CN-121977460-A - Device and method for improving film thickness measurement precision

CN121977460ACN 121977460 ACN121977460 ACN 121977460ACN-121977460-A

Abstract

The invention provides a device and a method for improving the measurement precision of film thickness, which relate to the technical field of film thickness measurement based on optics, wherein the device comprises a broadband light source, a spatial filter, a collimator, a measuring device, an imaging lens and a spectrometer, the measuring device comprises a reference mirror and a beam-splitting prism, and the method comprises the steps of calibrating parameters of a measuring system; the method comprises the steps of placing a sample to be detected into a detection light branch, acquiring spectrum interference fringe data of two-dimensional distribution corresponding to different OPD values through single acquisition of an imaging spectrometer, preprocessing the spectrum interference fringe data based on nonlinear fitting iteration, acquiring an experimental measurement value of SRPS based on the preprocessed spectrum interference fringe data, acquiring a theoretical value of SRPS, and obtaining a thickness value of a film and the OPD of an initial position of the sample through cross-correlation operation of the theoretical value of SRPS and the experimental measurement value. The invention has the advantages of realizing a measuring method with higher precision and lower cost through single measurement.

Inventors

FAN WEI
GUAN ZANYANG
CHEN CHAOXIN
PENG XIAOSHI
LIU XIANGMING
LIU YAOYUAN
LI YULONG
LIU YONGGANG
JIANG XIAOHUA

Assignees

中国工程物理研究院激光聚变研究中心

Dates

Publication Date: 20260505
Application Date: 20260408

Claims (10)

1. The device for improving the film thickness measurement precision is characterized by comprising a broadband light source, a spatial filter, a collimator, a measuring device, an imaging lens and a spectrometer, wherein the measuring device and a sample to be measured form a Michelson interference unit, and the measuring device comprises a reference mirror and a beam splitting prism; The broadband light source emits broadband light beams, high-frequency spatial modulation of the broadband light beams is filtered through the spatial filter, low-frequency light beams with slow spatial variation are obtained, the low-frequency light beams become collimated light beams after passing through the collimator, and the collimated light beams are transmitted to the measuring device; The sample to be measured is aligned with the beam splitter prism, inclination angle of reference mirror relative to sample to be measured ; The reference light and the detection light pass through the beam splitting prism, pass through the imaging lens and enter the spectrometer.
2. A method for improving the film thickness measurement accuracy, which is applied to the device for improving the film thickness measurement accuracy as set forth in claim 1, and is characterized by comprising the following steps: calibrating parameters of a measurement system, wherein the parameters comprise the amplitude splitting ratio of the probe light to the reference photoelectric field Relative distribution of reference optical electric field at coordinate value x of coordinate axis And detecting the relative distribution of the optical electric field at the coordinate value x of the coordinate axis The coordinate axis is arranged along the slit direction of the spectrometer; Placing a sample to be detected into a detection light branch, and adjusting the position and the posture of the sample to be detected so that the detection light is normally incident on the surface of the sample to be detected, and acquiring spectrum interference fringe data of two-dimensional distribution corresponding to different OPD values through single acquisition of an imaging spectrometer; based on nonlinear fitting iteration, preprocessing of spectrum interference fringe data is realized; Acquiring SRPS experimental measurement values based on the preprocessed spectrum interference fringe data, and acquiring SRPS theoretical values; And carrying out cross-correlation operation on the theoretical value and the experimental measurement value of SRPS to obtain the thickness value of the film and the OPD of the initial position of the sample.
3. The method for improving the measurement accuracy of the film thickness according to claim 2, wherein the method for calibrating the parameters of the measurement system is as follows: Placing a reference mirror in a detection light branch to place the sample to be detected; Turning on the broadband light source, blocking the reference light after the light source stably operates, and measuring to obtain the spectral distribution of the detection light , Representing the coordinate value x at the coordinate axis and at the wavelength The spectral intensity of the probe light; Turning on the broadband light source, blocking the detection light after the light source stably operates, and measuring to obtain the spectrum distribution of the reference light , Representing the coordinate value x in the coordinate axis and in the spectral dimension The reference light spectrum intensity below; According to the spectral distribution of the detected light And a reference light spectral distribution Calculating the parameters: ; Wherein, the Is the coordinate value of the coordinate axis along the wavelength direction, Is the coordinate value of the coordinate axis along the slit direction of the spectrometer.
4. The method for improving the film thickness measurement accuracy according to claim 2, wherein the method based on nonlinear fitting iteration is as follows: Step S301, initializing the iterative optical path difference correlation ; Step S302, establishing a relation function of the spectrum intensity and the optical path difference correlation quantity of different positions of the film sample; step S303, fixing the wavelengths one by one in the spectrum range of the light source Obtaining experimental measurement values of spectral intensity Based on the spectral intensity in the spectral interference fringe data And a relation function, wherein the function constant in the relation function is determined through cosine fitting, and the obtained new function constant is updated to the function constant for iteration; Step S304, using the correlation value of the path difference in iteration Under the condition of obtaining experimental measurement value of spectrum intensity Based on the spectral intensity in the spectral interference fringe data And a relation function, obtaining a new optical path difference correlation quantity through nonlinear fitting, and updating the obtained new optical path difference correlation quantity to an iterative optical path difference correlation quantity; Step S305, repeating the step3 and the step 4 until the experimental measurement value And if the difference value between the result calculated by the relation function and the result calculated by the relation function is smaller than a preset difference value threshold, ending iteration to obtain a preprocessing result.
5. The method of claim 4, wherein the spectral intensity is related to the optical path difference at different locations of the film sample The relationship function of (2) is: ; ; Wherein, the To be related by optical path difference And a spectral intensity determined by a function constant including DC term DC in the interference fringe and amplitude of AC term in the interference fringe And , The spectral phase difference of the reference light-detecting light introduced for the film, k being the wave vector, Is a constant.
6. The method for improving the measurement accuracy of the film thickness according to claim 5, wherein the cosine fitting is performed by the following expression: 。
7. the method for improving the measurement accuracy of the film thickness according to claim 6, wherein the nonlinear fitting is performed by the following expression: 。
8. The method of claim 7, wherein terminating the iteration is performed under the following conditions: ; Wherein, the And the difference value is a preset difference value threshold value.
9. The method for improving the film thickness measurement accuracy according to claim 2, wherein the method for performing the cross-correlation operation is as follows: defining a cross-correlation function with respect to the thickness value and the OPD; when the value of the cross-correlation function is maximum, the corresponding thickness value and the value of the OPD in the cross-correlation function are respectively the thickness value of the film and the OPD of the initial position of the sample.
10. The method for improving the film thickness measurement accuracy according to claim 9, wherein the cross correlation function is expressed as: ; Wherein, the As a function of the cross-correlation, The value of wave vector is And the value of OPD is At the time of SRPS's experimental measurement, The value of wave vector is And the value of OPD is The theoretical value of SRPS is that M and i are the total number and number of wave vectors, N and p are the total number and number of OPD, d is thickness value, The OPD which is a constant i.e. the initial position of the sample, The optical path difference correlation amounts for different positions of the film sample.

Description

Device and method for improving film thickness measurement precision Technical Field The invention relates to the technical field of film thickness measurement based on optics, in particular to a device and a method for improving film thickness measurement precision. Background The film is widely applied in the technical fields of optical and new energy sources and the like at the front edge and is still rapidly developed. The effect of physical thickness as a fundamental parameter of the film on the device performance is obvious, and thus it is of great importance to make accurate measurements. Currently, ellipsometry, reflectance spectroscopy, white light frequency domain interferometry, and the like are several commonly used non-contact non-destructive testing methods. However, the structure of the instrument used by the ellipsometry is complex, the detection result is often related to the experience of operators, the reflection spectroscopy generally needs to use a light source with a spectrum width of hundreds of nanometers to improve the measurement accuracy, the ultra-wideband light source with proper wavelength and spectrum distribution can greatly increase the system cost, and the white light frequency domain interferometry is not suitable for the detection of an ultra-thin film because of the data noise which is difficult to suppress in the collected interference fringes. Besides, in the prior art, accurate measurement of the thickness of the ultrathin film is realized based on white light spectrum interference fringes with a plurality of sequence periods, however, a piezoelectric sensing device is adopted to control the detection mode of the interference fringe periods, so that time and effort are often consumed, and the vibration amplitude of a measurement platform is required to be controlled in the measurement process. Therefore, there is a need to optimize thin film measurement methods to achieve higher accuracy and lower cost measurement methods with a single measurement. Disclosure of Invention The invention aims to provide a device and a method for improving the measurement precision of the thickness of a film, which can realize a measurement method with higher precision and lower cost through single measurement. The invention is realized by the following technical scheme: The device for improving the film thickness measurement precision comprises a broadband light source, a spatial filter, a collimator, a measuring device, an imaging lens and a spectrometer, wherein the measuring device and a sample to be measured form a Michelson interference unit, and the measuring device comprises a reference mirror and a beam-splitting prism; The broadband light source emits broadband light beams, high-frequency spatial modulation of the broadband light beams is filtered through the spatial filter, low-frequency light beams with slow spatial variation are obtained, the low-frequency light beams become collimated light beams after passing through the collimator, and the collimated light beams are transmitted to the measuring device; The sample to be measured is aligned with the beam splitter prism, inclination angle of reference mirror relative to sample to be measured ; The reference light and the detection light pass through the beam splitting prism, pass through the imaging lens and enter the spectrometer. The invention also provides a method for improving the film thickness measurement precision, which is applied to the device for improving the film thickness measurement precision and comprises the following steps: calibrating parameters of a measurement system, wherein the parameters comprise the amplitude splitting ratio of the probe light to the reference photoelectric field Relative distribution of reference optical electric field at coordinate value x of coordinate axisAnd detecting the relative distribution of the optical electric field at the coordinate value x of the coordinate axisThe coordinate axis is arranged along the slit direction of the spectrometer; Placing a sample to be detected into a detection light branch, and adjusting the position and the posture of the sample to be detected so that the detection light is normally incident on the surface of the sample to be detected, and acquiring spectrum interference fringe data of two-dimensional distribution corresponding to different OPD values through single acquisition of an imaging spectrometer; based on nonlinear fitting iteration, preprocessing of spectrum interference fringe data is realized; Acquiring SRPS experimental measurement values based on the preprocessed spectrum interference fringe data, and acquiring SRPS theoretical values; And carrying out cross-correlation operation on the theoretical value and the experimental measurement value of SRPS to obtain the thickness value of the film and the OPD of the initial position of the sample. Preferably, the method for calibrating the parameters of the measurement system comprises