# US 2019/0317010 A1 · Method for conducting optical measurement usingfull mueller matrix ellipsometer

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- Number: US 2019/0317010 A1
- Document ID: US20190317010A1
- Status: Published application
- Kind: A1
- Application number: 16/317,007
- Filed: 2014-08-19
- Published: 2019-10-17
- Earliest claimed: 2013-11-26
- Assignees: Bei Optics Technology Company Limited
- Applicants: Bei Optics Technology Company Limited
- Inventors: Tao LIU; Gaozeng CUI; Guoguang LI; Wei XIONG; Langfeng WEN
- Web page: https://patentgrep.com/patent/US20190317010A1

## CPC

- G01N 21/211: {Ellipsometry (optical thickness measurement G01B11/06)}
- G01N 21/274: {Calibration, base line adjustment, drift correction}
- G01N 2021/213: {Spectrometric ellipsometry}
- G01N 2201/127: Calibration; base line adjustment; drift compensation
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A method for conducting optical measurement using a full Mueller matrix ellipsometer, which belongs to the technical field of optical measurements. The optical measurement method comprises: constructing an experimental optical path of a full Mueller matrix ellipsometer; conducting complete regression calibration on the full Mueller matrix ellipsometer; placing a sample to be measured on a sample platform, and obtaining an experimental Fourier coefficient of the sample to be measured; and according to the experimental Fourier coefficient of the sample to be measured, obtaining information about the sample to be measured. Since a calibration method for the full Mueller matrix ellipsometer is not only simple in operation process, but also makes full use of data of the full Mueller matrix ellipsometer measured at the same time, the introduced error is relatively small and the parameter obtained by calibration is more accurate, so that the measurement result is more accurate when the sample to be measured is measured. Thus, the process of the optical measurement method is simplified.

## Claims

### Claim 1

A method for conducting optical measurement with a full Mueller matrix ellipsometer, comprising the following steps:
constructing an experimental optical path of the full Mueller matrix ellipsometer, the experimental optical path of the full Mueller matrix ellipsometer including a light source, a polarizer, a first phase compensator, an analyzer, a second phase compensator, a spectrometer, and a sample stage;
performing a total regression calibration on operating parameters of the full Mueller matrix ellipsometer;
placing a sample to be tested on the sample stage, and obtaining experimental Fourier coefficients of the sample to be tested with the full Mueller matrix ellipsometer;
obtaining information of the sample to be tested based on the experimental Fourier coefficients of the sample to be tested;
wherein a method for calibrating the full Mueller matrix ellipsometer comprises the following steps:
setting rotational speeds of the first phase compensator and the second phase compensator;
setting a frequency of the spectrometer for measuring light intensity data, so that the spectrometer measures the light intensity data every T/N time, wherein a total of N sets of light intensity data are acquired, where N≥25, and T is a period of measurement;
acquiring the light intensity data measured by the spectrometer;
obtaining respective experimental Fourier coefficients α′2n, β′2n from N relation formulas between the light intensity data and experimental Fourier coefficients formed by the N sets of light intensity data, based on the light intensity data acquired by a data acquisition module of the spectrometer;
obtaining respective theoretical Fourier coefficients α2n, β2n based on the respective experimental Fourier coefficients, an initial polarization angle Cs1 of the first phase compensator and an initial polarization angle Cs2 of the second phase compensator which have been calibrated;
obtaining, by a phase retardation calculation module for the first phase compensator, a phase retardation δ1 of the first phase compensator based on the respective theoretical Fourier coefficients, a polarization angle Ps of the polarizer and a polarization angle As of the analyzer which have been calibrated, on the basis that a reference sample is isotropic and uniform;
obtaining, by a phase retardation calculation module for the second phase compensator, a phase retardation δ2 of the second phase compensator, based on the respective theoretical Fourier coefficients, the polarization angle Ps of the polarizer and the polarization angle As of the analyzer which have been calibrated, on the basis that the reference sample is isotropic and uniform;
obtaining accurate values of all operating parameters (d, θ, Ps, As, Cs1, Cs2, δ1, δ2) of the full Mueller matrix ellipsometer through least square fitting according to the relation formulas between the theoretical Fourier coefficients and the operating parameters, with (d, θ, Ps, As, Cs1, Cs2, δ1, δ2) being as variables, and with the initial polarization angle Cs1 of the first phase compensator, the initial polarization angle Cs2 of the second phase compensator, the polarization angle Ps of the polarizer, the polarization angle As of the analyzer, the phase retardation δ1 of the first phase compensator and the phase retardation δ2 of the second phase compensator, which have been calibrated, being as initial values, where d is a thickness of the reference sample, and θ is an angle at which light is incident on the reference sample.

### Claim 2 (depends on 1)

The method of claim 1, further comprising the following steps:
obtaining respective θ2n=tan−1(β′2n/α′2n) based on the respective experimental Fourier coefficients α′2n, β′2n;
obtaining the initial polarization angle Cs1 of the first phase compensator based on the respective θ2n;
obtaining the initial polarization angle Cs2 of the second phase compensator based on the respective θ2n;
obtaining the polarization angle Ps of the polarizer based on the respective θ2n; and
obtaining the polarization angle As of the analyzer based on the respective θ2n.

### Claim 3 (depends on 1)

The method of claim 1, wherein N=25, and an experimental Fourier coefficient calculation module directly obtains the respective experimental Fourier coefficients α′2n, β′2n based on N relation formulas between the light intensity data and experimental Fourier coefficients formed by the N sets of light intensity data.

### Claim 4 (depends on 1)

The method of claim 1, wherein N>25, and an experimental Fourier coefficient calculation module obtains the respective experimental Fourier coefficients α′2n, β′2n through least square method based on N relation formulas between the light intensity data and experimental Fourier coefficients formed by the N set of light intensity data.

### Claim 5 (depends on 1)

The method of claim 1, wherein the light source is a broad spectrum light source, and the number of wavelengths of light which can be generated by the light source is N′, and the number of relation formulas between the theoretical Fourier coefficients and the operating parameters is 24×N′.

### Claim 6 (depends on 5)

The method of claim 5, wherein the number of the reference samples which are isotropic and uniform is m, and the number of relation formulas between the theoretical Fourier coefficients and the operating parameters is 24×N′×m.

### Claim 7 (depends on 1)

The method of claim 1, wherein the reference sample is a silicon dioxide film with silicon as a substrate.