An optical protective film thickness measurement method, device and system

Abstract

The application relates to the technical field of thickness measurement, in particular to an optical protective film thickness measurement method, device and system, which specifically comprises the following steps: mode decomposition is carried out on the reflection spectrum of each measurement point on the optical film to be measured, the fluctuation characteristics of high-frequency mode components are analyzed, and interference corresponding indexes are constructed; the position sequence difference between each measurement point and other measurement points and the interference corresponding index difference are analyzed, the repeatability and position consistency of each mode component at the positions of multiple measurement points are judged, the interference confidence is constructed in combination with the interference corresponding indexes; the target component corresponding to the maximum interference confidence of each measurement point is selected to measure the film thickness of each measurement point; the mode component corresponding to the interference signal of each measurement point can be accurately identified, the problem that external interference greatly affects the identification of the interference signal and causes the interference signal to be misjudged can be avoided, and the precision of the optical film thickness measurement is improved.

Description

Technical Field

[0001] This application relates to the field of thickness measurement technology, specifically to a method, apparatus, and system for measuring the thickness of optical protective films. Background Technology

[0002] Optical thin films are used to improve the reflectivity and absorptivity of optical systems. For optical thin films, the film thickness directly determines their optical performance. The thickness of the film is affected by many factors, such as the precision of the manufacturing process, the cleanliness of the processing environment, and the errors of the processing equipment. All of these can cause changes in the film thickness, thereby affecting the performance of the thin film product.

[0003] Current technologies for measuring the thickness of optical thin films address the issue of low-frequency characteristics in the spectral data acquired by spectrometers. They employ mode decomposition algorithms to decompose the spectral data and then use amplitude matching to identify the thin film interference spectrum from the decomposed mode components, thereby measuring the film thickness. However, these technologies do not adequately consider the interference from weak interference signals caused by surface dust and stray light from the environment. Therefore, relying solely on amplitude matching for interference signal identification can lead to significant errors, potentially causing misinterpretations and affecting the accuracy of subsequent thin film thickness measurements. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to provide a method, apparatus, and system for measuring the thickness of optical protective films. The specific technical solution adopted is as follows:

[0005] In a first aspect, embodiments of this application provide a method for measuring the thickness of an optical protective film, the method comprising the following steps:

[0006] Collect the reflection spectrum at each measurement point on the optical thin film under test;

[0007] Modal decomposition is performed on each reflection spectrum. Based on the fluctuation periodicity of each modal component and the degree of waveform oscillation regularity in the modal component, the interference correspondence index of each modal component is constructed.

[0008] Modal components are screened based on the signal frequency difference characteristics between thin-film interference spectra and light source spectra to obtain target components; based on the difference between the interference correspondence indices of each target component at each measurement point and the target components at other measurement points, the corresponding target components of each target component at each measurement point are determined; based on the difference between the interference correspondence indices of each target component and its corresponding target component and the corresponding modal component position difference, combined with the interference correspondence indices of each target component, the interference confidence of each target component is constructed.

[0009] The target component corresponding to the maximum interference confidence level at each measurement point is selected to measure the film thickness at each measurement point.

[0010] In one embodiment, the process of obtaining the interference corresponding index is as follows:

[0011] Calculate a series of autocorrelation coefficients for each modal component using the autocorrelation function; and denote the mean of the absolute values ​​of all autocorrelation coefficients for each modal component as the first mean.

[0012] Obtain all zero-crossing points in each modal component, and record the degree of dispersion of the distribution of the x-coordinate interval of all adjacent zero-crossing points as the first discrete value;

[0013] Interference correspondence indices for each modal component are constructed based on the first mean and the first discrete value. The interference correspondence indices are directly proportional to the first mean and inversely proportional to the first discrete value.

[0014] In one embodiment, the first discrete value is the variance of the x-coordinate intervals of all adjacent zero-crossing points.

[0015] In one embodiment, the process of acquiring the target component is as follows:

[0016] Based on the vibration frequency of the modal components, all modal components at each measurement point are divided into two parts: high-frequency signal and low-frequency signal. The high-frequency signal is then used as the target component selected for each measurement point.

[0017] In one embodiment, the step of dividing all modal components at each measurement point into high-frequency and low-frequency signals based on the vibration frequency of the modal components specifically involves:

[0018] All modal components at each measurement point are arranged in descending order of frequency. The modal components with the first preset percentage are taken as high-frequency signals, and the remaining modal components are taken as low-frequency signals.

[0019] In one embodiment, the process of obtaining the corresponding target component is as follows:

[0020] Calculate the interference correspondence index difference between each target component at each measurement point and each target component at any other measurement point; take the target component corresponding to the minimum interference correspondence index difference among the target components at any other measurement point as the corresponding target component of each target component at each measurement point in the target components at any other measurement point.

[0021] In one embodiment, the process of obtaining the interference confidence level is as follows:

[0022] Calculate the mean of the difference in interference correspondence index between each target component and all its corresponding target components, and denote it as the second mean;

[0023] Obtain the position order of each target component at each measurement point among all modal components at each measurement point; calculate the degree of dispersion of the position order difference between each target component and all its corresponding target components, and denot it as the second discrete value;

[0024] The interference confidence level of each target component is determined based on the interference correspondence index of each target component, the second mean, and the second discrete value. The interference confidence level is positively correlated with the interference correspondence index and negatively correlated with the second mean and the second discrete value, respectively.

[0025] In one embodiment, the second discrete value is the standard deviation of the positional difference between each target component and all its corresponding target components.

[0026] Secondly, embodiments of this application also provide an optical protective film thickness measuring device, wherein the device stores a computer program, and when the computer program is executed by a processor, it implements the steps of the method described in the first aspect above.

[0027] Thirdly, embodiments of this application also provide an optical protective film thickness measurement system, including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the steps of the method described in the first aspect above.

[0028] The embodiments of this application have at least the following beneficial effects:

[0029] This application performs mode decomposition on the reflection spectrum at various measurement points on the optical thin film under test, analyzes the fluctuation characteristics of the mode components to construct the interference correspondence index, thereby enabling analysis of whether the mode component data conforms to the characteristics of the interference signal and suppressing the influence of noise. By screening high-frequency mode components, the influence of light source fluctuations is avoided, making the phase information of the interference fringes more reliable. By analyzing the positional differences and interference correspondence index differences between the corresponding mode components of each measurement point and other measurement points, the repeatability and positional consistency of each mode component at multiple measurement points are determined. Combined with the interference correspondence index, an interference confidence level is constructed. This allows for the accurate identification of the mode components corresponding to the interference signal at each measurement point by combining the data variation characteristics of the mode components at a single measurement point with the repeatability characteristics at multiple measurement points. This avoids the problem of large errors in the identification of interference signals due to external interference, which leads to misjudgment of interference signals, and improves the accuracy of optical thin film thickness measurement. Attached Figure Description

[0030] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A flowchart illustrating the steps of an optical protective film thickness measurement method according to one embodiment of this application;

[0032] Figure 2 This is a schematic diagram illustrating the process of obtaining the interference confidence level. Detailed Implementation

[0033] To further illustrate the technical means and effects adopted by this application to achieve the intended inventive purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of an optical protective film thickness measurement method, apparatus, and system proposed in this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0035] The following description, in conjunction with the accompanying drawings, details the specific scheme of the optical protective film thickness measurement method, apparatus, and system provided in this application.

[0036] Please see Figure 1 The diagram illustrates a flowchart of a method for measuring the thickness of an optical protective film according to an embodiment of this application. The method includes the following steps:

[0037] Step S1: Collect the reflection spectrum at each measurement point on the optical thin film under test.

[0038] The optical film to be tested is fixed on an electric translation stage, which is driven by a servo motor and the displacement is fed back in real time by a grating ruler, forming a closed-loop position control to ensure the smooth movement and precise positioning of the sample during the scanning process.

[0039] This application uses an LED lamp with a complete visible light band as the illumination source; a miniature fiber optic spectrometer is used as the detection unit to perform a vertical incident scan of the optical thin film under test. The spectrometer's scanning step size is set to 0.1 mm, the single scan length is 2 mm, and the scanning wavelength range is 400-900 nm. Nine measurement points with consistent spacing are selected on the optical thin film under test, and the reflectance spectral signal at each measurement point is measured by the spectrometer. The spectrometer's scanning step size, average scan length, and number of measurement points can be set by the implementer, and this application does not impose any restrictions.

[0040] Since the initial spectral data collected is in the wavelength domain, it may introduce errors into subsequent calculations. Therefore, the reflectance spectral data is converted from the wavelength domain to the wavenumber domain. The conversion to the wavenumber domain is a well-known technique and will not be elaborated here.

[0041] Step S2: Perform mode decomposition on each reflection spectrum, and construct the interference correspondence index of each mode component based on the fluctuation periodicity of each mode component and the degree of waveform oscillation regularity in the mode component.

[0042] When light passes through an optical thin film, it undergoes multiple reflections and transmissions on its upper and lower surfaces. The superposition of these beams creates an interference effect, which ultimately manifests as interference oscillations in the reflection or transmission spectrum. The interference oscillation data of the spectrum are directly related to the refractive index and geometric thickness of the optical thin film under test, and are the core basis for thickness measurement.

[0043] However, in the actual measurement of film thickness, the spectral data obtained by the spectrometer often contains additional interference, such as trace amounts of dust in the optical film under test, noise introduced by the measurement system, and the spectral data of the light source itself. Since both noise data and light source spectral data can introduce errors into the calculation of film thickness, it is necessary to accurately identify the oscillating spectral data caused by film interference from the overall spectral data to improve the accuracy of the film thickness measurement results.

[0044] Taking the reflectance spectrum data obtained at the i-th measurement point as an example, the reflectance spectrum data at the i-th measurement point is used as input to a mode decomposition algorithm to perform mode decomposition, thereby obtaining a series of mode components arranged from high frequency to low frequency. In this embodiment, the mode decomposition algorithm used is the EMD algorithm. Many existing mode decomposition algorithms exist, and implementers can also use other mode decomposition algorithms, such as the VMD algorithm, EEMD algorithm, etc., to perform mode decomposition on the reflectance spectrum data. This application does not impose specific limitations. Furthermore, taking each mode component at this measurement point as an example, it is determined whether it corresponds to the mode component of the interference signal.

[0045] Interference signals originate from the superposition of multiple reflections and transmissions of light within a thin film, and therefore, after decomposition, they typically appear as continuous signals with periodic or quasi-periodic oscillations. Conversely, the noise signals obtained from decomposition are mostly high-frequency, random, and irregular signals, lacking periodicity, and exhibiting random jitter with spikes and peaks.

[0046] The spectral data within each modal component are used as input to the autocorrelation function, where the hysteresis ranges from [1, T / 10], T is the length of the spectral data, and the difference between adjacent hysteresis values ​​is 1 wavenumber. This yields a series of autocorrelation coefficients, and the mean of the absolute values ​​of all autocorrelation coefficients for that modal component is denoted as the first mean. The absolute value of the autocorrelation coefficient reflects whether there is a strong correlation between the spectral data within that modal component and the spectral data under each hysteresis. The larger the value, the stronger the autocorrelation of that modal component. Therefore, the larger the first mean, the greater the probability that the spectral data within that modal component exhibits periodic characteristics, and the greater the probability that it is an interference signal.

[0047] Furthermore, since the interference signal originates from the reciprocating reflection of light within the thin film, its oscillation process exhibits clear physical characteristics. Therefore, after mode decomposition of the complete spectral signal, the zero-crossing points of the modal component data corresponding to the interference signal will be relatively uniformly distributed and their intervals relatively stable. In contrast, noise signals, originating from random disturbances, lack true physical intrinsic laws, resulting in random characteristics such as disordered positions and inconsistent intervals in the zero-crossing points of the modal component data corresponding to noise signals.

[0048] All zero-crossing points in the spectral data of each modal component are acquired and sorted in ascending order of their corresponding wavenumber values. The wavenumber interval between any two adjacent zero-crossing points is calculated. The dispersion of the wavenumber intervals between all adjacent zero-crossing points in the spectral data of that modal component is also calculated and denoted as the first discrete value. The dispersion can be variance, standard deviation, coefficient of variation, etc. In this embodiment, the first discrete value is the variance of the wavenumber intervals between all adjacent zero-crossing points. The first discrete value reflects the randomness of the distribution of zero-crossing point data within each modal component. The smaller the value, the more stable the interval of the zero-crossing point data, which better matches the interval variation characteristics caused by the round-trip propagation of light in a thin film of fixed thickness, and the greater the probability that it corresponds to the component of the interference signal.

[0049] The first discrete value of all modal components at each measurement point is normalized using the maximum value normalization method. It should be noted that there are many existing normalization methods, and implementers may also use other normalization methods to normalize the first discrete value; this application does not impose any specific restrictions.

[0050] Based on the above analysis, the interference correspondence index for each modal component of the reflection spectrum at each measurement point is constructed. Preferably, in this embodiment, the expression for the interference correspondence index is:

[0051]

[0052] In the formula, Let be the interferometric correspondence index of the u-th modal component of the reflection spectrum at the i-th measurement point. The first mean value of the u-th modal component of the reflection spectrum at the i-th measurement point; Let be the first discrete value of the u-th modal component of the reflection spectrum at the i-th measurement point; This is a parameter tuning factor, used to avoid a denominator of 0. In this embodiment, it will be... The value is set to 0.001.

[0053] In other embodiments of this application, the expression for the interference-corresponding index may also be: ,in, It is an exponential function with the natural constant e as the base.

[0054] The interferometric correspondence index reflects the probability that each modal component is the modal component corresponding to the interference signal. The larger the interferometric correspondence index, the more obvious the periodic characteristics of the signal in each modal component, the more stable the oscillation interval of the signal, and the greater the probability that it is the modal component corresponding to the interference signal.

[0055] In other embodiments of this application, It can also be calculated in the following ways:

[0056] For the u-th mode component of the reflectance spectrum at the i-th measurement point, this mode component is used as input to a sequence segmentation algorithm to segment the data into sub-sequences. The DTW distance between two adjacent sub-sequences is calculated, and the reciprocal of the sum of the natural number 1 and the DTW distance is taken as the DTW similarity between the two adjacent sub-sequences. The mean of the DTW similarities of all adjacent sub-sequences in the u-th mode component is recorded as the first mean of this mode component. The sequence segmentation algorithm and DTW distance are well-known techniques, and their specific processes will not be elaborated further. The larger the DTW similarity, the higher the similarity between two adjacent sub-sequences. Therefore, the larger the first mean, the more consistent the data characteristics of each sub-sequence, and the greater the probability that the u-th mode component signal is periodic.

[0057] It should be noted that this application provides only one similarity algorithm for calculating the similarity between adjacent subsequences. There are many existing similarity algorithms, and implementers may also use other similarity algorithms to calculate the similarity between adjacent subsequences. This application does not impose any specific restrictions.

[0058] Step S3: Based on the signal frequency difference characteristics between the thin-film interference spectrum and the light source spectrum, modal components are screened to obtain target components; based on the difference between the interference correspondence index of each target component at each measurement point and that of each target component at other measurement points, the corresponding target component of each target component at each measurement point is determined; based on the difference between the interference correspondence index of each target component and its corresponding target component and the corresponding modal component position difference, combined with the interference correspondence index of each target component, the interference confidence of each target component is constructed.

[0059] Since the measured spectral data may contain low-frequency data such as light source background, after mode decomposition, the modal component data corresponding to the low-frequency data may show relatively gentle changes, sparse zero crossings, and low distribution dispersion. This may result in a large interference index, which may lead to the risk of misjudgment. Therefore, modal component screening is performed based on the signal frequency difference characteristics between thin film interference spectrum and light source spectrum to avoid the influence of low-frequency data such as light source background.

[0060] Preferably, in this embodiment, the modal component screening method is as follows:

[0061] Since interference signals exhibit continuous and uniform oscillation characteristics, while low-frequency spectral data show gradual changes and fewer oscillations, an extreme value detection algorithm is used to obtain all peak and valley values ​​in each modal component data, and the number of all peaks and valleys is recorded as the number of oscillations for each modal component.

[0062] The oscillation counts of all modal components in the reflectance spectrum at each measurement point are used as input to the Otsu threshold method to divide the modal components into two parts. The modal component with the largest average oscillation count in the two parts is selected and recorded as the target component. The target components at each measurement point are then analyzed to distinguish low-frequency modal components and avoid misjudgments in subsequent analyses.

[0063] Preferably, in other embodiments of this application, the modal component screening method is as follows:

[0064] Since the modal components after modal decomposition are arranged from high frequency to low frequency, and the interference signal is a high-frequency signal while the light source spectral data is a low-frequency signal, the first three-quarters of the modal components of the spectral data at each measurement point are taken as high-frequency signals and recorded as the target components, while the remaining modal components are taken as low-frequency signals. This removes low-frequency data from the light source spectrum, improves the recognition effect of the interference signal, and thus improves the measurement accuracy of the thin film thickness. It should be noted that if the three-quarters of the data is not an integer, it is rounded down.

[0065] Since the thickness measurement of the thin film is performed in an industrial environment with stable light source intensity, and the optical thin film is prepared by automated equipment, its thickness exhibits good uniformity. Therefore, although random system noise is inevitably introduced during the measurement process, when multiple measurements are performed on the same thin film sample, the modal component data generated by true interference at each measurement point will show high consistency, and the order of the modal components will be relatively corresponding. In contrast, spurious interference signals caused by air dust, stray light, or random noise often exhibit large fluctuations in the corresponding modal component data. Therefore, more in-depth analysis can be performed by combining spectral data from other measurement points.

[0066] Taking the v-th target component at the i-th measurement point as the current target component, the corresponding target components of the current target component in the target components at other measurement points are obtained. Specifically, taking the j-th measurement point as an example, the interference correspondence index difference between each target component at the j-th measurement point and the current target component is calculated. The target component corresponding to the minimum interference correspondence index difference at the j-th measurement point is denoted as the corresponding target component of the current target component at the j-th measurement point, and the minimum interference correspondence index difference is denoted as the minimum difference. Here, the difference can be the absolute value of the difference, the square of the difference, the ratio, etc. In this embodiment, the interference correspondence index difference is the absolute value of the difference between the interference correspondence indices of the target components.

[0067] The minimum difference reflects the degree of consistency between the current target component and each target component within the j-th measurement point in terms of interference characteristics; the smaller the value, the closer the interference characteristics are, and the more the current target component conforms to the repeatability characteristics that a real interference signal should have on a thin film of the same thickness.

[0068] Furthermore, the mean of the minimum differences between the current target component and the corresponding target components at all other measurement points is calculated and denoted as the second mean of the current target component. The smaller the second mean, the more likely the current target component exhibits highly similar interference behavior at multiple measurement point locations, and the more likely it is an interference signal of a thin film rather than random noise data.

[0069] The second mean can only be used to analyze whether there are modal components in other measurement points that are relatively consistent with the current target component in terms of data changes. It cannot verify whether the sorting positions of such relatively consistent modal components correspond between their respective measurement points.

[0070] The modal components after modal decomposition are arranged in order from high frequency to low frequency, and the positional value of each modal component at each measurement point is obtained. The dispersion of the positional value of the current target component and the positional values ​​of all its corresponding target components is calculated and denoted as the second discrete value of the current target component. In this embodiment, the second discrete value is the standard deviation of the positional value of the current target component and the positional values ​​of all its corresponding target components.

[0071] The second discrete value can reflect the stability of the modal hierarchy distribution of the current target component and its corresponding target component between different measurement points; the smaller the value, the more consistent the position of the current target component and its corresponding target component is, which is more in line with the physical characteristics of the interference signal exhibiting the same frequency band at each measurement point due to the uniform thickness of the thin film.

[0072] Based on the above analysis, the interferometric confidence level for each target component at each measurement point is constructed. Preferably, in this embodiment, the expression for the interferometric confidence level is:

[0073]

[0074] In the formula, Let be the interferometric confidence level of the v-th target component at the i-th measurement point. The interferometric correspondence index of the v-th target component at the i-th measurement point; , These are the second mean and the second discrete value of the v-th target component at the i-th measurement point, respectively.

[0075] In other embodiments of this application, the expression for the interference confidence level may also be: ,in, It is an exponential function with the natural constant e as the base.

[0076] Interference confidence level combines the modal characteristics of a single measurement point with the spatial consistency of multiple measurement points, thus comprehensively reflecting the probability that each target component is the corresponding component of the interference signal. The larger the value, the more likely that each target component not only conforms to the interference law in its own characteristics, but also exhibits good repeatability and positional consistency among multiple measurement points, and is more likely to be the modal component corresponding to the real interference signal.

[0077] in, This reflects whether the modal component data conforms to the variation characteristics of the interference signal; Analyze whether the data variation characteristics of the target component are repeatable across various measurement points; Analyze whether the positional order of the target component and its corresponding component among all modal components is concentrated and stable. This comprehensively reflects the probability that the target component is the modal component corresponding to the interference signal.

[0078] Step S4: Select the target component corresponding to the maximum interference confidence level of each measurement point to measure the film thickness at each measurement point.

[0079] Furthermore, the target component corresponding to the maximum interference confidence value among all target components at each measurement point is obtained as the thin film interference component at each measurement point. Then, the thickness of the thin film interference component at each measurement point is calculated using the full-spectrum fitting method, thereby obtaining the optical thin film thickness at each measurement point and realizing the measurement of the optical thin film thickness. The full-spectrum fitting method is a well-known technique, and its specific process will not be elaborated further.

[0080] A schematic diagram of the process for obtaining interference confidence is shown below. Figure 2 As shown.

[0081] Based on the same inventive concept as the above method, this application also provides an optical protective film thickness measuring device, wherein the device stores a computer program, and when the computer program is executed by a processor, it implements the steps of any one of the above-described optical protective film thickness measuring methods.

[0082] Based on the same inventive concept as the above method, this application embodiment also provides an optical protective film thickness measurement system, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above-described optical protective film thickness measurement methods.

[0083] In summary, this application provides a method for measuring the thickness of an optical protective film. By performing modal decomposition on the reflection spectrum at each measurement point on the optical film under test, analyzing the fluctuation characteristics of the modal components, and constructing an interference correspondence index, it is possible to analyze whether the modal component data conforms to the characteristics of the interference signal and suppress the influence of noise. By screening high-frequency modal components, the influence of light source fluctuations is avoided, making the phase information of the interference fringes more reliable. By analyzing the positional differences and interference correspondence index differences between the corresponding modal components of each measurement point and other measurement points, the repeatability and positional consistency of each modal component at multiple measurement points are determined. Combined with the interference correspondence index, an interference confidence level is constructed. This method can combine the data variation characteristics of the modal components at a single measurement point with the repeatability characteristics of multiple measurement points, thereby accurately identifying the modal components corresponding to the interference signal at each measurement point. This avoids the problem of large errors in the identification of interference signals due to external interference, which leads to misjudgment of interference signals, and improves the accuracy of optical film thickness measurement.

[0084] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, the above description focuses on specific embodiments of this application. Additionally, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some implementations, multitasking and parallel processing are possible or may be advantageous.

[0085] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0086] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the protection scope of this application.

Claims

1. A method for measuring the thickness of an optical protective film, characterized in that, The method includes the following steps: Collect the reflection spectrum at each measurement point on the optical thin film under test; Modal decomposition is performed on each reflection spectrum. Based on the fluctuation periodicity of each modal component and the degree of waveform oscillation regularity in the modal component, the interference correspondence index of each modal component is constructed. Modal components are screened based on the signal frequency difference characteristics between thin-film interference spectra and light source spectra to obtain target components; based on the difference between the interference correspondence indices of each target component at each measurement point and the target components at other measurement points, the corresponding target components of each target component at each measurement point are determined; based on the difference between the interference correspondence indices of each target component and its corresponding target component and the corresponding modal component position difference, combined with the interference correspondence indices of each target component, the interference confidence of each target component is constructed. The target component corresponding to the maximum interference confidence level at each measurement point is selected to measure the film thickness at each measurement point.

2. The method for measuring the thickness of an optical protective film as described in claim 1, characterized in that, The process for obtaining the interference-corresponding index is as follows: Calculate a series of autocorrelation coefficients for each modal component using the autocorrelation function; and denote the mean of the absolute values ​​of all autocorrelation coefficients for each modal component as the first mean. Obtain all zero-crossing points in each modal component, and record the degree of dispersion of the distribution of the x-coordinate interval of all adjacent zero-crossing points as the first discrete value; Interference correspondence indices for each modal component are constructed based on the first mean and the first discrete value. The interference correspondence indices are directly proportional to the first mean and inversely proportional to the first discrete value.

3. The method for measuring the thickness of an optical protective film as described in claim 2, characterized in that, The first discrete value is the variance of the x-coordinate interval of all adjacent zero-crossing points.

4. The method for measuring the thickness of an optical protective film as described in claim 1, characterized in that, The process of obtaining the target component is as follows: Based on the vibration frequency of the modal components, all modal components at each measurement point are divided into two parts: high-frequency signal and low-frequency signal. The high-frequency signal is then used as the target component selected for each measurement point.

5. The method for measuring the thickness of an optical protective film as described in claim 4, characterized in that, The method of dividing all modal components at each measurement point into high-frequency and low-frequency signals based on the vibration frequency of the modal components is as follows: All modal components at each measurement point are arranged in descending order of frequency. The modal components with the first preset percentage are taken as high-frequency signals, and the remaining modal components are taken as low-frequency signals.

6. The method for measuring the thickness of an optical protective film as described in claim 1, characterized in that, The process of obtaining the corresponding target component is as follows: Calculate the interference correspondence index difference between each target component at each measurement point and each target component at any other measurement point; take the target component corresponding to the minimum interference correspondence index difference among the target components at any other measurement point as the corresponding target component of each target component at each measurement point in the target components at any other measurement point.

7. The method for measuring the thickness of an optical protective film as described in claim 1, characterized in that, The process of obtaining the interference confidence level is as follows: Calculate the mean of the difference in interference correspondence index between each target component and all its corresponding target components, and denote it as the second mean; Obtain the position order of each target component at each measurement point among all modal components at each measurement point; calculate the degree of dispersion of the position order difference between each target component and all its corresponding target components, and denot it as the second discrete value; The interference confidence level of each target component is determined based on the interference correspondence index of each target component, the second mean, and the second discrete value. The interference confidence level is positively correlated with the interference correspondence index and negatively correlated with the second mean and the second discrete value, respectively.

8. The method for measuring the thickness of an optical protective film as described in claim 7, characterized in that, The second discrete value is the standard deviation of the positional difference between each target component and all its corresponding target components.

9. An optical protective film thickness measuring device, wherein the device stores a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the optical protective film thickness measurement method as described in any one of claims 1-8.

10. An optical protective film thickness measurement system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the optical protective film thickness measurement method as described in any one of claims 1-8.

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