Wavelength calibration method of measurement equipment

Abstract

The invention provides a wavelength calibration method for measuring equipment, which comprises the following steps: acquiring full-wave-band light intensity information of a standard sample piece, and performing Fourier transform on the full-wave-band light intensity information to obtain an actually measured Fourier coefficient; performing iterative fitting on the actually measured Fourier coefficient and the theoretical Fourier coefficient to obtain a system parameter, an incident angle, a standard sample piece thickness and a wavelength deviation of the measurement equipment under each wavelength; acquiring full-wave-band light intensity information of the sample piece to be measured, and performing Fourier transform on the full-wave-band light intensity information to obtain an actually measured Fourier coefficient; and calculating the full-wave band spectrum Mueller matrix of the sample piece to be measured according to the system parameter under each wavelength, the wavelength deviation and the actually measured Fourier coefficient of the sample piece to be measured. Through the method provided by the invention, the wavelength of a measurement sample piece of measurement equipment such as an ellipsometer can be calibrated, and the problem of system deviation between the display wavelength and the actual wavelength caused by factors such as external temperature, pressure intensity, mechanical and optical defects of optical devices and the like in the use process of a spectrograph is solved.

Description

Technical Field

[0001] The present invention relates to the field of optics / materials, and more specifically, to a wavelength calibration method for a measuring device. Background Art

[0002] In the semiconductor industry, the measurement of optical critical dimension (OCD) and the measurement of the thickness of fine structure films are directly related to the accuracy and yield of production samples. Due to its advantages such as non-contact, non-destructive, fast, and high precision, ellipsometers are widely used in semiconductor process monitoring.

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

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

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

[0006] 2. The polarized light is reflected or transmitted through a standard sample material to obtain a new polarized light;

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

[0008] 4. The measured light intensity variation information is processed to obtain system parameters.

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

[0010] 6. Calculate the Mueller matrix of the sample using the system parameters and the Fourier coefficients of the sample to be measured.

[0011] 7. Iteratively obtain information such as the film thickness and complex refractive index of the sample using the calculated Mueller matrix of the sample and the simulated Mueller matrix.

[0012] During the use of a spectrometer, due to factors such as external temperature, pressure, mechanical and optical defects of optical devices, there is a systematic deviation between the displayed wavelength and the actual wavelength. Therefore, wavelength calibration of the spectrometer is required. Summary of the Invention

[0013] In view of the technical problems existing in the prior art, the present invention provides a wavelength calibration method for a measuring device, including:

[0014] The full-band light intensity information of a standard sample is obtained based on a measuring device, and Fourier transform is performed on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength.

[0015] The measured Fourier coefficients corresponding to each wavelength and the theoretical Fourier coefficients are iteratively fitted to obtain the system parameters, incident angle, thickness of the standard sample, and wavelength deviation of the measuring device at each wavelength.

[0016] The full-band light intensity information of a sample to be measured is obtained based on the measuring device, and Fourier transform is performed on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength.

[0017] According to the system parameters, wavelength deviation at each wavelength, and the measured Fourier coefficients corresponding to each wavelength of the sample to be measured, the full-band spectral Mueller matrix of the sample to be measured is calculated.

[0018] A wavelength calibration method for a measuring device provided by the present invention can calibrate the wavelength of a sample measured by a measuring device such as an ellipsometer, overcoming the problem that there is a systematic deviation between the displayed wavelength and the actual wavelength due to factors such as external temperature, pressure, mechanical and optical defects of optical devices during the use of a spectrometer. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of an ellipsometer;

[0020] Figure 2 It is a flowchart of a wavelength calibration method for a measuring device provided by the present invention. Detailed Embodiment

[0021] To make the objectives, 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 with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. In addition, the technical features in each embodiment or a single embodiment provided by the present invention can be combined with each other arbitrarily to form a feasible technical solution. This combination is not restricted by the order of steps and / or the structural composition mode, but must be based on what can be achieved by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0022] It is understandable that in actual applications, factors such as the external environmental temperature, pressure, mechanical and optical defects of optical devices will affect the wavelength accuracy of the spectrometer. Therefore, an ellipsometer is needed to calibrate the wavelength of the spectrometer.

[0023] Figure 2 The flowchart of the wavelength calibration method for a measurement device provided by the present invention is as Figure 2 shown, and the method includes:

[0024] Step 1: Based on the measurement device, obtain the full-band light intensity information of the standard sample, and perform Fourier transform on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength.

[0025] It is understandable that, for example, first collect the full-band spectral light intensity information of light sources such as mercury lamps through a spectrometer to obtain the light intensity change information of the standard sample. Perform Fourier processing on the light intensity information at each wavelength to obtain the measured Fourier coefficients.

[0026] Step 2: Iteratively fit the measured Fourier coefficients corresponding to each wavelength and the theoretical Fourier coefficients to obtain the system parameters, incident angle, thickness of the standard sample, and wavelength deviation of the measurement device at each wavelength.

[0027] It is understandable that an optical system model of the measurement device is constructed as follows:

[0028] S out = D × [M A R(A)] × [R(-ω2t - C2)M(δ2)R(ω2t + C2)] × Ms(Thk, AOI, wvl0 + δwvl) × [R(-ω1t - C1)M(δ1)R(ω1t + C1)] × [R(-P)M P × S in (1);

[0029] where M S is the Mueller matrix of the sample, D is the detection vector [1, 0, 0, 0] of the spectrometer, M P , M A are the Mueller matrices of the polarizers in the polarizing arm and the analyzing arm, ω1, ω2 are the rotation speeds of the first motor and the second motor, M(δ1) and M(δ2) are the Mueller matrices of the phase retardation amounts of the polarizing composite waveplate and the analyzing composite waveplate, R is the rotation matrix, P, A, C1, C2 are the azimuth angles of the polarizer, the analyzer, the polarizing composite waveplate, and the analyzing composite waveplate respectively, δ1 is the phase retardation amount of the polarizing composite waveplate, δ2 is the phase retardation amount of the analyzing composite waveplate, S inis the Stokes vector of the normalized natural light, wvl0 is the original wavelength of the spectrometer, Thk is the thickness of the sample, AOI is the angle of incidence, and δwvl is the wavelength deviation.

[0030] Among them, P, A, C1, C2, δ1, and δ2 are used as the system parameters to be calibrated. The thickness of the sample Thk, the angle of incidence AOI, and the wavelength deviation δwvl are also used as the parameters to be calibrated.

[0031] During the calibration process, at each wavelength, set the initial system parameters, initial angle of incidence, initial sample thickness, and initial wavelength deviation, and calculate the corresponding theoretical light intensity information based on the optical system model; perform Fourier transform on the theoretical light intensity information to obtain the theoretical Fourier coefficients; calculate the difference between the theoretical Fourier coefficients and the measured Fourier coefficients at each wavelength; when the difference is less than the preset difference threshold, obtain the initial system parameters, initial angle of incidence, initial sample thickness, and initial wavelength deviation. When the difference is greater than the preset difference threshold, adjust the initial system parameters, initial angle of incidence, initial sample thickness, and initial wavelength deviation, recalculate the theoretical light intensity information, and iterate cyclically to calculate the difference value after each iteration until the difference value is less than the preset difference threshold, and obtain the system parameters, angle of incidence, sample thickness, and wavelength deviation at each wavelength.

[0032] Correct the original wavelength according to the wavelength deviation of each wavelength to obtain each corrected wavelength wvl r :

[0033] wvl r = δwvl + wvl0 (2).

[0034] Among them, the fitting iteration implementation methods include but are not limited to the traversal method, global optimization methods (such as particle swarm algorithm, ant colony algorithm, etc.) and local optimization algorithms (such as Levenberg-Marquardt method, Newton method, gradient descent method, conjugate gradient method, etc.).

[0035] Step 3: Obtain the full-band light intensity information of the sample to be measured based on the measuring device, and perform Fourier transform on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength.

[0036] It can be understood that, for example, the full-band spectral light intensity information of the sample to be measured is measured by collecting light sources such as mercury lamps through a spectrometer, and the light intensity change information of the sample to be measured is obtained. Perform Fourier processing on the light intensity information of each wavelength to obtain the measured Fourier coefficients of the sample to be measured at each wavelength.

[0037] Step 4: Calculate the full-band spectral Mueller matrix of the sample to be measured based on the system parameters, wavelength deviation, and the measured Fourier coefficients corresponding to each wavelength of the sample to be measured.

[0038] It can be understood that by substituting the measured Fourier coefficients of the sample to be measured at each wavelength, the system calibration parameters, the corrected wavelength, etc. into formula (3), the full-spectrum Mueller matrix M of the sample is calculated. s :

[0039] M s = function(Fourier, A, P, C1, C2, δ1, δ2, wvl r ) (3);

[0040] Among them, Fourier represents the measured Fourier coefficients.

[0041] Among them, the principle of using the calibration wavelength of the sample is as follows: The complex refractive index N of the standard sample at each wavelength can be obtained accurately from the experimental database. Therefore, different theoretical N values can be obtained by changing the wavelength, and then the Mueller matrix corresponding to the wavelength can be simulated. By iterating the Mueller matrix after changing the wavelength and the Fourier coefficients simulated by the system model with the measured Fourier coefficients, the wavelength deviation value of the collected data can be obtained, thereby correcting the wavelength of the entire spectrometer.

[0042] A wavelength calibration method for a measuring device provided by the present invention includes obtaining the full-band light intensity information of a standard sample, performing Fourier transform on the full-band light intensity information to obtain measured Fourier coefficients; iteratively fitting the measured Fourier coefficients and the theoretical Fourier coefficients to obtain the system parameters, incident angle, standard sample thickness, and wavelength deviation of the measuring device at each wavelength; obtaining the full-band light intensity information of the sample to be measured, performing Fourier transform on the full-band light intensity information to obtain measured Fourier coefficients; and calculating the full-band spectral Mueller matrix of the sample to be measured based on the system parameters, wavelength deviation, and measured Fourier coefficients at each wavelength. Through the method of the present invention, the wavelength of a sample measured by a measuring device such as an ellipsometer can be calibrated, overcoming the problem that there is a systematic deviation between the displayed wavelength and the actual wavelength due to factors such as external temperature, pressure, mechanical and optical defects of optical devices during the use of the spectrometer.

[0043] It should be noted that in the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0044] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0045] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A wavelength calibration method for a measuring device, characterized in that, Including: Based on a measurement device, obtaining the full-band light intensity information of a standard sample, and performing Fourier transform on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength; Iteratively fitting the measured Fourier coefficients corresponding to each wavelength and the theoretical Fourier coefficients to obtain the system parameters, incident angle, thickness of the standard sample, and wavelength deviation of the measurement device at each wavelength; Based on the measurement device, obtaining the full-band light intensity information of the sample to be measured, and performing Fourier transform on the light intensity information at each wavelength to obtain the measured Fourier coefficients corresponding to each wavelength; According to the system parameters, wavelength deviation at each wavelength, and the measured Fourier coefficients corresponding to each wavelength of the sample to be measured, calculating the full-band spectral Mueller matrix of the sample to be measured.

2. The wavelength calibration method of the measuring device according to claim 1, characterized in that The iterative fitting of the measured Fourier coefficients corresponding to each wavelength and the theoretical Fourier coefficients to obtain the system parameters, incident angle, sample thickness, and wavelength deviation of the measurement device at each wavelength includes: Constructing an optical system model of the measurement device; At each wavelength, setting the initial system parameters, initial incident angle, initial sample thickness, and initial wavelength deviation, and calculating the corresponding theoretical light intensity information based on the optical system model; Performing Fourier transform on the theoretical light intensity information to obtain the theoretical Fourier coefficients; Calculating the difference between the theoretical Fourier coefficients and the measured Fourier coefficients at each wavelength; When the difference is less than the preset difference threshold, obtaining the initial system parameters, initial incident angle, initial sample thickness, and initial wavelength deviation; When the difference is greater than the preset difference threshold, adjusting the initial system parameters, initial incident angle, initial sample thickness, and initial wavelength deviation, iteratively calculating the difference value after each iteration until the difference value is less than the preset difference threshold, and obtaining the system parameters, incident angle, sample thickness, and wavelength deviation at each wavelength.

3. The wavelength calibration method of the measuring device according to claim 2, characterized in that, The optical system model of the measurement device is: S out = D × [M A R(A)] × [R(-ω2t - C2)M(δ2)R(ω2t + C2)] × Ms(Thk, AOI, wvl0 + δwvl) × [R(-ω1t - C1)M(δ1)R(ω1t + C1)] × [R(-P)M P × S in (1); Among them, M S is the Mueller matrix of the sample, D is the detection vector [1, 0, 0, 0] of the spectrometer, M P , M A are the Mueller matrices of the polarizers in the polarization arm and the analyzer arm, ω1 and ω2 are the rotation speeds of the first motor and the second motor, M(δ1) and M(δ2) are the Mueller matrices of the phase retardation amounts of the polarization composite wave plate and the analyzer composite wave plate, R is the rotation matrix, P, A, C1, and C2 are the azimuth angles of the polarizer, analyzer, polarization composite wave plate, and analyzer composite wave plate respectively, δ1 is the phase retardation amount of the polarization composite wave plate, δ2 is the phase retardation amount of the analyzer composite wave plate, S in is the Stokes vector of the normalized natural light, wvl0 is the original wavelength of the spectrometer, Thk is the thickness of the sample, AOI is the angle of incidence, and δwvl is the wavelength deviation.

4. The wavelength calibration method of the measuring device according to claim 3, characterized in that, The calculating the full-band spectral Mueller matrix of the sample to be measured according to the system parameters, wavelength deviation at each wavelength, and the measured Fourier coefficients corresponding to each wavelength of the sample to be measured includes: Correcting the original wavelength of the spectrometer according to the wavelength deviation at each wavelength to obtain each corrected wavelength, and the corrected wavelength is expressed as: wvl r = δwvl + wvl0 (2); wherein, wvl r is the corrected wavelength; According to the system parameters, corrected wavelength at each corrected wavelength, and the measured Fourier coefficients corresponding to each corrected wavelength of the sample to be measured, calculating the full-band spectral Mueller matrix of the sample to be measured.

5. The wavelength calibration method of the measuring device according to claim 4, characterized in that Substituting the system parameters, corrected wavelength at each corrected wavelength, and the measured Fourier coefficients corresponding to each corrected wavelength of the sample to be measured into the following formula (3) to calculate the full-band spectral Mueller matrix Ms of the sample to be measured: M s = function(Fourier, A, P, C1, C2, δ1, δ2, wvl r ) (3); Wherein, Fourier represents the measured Fourier coefficient, and function represents the function.

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