration of an optical measurement system according to claim 4, characterized in that, The method comprises the following steps: The theoretical Fourier system iteratively solved through the four system models is acquired, the mean square error (MSE) between the theoretical Fourier coefficients and the measured Fourier coefficients of the standard sample is calculated, and the global system parameters corresponding to the minimum mean square error (MSE) are determined as the correct global system parameters; Or, the difference ratio between the theoretical system parameters of the four system model iteration solutions and the design parameters is obtained, and the global system parameters corresponding to the minimum difference ratio are determined as the correct global system parameters.

6. The method of global calibration of an optical measurement system according to claim 1, characterized in that, According to the measured Fourier coefficients of the sample to be measured and the global system parameters, the sample parameters are iteratively solved through the system model corresponding to the current installation mode of the optical measurement system, including: According to the determined global system parameters, the initial sample parameters to be measured are determined, the theoretical light intensity information is calculated through the system model corresponding to the current installation mode of the optical measurement system, the Fourier transform is performed on the theoretical light intensity information, and the theoretical Fourier coefficients are obtained. The sample parameters to be measured are continuously adjusted, the corresponding theoretical Fourier coefficients are calculated through the system model, and the calculation of the theoretical Fourier coefficients is close to the measured Fourier coefficients of the sample to be measured until the sample parameters to be measured Ms are obtained.

7. A method of global calibration of an optical measurement system according to claim 1 or 6, characterized in that, The sample parameters to be measured are the Mueller matrix spectrum of the sample to be measured.

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