CN112345464A - Ellipsometer optimization calibration method - Google Patents
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
- G01N21/211—Ellipsometry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
- G01N21/211—Ellipsometry
- G01N2021/213—Spectrometric ellipsometry
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- G01N2201/12—Circuits of general importance; Signal processing
- G01N2201/127—Calibration; base line adjustment; drift compensation
Abstract
The embodiment of the invention provides an ellipsometer optimization calibration method, which comprises the following steps: step 1, selecting a standard sample with any thickness as a sample to be measured, and performing system calibration on each ellipsometer to obtain system parameters of the ellipsometer, so that each ellipsometer can perform normal measurement; step 2, using each ellipsometer to measure a sample with a specific thickness and an optical constant to calibrate and optimize the angle, and ensuring that the actual measurement angle of each ellipsometer is consistent with the theoretical angle; step 3, using each ellipsometer to measure a standard sample with known thickness and optical constant to carry out wavelength calibration, and fitting to obtain a wavelength correction coefficient of each ellipsometer; and 4, performing system calibration on each instrument again, writing the wavelength correction coefficient into the system model, updating system parameters, and completing the optimized calibration of the plurality of ellipsometers. According to the embodiment of the invention, the plurality of ellipsometers are respectively optimized and calibrated, so that the consistency of the measurement results of the plurality of ellipsometers is improved.
Description
Technical Field
The embodiment of the invention relates to the field of optical measuring instruments, in particular to an ellipsometer optimization calibration method.
Background
In the production and manufacturing process of semiconductor integrated circuits, the accurate control of manufacturing process procedures and parameters is the key to realize process stability and improve product yield. The process stability is mainly realized by monitoring the product performance before and after the process and controlling parameters. In order to achieve effective process monitoring and parameter optimization, it is important to measure the structure dimensions of the IC structure rapidly and accurately during the manufacturing process. The ellipsometer is used as a precise optical measuring instrument, and has been widely applied to process monitoring in the manufacturing process of integrated circuits by virtue of the advantages of no damage and high speed. Optical metrology devices based on ellipsometry have been used to measure critical dimensions of semiconductor nanostructures, film thickness, material composition, and other parameters.
Ellipsometry is not what is seen, i.e., what is obtained, but a measurement based on model fitting. Partial prior parameters of a sample need to be obtained in advance, a theoretical model of the sample needs to be established, and then the parameter to be measured of the sample can be extracted by matching and fitting the measurement result with the theoretical model. The ellipsometry measurement is greatly related to the calibrated system parameters. In the manufacturing process of each ellipsometer, certain random deviation exists between optical components and light path debugging, so that system parameters obtained by calibrating each ellipsometer have certain difference, and the consistency of the measurement results of each ellipsometer cannot be ensured.
However, in the semiconductor manufacturing process, a large number of measurement devices are required to monitor the process parameters, and in order to ensure the stability of the manufacturing process, a plurality of measurement devices are required to have a good measurement consistency result. Ellipsometer-based measurement devices require that the ellipsometer probe itself have a good measurement. The method not only can adapt to different application scenes, but also can be maintained for a long time.
The consistency of measurements from multiple ellipsometers is verified by using them to measure one or more standard samples of known thickness and optical parameters, respectively. The standard sample is always placed in a stable environment, so that the change of the thickness and the optical constant of the sample caused by the environmental change of temperature, humidity and the like is avoided, and the result obtained by each ellipsometer is consistent with the standard result.
In order to achieve measurement consistency of multiple ellipsometers, the current practice is to correct the measured spectrum of different ellipsometers, so that the measured spectrum is close to the theoretical spectrum of the sample, thereby improving the measurement consistency of different ellipsometers. The optimized parameters of the method are the spectral parameters measured by the ellipsometer and are not the system parameters of the ellipsometer. Therefore, when different to-be-measured and parameters are faced, the measurement spectrum of each sample needs to be modeled and calculated, the stored database file is huge, the overall hardware cost is high, the calculation time based on library matching is long, and the measurement speed of the instrument is influenced.
Disclosure of Invention
Embodiments of the present invention provide an ellipsometer optimized calibration method that overcomes, or at least partially solves, the above-mentioned problems.
The embodiment of the invention provides an ellipsometer optimization calibration method, which comprises the following steps:
step 1, measuring a standard sample with any thickness by using an ellipsometer to be calibrated, acquiring system parameters of the ellipsometer to be calibrated, and performing system calibration on the ellipsometer to be calibrated so that the ellipsometer after calibration can normally measure;
and 4, carrying out system calibration on the ellipsometer to be calibrated again, writing the wavelength correction coefficient into the ellipsometer system model, and updating the parameters of the ellipsometer system model.
On the basis of the above technical solutions, the embodiments of the present invention may be further improved as follows.
Further, the step of measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calibrating and adjusting the angle of the ellipsometer to be calibrated so that the actual measurement angle and the theoretical angle of the ellipsometer after calibration are consistent comprises:
measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calculating the actual measurement angle of the ellipsometer to be calibrated;
and calibrating and adjusting the actual measurement angle of the ellipsometer to be calibrated according to the deviation between the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated, so that the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated are kept consistent.
Further, the measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calculating an actual measurement angle of the ellipsometer to be calibrated includes:
calculating to obtain an ellipsometry parameter of the sample according to the system parameter of the polarizing arm of the ellipsometer to be calibrated, the system parameter of the analyzing arm of the ellipsometer to be calibrated and the light intensity data collected by the sample measured by the ellipsometer to be calibrated;
and calculating to obtain the actual measurement incident angle of the ellipsometer to be calibrated according to the ellipsometry parameters of the sample.
Further, the calibrating and adjusting the actual measurement angle of the ellipsometer to be calibrated according to the deviation between the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated includes:
the system parameters are changed by adjusting the optical path structures and the optical element positions of the polarizing arm and the analyzing arm of the ellipsometer to be calibrated, and the actual measurement incident angle of the ellipsometer after calibration is repeatedly measured and calculated until the calculated actual measurement incident angle of the ellipsometer after calibration is consistent with the theoretical angle.
Further, the measuring a standard sample with known thickness and optical constant by using the ellipsometer to be calibrated to obtain a wavelength correction coefficient of the ellipsometer to be calibrated, and the wavelength calibration of the ellipsometer to be calibrated includes:
measuring the standard thicknesses d1 and d2 and the standard optical constants N1 and N2 of the two samples by using a standard ellipsometer;
calculating theoretical ellipsometry parameters Ms1 'and Ms2' of the two samples according to the standard thicknesses d1 and d2, the standard optical constants N1 and N2 and the theoretical incident angle of the two samples;
measuring two samples by using an ellipsometer to be calibrated, and calculating to obtain actual measurement ellipsometry parameters Ms1 and Ms2 of the two samples;
and performing model reconstruction on the sample according to the actual measurement ellipsometry parameters Ms1 and Ms2 and the theoretical ellipsometry parameters Ms1 'and Ms2' of the two measured samples to obtain the wavelength correction coefficient of the ellipsometer to be calibrated.
Further, the measuring two samples by using the ellipsometer to be calibrated, and calculating actual measurement ellipsometry parameters Ms1 and Ms2 of the two samples includes:
the actual measured ellipsometric parameters for each sample were calculated by the following formula:
Mp*Ms*Ma＝Sout；
wherein M ispFor the system parameters of the polarizing arm of the ellipsometer to be calibrated, MaFor the system parameters of the ellipsometer arm to be calibrated, SoutLight intensity signal, M, obtained for the measurement of a sample by an ellipsometer to be calibratedsEllipsometric parameters were actually measured for the samples.
Further, the obtaining of the wavelength correction coefficient of the ellipsometer to be calibrated by performing model reconstruction on the sample according to the actually measured ellipsometric parameters Ms1 and Ms2 and the theoretical ellipsometric parameters Ms1 'and Ms2' of the two measured samples includes:
the following equations were established for the actual measured ellipsometric parameters Ms1 and Ms2 and the theoretical ellipsometric parameters Ms1 'and Ms2' for both samples:
∏(Ms1，Ms2，λ)＝∏(Ms1’，Ms2’)；
by the formula, the wavelength correction coefficient of the ellipsometer to be calibrated can be obtained.
The ellipsometer optimization calibration method provided by the embodiment of the invention comprises the following steps of 1, selecting a standard sample with any thickness as a sample to be measured, and performing system calibration on each ellipsometer to obtain system parameters of the ellipsometer, so that each ellipsometer can perform normal measurement; step 2, using each ellipsometer to measure a sample with a specific thickness and an optical constant to calibrate and optimize the angle, and ensuring that the actual measurement angle of each ellipsometer is consistent with the theoretical angle; step 3, using each ellipsometer to measure a standard sample with known thickness and optical constant to carry out wavelength calibration, and fitting to obtain a wavelength correction coefficient of each ellipsometer; and 4, performing system calibration on each instrument again, writing the wavelength correction coefficient into the system model, updating system parameters, and completing the optimized calibration of the plurality of ellipsometers. According to the embodiment of the invention, the plurality of ellipsometers are respectively optimized and calibrated, so that the consistency of the measurement results of the plurality of ellipsometers is improved.
Drawings
Fig. 1 is a flowchart of an ellipsometer optimization calibration method according to an embodiment of the present invention;
FIG. 2 is a schematic view of beam transmission for a single layer film sample structure;
FIG. 3 is a schematic flow chart of an angle optimization calibration algorithm according to an embodiment of the present invention;
FIG. 4 is a schematic flow chart of a wavelength optimization calibration algorithm according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a single-rotation compensator type spectroscopic ellipsometer according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating the difference between spectra obtained by measuring the same sample with different ellipsometers in accordance with an embodiment of the present invention;
fig. 7 is a diagram illustrating the differences in spectra obtained by measuring the same sample with different ellipsometers after optimized calibration in the embodiment of the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Fig. 1 is a flowchart of an ellipsometer optimization calibration method according to an embodiment of the present invention, as shown in fig. 1, the method includes: step 1, measuring a standard sample with any thickness by using an ellipsometer to be calibrated, acquiring system parameters of the ellipsometer to be calibrated, and performing system calibration on the ellipsometer to be calibrated so that the ellipsometer after calibration can normally measure; step 2, measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calibrating and adjusting the angle of the ellipsometer to be calibrated so that the actual measurement angle and the theoretical angle of the ellipsometer after calibration are kept consistent; step 3, measuring a standard sample with known thickness and optical constant by using the ellipsometer to be calibrated to obtain a wavelength correction coefficient of the ellipsometer to be calibrated, and calibrating the wavelength of the ellipsometer to be calibrated; and 4, carrying out system calibration on the ellipsometer to be calibrated again, writing the wavelength correction coefficient into the ellipsometer system model, and updating the parameters of the ellipsometer system model.
It can be understood that the ellipsometry measurement result and the calibrated system parameter have a great relationship, and a certain random deviation exists between the optical components and the optical path debugging of each ellipsometer in the manufacturing process, so that the system parameter calibrated by each ellipsometer has a certain difference, and it cannot be ensured that the measurement result of each ellipsometer is consistent.
Based on this, the embodiment of the invention provides an optimized calibration method for ellipsometers, which performs optimized calibration on each ellipsometer.
The ellipsometer is used for measuring the thickness value of the sample or other information to be measured by acquiring light intensity data of the sample, calculating ellipsometry parameters of the sample according to a system model and extracting the thickness value or other information to be measured of the sample through an optical model of the sample.
For a typical film sample, the structure is shown in FIG. 2, where the complex refractive index of the base layer is N2Complex refractive index of the thin film layer is N1Thickness of d, N0Is the refractive index of the surrounding medium of the sample to be measured, and when the surrounding medium is air, N01. The complex refractive index N is defined as N-ik, N and k are the refractive index and extinction coefficient, respectively, of the medium, and i is an imaginary unit. In the embodiment of the invention, the standard samples are all optical constants N1And an optical film of known thickness d.
Wherein, theta0Denotes the incident angle (in this case, the incident angle θ ═ θ)0)，θ1Angle of refraction, θ, of light beam after entering the thin film layer from the surrounding medium2Is the angle of refraction of the light beam after it enters the substrate layer from the thin film layer. According to Snell's law, it can be known that:
N0sinθ0＝N1sinθ1＝N2sinθ2； (1)
according to the formula (1), the amplitude reflection coefficients r corresponding to p light and s light after the light beam is incident to the thin film sample for reflection can be obtainedppAnd rssRespectively are (in this case, the amplitude reflection coefficient rpp＝rss＝0)：
Wherein the content of the first and second substances,
from equations (2) and (3), the relationship between the amplitude ratio Ψ and the phase difference Δ can be obtained, i.e.:
and (4) determining the amplitude ratio angle psi and the phase difference angle delta, namely the ellipsometry parameters of the sample.
As can be seen from the formulas (1) to (4), the thickness and other parameters to be measured of the sample to be measured are mainly related to three parameters, namely the incident angle of the instrument, the wavelength parameter and the optical constant of the sample. When the consistency verification is carried out, the measured sample is the same standard sample, so that the optical constant and the thickness of the sample are fixed and unchanged. Common angles of incidence for ellipsometers range from 45 ° to 90 °, but the actual measured angle for an ellipsometer is angularly offset from the theoretical angle by ± 1 °. Therefore, the uniformity of the ellipsometer can be effectively improved by adjusting the incident angle theta and the wavelength lambda of the ellipsometer.
Therefore, the embodiment of the invention performs optimized calibration on the ellipsometer mainly by calibrating the incident angle θ and the wavelength λ of the ellipsometer. Firstly, the system parameters of the ellipsometer to be calibrated are calibrated, so that the calibrated ellipsometer can normally measure. After the calibration of the system parameters is performed on the ellipsometer, the calibration of the measurement angle (incident angle) and the wavelength parameters is performed on the ellipsometer, and finally the calibration of the system parameters is performed on the ellipsometer again, so that the whole calibration process of the ellipsometer is realized.
The embodiment of the invention can automatically complete the optimized calibration of a plurality of ellipsometers and improve the consistency of the measurement results of the plurality of ellipsometers.
In a possible embodiment, the calibration of the system parameters of the ellipsometer to be calibrated in step 1 is performed by using each ellipsometer to measure the same standard sample with any thickness, performing system calibration, and obtaining the system parameters of the instrument, so that the instrument can perform normal measurement. The measured data analysis method can refer to the patent: 201310040730.X (rotating device type spectroscopic ellipsometer system parameter calibration method), which details the system calibration method and steps for the ellipsometer.
In a possible embodiment, the step of calibrating the angle of the ellipsometer in step 2 can be seen in fig. 3, and first, a standard sample is measured using the ellipsometer to be calibrated, the actual measured incident angle of the ellipsometer is calibrated, and the deviation between the actual measured incident angle and the theoretical incident angle is calculated. And when the deviation is larger than 0.05 degrees, adjusting the optical path structures and the optical element positions of the polarizing arm and the analyzing arm of the ellipsometer to be calibrated, and repeatedly measuring and adjusting until the deviation between the actually measured incident angle and the theoretical incident angle is smaller than 0.05 degrees, so that the ellipsometer does not need to be subjected to angle optimization calibration.
1. The system model of the ellipsometer satisfies equation (5), where MsAs ellipsometric parameters or Mueller matrices of the samples, MpSystem parameters for the polarizing arm of an ellipsometer, MaSystem parameters for the ellipsometer analyzer arm, SoutThe ellipsometer measures the light intensity data collected by the sample.
Mp*Ms*Ma＝Sout； (5)
Ellipsometer M calibrated by systempAnd MaAll are known, the ellipsometer can analyze, calculate and analyze the ellipsometry parameters or the Mueller matrix M of the sample according to the obtained light intensity datasEllipsometric parameters or Muller matrix M of the samplesWhich may mainly include the amplitude specific angle Ψ and the phase difference angle Δ of the sample. Each ellipsometer is subjected to angle calibration, and each ellipsometer is used to measure a standard sample with the same thickness and known optical constants. According to equations (1) - (5), the actual measured angle (incident angle) for each ellipsometer can be extracted in combination with the known sample thickness and optical constants.
When the actual measurement angle of each ellipsometer is extracted by combining the known thickness and optical constant of the sample, the ellipsometry parameter M of the sample can be calculated by formula (5)sNamely, the amplitude ratio angle Ψ and the phase difference angle Δ of the sample in equation (4). Rho can be obtained from equation (4), and theta can be obtained from equation (3)1Further, the actual measured incident angle θ of the ellipsometer can be obtained according to the formula (1)0。
2. Because of the installation and commissioning tolerances of each ellipsometer, the actual measured angle θ and the theoretical angle of each ellipsometer are different. In order to eliminate the measured angle deviation of each ellipsometer, the actual measured angle of the ellipsometer is corrected to a theoretical angle. According to the formula (5), adjusting the deviation of the incident angle requires adjusting the polarizing arm system parameter M of the ellipsometerpOr analyzing the system parameter M of the arma. Wherein the parameter M of the polarizing arm system is adjustedpIncludes adjusting the incident angle of the incident sample surface, adjusting the parameter M of the analyzer arm systemaIncluding adjusting the angle at which the reflected light enters the analyzer arm. After the light paths of the polarizing arm and the polarization analyzing arm of the ellipsometer are adjusted, calibrating and adjusting the measurement angle of each ellipsometer again.
3. If the calibrated measurement angle after adjustment is equal to the theoretical angle, the angle adjustment is not needed, and the adjusted measurement angle is written into the system model; if the calibrated measurement angle and the theoretical angle still have a deviation, the step 2 needs to be repeated until the measurement angle of each ellipsometer is the same as the theoretical angle.
In a possible embodiment, the step of calibrating the wavelength parameter of the ellipsometer in step 3 can be seen in fig. 4, which mainly includes:
1. two samples of standard optical film were prepared, with thicker and thinner thicknesses being recommended, and the standard thicknesses d1, d2 and the standard optical constants N1, N2 were measured for the two samples using a standard ellipsometer.
2. Two standard samples were measured using the ellipsometer to be calibrated, and the actual measured ellipsometric parameters Ms1 and Ms2 of the two samples were obtained according to equation (5). The thicknesses d1 and d2, the optical constants N1 and N2 and the theoretical incident angle of the sample are measured by a standard ellipsometer, and theoretical ellipsometry parameters Ms1 'and Ms2' of the sample are calculated according to the formulas (1) to (4). If the measurement results for each ellipsometer are not consistent, there is some difference between the actual measured ellipsometric parameters Ms1 and Ms2 and the theoretical ellipsometric parameters Ms1 'and Ms 2'.
3. According to the formulas (1) to (4), the thickness, the optical constant and the incident angle of the ellipsometer are known, so that the ellipsometric parameters actually measured by each ellipsometer and the theoretical ellipsometric parameters of the sample are related to the wavelength of each ellipsometer, and according to the formula (6), the measured ellipsometric parameters and the theoretical ellipsometric parameters can be ensured to be the same by correcting the wavelength of each ellipsometer, wherein λ in the formula (6) is the wavelength correction coefficient of the ellipsometer to be obtained.
∏(Ms1，Ms2，λ)＝∏(Ms1′，Ms2′)； (6)
4. Extracting the wavelength correction parameters is an inverse problem solving process. The input of the solving process is the actually measured ellipsometry parameter of the standard sample, and the output is the correction coefficient of the wavelength. The objective of solving the inverse problem is to find a set of wavelength correction coefficients by measuring the ellipsometric parameters using the standard sample of each ellipsometer, so that the theoretical ellipsometric parameters can be optimally matched with the actual ellipsometric parameters. The above inverse problem solving process can be expressed in mathematical language as:
wherein, yex(p，λiθ) denotes an i (i ═ 1, 2.., N) th wavelength point λiEllipsometry data corresponding to the incident angle theta; y iscal(p，λiAnd theta) represents the corresponding wavelength lambdaiAnd theoretical ellipsometry data under the condition of an incident angle theta, p is a K-dimensional vector consisting of ellipsometry parameters of a standard film sample, omega is the value range of the parameter to be measured,
the final wavelength correction coefficient; δ y represents the standard deviation of ellipsometric data; for the solution of equation (7), a non-linear regression method such as the Levenberg-Marquardt algorithm may be specifically employed.
In a possible embodiment, the performing the system calibration again on the ellipsometer to be calibrated in step 4 includes performing the system calibration on a sample with any thickness measured by each ellipsometer, writing a wavelength correction coefficient obtained by the wavelength calibration fitting into the system model, and updating the system parameters of each ellipsometer, so that the optimization calibration of the ellipsometer to be calibrated is completed.
Below with PCrThe single rotation compensator type spectroscopic ellipsometer of SA configuration is taken as an example to illustrate an application example of the optimization algorithm provided by the embodiment of the present invention in ellipsometer calibration. The schematic structural diagram of the single-rotation compensator type spectroscopic ellipsometer is shown in fig. 5, and an optical path system of the spectroscopic ellipsometer mainly comprises a polarizing arm, a sample to be measured and an analyzing arm. The polarizing arm comprises a light source 1, a collimating lens 2, a polarizer 3, a hollow motor 4, a phase compensator 5 and a micro speckle lens 6; a sample to be tested 7; the polarization analyzing arm comprises a micro light spot lens 8, a polarization analyzer 9, a converging lens 10 and a detector 11. The hollow motor 4 of the polarizing arm drives the phase compensator 5 to rotate at a constant speed, and a periodically-changing polarization state signal is generated. The analyzing arm analyzes the periodic polarization state signal, and finally the detector 11 acquires a light intensity signal of the sample to be detected. By modelling and analysing the light intensity signalAnd calculating to obtain the ellipsometry parameters and the information to be measured of the sample.
Two selected PCsrA single rotation compensator type spectroscopic ellipsometer in SA configuration. Firstly, a series of standard SiO2 thin film samples Sample A with the same optical constant and different thicknesses are measured by using two ellipsometers A and B which are not optimally calibrated, the areas of the measured samples are ensured to be consistent in the measurement process, and the measurement deviation caused by the uneven thickness of the samples is avoided.
Since the two ellipsometers are not optimally calibrated, there is a significant difference in the actually measured spectra, as shown in fig. 6. The thickness of the sample extracted according to the measured spectrum has a large difference, and the measurement indexes of the two ellipsometers are poor, so that the ellipsometers need to be calibrated.
The first step of optimizing a calibration algorithm for an ellipsometer, system calibration, comprises:
1. and respectively measuring the same standard sample with any thickness by using the ellipsometers A and B, calibrating the system, and acquiring system parameters of the instrument to enable the instrument to perform normal measurement.
And a second step of optimizing a calibration algorithm, namely angle optimization calibration, wherein a specific flow chart is shown in figure 3, and the method comprises the following steps:
1. standard samples of known thickness and optical constants were measured using ellipsometers a and B, respectively, and angle calibration was performed. And fitting the incidence angle serving as a parameter to be measured so as to obtain the deviation of the measured angle and the theoretical angle of the ellipsometers A and B. If the deviation is less than 0.05 °, ellipsometers a and B may not be calibrated for angle optimization; if the deviation is greater than 0.05 deg., the ellipsometers a and B need to be angularly adjusted.
2. The angle adjustment can be realized by adjusting the position of the collimating lens on the polarizing arm of the ellipsometer and the incident angle of the glimmer spot lens on the polarizing arm at the azimuth angle of the polarizer, so as to correct the system parameter M of the polarizing armp(ii) a Or correcting the system parameter M of the polarization analyzing arm by adjusting the reflected light receiving angle of the micro light spot on the polarization analyzing arm, the position of the converging lens and the position of the detectoraAnd finally, carrying out system calibration and angle calibration on the ellipsometers A and B again.
3. If the measured and theoretical angles calibrated by ellipsometers a and B are less than 0.05 °, the measured angles can be written into the system model. If the measured angle and the theoretical angle calibrated by the ellipsometers a and B are greater than 0.05 °, the step 2 needs to be repeated until the measured angle and the theoretical angle calibrated by the ellipsometers a and B are less than 0.05 °.
The ellipsometers a and B after the angle optimization calibration are used for measuring the standard SiO2 thin film sample SampleA, and the comparison of the measurement results before and after the angle optimization calibration of the two ellipsometers is shown in fig. 6. It can be seen from fig. 6 that angle-optimized calibration alone does not ensure that the measurement results of the two ellipsometers are consistent for all thicknesses of the sample, and that there is good measurement consistency only for the thinner sample and still a large deviation for the thicker sample.
And the third step of optimizing a calibration algorithm, namely optimizing and calibrating the wavelength, wherein a specific flow chart is shown in figure 4 and comprises the following steps:
1. two standard optical samples, Sample B, were prepared, the thickness of which was suggested to be thicker and thinner, and the thickness d1, d2 and the optical constants N1, N2 of the two samples were measured using a standard ellipsometer. Two standard optical samples SampleB were measured using an ellipsometer a to obtain measured ellipsometric parameters Ms1 and Ms2 of the two standard optical samples SampleB, and reference may be made to the aforementioned formula (5).
2. Theoretical ellipsometry parameters Ms1 'and Ms2' of the two standard optical samples Sample B are obtained according to the calculations of the formulas (1) to (4) based on the thicknesses d1 and d2, the optical constants N1 and N2, and the theoretical incident angle of the two standard optical samples Sample B.
3. According to the formulas (6) to (7), model reconstruction is carried out on the standard Sample B, data fitting is carried out on the measured ellipsometric parameters Ms1 and Ms2 and the theoretical ellipsometric parameters Ms1 'and Ms2', and a wavelength correction coefficient is output.
A fourth step of optimizing a calibration algorithm, the system calibration, comprising:
1. and respectively measuring the same sample with any thickness by using the ellipsometers A and B to carry out system calibration, writing the wavelength correction coefficient into a system model, and updating the system parameters of the ellipsometers A and B.
The ellipsometers a and B which have completed the optimized calibration algorithm proposed in the embodiment of the present invention are subjected to measurement consistency verification, and the results of measuring SampleA of the standard SiO2 film sample are compared with the results of measuring the ellipsometers a and B before and after wavelength optimized calibration, which are detailed in tables 1, 2, and 3, where table 1 is a table of comparing thicknesses of SampleA samples measured before optimized calibration, table 2 is a table of comparing thicknesses of SampleA samples measured after angle optimized calibration, and table 3 is a table of comparing thicknesses of SampleA samples measured after wavelength optimized calibration.
TABLE 1
TABLE 2
TABLE 3
It can be seen from tables 2 and 3 that the measurement consistency indexes of the ellipsometers a and B are obviously improved after the calculation by the optimized calibration algorithm provided in the embodiment of the present invention, as shown in fig. 7, fig. 7 shows a schematic diagram of the difference between the spectra obtained by measuring the same sample by different ellipsometers after the optimized calibration, and it can be seen that the spectra obtained by measuring the same sample by the ellipsometers a and B after the optimized calibration have consistency.
The embodiment of the invention provides an optimization calibration method for ellipsometers, which is used for improving the measurement consistency results of a plurality of ellipsometers. The first step of system calibration comprises the steps of measuring the same standard sample with any thickness by using each ellipsometer to obtain system parameters of each instrument, and ensuring that each instrument can carry out normal measurement; the second step angle optimization calibration module includes: measuring the same standard sample by using a plurality of ellipsometers, calibrating and adjusting the angle, performing angle optimization adjustment according to the deviation of the actual measurement angle and the theoretical angle of each ellipsometer, and finally realizing that the actual measurement angle of each ellipsometer is equal to the theoretical angle to finish angle optimization calibration; the third step of wavelength optimization calibration comprises the following steps: two standard samples of different thicknesses were first measured using a multi-station ellipsometer, resulting in the actual measured ellipsometric parameters Ms1 and Ms2 for the two samples. And then carrying out forward modeling according to the thicknesses, optical constants and theoretical incident angles of the two standard samples to obtain theoretical ellipsometry parameters Ms1 'and Ms2' of the two samples. Fitting the actually measured ellipsometry parameters and the theoretical ellipsometry parameters through sample model reconstruction to obtain a wavelength correction coefficient of each ellipsometer; and fourthly, calibrating the system, namely measuring the same standard sample with any thickness by using each ellipsometer, writing the obtained wavelength correction coefficient into a system model of each ellipsometer, and updating the system parameters of each ellipsometer. Therefore, the algorithm for ellipsometer optimization calibration provided by the embodiment of the invention can ensure that a plurality of ellipsometers can ensure better measurement results in the measurement of samples with different thicknesses, and can rapidly and low-cost improve the measurement consistency index of the ellipsometers without adding additional database files.
It should be noted that, in the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to relevant descriptions of other embodiments for parts that are not described in detail in a certain embodiment.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may 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 flow or flows and/or block diagram block or blocks.
These computer program instructions may 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 instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may 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 functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all alterations and modifications as fall within the scope of the application.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include such modifications and variations.
Claims (7)
1. An ellipsometer optimization calibration method is characterized by comprising the following steps:
step 1, measuring a standard sample with any thickness by using an ellipsometer to be calibrated, acquiring system parameters of the ellipsometer to be calibrated, and performing system calibration on the ellipsometer to be calibrated so that the ellipsometer after calibration can normally measure;
step 2, measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calibrating and adjusting the angle of the ellipsometer to be calibrated so that the actual measurement angle and the theoretical angle of the ellipsometer after calibration are kept consistent;
step 3, measuring a standard sample with known thickness and optical constant by using the ellipsometer to be calibrated to obtain a wavelength correction coefficient of the ellipsometer to be calibrated, and calibrating the wavelength of the ellipsometer to be calibrated;
and 4, carrying out system calibration on the ellipsometer to be calibrated again, writing the wavelength correction coefficient into the ellipsometer system model, and updating the parameters of the ellipsometer system model.
2. The ellipsometer optimized calibration method according to claim 1, wherein said measuring a sample with known thickness and optical constants by using the ellipsometer to be calibrated, and calibrating the ellipsometer to be calibrated so that the actual measurement angle and the theoretical angle of the ellipsometer after calibration are consistent comprises:
measuring a sample with known thickness and optical constant by using the ellipsometer to be calibrated, and calculating the actual measurement angle of the ellipsometer to be calibrated;
and calibrating and adjusting the actual measurement angle of the ellipsometer to be calibrated according to the deviation between the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated, so that the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated are kept consistent.
3. The ellipsometer optimized calibration method according to claim 2, wherein said measuring a sample with known thickness and optical constants using the ellipsometer to be calibrated, calculating an actual measurement angle of the ellipsometer to be calibrated comprises:
calculating to obtain an ellipsometry parameter of the sample according to the system parameter of the polarizing arm of the ellipsometer to be calibrated, the system parameter of the analyzing arm of the ellipsometer to be calibrated and the light intensity data collected by the sample measured by the ellipsometer to be calibrated;
and calculating to obtain the actual measurement incident angle of the ellipsometer to be calibrated according to the ellipsometry parameters of the sample.
4. The ellipsometer optimized calibration method according to claim 2 or 3, wherein the calibrating and adjusting the actual measurement angle of the ellipsometer to be calibrated according to the deviation between the actual measurement angle and the theoretical angle of the ellipsometer to be calibrated comprises:
the system parameters are changed by adjusting the optical path structures and the optical element positions of the polarizing arm and the analyzing arm of the ellipsometer to be calibrated, and the actual measurement incident angle of the ellipsometer after calibration is repeatedly measured and calculated until the calculated actual measurement incident angle of the ellipsometer after calibration is consistent with the theoretical angle.
5. The ellipsometer optimized calibration method according to claim 1, wherein said measuring a standard sample with known thickness and optical constant with the ellipsometer to be calibrated to obtain the wavelength correction coefficient of the ellipsometer to be calibrated, the wavelength calibration of the ellipsometer to be calibrated includes:
measuring the standard thicknesses d1 and d2 and the standard optical constants N1 and N2 of the two samples by using a standard ellipsometer;
calculating theoretical ellipsometry parameters Ms1 'and Ms2' of the two samples according to the standard thicknesses d1 and d2, the standard optical constants N1 and N2 and the theoretical incident angle of the two samples;
measuring two samples by using an ellipsometer to be calibrated, and calculating to obtain actual measurement ellipsometry parameters Ms1 and Ms2 of the two samples;
and performing model reconstruction on the sample according to the actual measurement ellipsometry parameters Ms1 and Ms2 and the theoretical ellipsometry parameters Ms1 'and Ms2' of the two measured samples to obtain the wavelength correction coefficient of the ellipsometer to be calibrated.
6. The ellipsometer optimized calibration method according to claim 5, wherein said measuring two samples with the ellipsometer to be calibrated, and calculating actual measured ellipsometric parameters Ms1 and Ms2 of the two samples comprises:
the actual measured ellipsometric parameters for each sample were calculated by the following formula:
Mp*Ms*Ma＝Sout；
wherein M ispFor the system parameters of the polarizing arm of the ellipsometer to be calibrated, MaFor the system parameters of the ellipsometer arm to be calibrated, SoutLight intensity signal, M, obtained for the measurement of a sample by an ellipsometer to be calibratedsEllipsometric parameters were actually measured for the samples.
7. The ellipsometry optimization calibration method according to claim 5, wherein said performing model reconstruction on the sample according to the actual measured ellipsometry parameters Ms1 and Ms2 and the theoretical ellipsometry parameters Ms1 'and Ms2' of the two samples to obtain the wavelength correction coefficient of the ellipsometry to be calibrated comprises:
the following equations were established for the actual measured ellipsometric parameters Ms1 and Ms2 and the theoretical ellipsometric parameters Ms1 'and Ms2' for both samples:
Π(Ms1，Ms2，λ)＝Π(Ms1'，Ms2')；
by the formula, the wavelength correction coefficient of the ellipsometer to be calibrated can be obtained.
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