A method and system for measuring film thickness based on white light interferometry

Abstract

The invention discloses a film thickness measurement method and system based on white light interference. The method comprises: controlling a light source to emit white light to be vertically incident on a film to be measured, and forming interference light after reflection and refraction; analyzing the interference light, and obtaining a measured interference light intensity curve according to the measured interference light intensities at multiple wavelengths; when the thickness of the film to be measured is within a first preset thickness range, converting the measured interference light intensity curve to obtain a measured reflectivity curve, calculating a matching degree according to the sample reflectivity curve and the measured reflectivity curve, and calculating the thickness of the film to be measured according to the matching degree; when the thickness of the film to be measured is within a second preset thickness range, performing Fourier transform and frequency domain interpolation processing based on the measured interference light intensity curve to obtain an interpolation frequency, and calculating the thickness of the film to be measured according to the interpolation frequency; the method can improve the efficiency of film thickness detection and ensure the accuracy of detection.

Description

Technical Field

[0001] The present invention relates to the technical field of optical thickness measurement, and in particular to a thin film thickness measurement method and system based on white light interference. Background Art

[0002] As a special microstructure, thin films have been widely used in electronics, tribology, and modern optics in recent years, and thin film testing technology has become increasingly important. Especially in the specific direction of thickness, the size is very small and basically measurable at the microscopic level. Therefore, in the field of micro-nano measurement, the testing of film thickness is a very important and practical research direction. In industrial production, the thickness of the film is directly related to whether the film can work normally. In the semiconductor industry, the measurement of film thickness is an important means of controlling the thermal oxidation thickness and flatness quality of the silicon single crystal surface. The thickness of the film affects the electromagnetic properties, mechanical properties, and optical properties of the film, so accurately measuring the thickness of the film has become a key technology.

[0003] At present, there are many methods for measuring film thickness, mainly including ellipsometry, reflection spectroscopy, mechanical stylus method and white light vertical scanning interferometry.

[0004] As a non-contact measurement method, ellipsometry plays an important role in the field of film thickness measurement. The incident light hits the film at a small angle and is reflected on the upper surface, and the polarization state of the reflected light changes. The change in the intensity of the reflected light with the angle is measured, and the refractive index and thickness of the film are calculated.

[0005] Reflection spectroscopy is a method of measuring the reflection spectrum curve of light with a spectrophotometer when the light is incident vertically, ignoring the polarization effect, and then using some mathematical tools to calculate the thickness and optical constants of the film. Reflection spectroscopy is widely used due to its simple test, convenient operation and high accuracy.

[0006] Mechanical stylus method is a contact measurement method, also known as mechanical stylus profilometry, which is a basic measurement method in the manufacturing industry with the advantages of easy use, high measurement accuracy, and large measurement range. It can measure both microstructure surfaces and film thickness.

[0007] White light scanning interferometry uses white light as the light source, piezoelectric ceramics drive the reference mirror to scan, interference fringes sweep across the measured surface, and the surface morphology information is obtained by sensing the position of the coherent peak. For the measurement of thin films, the upper and lower surface morphology, roughness, thickness and other information can be obtained through one measurement.

[0008] The performance comparison of the above methods is shown in Table 1:

[0009]

[0010] Table 1

[0011] In addition to analyzing the reflected light intensity, the ellipsometry also analyzes the polarization intensity, and polarization analysis requires expensive precision mobile optical instruments, which increases the overall cost. Moreover, the data obtained by the ellipsometry method requires very complex and tedious mathematical processing, which affects the widespread application of this method.

[0012] Reflection spectroscopy requires the design of a spectroscopic optical path and is complex to use. The calculation process is heavily dependent on the initial value setting and is only suitable for thickness detection of thin films (micrometer level and below). For thicker films, the test error is large and even invalid values ​​may occur, which limits its application.

[0013] The mechanical stylus method is suitable for measuring static objects. When measuring dynamic objects, it is easy to damage the measuring instrument, the surface of the object to be measured, and errors are easily generated due to vibration. In addition, when measuring the thickness of a thin film, the sample must be prepared in advance, which is a cumbersome operation.

[0014] The basic idea of ​​white light scanning interferometry is: through the interference optical path, the measurement light reflected from the surface of the object is converged with the reference light in the interference objective to obtain interference fringes; then the phase is modulated by a specific phase shift method, and the initial phase of each data point is calculated by detecting the change in light intensity in the interference field; finally, the surface morphology is obtained using the relationship between phase and height. For example, patent document CN113834430B discloses a method for measuring film thickness and refractive index, which obtains a measured nonlinear phase related only to the film itself through white light spectral phase shift measurement, and reconstructs white light vertical scanning data by vertically scanning the film, integrating the recorded white light spectral signal with wavelength, and obtaining nonlinear fitting constraints. The theoretical nonlinear phase obtained according to the theoretical model of the reflection coefficient and the measured nonlinear phase are subjected to nonlinear fitting with constraints to obtain the thickness and refractive index of the film.

[0015] If the film thickness is to be measured by white light scanning interferometry, it is necessary to extract the signal of the interference fringes generated by the reflected light from the upper and lower surfaces of the film and the reference light of the interference objective lens, and solve the thickness information of the film, which increases the complexity of the algorithm. White light scanning interferometry is completed by measuring the interference fringes, and the clarity of the interference fringes directly affects the test accuracy. Therefore, in order to improve the accuracy, a more complex optical system is required, which makes the measurement of interference fringes a laborious and time-consuming task. In addition, when measuring the thickness of the film by white light scanning interferometry, due to the reflection of the upper and lower surfaces of the film, the extracted white light interference signal will appear in a double peak form, which becomes more complicated. And this method requires a scanning process, so the measurement time is long and it is susceptible to external interference. Summary of the invention

[0016] The present invention provides a film thickness measurement method and system based on white light interference, which can improve the efficiency of film thickness detection and ensure the accuracy of detection.

[0017] A film thickness measurement method based on white light interferometry, comprising:

[0018] Control the light source to emit white light vertically incident on the film to be measured, form interference light after reflection and refraction, and control the spectrometer to collect the interference light;

[0019] Controlling a spectrometer to analyze the interference light to obtain the measured interference light intensities at multiple wavelengths;

[0020] Obtaining a measured interference light intensity curve according to the measured interference light intensities at multiple wavelengths;

[0021] When the thickness of the film to be measured is within a first preset thickness range, samples of different known thicknesses of the same material as the film to be measured are used in advance for calculation to obtain reflectance curves of samples of different thicknesses; the measured interference light intensity curve is converted to obtain a measured reflectance curve, a matching degree is calculated based on the sample reflectance curve and the measured reflectance curve, and the thickness of the film to be measured is calculated based on the matching degree;

[0022] When the thickness of the film to be measured is within a second preset thickness range, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain an interpolation frequency, and the thickness of the film to be measured is calculated according to the interpolation frequency;

[0023] The first preset thickness range is smaller than the second preset thickness range.

[0024] Furthermore, the first preset thickness range is 3-3000 nm, and the second preset thickness range is 3-3000 μm.

[0025] Furthermore, samples of different known thicknesses made of the same material as the film to be measured are used in advance for calculation to obtain reflectivity curves of samples of different thicknesses, including:

[0026] Assuming that white light with initial intensity is incident vertically on the sample surface, calculate the first reflectivity of the interface between air and sample coating;

[0027] Calculate the theoretical reflected light intensity occurring at the interface between air and sample coating according to the first reflectivity and the initial intensity;

[0028] Calculating a second reflectivity of an interface between the coating layer and the substrate of the sample;

[0029] Calculating theoretical refracted light intensities at multiple wavelengths from the sample to the air according to the second reflectivity, the thickness of the sample, the initial intensity, and the absorption coefficient of the sample;

[0030] Calculating and obtaining theoretical interference light intensities at multiple wavelengths according to the theoretical reflected light intensities and the theoretical refracted light intensities at multiple wavelengths;

[0031] According to the theoretical interference light intensities at multiple wavelengths, a theoretical interference light intensity curve is obtained;

[0032] The theoretical interference light intensity curves at different thicknesses are calculated and converted to obtain the reflectivity curves of samples with different thicknesses.

[0033] Further, the first reflectivity is calculated based on the coating refractive index and coating extinction coefficient of the sample;

[0034] The second reflectivity is calculated based on the coating refractive index, coating extinction coefficient, substrate refractive index and substrate extinction coefficient of the sample.

[0035] Furthermore, the measured interference light intensity curve is converted to obtain a measured reflectivity curve, including:

[0036] Collecting background light intensity and substrate reflected light intensity of the film substrate being tested;

[0037] Obtaining the measured interference light intensity at different wavelengths according to the measured interference light intensity curve, and calculating the measured reflectivity according to the background light intensity, the substrate reflected light intensity and the measured interference light intensity;

[0038] The measured reflectivity curve is obtained according to the measured reflectivity at different wavelengths.

[0039] Further, the matching degree is a standard deviation of the sample reflectance curve and the measured reflectance curve calculated at multiple sampling points;

[0040] The sample thickness value corresponding to the minimum matching value is taken as the thickness value of the film to be measured.

[0041] Further, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain an interpolation frequency, and the thickness of the measured film is calculated according to the interpolation frequency, including:

[0042] Performing Fourier transform on the measured interference light intensity curve to obtain the frequency corresponding to the peak value of the measured interference light intensity;

[0043] Perform frequency domain interpolation on the frequency corresponding to the peak value of the measured interference light intensity to obtain the interpolation frequency;

[0044] Selecting an interference band according to the measured interference light intensity curve;

[0045] The thickness of the film to be measured is calculated according to the starting wavelength and the ending wavelength of the interference waveband, the refractive index of the film to be measured, and the interpolation frequency.

[0046] Furthermore, the interpolation frequency is calculated according to the following formula:

[0047] ;

[0048] in, f p represents the interpolation frequency point, f m Indicates the frequency value corresponding to the peak value of the measured interference light intensity, f 0 represents the frequency interval, A( f m ) indicates frequency f m The corresponding amplitude, A( f m -f 0 ) indicates the frequency f m Before the interval f 0 The amplitude corresponding to the frequency, A ( f m +f 0 ) indicates the frequency f m After that, an interval f 0 The amplitude corresponding to the frequency.

[0049] Furthermore, according to the starting wavelength and the ending wavelength of the interference band, the refractive index of the film to be measured, and the interpolation frequency, the thickness of the film to be measured is calculated by the following formula:

[0050] d = λ start ·λ stop / 2n·f p ;

[0051] in, d Indicates the thickness of the film being measured, λ start represents the starting wavelength of the interference band, λ stop represents the end wavelength of the interference band, n represents the refractive index of the film being measured, f p Represents the interpolation frequency.

[0052] A film thickness measurement system based on white light interferometry includes a light source, a Y-type optical fiber, a spectrometer, a processor and a storage device;

[0053] The light source is used to emit white light to be incident on the film to be measured through the Y-type optical fiber, and the spectrometer is used to collect interference light formed after reflection and refraction by the film to be measured through the Y-type optical fiber, and analyze the interference light to obtain the measured interference light intensity at multiple wavelengths;

[0054] The storage device stores a plurality of instructions, and the processor is used to read the instructions and execute the above method.

[0055] The thin film thickness measurement method and system based on white light interferometry provided by the present invention have at least the following beneficial effects:

[0056] (1) The reflected light and refracted light of the film to be measured are used as interference light. For films of different thicknesses, different methods are used to measure the films. Only one signal processing is required to obtain the thickness result. The operation speed is in the millisecond level, which is more suitable for industrial production. The existing white light scanning method requires a scanning process, which has the disadvantages of long measurement time and greater influence of external environmental interference. The method proposed in the above embodiment does not require scanning and displacement devices, saves costs, and greatly improves the detection speed. Therefore, the efficiency of film thickness detection can be improved. Since the detection process is completed in a very short time, the influence of external environmental changes on the measurement results is effectively reduced, thereby ensuring the accuracy of detection.

[0057] (2) For thin films with smaller thickness, the thickness is determined based on the matching degree. After establishing the reflectivity curves of samples with different thicknesses, the thickness of the thin film can be obtained by only one signal processing. The process is simple, with fewer calculation steps and no need to process the signal too much. It is more suitable for occasions with higher requirements on detection speed.

[0058] (3) For thicker films, frequency domain interpolation processing is used to significantly improve the thickness resolution, which is suitable for online measurement of thick films;

[0059] (4) It can detect the thickness of thin films with a wide range of thicknesses. When testing samples with large thickness differences, there is no need to replace accessories or adjust the optical path, which effectively simplifies the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The present invention provides a flowchart of an embodiment of a thin film thickness measurement method based on white light interference.

[0061] Figure 2 This is a schematic diagram of the white light interference principle in the thin film thickness measurement method based on white light interference provided by the present invention.

[0062] Figure 3 The present invention provides a flowchart of an embodiment of calculating a sample reflectivity curve in a thin film thickness measurement method based on white light interference.

[0063] Figure 4 The present invention provides a flowchart of an embodiment of calculating a sample reflectivity curve in a thin film thickness measurement method based on white light interference.

[0064] Figure 5 The present invention provides a flowchart of an embodiment of calculating a measured reflectivity curve in a thin film thickness measurement method based on white light interference provided by the present invention.

[0065] Figure 6 The present invention provides a flowchart of an embodiment of calculating thickness by Fourier transform and frequency domain interpolation processing in a thin film thickness measurement method based on white light interference provided by the present invention.

[0066] Figure 7 A schematic structural diagram of an embodiment of a thin film thickness measurement system based on white light interferometry provided by the present invention. DETAILED DESCRIPTION

[0067] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0068] refer to Figure 1 In some embodiments, a method for measuring film thickness based on white light interferometry is provided, comprising:

[0069] S1, controlling the light source to emit white light vertically incident on the film to be measured, forming interference light after reflection and refraction, and controlling the spectrometer to collect the interference light;

[0070] S2, controlling the spectrometer to analyze the interference light to obtain the measured interference light intensity at multiple wavelengths;

[0071] S3, obtaining a measured interference light intensity curve according to the measured interference light intensities at multiple wavelengths;

[0072] S4, when the thickness of the film to be measured is within a first preset thickness range, samples of different known thicknesses of the same material as the film to be measured are used in advance for calculation to obtain reflectance curves of samples of different thicknesses; the measured interference light intensity curve is converted to obtain a measured reflectance curve, a matching degree is calculated based on the sample reflectance curve and the measured reflectance curve, and the thickness of the film to be measured is calculated based on the matching degree;

[0073] S5. When the thickness of the film to be measured is within a second preset thickness range, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain interpolation frequency points, and the thickness of the film to be measured is calculated according to the interpolation frequency points;

[0074] The first preset thickness range is smaller than the second preset thickness range.

[0075] Specifically, refer to Figure 2 The film includes a coating and a substrate. Light is incident on the coating surface 3 of the film and is reflected to form reflected light 1. Part of the light enters the interior of the film and is refracted. The refracted light is then reflected by the surface of the substrate 4 of the film and emitted from the surface of the film to form refracted light 2.

[0076] In step S1, the light source is a white light source, and the white light is a mixture of lights of multiple wavelengths. After the white light is vertically incident on the film to be measured, part of it forms reflected light on the surface of the film to be measured, and part of it enters the film to be measured, forming refraction inside the film to be measured, and is reflected by the bottom of the substrate of the film to be measured and emitted from the surface of the film to be measured to form refracted light. The refracted light and the reflected light together form the interference light. The interference light formed by the white light passing through the film to be measured can be regarded as the superposition of a large number of incoherent monochromatic light interference signals, and the interference light is collected by a spectrometer.

[0077] Furthermore, in step S2, the spectrometer is controlled to analyze the interference light. The spectrometer has a built-in grating or prism. The interference light is imaged on the slit at the front end of the spectrometer. The spectrometer analyzes the light intensity signal of each point passing through the slit. Therefore, the spectrometer can obtain the measured interference light intensity at multiple wavelengths.

[0078] Furthermore, in step S3, a measured interference light intensity curve is established based on the measured interference light intensities at multiple wavelengths. Specifically, in a coordinate system, the wavelength is used as the horizontal coordinate, and the interference light intensity is used as the vertical coordinate. The measured interference light intensities at multiple wavelengths obtained by the spectrometer are fitted to obtain the measured interference light intensity curve.

[0079] In some embodiments, different measurement methods are used for films to be measured with different thickness ranges. When the thickness of the film to be measured is within a first preset thickness range, samples of different known thicknesses made of the same material as the film to be measured are used in advance for calculation to obtain reflectance curves of samples of different thicknesses. When the thickness of the sample is also within the first preset thickness range, the measured interference light intensity curve is converted to obtain a measured reflectance curve, a matching degree is calculated based on the sample reflectance curve and the measured reflectance curve, and the thickness of the film to be measured is calculated based on the matching degree. When the thickness of the film to be measured is within a second preset thickness range, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain an interpolation frequency, and the thickness of the film to be measured is calculated based on the interpolation frequency, wherein the first preset thickness range is smaller than the second preset thickness range.

[0080] In some embodiments, the first preset thickness ranges from 3 to 3000 nm, and the second preset thickness ranges from 3 to 3000 μm.

[0081] Specifically, when the thickness of the film to be measured is within the first preset thickness range, that is, the thickness of the film to be measured is relatively low, within the limited spectral wavelength range, the light intensity curve does not have a relatively good periodic structure, and may even be a spectrum without a peak, so the method based on frequency domain analysis is not applicable. At this time, the matching fitting method can better calculate the thickness of the film to be measured. When the thickness of the film to be measured is within the second preset thickness range, that is, the thickness of the film to be measured is relatively thick, the frequency domain analysis method can be used to calculate the thickness of the film to be measured.

[0082] Specifically, refer to Figure 3 In step S4, when the thickness of the film to be measured is within the first preset thickness range, samples of different known thicknesses of the same material as the film to be measured are used in advance for calculation to obtain reflectivity curves of samples of different thicknesses, including:

[0083] S41, assuming that white light with initial intensity is vertically incident on the sample surface, calculating the first reflectivity of the interface between air and the sample coating;

[0084] S42, calculating the theoretical reflected light intensity occurring at the interface between air and sample coating according to the first reflectivity and the initial intensity;

[0085] S43, calculating a second reflectivity of an interface between the coating layer and the substrate of the sample;

[0086] S44, calculating theoretical refracted light intensities at multiple wavelengths from the sample to the air according to the second reflectivity, the thickness of the sample, the initial intensity, and the absorption coefficient of the sample;

[0087] S45, calculating and obtaining theoretical interference light intensities at multiple wavelengths according to the theoretical reflected light intensities and the theoretical refracted light intensities at multiple wavelengths;

[0088] S46, obtaining a theoretical interference light intensity curve according to the theoretical interference light intensities at multiple wavelengths;

[0089] S47, calculating and converting theoretical interference light intensity curves at different thicknesses to obtain reflectivity curves of samples at different thicknesses.

[0090] Specifically, a plurality of samples with a plurality of thicknesses made of the same material as the film to be tested are prepared, wherein the thicknesses are known and the thicknesses of the samples are also within a first preset thickness range.

[0091] In step S41, assuming that the initial intensity of white light vertically incident on the sample surface is I0, it is first reflected by the air and the sample coating surface, and the first reflectivity r1 of the air-sample coating interface is calculated based on the sample coating refractive index n1 and the coating extinction coefficient k1.

[0092] Specifically, the first reflectivity is calculated by the following formula:

[0093] ; (1)

[0094] Wherein, r1 represents the first reflectivity, n1 represents the coating refractive index, and k1 represents the coating extinction coefficient.

[0095] The extinction coefficient of the coating can be measured by spectral ellipsometry, spectral breadth method, integrating sphere method, etc., and the refractive index of the coating can be measured by deflection angle method, autocollimation method, etc.

[0096] Further, in step S42, the theoretical reflected light intensity occurring at the interface between the air and the sample coating is calculated according to the first reflectivity r1 and the initial intensity I0, and is calculated by the following formula:

[0097] I1= r1I0; (2)

[0098] Wherein, I1 represents the theoretical reflected light intensity, r1 represents the first reflectivity, and I0 represents the initial intensity.

[0099] Furthermore, in step S43, the light entering the sample will be absorbed when passing through the sample with a thickness of d and an absorption coefficient of α, so the intensity of the light will decrease after passing through the sample, and the light entering the interior of the sample will encounter the coating-substrate interface, and after being reflected there, it will pass through the sample with a thickness of d again and encounter the film-air interface to be refracted into the air. The second reflectivity r2 of the interface between the coating and the substrate is calculated based on the coating refractive index n1, the coating extinction coefficient k1, the substrate refractive index n2 and the substrate extinction coefficient k2 of the sample.

[0100] Specifically, the second reflectivity is calculated by the following formula:

[0101] ; (3)

[0102] Among them, r1 represents the first reflectivity, n1 represents the refractive index of the coating, k1 represents the extinction coefficient of the coating, r2 represents the second reflectivity, n2 represents the refractive index of the substrate, and k2 represents the extinction coefficient of the substrate.

[0103] Similarly, the extinction coefficient of the substrate can be measured by spectral ellipsometry, spectral breadth method, integrating sphere method, etc., and the refractive index of the substrate can be measured by deflection angle method, autocollimation method, etc.

[0104] Further, in step S44, the light entering the sample will be absorbed when passing through the sample with a thickness of d and an absorption coefficient of α, and the intensity of the light after passing through the sample is reduced to:

[0105] I0(1-r1)e -αd ; (4)

[0106] The light passing through the film will encounter the coating-substrate interface, where it will be reflected and then pass through the film with a thickness of d again to encounter the film-air interface and be refracted into the air. The theoretical refracted light intensity is calculated by the following formula:

[0107] I2 = I0 (1- r1)2·r2·e -2αd ; (5)

[0108] Wherein, I0 represents the initial intensity, I2 represents the theoretical refracted light intensity, r1 represents the first reflectivity, r2 represents the second reflectivity, d represents the thickness of the sample, α represents the absorption coefficient of the sample, α=4k1π / λ, k1 represents the extinction coefficient of the coating, and λ represents the wavelength.

[0109] Further, in step S45, the theoretical interference light intensity at multiple wavelengths is calculated based on the theoretical reflected light intensity and the theoretical refracted light intensity at multiple wavelengths. The theoretical interference light intensity is calculated by the following formula:

[0110] I = I1 + I2 + 2 (I1I2) 1 / 2 cosδ; (6)

[0111] Among them, I represents the theoretical interference light intensity, I1 represents the theoretical reflected light intensity, I2 represents the theoretical refracted light intensity, δ is the phase difference between the reflected light and the refracted light, δ=2π / λ·△l, △l=2 n1d is the optical path difference between the two.

[0112] Furthermore, in step S46, a theoretical interference light intensity curve is obtained based on the theoretical interference light intensities at multiple wavelengths, that is, in a coordinate system, the wavelength is used as the horizontal coordinate, and the theoretical interference light intensity is used as the vertical coordinate, and the theoretical interference light intensities at multiple wavelengths obtained by calculation are fitted to obtain the theoretical interference light intensity curve.

[0113] Further, refer to Figure 4 In step S47, the theoretical interference light intensity curves at different thicknesses are calculated and converted to obtain the reflectivity curves of samples at different thicknesses, which specifically includes:

[0114] S471, collecting background light intensity and substrate reflected light intensity of the sample substrate;

[0115] S472, obtaining theoretical interference light intensities at different wavelengths according to the theoretical interference light intensity curve, and calculating theoretical reflectivity of the sample according to the background light intensity, substrate reflected light intensity and theoretical interference light intensity;

[0116] S473. Obtain the sample reflectance curve according to the theoretical reflectance of the sample at different wavelengths.

[0117] Specifically, in step S471, the background light intensity is the light intensity collected by the spectrometer after the light source is turned off, and the substrate reflected light intensity is the intensity of the light after being reflected by the substrate of the sample.

[0118] In step S472, the theoretical reflectivity of the sample is calculated using the following formula:

[0119] ; (7)

[0120] Among them, R 样 represents the theoretical reflectivity of the sample, I represents the theoretical interference light intensity, and I 背景 Represents the background light intensity, I 基材 Indicates the intensity of light reflected by the substrate.

[0121] Further, refer to Figure 5 In step S4, the measured interference light intensity curve is converted to obtain a measured reflectivity curve, including:

[0122] S48, collecting background light intensity and substrate reflected light intensity of the film substrate to be measured;

[0123] S49, obtaining the measured interference light intensity at different wavelengths according to the measured interference light intensity curve, and calculating the measured reflectivity according to the background light intensity, the substrate reflected light intensity and the measured interference light intensity;

[0124] S410, obtaining the measured reflectivity curve according to the measured reflectivities at different wavelengths.

[0125] Specifically, in step S48, the background light intensity is the light intensity collected by the spectrometer after the light source is turned off, and the substrate reflected light intensity is the intensity of the light after being reflected by the substrate of the film to be measured.

[0126] In step S49, the measured reflectivity is calculated using the following formula:

[0127] ; (8)

[0128] Among them, R 测 Indicates the measured reflectivity, I 测 Indicates the measured interference light intensity, I 背景 Represents the background light intensity, I 基材 Indicates the intensity of light reflected by the substrate.

[0129] Furthermore, in step S410, after the measured reflectivity at different wavelengths is calculated, the measured reflectivity curve can be obtained.

[0130] Further, in step S4, after obtaining the sample reflectivity curve and the measured reflectivity curve, the matching degree is calculated. In some embodiments, the matching degree is the standard deviation of the sample reflectivity curve and the measured reflectivity curve calculated at multiple sampling points; it is specifically calculated by the following formula:

[0131] ; (9)

[0132] Among them, s represents the matching degree, n represents the number of sampling points, R 样i is the theoretical reflectance of the sample at the i-th sampling point, R 测i is the measured reflectivity of the i-th sampling point.

[0133] In some embodiments, the matching degree between the sample reflectivity curve at multiple angles and the measured reflectivity curve is calculated, and the sample thickness value corresponding to the minimum matching value is used as the thickness value of the measured film.

[0134] Further, refer to Figure 6 In step S5, when the thickness of the film to be measured is within the second preset thickness range, the thickness value of the film to be measured can be obtained based on spectrum analysis. Specifically, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain the interpolation frequency, and the thickness of the film to be measured is calculated based on the interpolation frequency point, including:

[0135] S51, performing Fourier transform on the measured interference light intensity curve to obtain the frequency corresponding to the peak value of the measured interference light intensity;

[0136] S52, performing frequency domain interpolation on the frequency corresponding to the peak value of the measured interference light intensity to obtain an interpolation frequency;

[0137] S53, selecting an interference band according to the measured interference light intensity curve;

[0138] S54, calculating and obtaining the thickness of the film to be measured according to the starting wavelength and the ending wavelength of the interference waveband, the refractive index of the film to be measured and the interpolation frequency.

[0139] Specifically, in step S51, the detection structure of the film to be tested remains unchanged. After the spectrometer receives the interference light from the film to be tested, the measured interference light intensity curve is obtained. Unlike the low-coherence interference detection image method, there is no need to eliminate DC interference terms and resampling. An interference band with strong periodicity is selected, and the measured interference light intensity curve is fast Fourier transformed. The peak value is extracted using the maximum value method from the obtained spectrum data, thereby obtaining the frequency corresponding to the peak value of the measured interference light intensity.

[0140] Furthermore, in step S52, due to the fence effect, the frequency resolution after Fourier transform is low, resulting in low thickness resolution. In order to solve this problem, the three-point Gaussian difference method is used to improve the frequency accuracy, and the frequency value corresponding to the peak value of the measured interference light intensity is interpolated in the frequency domain to obtain the interpolation frequency, which is specifically:

[0141] ; (7)

[0142] in, f p represents the interpolation frequency point, f m Indicates the frequency value corresponding to the peak value of the measured interference light intensity, f 0 represents the frequency interval, A( f m ) indicates frequency f m The corresponding amplitude, A( f m -f 0 ) indicates the frequency f m Before the interval f 0 The amplitude corresponding to the frequency, A ( f m +f 0 ) indicates the frequency f m After that, an interval f 0 The amplitude corresponding to the frequency.

[0143] After frequency domain interpolation, the resolution of thickness is significantly improved, which is suitable for online measurement of film thickness.

[0144] Furthermore, in step S54, the thickness of the film to be measured is calculated by the following formula according to the starting wavelength and the ending wavelength of the interference band, the refractive index of the film to be measured and the interpolation frequency:

[0145] d = λ start ·λ stop / 2n·f p ; (8)

[0146] in, d Indicates the thickness of the film being measured, λ start represents the starting wavelength of the interference band, λ stop represents the end wavelength of the interference band, n represents the refractive index of the film being measured, f p Represents the interpolation frequency.

[0147] refer to Figure 7 In some embodiments, a thin film thickness measurement system based on white light interferometry is provided, comprising a light source 101, a Y-type optical fiber 102, a spectrometer 103, a processor 104, and a storage device 105;

[0148] The light source 101 is used to emit white light and incident on the film to be measured through the Y-type optical fiber 102. The spectrometer 103 is used to collect interference light formed after reflection and refraction by the film to be measured through the Y-type optical fiber 102, and analyze the interference light to obtain the measured interference light intensity at multiple wavelengths;

[0149] The storage device 105 stores a plurality of instructions, and the processor 104 is used to read the instructions and execute the above method.

[0150] The film thickness measurement method and system based on white light interferometry provided in the above embodiments have at least the following beneficial effects:

[0151] (1) The reflected light and refracted light of the film to be measured are used as interference light. For films of different thicknesses, different methods are used to measure the films. Only one signal processing is required to obtain the thickness result. The operation speed is in the millisecond level, which is more suitable for industrial production. The existing white light scanning method requires a scanning process, which has the disadvantages of long measurement time and greater influence of external environmental interference. The method proposed in the above embodiment does not require scanning and displacement devices, saves costs, and greatly improves the detection speed. Therefore, the efficiency of film thickness detection can be improved. Since the detection process is completed in a very short time, the influence of external environmental changes on the measurement results is effectively reduced, thereby ensuring the accuracy of detection.

[0152] (2) For thin films with smaller thickness, the thickness is determined based on the matching degree. After the reflectivity curves of samples with different thicknesses are established, the thickness of the thin film can be obtained by only one signal processing. The process is simple, with fewer calculation steps and no need to process the signal too much. It is more suitable for occasions with higher requirements on detection speed.

[0153] (3) For thicker films, frequency domain interpolation processing is used to significantly improve the thickness resolution, which is suitable for online measurement of thick films;

[0154] (4) It can detect the thickness of thin films with a wide range of thicknesses. When testing samples with large thickness differences, there is no need to replace accessories or adjust the optical path, which effectively simplifies the production process.

[0155] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. 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. 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 these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for measuring film thickness based on white light interferometry, characterized in that: include: Control the light source to emit white light vertically incident on the film to be measured, form interference light after reflection and refraction, and control the spectrometer to collect the interference light; Controlling a spectrometer to analyze the interference light to obtain the measured interference light intensities at multiple wavelengths; Obtaining a measured interference light intensity curve according to the measured interference light intensities at multiple wavelengths; When the thickness of the film to be measured is within a first preset thickness range, samples of different known thicknesses of the same material as the film to be measured are used in advance for calculation to obtain reflectivity curves of samples of different thicknesses; Converting the measured interference light intensity curve to obtain a measured reflectivity curve, calculating a matching degree according to the sample reflectivity curve and the measured reflectivity curve, and calculating the thickness of the measured film according to the matching degree; When the thickness of the film to be measured is within a second preset thickness range, Fourier transform and frequency domain interpolation processing are performed based on the measured interference light intensity curve to obtain an interpolation frequency, and the thickness of the film to be measured is calculated according to the interpolation frequency; Wherein, the first preset thickness range is smaller than the second preset thickness range; Converting the measured interference light intensity curve to obtain a measured reflectivity curve includes: Collecting background light intensity and substrate reflected light intensity of the film substrate being tested; Obtaining the measured interference light intensity at different wavelengths according to the measured interference light intensity curve, and calculating the measured reflectivity according to the background light intensity, the substrate reflected light intensity and the measured interference light intensity; Obtaining the measured reflectivity curve according to the measured reflectivity at different wavelengths; Performing Fourier transform and frequency domain interpolation processing based on the measured interference light intensity curve to obtain an interpolation frequency, and calculating the thickness of the measured film according to the interpolation frequency, including: Performing Fourier transform on the measured interference light intensity curve to obtain the frequency corresponding to the peak value of the measured interference light intensity; Perform frequency domain interpolation on the frequency corresponding to the peak value of the measured interference light intensity to obtain the interpolation frequency; Selecting an interference band according to the measured interference light intensity curve; Calculate the thickness of the film to be measured according to the starting wavelength and the ending wavelength of the interference band, the refractive index of the film to be measured and the interpolation frequency; According to the starting wavelength and the ending wavelength of the interference band, the refractive index of the film to be measured and the interpolation frequency, the thickness of the film to be measured is calculated by the following formula: d = λ start ·λ stop / 2n·f p ； in, d Indicates the thickness of the film being measured, λ start represents the starting wavelength of the interference band, λ stop represents the end wavelength of the interference band, n represents the refractive index of the film being measured, f p Represents the interpolation frequency.

2. The method according to claim 1, characterized in that The first preset thickness range is 3-3000 nm, and the second preset thickness range is 3-3000 μm.

3. The method according to claim 1, characterized in that Samples of different known thicknesses of the same material as the film to be measured are used in advance for calculation to obtain reflectivity curves of samples of different thicknesses, including: Assuming that white light with initial intensity is incident vertically on the sample surface, calculate the first reflectivity of the interface between air and sample coating; Calculate the theoretical reflected light intensity occurring at the interface between air and sample coating according to the first reflectivity and the initial intensity; Calculating a second reflectivity of an interface between the coating layer and the substrate of the sample; Calculating theoretical refracted light intensities at multiple wavelengths from the sample to the air according to the second reflectivity, the thickness of the sample, the initial intensity, and the absorption coefficient of the sample; Calculating and obtaining theoretical interference light intensities at multiple wavelengths according to the theoretical reflected light intensities and the theoretical refracted light intensities at multiple wavelengths; According to the theoretical interference light intensities at multiple wavelengths, a theoretical interference light intensity curve is obtained; The theoretical interference light intensity curves at different thicknesses are calculated and converted to obtain the reflectivity curves of samples with different thicknesses.

4. The method according to claim 3, characterized in that The first reflectivity is calculated based on the coating refractive index and coating extinction coefficient of the sample; The second reflectivity is calculated based on the coating refractive index, coating extinction coefficient, substrate refractive index and substrate extinction coefficient of the sample.

5. The method according to claim 1, characterized in that The matching degree is the standard deviation of the sample reflectance curve and the measured reflectance curve calculated at multiple sampling points; The sample thickness value corresponding to the minimum matching value is taken as the thickness value of the film to be measured.

6. The method according to claim 1, characterized in that The interpolation frequency is calculated according to the following formula: ； in, f p represents the interpolation frequency, f m Indicates the frequency corresponding to the peak value of the measured interference light intensity, f 0 represents the frequency interval, A( f m ) indicates frequency f m The corresponding amplitude, A( f m -f 0 ) indicates the frequency f m Before the interval f 0 The amplitude corresponding to the frequency, A ( f m + f 0 ) indicates the frequency f m After that, an interval f 0 The amplitude corresponding to the frequency.

7. A film thickness measurement system based on white light interferometry, characterized in that: It includes a light source, a Y-type optical fiber, a spectrometer, a processor and a storage device; The light source is used to emit white light to be incident on the film to be measured through the Y-type optical fiber, and the spectrometer is used to collect interference light formed after reflection and refraction by the film to be measured through the Y-type optical fiber, and analyze the interference light to obtain the measured interference light intensity at multiple wavelengths; The storage device stores a plurality of instructions, and the processor is used to read the instructions and execute the method according to any one of claims 1-6.

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