Ellipsometer micro-spot calibration method

Abstract

The present application relates to a kind of ellipsometer micro light spot calibration method, select a standard measurement sample, the first reflected light intensity signal of the standard measurement sample is measured in the large light spot mode of ellipsometer;Based on the system model in the large light spot mode of ellipsometer, the first reflected light intensity signal is used to calibrate the ellipsometer in the large light spot mode, and system parameter is obtained;Using the system parameter after calibration, the second reflected light intensity signal of the standard measurement sample is measured in the micro light spot mode of ellipsometer;Based on the system model in the micro light spot mode of ellipsometer, the second reflected light intensity signal is used to calibrate the ellipsometer in the micro light spot mode for second time, and micro light spot parameter is obtained.The present application method can be based on the ellipsometer system calibration in the micro light spot mode in full wave band.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical scattering measurement, in particular to an ellipsometer micro light spot calibration method. BACKGROUND

[0002] Compared with scanning electron microscope, atomic force microscope and other microscopic morphology measurement methods, ellipsometry has the advantages of fast speed, low cost, non-contact and non-destructive, and is widely used in the field of advanced process online monitoring. The measurement process of ellipsometer can be summarized as follows: the light emitted by the light source is modulated in phase by the polarizer and wave plate in the polarizing arm, then is projected onto the surface of the sample to be measured and is reflected, and the reflected light carrying the information of the sample to be measured is demodulated in phase by the wave plate and polarizer in the detection arm, and then is received by the light intensity detector. It is easy to understand that the light intensity finally received by the detector is not only related to the sample to be measured itself, but also related to the system parameters of the ellipsometer (including the incident angle, the characteristic parameters and the placement azimuth angle of the polarizer itself such as the polarizer and wave plate used). Therefore, in order to accurately obtain the sample information from the received light intensity, the ellipsometer must be accurately calibrated.

[0003] With the continuous reduction of semiconductor technology nodes, semiconductor devices are also developing towards miniaturization, and the chip processing area size on the wafer has been reduced to tens of microns. In order to meet the needs of micro-area measurement, the ellipsometer must be equipped with a micro light spot assembly composed of multiple lenses to reduce the probe light spot size from several millimeters to tens of microns. However, the lenses in the micro light spot assembly usually have stress birefringence effect, which exhibits a certain phase delay effect and will affect the final received light intensity, and then affect the final measurement of the sample to be measured. Therefore, in order to accurately measure the information of the sample to be measured, the micro light spot effect must be accurately calibrated during the system calibration process. SUMMARY

[0004] The present application provides an ellipsometer micro light spot calibration method to solve the technical problems in the prior art, which comprises the following steps:

[0005] A standard measurement sample is selected, and a first reflected light intensity signal of the standard measurement sample is measured in the large light spot mode of the ellipsometer;

[0006] Based on the system model in the large light spot mode of the ellipsometer, the first reflected light intensity signal is used to calibrate the ellipsometer in the large light spot mode, and the system parameters are obtained;

[0007] Using the calibrated system parameters, a second reflected light intensity signal of the standard measurement sample is measured in the micro light spot mode of the ellipsometer;

[0008] Based on the system model in the micro light spot mode of the ellipsometer, the second reflected light intensity signal is used to calibrate the ellipsometer in the micro light spot mode, and the micro light spot parameters are obtained.

[0009] Further, the system model of the ellipsometer in the large spot mode is:

[0010] I out = [1, 0, 0, 0] x [M A R(A)] x [R(-ω2t+C2)M C (δ2)R(ω2t-C2)] x M S (AOI, THK)

[0011] x [R(-ω1t+C1)M C (δ1)R(ω1t-C1)] x [R(-P)M P ] x S in

[0012] wherein t represents time, S in is a Stokes vector of light emitted by a light source, I out represents light intensity output by the system; P, A, C1, C2 are respectively a polarizing plate azimuth angle of a polarizing arm, a polarizing plate azimuth angle of an analyzing arm, a first rotating wave plate initial azimuth angle, and a second rotating wave plate initial azimuth angle of the dual-rotating wave plate ellipsometer; δ1 and δ2 are respectively phase retardation amounts of the first rotating wave plate and the second rotating wave plate; M A and M P are characteristic Mueller matrices of the polarizing plates, M C is a characteristic Mueller matrix of the phase retarder; R is a rotation matrix; M s is a characteristic Mueller matrix of a sample, which depends on an incident angle AOI and a sample film thickness THK; ω1 and ω2 are respectively angular frequencies of the first rotating wave plate and the second rotating wave plate.

[0013] Further, based on the system model of the ellipsometer in the large spot mode, the ellipsometer in the large spot mode is calibrated by using a first reflected light intensity signal to obtain system parameters, including:

[0014] S301, selecting a certain section as an analysis band in a full wave band, calibrating system parameters P, A, C1, C2, δ1, δ2, and the incident angle AOI and the sample thickness THK in the band to obtain corresponding parameter extraction values at each wavelength point;

[0015] S302, taking an average of the incident angle AOI and the sample thickness THK at each wavelength;

[0016] S303, calibrating system parameters P, A, C1, C2, δ1, δ2 in the full wave band by using the average of the incident angle AOI and the sample thickness THK.

[0017] Further, the analysis band is selected in a visible light range.

[0018] Further, the system parameter calibration process comprises:

[0019] Converting the periodic light intensity actually measured by the ellipsometer into Fourier coefficients;

[0020] Writing a system model function, whose input is the parameter to be calibrated and whose output is the Fourier coefficients of the simulated output light intensity of the system model;

[0021] Adjusting the input parameter value of the system model function through a nonlinear fitting algorithm so that the output simulated Fourier coefficients coincide with the actually measured Fourier coefficients.

[0022] Further, the system model of the ellipsometer under the micro light spot mode is:

[0023]

[0024] wherein μ1 and μ2 are the phase retardation amounts of the first micro light spot component and the second micro light spot component in the double-rotating wave plate ellipsometer respectively, Δ offset is the micro light spot phase difference; M s is the Mueller matrix of the sample feature, and Δ s is the ellipsometric parameter of the sample, which depends on the sample film thickness THK and the incident angle AOI, i.e. Δ S = Δ S (AOI, THK).

[0025] Further, based on the system model of the ellipsometer under the micro light spot mode, the second reflection light intensity signal is used to perform secondary calibration on the ellipsometer under the micro light spot mode to obtain the micro light spot parameters, comprising:

[0026] S701, selecting a certain section as an analysis band within the full wave band, fixing the micro light spot phase difference Δ offset at a certain determined value, calibrating the phase retardation amounts μ1 and μ2 of the first micro light spot component and the second micro light spot component, and the incident angle AOI and the sample film thickness THK within the analysis band, and calculating the variance of the film thickness and the incident angle calibration value within the analysis band;

[0027] S702, traversing the micro light spot phase difference Δ offset , repeating step S701 to obtain the curve of the film thickness and the incident angle variance with the change of the micro light spot phase difference Δ offset , fitting the curve with a quadratic function and finding the lowest point of the curve; if the lowest points of the film thickness variance curve and the incident angle variance curve correspond to the same micro light spot phase difference, it is considered that the micro light spot phase difference corresponding to the lowest point is its true value;

[0028] S703, fixing the micro-spot phase difference at its true value, calibrating the micro-spot phase retardation μ1 and μ2, the incident angle AOI and the sample film thickness THK in the selected analysis wavelength band, and averaging the AOI and THK;

[0029] S704, calibrating the micro-spot phase retardation μ1 and μ2, and the micro-spot phase difference in the full wavelength band range by using the average of the incident angle AOI and the sample film thickness THK.

[0030] Further, if the micro-spot phase difference corresponding to the lowest point of the film thickness variance curve and the lowest point of the incident angle variance curve is inconsistent, the true value of the micro-spot phase difference is determined according to the following steps:

[0031] S801, taking the micro-spot phase difference corresponding to the lowest point of the film thickness variance curve and the lowest point of the incident angle variance curve as the interval end value, and discretizing the parameter interval to obtain a series of values of the micro-spot phase difference;

[0032] S802, fixing the micro-spot phase difference at a certain number in the series of values, calibrating the micro-spot phase retardation μ1 and μ2, the incident angle AOI and the sample film thickness THK in the analysis wavelength band, and averaging the AOI and THK;

[0033] S803, fixing the AOI and THK at the average values obtained in step S802, calibrating the micro-spot phase retardation μ1 and μ2, and the micro-spot phase difference in the full wavelength band range, and calculating the calibration residual according to the following formula:

[0034]

[0035] Wherein, a and b represent the Fourier coefficients corresponding to the measured light intensity and the Fourier coefficients output by the system model respectively; subscript i represents the index of the 24 Fourier coefficients; subscript j represents the index of the wavelength point, and N represents the number of analysis wavelength points;

[0036] S804, traversing the series of values of the micro-spot phase difference, repeating steps S802 and S803, and selecting the micro-spot phase difference corresponding to the minimum value of the calibration residual norm, which is the true value.

[0037] The present application has the advantages that the method can realize the calibration of the ellipsometer system based on the micro-spot mode in the full wavelength band. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 A flowchart of an ellipsometer micro-spot calibration method provided by the embodiment of the present application is shown in the figure;

[0039] Figure 2 A schematic diagram of the principle of a typical double-rotating-wave-plate ellipsometer provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0040] The principles and features of the present application are described below in conjunction with the accompanying drawings, which are provided only for explanation of the present application and are not intended to limit the scope of the present application.

[0041] As shown in Figure 1 , the embodiment of the present application provides an ellipsometer micro light spot calibration method, which comprises the following steps:

[0042] Selecting a standard measurement sample, measuring a first reflected light intensity signal of the standard measurement sample under an ellipsometer large light spot mode (i.e. without installing a micro light spot assembly);

[0043] Based on a system model under the ellipsometer large light spot mode, calibrating the ellipsometer under the large light spot mode by using the first reflected light intensity signal to obtain system parameters;

[0044] Using the calibrated system parameters, measuring a second reflected light intensity signal of the standard measurement sample under an ellipsometer micro light spot mode;

[0045] Based on a system model under the ellipsometer micro light spot mode (i.e. with the micro light spot assembly installed), performing secondary calibration of the ellipsometer under the micro light spot mode by using the second reflected light intensity signal to obtain micro light spot parameters.

[0046] The principle of a typical double-rotating wave plate ellipsometer is shown in Figure 2 , which includes a light source, a polarizing arm (mainly composed of a polarizer, a first rotating wave plate, and a first micro light spot assembly), a sample stage, an analyzing arm (mainly composed of an analyzer, a second rotating wave plate, and a second micro light spot assembly), and a detector. Among them, the micro light spot assembly can be detached, when the assembly is detached, the ellipsometer measurement light spot size can reach several millimeters, which is called a large light spot mode; when the assembly is installed, the ellipsometer measurement light spot size is only several tens of microns, which is called a micro light spot mode.

[0047] According to Figure 2 the measurement principle diagram of the ellipsometer, the system model under the ellipsometer large light spot mode can be obtained as:

[0048] I out = [1, 0, 0, 0] x [M A R(A)] x [R(-ω2t+C2)M C (δ2)R(ω2t-C2)] x M S (AOI, THK)

[0049] x [R(-ω1t+C1)M C (δ1)R(ω1t-C1)] x [R(-P)M P ] x S in

[0050] where t represents time, S in is the Stokes vector of the light emitted by the light source, I out represents the light intensity output by the system; P, A, C1, C2 are the azimuth angle of the polarizing plate of the polarizing arm, the azimuth angle of the polarizing plate of the analyzing arm, the initial azimuth angle of the first rotating wave plate, and the initial azimuth angle of the second rotating wave plate, respectively; δ1 and δ2 are the phase retardation of the first rotating wave plate and the second rotating wave plate, respectively; M A and M P is the Mueller matrix of the polarizing plate; M C is the Mueller matrix of the phase retarder; R is the rotation matrix; M s is the Mueller matrix of the sample, which depends on the incident angle AOI and the sample film thickness THK; ω1 and ω2 are the angular frequencies of the first rotating wave plate and the second rotating wave plate, respectively.

[0051] Further, based on the system model of the ellipsometer under the large light spot mode, the first reflected light intensity signal is used to calibrate the ellipsometer under the large light spot mode, and the system parameters are obtained, including:

[0052] S301, a certain section is selected as an analysis band within the full wave band, and the system parameters P, A, C1, C2, δ1, δ2, and the incident angle AOI and the sample thickness THK are calibrated in the wave band to obtain the corresponding parameter extraction value at each wavelength point;

[0053] S302, the incident angle AOI and the sample thickness THK at each wavelength are averaged;

[0054] S303, using the average of the incident angle AOI and the sample thickness THK, the system parameters P, A, C1, C2, δ1, δ2 are calibrated in the full wave band.

[0055] Further, the analysis band is selected in the visible light range, because generally the light intensity is relatively strong and the noise is relatively weak in the visible light range, so that the analysis result is more accurate.

[0056] Further, the system parameter calibration process can be realized by the following way: first, the periodic light intensity obtained by the actual measurement of the ellipsometer is converted into Fourier coefficients; then a system model function is written, the input of which is the parameter to be calibrated, and the output is the Fourier coefficient of the simulated output light intensity of the system model; the input parameter value of the system model function is adjusted through a nonlinear fitting algorithm, so that the simulated Fourier coefficient and the measured Fourier coefficient are consistent. There are a lot of related materials about the calibration method, which will not be expanded here.

[0057] According to the measurement principle diagram of the ellipsometer in Figure 2 , the system model of the ellipsometer under the micro light spot mode can be obtained as follows:

[0058]

[0059] wherein μ1 and μ2 are the phase retardation of the first and second micro-spot components respectively, Δ offset is the micro-spot phase difference; M s is the sample feature Mueller matrix, and Δ s are the sample ellipsometric parameters, both of which depend on the sample film thickness THK and the incident angle AOI, i.e. Δ S = Δ S (AOI, THK).

[0060] After the light intensity data acquisition in the large-spot mode, the micro-spot components are installed to the ellipsometer and the light intensity data acquisition is performed in the micro-spot mode. It is easy to understand that the polarizer and the rotating wave plate do not change in this process, so the system parameters P, A, C1, C2, δ1, δ2 in the micro-spot and large-spot modes remain consistent. When the light intensity data in the micro-spot mode is used to calibrate the system, the above six system parameters can be fixed at the calibration results of the system parameters in the large-spot mode. However, the installation deviation of the micro-spot components can slightly change the incident angle, and the irradiation ranges of the large-spot and micro-spot on the sample surface are different, and the unevenness of the sample can cause slight differences in the film thickness within the irradiation range. Therefore, in addition to the micro-spot parameters, the incident angle AOI and the sample film thickness THK also need to be recalibrated in the micro-spot mode relative to the large-spot mode.

[0061] Based on the system model in the micro-spot mode of the ellipsometer, the second light intensity signal is used to perform secondary calibration on the ellipsometer in the micro-spot mode, to obtain the micro-spot parameters, including:

[0062] S701, select a certain section as an analysis band within the full wave band, fix the micro-spot phase difference Δ offset at a certain determined value, calibrate the phase retardation μ1 and μ2 of the first and second micro-spot components, and the incident angle AOI and the standard sample film thickness THK in the analysis band, and calculate the variance of the film thickness and incident angle calibration values in the analysis band.

[0063] The sample ellipsometric parameters and Δ s depend on the film thickness THK and the incident angle AOI, so it is easy to find from the system model formula that the micro-spot phase difference Δ offset has a strong coupling with the film thickness THK and the incident angle AOI. If the incident angle AOI, the sample film thickness THK and the micro-spot phase difference Δ offset are calibrated at the same time, it is usually difficult to obtain correct results. In order to decouple the parameters, the micro-spot phase difference Δoffset The fixed value is calibrated, and the variance of the film thickness THK and the incidence angle AOI in the analysis band is calculated.

[0064] S702, the micro light spot phase difference Δ is traversed offset , the step S701 is repeated, the curve of the film thickness and the incidence angle variance with the micro light spot phase difference Δ is obtained, the curve is fitted with a quadratic function, and the lowest point of the curve is found. offset

[0065] According to the analysis, the micro light spot phase difference Δ offset is extremely strongly coupled with the film thickness and the incidence angle. Therefore, when the micro light spot phase difference Δ offset is fixed at different values, the film thickness and the incidence angle obtained by calibration have significant differences. In principle, when the micro light spot phase difference Δ offset is fixed near the true value, the film thickness and the incidence angle in the analysis band are also closer to the true value, and the corresponding variances should be smaller. Therefore, the present application proposes that the micro light spot phase difference can be traversed, the step S701 is repeated, the curve of the film thickness and the incidence angle variance with the micro light spot phase difference is obtained, the curve is fitted with a quadratic function, and the micro light spot phase difference corresponding to the lowest point of the curve is found.

[0066] If the micro light spot phase difference corresponding to the lowest point of the film thickness variance curve and the lowest point of the incidence angle variance curve is consistent, the micro light spot phase difference corresponding to the lowest point is considered as the true value of the micro light spot phase difference;

[0067] S703, the micro light spot phase difference is fixed at the true value, the micro light spot phase delay μ1 and μ2, and the incidence angle AOI and the sample film thickness THK are calibrated in the selected analysis band, and the AOI and THK are averaged.

[0068] S704, the micro light spot phase delay μ1 and μ2, and the micro light spot phase difference are calibrated in the full-wave band range by using the average of the incidence angle AOI and the sample thickness THK.

[0069] Further, if the micro light spot phase difference corresponding to the lowest point of the film thickness variance curve and the lowest point of the incidence angle variance curve is inconsistent, the true value of the micro light spot phase difference is determined according to the following steps:

[0070] S801, the micro light spot phase difference corresponding to the lowest point of the film thickness variance curve and the lowest point of the incidence angle variance curve is taken as an interval end value, and a series of values of the micro light spot phase difference is obtained by discretizing the parameter interval.

[0071] S802, the micro light spot phase difference is fixed at a certain number in the series of values, the micro light spot phase delay μ1 and μ2, and the incidence angle AOI and the sample film thickness THK are calibrated in the analysis band, and the AOI and THK are averaged.​

[0072] S803, fixing AOI and THK at the mean value obtained in step S802, calibrating micro-spot phase retardation μ1 and μ2 and micro-spot phase difference in the full waveband range, and calculating calibration residual error according to the following formula:

[0073]

[0074] wherein a and b respectively represent Fourier coefficients corresponding to the measured light intensity and Fourier coefficients of the system model output; subscript i represents the index of 24 Fourier coefficients; subscript j represents the index of wavelength points, and N represents the number of analysis wavelength points;

[0075] S804, traversing the series of micro-spot phase difference values, repeating steps S802 and S803, and selecting the micro-spot phase difference corresponding to the minimum value of the calibration residual error norm, which is the true value of the micro-spot phase difference.

[0076] At this point, the ellipsometer system calibration is completed based on the micro-spot mode in the full waveband range.

[0077] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to the embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to cover all such changes and modifications that fall within the scope of the present application.

[0078] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. Thus, it is intended that the present application cover the modifications and changes as long as they come within the scope of the claims and their equivalents.

Claims

1. A method for calibrating a micro-spot on an ellipsometer, characterized in that, include: Select a standard measurement sample and measure the first reflected light intensity signal of the standard measurement sample in the large spot mode of the ellipsometer. Based on the system model of the ellipsometer in the large spot mode, the ellipsometer in the large spot mode is calibrated using the first reflected light intensity signal to obtain system parameters. These system parameters include at least the incident angle AOI, the sample film thickness THK, and the polarizer azimuth angles P (polarizer arm), A (analyzer arm), C1 (initial azimuth angle of the first rotating waveplate), C2 (initial azimuth angle of the second rotating waveplate), and the phase delay of the first rotating waveplate. Phase delay of the second rotating waveplate ; Using the calibrated system parameters, the second reflected light intensity signal of the standard measurement sample was measured in the micro-spot mode of the ellipsometer. Based on the system model in the micro-spot mode of the ellipsometer, the ellipsometer in the micro-spot mode is calibrated a second time using the second reflected light intensity signal to obtain micro-spot parameters. The micro-spot parameters include the phase delay of the first and second micro-spot components in the dual-rotating-waveplate ellipsometer. and and micro-spot phase difference ; Based on the system model in the micro-spot mode of the ellipsometer, the ellipsometer in the micro-spot mode is calibrated a second time using the second reflected light intensity signal to obtain the micro-spot parameters, including: S701 selects a segment within the entire wavelength range as the analysis band, and measures the phase difference of the micro-spot. The phase delay of the first and second micro-spot components is fixed at a certain value within the analysis band. and The incident angle AOI and standard film thickness THK were calibrated, and the variance of the film thickness and incident angle calibration values ​​in the analysis band was calculated. S702, Traversing the Phase Difference of Micro-spots Repeat step S701 to obtain the film thickness and incident angle variance as a function of the micro-spot phase difference. The changing curve is fitted with a quadratic function to find the lowest point of the curve; if the phase difference of the micro-spot corresponding to the lowest point of the film thickness variance curve and the lowest point of the incident angle variance curve is consistent, then the phase difference of the micro-spot corresponding to the lowest point is considered to be its true value. S703 fixes the phase difference of the microspot at its true value and calibrates the phase delay of the microspot within the selected analysis band. and The incident angle AOI and the standard film thickness THK were calculated, and the average values ​​of AOI and THK were taken. S704, using the average values ​​of the incident angle AOI and the sample thickness THK, calibrate the phase delay of the micro-spot across the entire wavelength range. and And the phase difference of the micro-spots.

2. The method according to claim 1, characterized in that, The system model of the ellipsometer in the large spot mode is as follows: Where t represents time, S in Let I be the Stokes vector of the light emitted by the light source. out The system output light intensity is represented by P, A, C1, and C2, which are the polarizer azimuth angles of the polarizer arm, the analyzer arm, the first rotating waveplate, and the second rotating waveplate, respectively. and These represent the phase delays of the first and second rotating waveplates, respectively; M A and M P M is the characteristic Mueller matrix of the polarizer. C R is the characteristic Mueller matrix of the phase delayer; R is the rotation matrix; M is the characteristic Mueller matrix of the phase delayer. s The Mueller matrix of the sample characteristics depends on the incident angle AOI and the sample film thickness THK; and These are the angular frequencies of the first and second rotating waveplates, respectively.

3. The method according to claim 2, characterized in that, Based on the system model of the ellipsometer in the large spot mode, the ellipsometer in the large spot mode is calibrated using the first reflected light intensity signal to obtain system parameters, including: S301, Select a segment within the entire band as the analysis band, and calibrate system parameters P, A, C1, C2 within this band. , The incident angle AOI and sample thickness THK are used to obtain the corresponding parameter extraction values ​​at each wavelength point; S302, take the average value of the incident angle AOI and the sample thickness THK at each wavelength; S303, using the average values ​​of the incident angle AOI and the sample thickness THK, calibrate system parameters P, A, C1, C2, and ... across the entire wavelength range. , .

4. The method according to claim 3, characterized in that, The analysis band is selected within the visible light range.

5. The method according to claim 3, characterized in that, The system parameter calibration process includes: The periodic light intensity obtained from the actual measurement by the ellipsometer is converted into Fourier coefficients. Write a system model function whose input is the parameter to be calibrated and whose output is the Fourier coefficient of the simulated light intensity of the system model; By adjusting the input parameter values ​​of the system model function using a nonlinear fitting algorithm, the output simulated Fourier coefficients are made to match the measured Fourier coefficients.

6. The method according to claim 2, characterized in that, The system model under the micro-spot mode of the ellipsometer is as follows: in, and These represent the phase delays of the first and second micro-spot components in the dual-rotating-waveplate ellipsometer, respectively. For the phase difference of the micro-spot; M s The Mueller matrix is ​​the feature matrix of the sample. and These are the ellipticity parameters of the sample, which depend on the sample film thickness THK and the incident angle AOI, i.e. , .

7. The method according to claim 6, characterized in that, If the phase difference between the micro-spot corresponding to the lowest point of the film thickness variance curve and the lowest point of the incident angle variance curve is inconsistent, the true value of the micro-spot phase difference is determined according to the following steps: S801, take the phase difference of the micro-spot corresponding to the lowest point of the film thickness variance curve and the lowest point of the incident angle variance curve as the interval endpoint value, and discretize the parameter interval to obtain a series of values ​​of the micro-spot phase difference. S802 fixes the phase difference of the micro-spot at a certain number in a series of values, and calibrates the phase delay of the micro-spot within the analysis band. and The incident angle AOI and the standard film thickness THK were calculated, and the average values ​​of AOI and THK were taken. S803, fix AOI and THK at the average value obtained in step S802, and calibrate the micro-spot phase delay across the entire wavelength range. and And the phase difference of the micro-spot, the calibration residual is calculated according to the following formula: in, and These represent the Fourier coefficients corresponding to the measured light intensity and the Fourier coefficients output by the system model, respectively; subscripts. i The index represents the 24 Fourier coefficients; in the table below, j represents the index of the wavelength point, and N represents the number of analysis wavelength points; S804, iterate through the series of micro-spot phase difference values, repeat steps S802 and S803, select the micro-spot phase difference corresponding to the minimum value of the calibration residual norm, and this value is its true value.

Images