A method for correcting measurement data of optical measuring equipment

Abstract

The present invention provides a method for correcting measurement data of an optical measuring device, comprising: obtaining measured light intensity data of a plurality of samples in a target wavelength band measured before and after an optical device in the optical measuring device is replaced; calculating a light intensity ratio curve, a weighted ratio curve, and a corrected ratio curve for each sample in the target wavelength band at each frame based on the measured light intensity data of the plurality of samples in the target wavelength band; and correcting the measured light intensity data after the optical device is replaced based on the corrected ratio curve to obtain corrected measured light intensity data. The present invention obtains a corrected ratio curve at each frame based on the measured light intensity data of the plurality of samples before and after the device is replaced, and corrects the light intensity data after the device is replaced using the corrected ratio curve, so that the film thickness and complex refractive index extracted from the corrected data are consistent with the film thickness and complex refractive index results before the device is replaced, thereby reducing unknown and difficult-to-characterize errors introduced by the device replacement.

Description

Technical Field

[0001] The present invention relates to spectral measurement in the field of optics / materials, and more particularly to a method for correcting measurement data of an optical measurement device. Background Art

[0002] In the semiconductor industry, the measurement of optical critical dimensions (OCDs) and fine structure film thickness is directly related to the accuracy and yield of production samples. Optical measurement equipment such as ellipsometers are widely used in semiconductor process monitoring due to their non-contact, non-destructive, fast, and high-precision advantages.

[0003] See also Figure 1 The basic configuration of the ellipsometer includes a light source 1, a polarizer 2, a first rotary motor 3, a first compensator 4, a sample to be measured 5, a second compensator 6, a second rotary motor 7, an analyzer 8 and a spectrometer 9.

[0004] The basic principle process of system calibration and measurement of ellipsometer is as follows:

[0005] 1. Natural light passes through a polarizer and a (rotating) wave plate to obtain polarized light;

[0006] 2. New polarized light obtained by reflection or transmission of polarized light through the standard sample material;

[0007] 3. The new polarized light passes through the (rotating) wave plate and analyzer of the analyzer arm to obtain the changed light intensity information;

[0008] 4. Process the measured light intensity change information to obtain system parameters.

[0009] 5. Measure the light intensity information of the sample to be tested, and perform Fourier transform on the measured light intensity to obtain the Fourier coefficient.

[0010] 6. Use the system parameters and the Fourier coefficients of the sample to be measured to calculate the Mueller matrix of the sample, and extract the complex refractive index and thickness of the sample through the Mueller matrix of the sample.

[0011] In actual applications, changes in devices (such as optical fibers) will introduce unknown and difficult-to-characterize errors, resulting in differences in the measured light intensity, which in turn leads to deviations in the film thickness results extracted from the data before and after the device replacement. Summary of the Invention

[0012] The present invention addresses the technical problems existing in the prior art and provides a method for correcting measurement data of an optical measuring device, comprising:

[0013] Obtaining light intensity data of multiple samples in a target wavelength band before and after the optical device in the optical measurement equipment is replaced;

[0014] Based on the measured light intensity data of multiple samples in the target band, a light intensity ratio curve of each sample in the target band at each frame number is calculated, wherein the light intensity ratio curve is the ratio of the measured light intensity data after the optical device is replaced to the measured light intensity data before the optical device is replaced;

[0015] Perform weighted processing on the light intensity ratio curves of the target band of multiple samples at the same frame number to obtain the weighted ratio curve of the target band at each frame number;

[0016] Perform filtering on the weighted ratio curve of the target band at each frame number to obtain a corrected ratio curve;

[0017] Based on the correction ratio curve, the measured light intensity data after the optical device is replaced is corrected to obtain corrected measured light intensity data.

[0018] On the basis of the above technical solution, the present invention can also make the following improvements.

[0019] Optionally, performing weighted processing on the light intensity ratio curves of the target waveband of the multiple samples at the same frame number to obtain the weighted ratio curve of the target waveband at each frame number includes:

[0020] Determine the weight parameters of each sample;

[0021] Based on the light intensity ratio curve of the target band of each sample at the same frame number and the corresponding weight parameters, the weighted ratio curve of the target band at each frame number is calculated.

[0022] Optionally, determining the weight parameter of each sample includes:

[0023] Determine the weight parameters of each sample based on the equal weight method or the non-equal weight method

[0024] Optionally, filtering the weighted ratio curve of the target band at each frame number to obtain a corrected ratio curve includes:

[0025] The filtering parameters are determined based on the wavelet filtering method or the smoothing filtering method, and the weighted ratio curve of the target band under each frame number is filtered to obtain the corrected ratio curve.

[0026] Optionally, based on the correction ratio curve, the measured light intensity data after the optical device is replaced is corrected to obtain the corrected measured light intensity data, including:

[0027] The measured light intensity data of the target band after the optical device is replaced is divided by the ratio of the correction ratio curve corresponding to the number of frames to obtain the corrected measured light intensity data.

[0028] Optionally, weight parameters and filter parameters are obtained through fitting iteration based on each sample parameter obtained from the corrected measured light intensity data and each sample parameter obtained from the measured light intensity data before the optical device is replaced.

[0029] Optionally, the sample parameters include film thickness and complex refractive index, and each sample parameter obtained according to the corrected measured light intensity data includes:

[0030] Output the film thickness or complex refractive index of each sample based on the initial weight parameters, initial filter parameters, and system parameters after optical device replacement;

[0031] Based on the film thickness or complex refractive index of each sample after the optical device is replaced and the film thickness or complex refractive index of each sample extracted before the optical device is replaced, calculate the mean square error of the film thickness or complex refractive index of the multiple samples before and after the optical device is replaced;

[0032] The weight parameters and the filter parameters are continuously adjusted to minimize the mean square error, and the weight parameters and the filter parameters are obtained.

[0033] The present invention provides a method for correcting measurement data of an optical measuring device. The method obtains a correction ratio curve at each frame number by measuring light intensity data of multiple samples before and after device replacement. The light intensity data after device replacement is corrected by the correction ratio curve so that the film thickness and complex refractive index extracted from the corrected data are consistent with the film thickness and complex refractive index results before device replacement, thereby reducing unknown and difficult-to-characterize errors introduced by device replacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the ellipsometer;

[0035] Figure 2 This is a flow chart of a method for correcting measurement data of an optical measurement device provided by the present invention.

[0036] In the accompanying drawings, the device names represented by the reference numbers are as follows:

[0037] 1. Light source, 2. Polarizer, 3. First rotary motor, 4. First compensator, 5. Sample to be measured, 6. Second compensator, 7. Second rotary motor, 8. Analyzer, 9. Spectrometer. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention can be arbitrarily combined with each other to form a feasible technical solution. This combination is not restricted by the sequence of steps and / or structural composition mode, but must be based on the ability of ordinary technicians in this field to implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0039] In actual applications, changes in devices (such as optical fibers) will introduce unknown and difficult-to-characterize errors, resulting in differences in the measured light intensity. This in turn leads to deviations in the film thickness results extracted from the data before and after the device replacement. In order to maintain consistency in the results, the measured light intensity data needs to be corrected.

[0040] Figure 2 The present invention provides a method for correcting measurement data of an optical measuring device, comprising:

[0041] Step 1: Obtain light intensity data of a plurality of samples in a target wavelength band before and after the optical device in the optical measurement equipment is replaced.

[0042] It is understandable that the measured light intensity data of the plurality of samples in the target band are respectively measured by the optical measuring equipment before the optical device is replaced.

[0043] Step 2: Based on the measured light intensity data of multiple samples in the target band, calculate the light intensity ratio curve of each sample in the target band at each frame number. The light intensity ratio curve is the ratio of the measured light intensity data after the optical device is replaced to the measured light intensity data before the optical device is replaced.

[0044] It can be understood that the light intensity ratio curves of the multiple samples are obtained by using the ratio of the measured light intensity data after the optical device of the target band is replaced to the measured light intensity data before the optical device is replaced at the same frame number of the multiple samples in step 1.

[0045] Step 3: Perform weighted processing on the light intensity ratio curves of the target band of multiple samples at the same frame number to obtain the weighted ratio curve of the target band at each frame number.

[0046] As an embodiment, the light intensity ratio curves of the target band of multiple samples at the same frame number are weighted to obtain the weighted ratio curve of the target band at each frame number, including: determining the weight parameter of each sample; based on the light intensity ratio curve of the target band of each sample at the same frame number, and the corresponding weight parameter, calculating the weighted ratio curve of the target band at each frame number.

[0047] It can be understood that the light intensity ratio curves of the multiple samples obtained in step 2 and the weight parameters of each sample are weighted to obtain the weighted ratio curve of the target band at each frame number.

[0048] Step 4: Filter the weighted ratio curve of the target band at each frame number to obtain a corrected ratio curve.

[0049] It is understandable that the weighted ratio curve at each frame number in step 3 is filtered, for example, optimized using wavelet filtering, smoothing filtering, etc., to obtain a corrected ratio curve.

[0050] Step 5: Based on the correction ratio curve, correct the measured light intensity data after the optical device is replaced to obtain corrected measured light intensity data.

[0051] The corrected measured light intensity data is obtained by dividing the measured light intensity data of the target band after the optical device is replaced by the ratio of the correction ratio curve corresponding to the number of frames.

[0052] It should be noted that the unequally weighted values, wavelet filter parameters, and smoothing points involved in steps 3 and 4 can be obtained by iterating the final weight parameters and filter parameters using the sample parameters extracted from the measured light intensity data after data correction and the sample parameters before replacing the optical device as the iterative objective function. Iterative fitting implementation methods include, but are not limited to, ergodic methods, global optimization methods (such as particle swarm optimization, ant colony optimization, etc.), and local optimization algorithms (such as Levenberg-Marquardt method, Newton method, gradient descent method, conjugate gradient method, etc.).

[0053] The specific principles of the measurement data correction method provided by the present invention are as follows:

[0054] By measuring the light intensity information of multiple pieces before and after replacing the optical device, the light intensity ratio curve of each sample in the target band at each frame number is obtained.

[0055]

[0056] Where IntenA and IntenB represent the measured light intensity information before and after the optical device is replaced, Ratio represents the light intensity ratio, i represents the i-th sample, j represents the j-th frame, and wvl represents the target band.

[0057] Then, the Ratio light intensity ratio is weighted to obtain the weighted ratio curve for each frame:

[0058]

[0059] Among them, RatioW is the weighted ratio, Weight is the weight parameter of the sample, and N represents the total number of samples.

[0060] Then use RatioW to perform filtering and smoothing to obtain the corrected ratio curve:

[0061] RatioR(j,wvl)=wavelet(RatioW(j,wvl),parameter) (3);

[0062] Among them, RatioR is the correction ratio curve, wavelet is the wavelet filter function, and parameter is the wavelet filter parameter. This step can also obtain the correction ratio curve by smoothing, high-frequency filtering, etc.

[0063] Finally, use the correction ratio curve to correct the light intensity data after the device is replaced:

[0064]

[0065] Where IntenR is the corrected measured light intensity data.

[0066] The weight parameter Weight and the filter parameter Parameter in equations (2) and (3) can be obtained by iterative fitting using the parameter measurements of the sample components before the replacement of the various components (e.g., thick film, complex refractive index, etc.) as iterative target values. The iterative fitting implementation methods include, but are not limited to, ergodic methods, global optimization methods (e.g., particle swarm optimization, ant colony optimization, etc.), and local optimization algorithms (e.g., Levenberg-Marquardt method, Newton method, gradient descent method, conjugate gradient method, etc.).

[0067] As an embodiment, the sample parameters include film thickness and complex refractive index. The parameters of each sample obtained according to the corrected measured light intensity data include: outputting the film thickness or complex refractive index of each sample according to the initial weight parameters, initial filtering parameters and system parameters after the optical device is replaced; calculating the mean square error of the film thickness or complex refractive index of multiple samples before and after the optical device is replaced based on the film thickness or complex refractive index of each sample after the optical device is replaced, and the film thickness or complex refractive index of each sample extracted before the optical device is replaced; continuously adjusting the weight parameters and filtering parameters to minimize the mean square error and obtain the weight parameters and filtering parameters.

[0068] Among them, based on the weight parameters, filter parameters and the system parameters of the optical measurement equipment after the optical device is replaced, the expression for calculating the film thickness and complex refractive index of the sample is:

[0069] [Thk,n,k]=function(IntenR(Weight,Parameter),System_Parameter) (5);

[0070] Where System_Parameter is the system parameter, Thk is the film thickness, n is the real part of the complex refractive index, and k is the imaginary part of the complex refractive index. In the function, you can input the weight, the filter parameter, and the system parameter System_Parameter to output the extracted values ​​of thickness Thk and complex refractive index n and k.

[0071] The measured values ​​Thk0, n0, k0 before replacing the optical device are used as the iterative targets. By continuously adjusting the weight parameters and filter parameters of each sample, the mean square error between the calculated film thickness or complex refractive index of each sample and the film thickness and complex refractive index of each sample calculated from the measured light intensity data before replacing the optical device is minimized, and the appropriate weight parameters Weight and filter parameters Parameter are obtained.

[0072] Based on appropriate weight parameters and filter parameters, a correction ratio curve is calculated, and based on the correction ratio curve, the measured light intensity data after the optical device is replaced is corrected.

[0073] The present invention provides a method for correcting measurement data of an optical measuring device. The method obtains a correction ratio curve at each frame number by measuring light intensity data of multiple samples before and after device replacement. The light intensity data after device replacement is corrected by the correction ratio curve so that the film thickness and complex refractive index extracted from the corrected data are consistent with the film thickness and complex refractive index results before device replacement, thereby reducing unknown and difficult-to-characterize errors introduced by device replacement.

[0074] It should be noted that, in the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0075] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0076] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for correcting measurement data of an optical measuring device, characterized in that: include: Obtaining light intensity data of multiple samples in a target wavelength band before and after the optical device in the optical measurement equipment is replaced; Based on the measured light intensity data of multiple samples in the target band, a light intensity ratio curve of each sample in the target band at each frame number is calculated, wherein the light intensity ratio curve is the ratio of the measured light intensity data after the optical device is replaced to the measured light intensity data before the optical device is replaced; Perform weighted processing on the light intensity ratio curves of the target band of multiple samples at the same frame number to obtain the weighted ratio curve of the target band at each frame number; Perform filtering on the weighted ratio curve of the target band at each frame number to obtain a corrected ratio curve; Based on the correction ratio curve, the measured light intensity data after the optical device is replaced is corrected to obtain corrected measured light intensity data.

2. The method for correcting measurement data according to claim 1, wherein: The weighted processing is performed on the light intensity ratio curves of the target waveband of the multiple samples at the same frame number to obtain the weighted ratio curve of the target waveband at each frame number, including: Determine the weight parameters of each sample; Based on the light intensity ratio curve of the target band of each sample at the same frame number and the corresponding weight parameters, the weighted ratio curve of the target band at each frame number is calculated.

3. The method for correcting measurement data according to claim 2, wherein: Determining the weight parameter of each sample includes: The weight parameters of each sample are determined based on the equal weight method or the non-equal weight method.

4. The method for correcting measurement data according to claim 3, wherein: The filtering process is performed on the weighted ratio curve of the target band at each frame number to obtain a corrected ratio curve, including: The filtering parameters are determined based on the wavelet filtering method or the smoothing filtering method, and the weighted ratio curve of the target band under each frame number is filtered to obtain the corrected ratio curve.

5. The method for correcting measurement data according to claim 1, wherein: The method of correcting the measured light intensity data after the optical device is replaced based on the correction ratio curve to obtain the corrected measured light intensity data includes: The measured light intensity data of the target band after the optical device is replaced is divided by the ratio of the correction ratio curve corresponding to the number of frames to obtain the corrected measured light intensity data.

6. The method for correcting measurement data according to claim 4, characterized in that: The weight parameters and the filter parameters are obtained through fitting iteration based on each sample parameter obtained from the corrected measured light intensity data and each sample parameter obtained from the measured light intensity data before the optical device is replaced.

7. The method for correcting measurement data according to claim 6, characterized in that: The sample parameters include film thickness and complex refractive index. Each sample parameter obtained based on the corrected measured light intensity data and each sample parameter obtained based on the measured light intensity data before the optical device is replaced, and weight parameters and filter parameters are obtained through fitting iteration, including: Output the film thickness or complex refractive index of each sample based on the initial weight parameters, initial filter parameters, and system parameters after optical device replacement; Based on the film thickness or complex refractive index of each sample after the optical device is replaced and the film thickness or complex refractive index of each sample extracted before the optical device is replaced, calculate the mean square error of the film thickness or complex refractive index of the multiple samples before and after the optical device is replaced; The weight parameters and the filter parameters are continuously adjusted to minimize the mean square error, and the weight parameters and the filter parameters are obtained.

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