A method for measuring film thickness based on chromaticity coordinates

Abstract

The application discloses a kind of based on color quality coordinate measurement obtains the method for obtaining film thickness.The present application uses optical fiber light guide, grating and surface array detection mode, obtains the spectral signal of sample, according to the conversion relationship of reflectance spectrum and color quality coordinate, the color quality coordinate of sample to be measured is calculated.The complete mapping relationship of color quality coordinate and thickness of film is obtained by theoretical calculation, and the color quality coordinate in the color quality coordinate of theoretical mapping relationship is compared with actually measured color quality coordinate, so the thickness information of film sample can be accurately obtained.The present application overcomes the shortcomings that wavelength scanning needs to rotate grating or prism in the measurement process in traditional spectral color measurement mode, realizes single full-spectrum measurement, and shortens the time required for measurement.At the same time, compared with wavelength interval in traditional measurement, the present application uses denser spectrum acquisition, so that the color information is more accurately obtained, and the thickness information of nanometer film is quickly and accurately obtained.

Description

Technical Field

[0001] This invention belongs to the field of optical electronic device technology, and specifically relates to a method for obtaining thin film thickness based on chromaticity coordinate measurement. Background Technology

[0002] Color measurement is important for manufacturers and users of many products, such as general lighting, light-emitting diodes (LEDs), displays, traffic lights, signs, printing, paint, plastics, and fabrics. The physical measurement of color is based on the acquisition of tristimulus values ​​in the CIE colorimetric system. The color of any object or light source is determined by its spectrum, which in turn determines the tristimulus values. The tristimulus values ​​of an object can be physically measured in two ways: one is using a tristimulus colorimeter, and the other is using a spectrometer that performs spectral calculations using color matching functions. Tristimulus colorimeters are fast, convenient, and inexpensive, making them suitable for production control and color difference measurement. However, tristimulus colorimeters inevitably suffer from spectral mismatch errors and are generally not suitable for high-precision absolute color measurement of various light sources or objects with different spectral distributions. Conversely, spectroscopic colorimetry based on spectrometers theoretically does not have this problem and can measure different colors more accurately. Spectroscopic colorimetry can also provide more information than tristimulus colorimeters, such as the color rendering index of the light source.

[0003] The color information of an object is determined by its spectrum, which is usually determined by the object's properties or structure. Therefore, structural information of an object can be obtained by measuring its chromaticity coordinates. For example, in the semiconductor and microelectronics fields, accurately obtaining the thickness and structure of various thin films is crucial. In earlier times, people inferred the thickness of thin films based on their color. This method was not very accurate, but the mapping relationship was relatively simple and convenient. Elliptic polarization spectroscopy has the advantages of high sensitivity, non-contact, and non-destructive nature, so it is often used in thin film thickness monitoring systems. However, this method is an indirect measurement method, requiring fitting of the raw data to obtain the thickness. Therefore, the mapping relationship is often complex and heavily reliant on the expertise and experience of technicians. Therefore, using spectrophotometry to replace human estimation can accurately obtain the chromaticity information of thin films and directly obtain the thickness of thin films through the mapping relationship between color and thickness, making it a simple and accurate measurement method. However, traditional spectrophotometry systems rely on wavelength scanning grating spectrometers. This mechanical scanning measurement mode is slow and not suitable for some scenarios requiring a large number of high-speed measurements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to propose a method for obtaining thin film thickness based on chromaticity coordinate measurement. The method involved in this invention is based on spectrophotometry. Compared with existing technologies, this invention employs fiber optic guidance, a grating, and a planar array detection mode to acquire spectral signals, overcoming the drawbacks of traditional spectrophotometry methods that require rotating gratings or prisms for wavelength scanning during measurement. This achieves a single full-spectrum measurement, shortening the measurement time. Furthermore, compared to the wavelength intervals in traditional measurements, this invention uses denser spectral acquisition, thus obtaining more accurate chromaticity information. In the thickness acquisition process, a theoretical mapping relationship between thin film thickness and chromaticity coordinates is first established. Then, spectrophotometry is performed on the thin film. During the measurement process, there is no mechanical rotation; the spectrum is imaged on a two-dimensional detector array. Data from each pixel of the two-dimensional detector is read and processed to obtain the chromaticity information of the thin film. This information is directly compared with the previously established mapping relationship to obtain the film thickness information, achieving fast, direct, and accurate measurement, overcoming the shortcomings of complex and slow traditional optical measurement methods.

[0005] The technical solution of the present invention is described in detail below.

[0006] This invention provides a method for obtaining film thickness based on chromaticity coordinate measurement, comprising the following steps:

[0007] (1) The reflectance spectrum R of the thin film sample under test is obtained by measuring the chromaticity information acquisition system based on area array spectral detection. s (λ); The colorimetric information acquisition system based on area array spectral detection includes a light source, a sample stage, an optical fiber, an optical fiber adapter, and a grating spectrometer. The light source is a continuous radiation source, the optical fiber probe is used to receive reflected light, the optical fiber adapter couples the reflected light signal into the grating spectrometer, and the grating spectrometer receives and acquires the light signal by the area array detector; the specific method is as follows:

[0008] ① First, rotate the optical fiber to an angle θ (to ensure high thickness resolution, it is recommended that the angle be between 0 and 40°). Light emitted from a continuous radiation source is incident on a thin film reference sample with a known thickness. After reflection, it enters the optical fiber and is transmitted to the grating spectrometer to obtain the reflection spectrum I. r (λ);

[0009] ② Calculate the spectral intensity I0(λ) of the incident light source:

[0010] I0(λ)=I r (λ) / R r (λ)

[0011] Where: R r (λ) represents the reflectance spectrum of the thin film reference sample at angle θ. r (λ), which is calculated based on the principle of optical thin films;

[0012] ③ Place the thin film sample to be tested on the sample stage, and at the incident angle θ, acquire the reflectance spectrum I using an optical fiber and grating spectrometer. s (λ);

[0013] ④ Calculate the reflection spectrum R of the thin film sample at angle θ. s (λ):

[0014] R s (λ)=I s (λ) / I0(λ);

[0015] (2) The reflection spectrum R s (λ) Substitute the spectral data of the D65 light source and the CIE1931 standard spectral tristimulus values ​​into the chromaticity coordinates to obtain the experimentally measured L*a*b*chromaticity coordinates of the thin film.

[0016] (3) Based on the theoretical model of thin film transfer matrix and reflection law, establish the mapping relationship between thin film thickness value and theoretical L*a*b* chromaticity coordinates, and calculate the theoretical L*a*b* chromaticity coordinates for different thickness values. Compare the experimentally measured L*a*b* chromaticity coordinates with the theoretical L*a*b* chromaticity coordinates, minimize the color difference between the two, obtain the optimal solution for thin film thickness, and calculate the thickness of the thin film sample to be tested.

[0017] In step ① above, the wavelength range of the light emitted by the continuous radiation source is 380-780 nanometers, and the wavelength interval is Δλ (the value range is generally 0.1 to 1 nanometer, for example 0.45 nanometers). At this time, rapid measurement of full spectrum data can be achieved by acquiring data in a single operation. The wavelength interval can be adjusted for different gratings and area array detectors.

[0018] In step (2) above, the wavelength range of the spectral distribution of the D65 standard light source and the tristimulus values ​​of the CIE1931 standard spectrum is 380-780 nm. The wavelength interval between the spectral distribution of the D65 standard light source and the tristimulus values ​​of the CIE1931 standard spectrum is interpolated to Δλ (the value range is generally 0.1-1 nm, for example 0.45 nm); the experimentally measured L*a*b* chromaticity coordinates (L* exp ,a* exp b* exp It is obtained through the following formula:

[0019] L* exp =116f(Y) exp / Y n )-16

[0020] a* exp =500[f(X) exp / X n )-f(Yexp / Y n )]

[0021] b* exp =200[f(Y exp / Y n )-f(Z exp / Z n )]

[0022] Among them, (X) n Y n Z n X represents the tristimulus value of the light source color. For a D65 standard light source, X... n =95.04, Y n =100, Z n =108.89, f(q) is obtained from the following formula:

[0023]

[0024] (X exp Y exp Z exp The tristimulus value of the sample color is obtained by the following formula:

[0025]

[0026]

[0027]

[0028]

[0029] Among them, R s (λ) is the measured reflectance spectrum of the thin film sample, I D65 (λ) is the spectral distribution of the D65 standard light source. It is the CIE1931 standard spectral tristimulus value.

[0030] In step (3) above, based on the theoretical model of the thin film transport matrix and the law of reflection, a mapping relationship between the thin film thickness value and the theoretical L*a*b* chromaticity coordinates is established. When calculating the theoretical L*a*b* chromaticity coordinates for different thickness values, the incident angle and the actual incident angle θ in the experiment are kept consistent. The thin film is represented by a three-layer structure from top to bottom: an air layer, a thin film layer, and a substrate layer. First, the theoretical reflection spectrum R of the sample thin film with different thicknesses d is calculated according to the thin film transport theory. mod (d,λ), then the reflection spectrum R mod Substituting (d,λ) into the spectral data of the D65 light source and the CIE 1931 standard spectral tristimulus values, we obtain the theoretical L*a*b* chromaticity coordinates (L*) for films of different thicknesses. mod(d), a* mod (d), b* mod (d)). During the calculation, the wavelength range of the spectral distribution of the D65 standard light source and the tristimulus values ​​of the CIE 1931 standard spectrum is 380-780 nm. The wavelength interval between the spectral distribution of the D65 standard light source and the tristimulus values ​​of the CIE 1931 standard spectrum is interpolated to Δλ (the value range is generally 0.1-1 nm, for example, 0.45 nm). Theoretical L*a*b*chromaticity coordinates (L* mod (d), a* mod (d), b* mod (d) is obtained from the following formula:

[0031] L* mod (d)=116f(Y mod (d) / Y n )-16

[0032] a* mod (d)=500[f(X mod (d) / X n )-f(Y mod (d) / Y n )]

[0033] b* mod (d)=200[f(Y mod (d) / Y n )-f(Z mod (d) / Z n )]

[0034] Among them, (X) n Y n Z n X represents the tristimulus value of the light source color. For a D65 standard light source, X... n =95.04, Y n =100, Z n =108.89, f(q) is obtained from the following formula:

[0035]

[0036] (X mod (d), Y mod (d), Z mod (d) represents the theoretical tristimulus values ​​for films of different thicknesses d, obtained by the following formula:

[0037]

[0038]

[0039]

[0040]

[0041] Among them, R mod (d,λ) is the reflectance spectrum of thin films of different thicknesses calculated based on thin film transport theory, I D65 (λ) is the spectral distribution of the D65 standard light source. It is the CIE1931 standard spectral tristimulus value.

[0042] Treating the thin film and substrate as an equivalent layer, the theoretical reflectance spectrum R of thin films with different thicknesses d is... mod (d,λ) is:

[0043] R mod (d,λ)=(|r s (d,λ)| 2 +|r p (d,λ)| 2 ) / 2

[0044] in, It is the complex reflection coefficient of s-rays. It is the complex reflection coefficient of p-rays.

[0045] In step (3) above, the optimal solution for the film thickness is obtained using the following formula, and the thickness of the film sample to be tested is calculated:

[0046]

[0047] Where, d opt The thickness of the thin film sample to be tested, (L*), is obtained according to the above method. exp ,a* exp b* exp (L*) represents the experimentally measured chromaticity coordinates. mod (d), a* mod (d), b* mod (d) represents the theoretically calculated chromaticity coordinates of a thin film with thickness d.

[0048] This invention employs a full-spectrum surface array detection method to acquire the chromaticity information of an object, enabling rapid and accurate acquisition of material thickness. Compared with existing technologies, the advantages of this invention are as follows:

[0049] This invention eliminates the need for complex modeling, directly obtaining thin film thickness values ​​from chromaticity information, and acquiring the full-spectrum reflectance signal of the thin film using fiber optics, gratings, and area array detection modes. This eliminates the shortcomings of traditional spectrophotometric methods that require rotating prisms or gratings to achieve wavelength scanning and acquire spectral signals, significantly improving the speed of reflectance spectrum acquisition. The acquisition time for the reflectance spectrum in the visible light band is better than 500 milliseconds, and the accuracy of thin film thickness reaches 0.2 nanometers. This invention proposes a method for obtaining thin film thickness based on area array detection spectrophotometry, enabling rapid and accurate acquisition of chromaticity information and direct and accurate thin film thickness. It has important applications in the structural judgment and calculation of mass-produced semiconductor devices, meeting the growing demand in scientific research and industry for rapid and accurate thin film thickness acquisition technology. Attached Figure Description

[0050] Figure 1 A flowchart illustrating the method of this invention.

[0051] Figure 2 A schematic diagram of the optical path of the system of this invention.

[0052] Figure 3 A schematic diagram of the thin film structure used to calculate the theoretical reflection spectrum.

[0053] Figure 4 Taking titanium dioxide thin film as an example, the reflectance spectrum of the sample to be tested is obtained.

[0054] Figure 5 A graph showing the relationship between color difference and thickness.

[0055] Figure 6 The reflection spectrum of the sample under test and the theoretical reflection spectrum at the optimal thickness.

[0056] The numbers in the diagram are: 1-light source, 2-film under test, 3-optical fiber, 4-optical fiber adapter, 5-two-dimensional surface array detector, 6-computer. Detailed Implementation

[0057] The technical solution of the present invention will be described in detail below through examples.

[0058] Figure 1 This is a flowchart illustrating the method of the present invention.

[0059] Figure 2 This is a schematic diagram of the optical path of the system of the present invention.

[0060] This invention provides a colorimetric information acquisition system based on a planar array detector spectrum, comprising a light source 1, a sample stage, an optical fiber 3, an optical fiber adapter 4, and a grating spectrometer. The grating spectrometer uses a two-dimensional planar array detector 5 to collect signals. The transverse pixel units of the detector serve as wavelength channels for the spectrum, and the longitudinal pixel data is used for summation to reduce random noise at each wavelength point. During operation, the light source 1 is a continuous radiation source. The light emitted by the continuous radiation source is incident on the thin film sample to be tested, reflected by the sample, and enters the optical fiber 3. After transmission, it enters the grating spectrometer through the optical fiber adapter 4. After grating dispersion, a spectral distribution is formed on the two-dimensional planar array detector 5. The colorimetric information of the thin film is then obtained through the conversion relationship between the spectrum and chromaticity coordinates.

[0061] In this invention, the light source 1 is a continuous radiation source, such as an LED. The light emitted by the light source 1 illuminates the sample surface at an incident angle of θ. After being reflected by the thin film 2 under test, the reflected light carries the spectral information of the sample. The reflected light enters the optical fiber 3, is transmitted to the optical fiber adapter 4, and then enters the spectrometer. The grating spectrometer splits the signal light, which is then converged by a focusing lens. At the focal plane of the focusing lens, the spectral signal is received by different pixels on the two-dimensional surface array detector 5, undergoes photoelectric signal conversion, and is converted into a digital signal. This digital signal is then input into the computer 6 for analysis and processing to obtain the colorimetric information and thickness of the thin film under test.

[0062] like Figure 3 As shown, the thin film structure used to calculate the theoretical reflection spectrum can be represented by a three-layer model, where the air layer has a refractive index of 1, the incident angle is θ, and the complex refractive index of the thin film is...

[0063] n1=n1-ik1 (1)

[0064] Where n1 is the refractive index of the thin film, k1 is the extinction coefficient of the thin film, the film thickness is d, and the refraction angle is θ1. The complex refractive index of the substrate is...

[0065] n s =n s -ik s (2)

[0066] Where, n s Let k be the refractive index of the substrate. s Let be the extinction coefficient of the substrate. Then, according to Snell's law, we have...

[0067]

[0068] in, Let n denote the angle of refraction in the thin film, and n0 be the refractive index of air. For p-polarized light with its polarization direction parallel to the plane of incidence, the admittance of the thin film is...

[0069] η s=n1 cosθ1 (4)

[0070] For s-polarized light vibrating perpendicular to the incident plane, the admittance of the thin film is:

[0071] η p =n1 2 / η s (5)

[0072] The phase introduced by light propagation in a thin film is

[0073]

[0074] The effect of the thin film on light with different polarizations can then be described by the transfer matrix.

[0075]

[0076] Among them, M p (d,λ) is the transport matrix of p-light in the thin film, M s (d,λ) is the transmission matrix of s-light in the thin film.

[0077] By considering the thin film and the substrate as an equivalent layer, the complex reflection coefficient of the structure for p- or s-beams can be obtained.

[0078]

[0079] Where η0 is the optical admittance of air;

[0080]

[0081] M(d,λ) is the thin-film transport matrix for p-light or s-light, η Si The admittance of the substrate when p-light or s-light is incident is calculated by the following formula:

[0082] η Si-s =n s cosθ s ,η Si-p =n s 2 / η Si-s (10)

[0083] in, It is the angle of refraction of light in the substrate. It is the complex refractive index of the substrate, η Si-s It is the substrate's admittance to s-beams, η Si-p It is the substrate's admittance to p-light.

[0084] The reflectance of the thin film to natural light is...

[0085] R mod (d,λ)=(|rs (d,λ)| 2 +|r p (d,λ)| 2 ) / 2 (11)

[0086] in, It is the complex reflection coefficient of s-rays. It is the complex reflection coefficient of p-rays.

[0087] For samples of different thicknesses, their theoretical reflectance spectrum R can be calculated based on the above theory. mod (d,λ);

[0088] Then according to

[0089]

[0090] and

[0091]

[0092] The theoretical chromaticity coordinates (L*) of films with different thicknesses were calculated. mod (d), a* mod (d), b* mod (d)). Among them, (X mod (d), Y mod (d), Z mod (d) represents the theoretical tristimulus values ​​for films of different thicknesses d, R mod (d,λ) is the reflectance spectrum of thin films of different thicknesses calculated based on thin film transport theory, I D65 (λ) is the spectral distribution of the D65 standard light source. These are the CIE 1931 standard spectral tristimulus values. (X) n Y n Z n X represents the tristimulus value of the light source color. For a D65 standard light source, X... n =95.04, Y n =100, Z n =108.89, f(q) is obtained from the following formula:

[0093]

[0094] The actual measurement process steps are as follows:

[0095] (1) First, rotate the optical fiber to an angle θ. Light emitted from a continuous radiation source is incident on a reference sample with a known reflection spectrum. After reflection, the light enters the optical fiber and is transmitted to the spectrometer to obtain the reflection spectrum I. r (λ);

[0096] (2) Calculate the spectral intensity I0(λ) of the incident light source:

[0097] I0(λ)=I r (λ) / R r (λ) (15)

[0098] Among them, R r (λ) is the reflection spectrum of the reference sample at angle θ;

[0099] (3) Place the thin film sample to be tested on the sample stage, and at a reflection angle θ, obtain its reflection spectrum I using an optical fiber and a spectrometer. s (λ);

[0100] (4) Calculate the reflectance spectrum R of the sample to be tested. s (λ):

[0101] R s (λ)=I s (λ) / I0(λ) (16)

[0102] (5) Substitute the spectral data of the D65 light source and the CIE1931 standard spectral tristimulus values, and obtain the L*a*b*chromatic coordinates of the sample to be tested according to formulas (17)-(18).

[0103]

[0104]

[0105] Among them, R s (λ) is the reflectance spectrum of the sample to be tested, (X) exp Y exp Z exp ) represents the tristimulus value of the sample to be tested, I D65 (λ) is the spectral distribution of the D65 standard light source. These are the CIE 1931 standard spectral tristimulus values. (X) n Y n Z n X represents the tristimulus value of the light source color. For a D65 standard light source, X... n =95.04, Y n =100, Z n =108.89, f(q) is determined by formula (14).

[0106] (6) By comparing the chromaticity coordinates in the theoretical mapping relationship with the measured chromaticity coordinates, the optimal solution for the film thickness is obtained according to equation (19).

[0107]

[0108] Where, d optThis represents the thickness of the thin film sample to be tested. The subscript exp indicates the experimental value, and the subscript mod indicates the model-calculated value.

[0109] Taking titanium dioxide nanofilm as an example, at a reflection angle θ of 25 degrees, the theoretical chromaticity coordinates of the material at different thicknesses are obtained according to the model in equations (1)-(14), with a thickness range of 0-300 nanometers. Then, the reflection spectrum of the sample at this angle is obtained according to measurement steps (1)-(4). Figure 4 The wavelength interval is 0.45 nm, and the wavelength range is 380-780 nm. Then, according to step (5), the L*a*b* chromaticity coordinates of the sample are obtained. The color difference between the experimentally measured chromaticity coordinates and the theoretically calculated chromaticity coordinates is calculated using equation (19) as a function of thickness. Figure 5 As can be seen, the color difference is minimal when the thickness is 77.1 nm. At this thickness, the reflectance spectrum of the sample matches the theoretical reflectance spectrum at the optimal thickness very well. Figure 6 The thickness of the film under test was obtained as 77.1 nm. The same film sample was measured using a rotomolded ellipsometry (RPAE) system with simultaneous rotation of the polarizer and analyzer, and the thickness and test time are listed in the table below:

[0110] Table 1

[0111]

Claims

1. A method for measuring the thickness of a thin film based on chromaticity coordinates, characterized in that, The method comprises the following steps: (1) The reflectance spectrum R is obtained by measuring the thin film sample to be measured by a color information acquisition system based on a surface array spectrum probe s (λ); the color information acquisition system based on the surface array spectrum probe comprises a light source, a sample stage, an optical fiber, an optical fiber adapter and a grating spectrometer, the light source adopts a continuous radiation light source, the optical fiber is used for receiving reflected light, the optical fiber adapter couples the reflected light signal into the grating spectrometer, and the grating spectrometer receives and collects and reads the light signal by a surface array detector; the specific method is as follows: First, the optical fiber is rotated to an angle θ, light emitted by the continuous radiation source is incident on a thin film reference sample with a known thickness, after reflection, it enters the optical fiber, is transmitted by the optical fiber, enters the grating spectrometer through the optical fiber adapter, and the reflection spectrum I is obtained r (λ); (2) calculating the spectral intensity I0(λ) of the incident light source: I0(λ) = I r (λ) / R r (λ) wherein: R r (λ) is the reflectance spectrum R r (λ) of the film reference sample at the angle θ, calculated from optical thin film principles; iii) placing the sample film on the sample stage, and obtaining the reflectance spectrum I(θ) using the fiber-optic probe and the spectrometer at an incident angle θ s (λ); (iv) calculating the reflectance spectrum R of the sample at the angle θ s (λ): R s (λ) = I s (λ) / I0(λ); (2) The reflectance spectrum R s (λ) is substituted into the spectral data of the D65 light source and the CIE 1931 standard spectral tristimulus values, and the film's experimentally measured L*a*b* color coordinates are converted with the chromaticity coordinates. (3) based on the theoretical model of the film transmission matrix and the law of reflection, a mapping relationship between the film thickness value and the theoretical L*a*b* color coordinates is established, and the theoretical L*a*b* color coordinates at different thickness values are calculated; the experimentally measured L*a*b* color coordinates are compared with the theoretical L*a*b* color coordinates, the color difference between the two is minimized, the optimal solution of the film thickness is obtained, and the thickness of the to-be-measured film sample is calculated; wherein: In step (3), based on the theoretical model of film transfer matrix and reflection law, the mapping relationship between the film thickness value and the theoretical L*a*b* color coordinates is established, and the theoretical L*a*b* color coordinates at different thickness values are calculated. The incident angle and the actual incident angle θ of the experiment are kept consistent. The film is represented by a three-layer structure of air layer, film layer and substrate layer from top to bottom. First, the theoretical reflectance spectrum R mod (d, λ) of the film with different thickness d is calculated according to the film transfer theory, then the reflectance spectrum R mod (d, λ) is substituted into the spectral data of D65 light source and the CIE1931 standard spectral tristimulus value to obtain the theoretical L*a*b* color coordinates (L mod (d), a* mod (d), b* mod (d)) of the film with different thickness; in the calculation process, the wavelength range of the spectral distribution of D65 standard light source and the CIE1931 standard spectral tristimulus value is 380-780 nanometers, and the wavelength interval of the spectral distribution of D65 standard light source and the CIE1931 standard spectral tristimulus value is interpolated as Δλ; the theoretical L*a*b* color coordinates (L mod (d), a* mod (d), b* mod (d)) are obtained by the following formula: L* mod (d) = 116f(Y mod (d) / Y n )-16 a* mod (d) = 500 [f(X mod (d) / X n )-f(Y mod (d) / Y n )] b* mod (d) = 200 [f(Y mod (d) / Y n )-f(Z mod (d) / Z n )] where (X n , Y n , Z n ) are the tristimulus values of the color of the light source, for the D65 standard light source X n = 95.04, Y n = 100, Z n = 108.89, and f(q) is obtained from the following equation: (X mod (d), Y mod (d), Z mod (d) are the theoretical tristimulus values of the film of different thickness d, obtained from the following formula: where R mod (d, λ) is the reflectance spectrum of a film of different thickness calculated from thin film transmission theory, I D65 (λ) is the spectral distribution of the D65 standard illuminant, are the CIE 1931 standard tristimulus values.

2. The method of claim 1, wherein, In step 1, the wavelength range of the light emitted by the continuous radiation light source is 380-780 nanometers, the wavelength interval is Δλ, and Δλ is between 0.1 and 1 nanometer; the angle θ is between 0 and 40 degrees.

3. The method of claim 1, wherein, In step (2), the spectral distribution of the D65 standard illuminant is over the wavelength range 380-780 nm, and the wavelength intervals of the spectral distribution of the D65 standard illuminant and the CIE 1931 standard spectral tristimulus values are interpolated to Δλ; the experimentally determined L*a*b* colorimetric coordinates (L exp , a* exp , b* exp ) of the film are obtained by the following formula: L* exp = 116f(Y exp / Y n )- 16 a* exp = 500 [f(X exp / X n ) - f(Y exp / Y n )] b* exp = 200 [f(Y exp / Y n ) - f(Z exp / Z n )] where (X n , Y n , Z n ) are the tristimulus values of the color of the light source, for the D65 standard light source X n = 95.04, Y n = 100, Z n = 108.89, and f(q) is obtained from the following equation: (X exp , Y exp , Z exp ) are the tristimulus values of the color of the sample, obtained from the formula: wherein R s (λ) is the measured reflectance spectrum of the film sample, I D65 (λ) is the spectral distribution of the D65 standard illuminant, are the CIE 1931 standard tristimulus values.

4. The method of claim 1, wherein, Theoretical reflectance spectrum R of thin films of different thickness d, considering the film and the substrate as an equivalent layer mod (d, λ) is: wherein is the complex reflection coefficient of s light, is the complex reflection coefficient of p light.

5. The method of claim 1, wherein, In step (3), the optimal solution d of the film thickness is obtained using the following equation opt The thickness of the film sample to be measured is obtained: where (L exp , a exp , b exp ) represents the experimentally measured color coordinates, and (L mod (d), a mod (d), b mod (d)) represents the theoretically calculated values of the color coordinates for a film having a thickness of d.

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