A method for characterizing optical constants of an ultrathin film

Abstract

The application discloses a method for characterizing optical constants of ultrathin optical films by using a spectrophotometer, and the method comprises the following steps: calculating the refractive index of an optically transparent glass substrate; depositing a reference film and calculating the refractive index of the reference film; depositing an ultrathin film to be measured and correcting the refractive index of the ultrathin film to be measured by using the refractive index of the reference film; and calculating the extinction coefficient of the ultrathin film to be measured. The application can characterize the refractive index and the extinction coefficient of the ultrathin optical film by using the transmission spectrum of the spectrophotometer, and the method is suitable for the optical transparent and weak absorption films.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for characterizing optical constants of optical thin films, in particular, a method for characterizing optical constants of ultra-thin optical thin films. BACKGROUND

[0002] Accurate characterization of optical constants of thin films is a prerequisite for realizing high-performance optical thin film elements. With the advancement of thin film preparation technology and thickness monitoring technology, there are often various thin film layers with different thicknesses in the design of film systems. Therefore, it is very important to characterize the optical constants of thin films of various thicknesses. When the optical thin film reaches a certain thickness, multiple extreme points will appear in the transmission spectrum curve of the optical thin film in the concerned wavelength range, and the envelope of the maximum and minimum values of the transmission can be used to calculate the refractive index and extinction coefficient of the optical thin film in the wavelength range. However, for thin film layers with thin thickness, especially ultra-thin optical thin films with a thickness of only tens of nanometers, the transmission spectrum curve in the concerned wavelength range does not have extreme points, and the calculation method based on the envelope of the maximum and minimum values of the transmission is no longer applicable. At present, the optical constants of ultra-thin optical thin films deposited on a silicon wafer are characterized and analyzed by using an ellipsometer. However, for different substrates, the characteristics of the thin films in the initial growth stage are different, and the optical constants of the ultra-thin optical thin films deposited on the silicon wafer and the glass substrate are different. SUMMARY

[0003] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a method for characterizing the optical constants of ultra-thin optical thin films by using a spectrophotometer. The method can be used to characterize the optical constants of ultra-thin thin films deposited on optically transparent glass substrates, and is applicable to both optically transparent ultra-thin films and ultra-thin films with weak absorption.

[0004] The technical solution of the present application is as follows:

[0005] A method for characterizing the optical constants of ultra-thin optical thin films, characterized in that the method comprises the following steps:

[0006] Step 1. Use a spectrophotometer to test the transmission spectrum of an optically transparent glass substrate S under normal incidence conditions, and calculate the refractive index n S (λ j ) of the optically transparent glass substrate S at each wavelength, wherein the wavelength is λ min ~ λ max , and the interval between each wavelength point is Δλ;

[0007] Step 2. Deposit a reference film A on the optically transparent glass substrate S to prepare a reference sample S A , wherein the optical thickness d A of the reference film A is not less than Using a spectrophotometer to test reference sample S A The transmission spectrum under normal incidence conditions is obtained, and the refractive index n of the reference thin film A at each wavelength is calculated. A (λ j );

[0008] Step 3. Deposit the ultrathin film B to be tested on the optically transparent glass substrate S to prepare the sample S. B The material of the ultrathin film B to be tested is the same as that of the reference film A, and the thickness d of the ultrathin film B is characterized by... B The sample S was tested using a spectrophotometer. B Transmission spectrum under normal incidence conditions. Assume the extinction coefficient k of the ultrathin film B under test at each wavelength. B (λ j Given that ) is 0, calculate the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j ). and use n A (λ j ) for n B (λ j Corrections are made to obtain the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j );

[0009] Step 4. Calculate the extinction coefficient k of the ultrathin film B to be tested. B (λ j ).

[0010] The method described above for characterizing the optical constants of ultrathin optical films using a spectrophotometer is characterized in that, in step 1, the transmission spectrum of an optically transparent glass substrate S under normal incidence conditions is measured using a spectrophotometer, and the refractive index n of the optically transparent glass substrate S at each wavelength is calculated. S (λ j The wavelength is λ. min ~λ max The wavelength points are spaced apart by Δλ. The specific steps are as follows:

[0011] a. The transmission spectrum of an optically transparent glass substrate S under normal incidence conditions was measured using a spectrophotometer to obtain the minimum wavelength λ of the optically transparent glass substrate S. min up to the maximum wavelength λ max Transmittance T at each wavelength point λ 0S (λ), with the interval between each wavelength point being Δλ;

[0012] b. Eliminate the influence of the back surface of the optically transparent glass substrate S according to formula (1), and obtain the transmittance T of the front surface of the optically transparent glass substrate S at each wavelength point λ.S (λ);

[0013]

[0014] c. According to formula (2), calculate the optically transparent glass substrate S at wavelength λ when j = 0. j =λ min The refractive index n at +j·Δλ S (λ j );

[0015]

[0016] Where n0 refers to the refractive index of air;

[0017] d. Let j = j + 1, and repeat step c until λ. j =λ max .

[0018] The method described above for characterizing the optical constants of ultrathin optical thin films using a spectrophotometer is characterized in that, in step 2, a reference thin film A is deposited on the optically transparent glass substrate S to prepare a reference sample S. A The optical thickness d of the reference thin film A A Not less than Using a spectrophotometer to test reference sample S A The transmission spectrum under normal incidence conditions is obtained, and the refractive index n of the reference thin film A at each wavelength is calculated. A (λ j The specific steps are as follows:

[0019] a. An optically transparent glass substrate S is ultrasonically cleaned. A reference thin film A is deposited on the cleaned optically transparent glass substrate S. The optical thickness d of the reference thin film A is... A Not less than

[0020] b. Using a spectrophotometer to test the reference sample S A The transmission spectrum of the reference sample S was obtained under normal incidence conditions. A At the minimum wavelength λ min up to the maximum wavelength λ max Transmittance T at each wavelength point λ between SA (λ); the reference sample S A By connecting the transmittance maxima and transmittance minima respectively, two envelope lines are drawn to obtain the minimum wavelength λ. min up to the maximum wavelength λ max Maximum transmittance T at each wavelength λ max (λ) and the minimum transmittance T min (λ).

[0021] c. Calculate the wavelength point λ of the reference thin film A when j = 0 according to formula (3). j =λ min The refractive index n at +j·Δλ A (λ j );

[0022]

[0023] In the formula,

[0024]

[0025] d. Let j = j + 1, and repeat step c until λ. j =λ max .

[0026] The method described above for characterizing the optical constants of ultrathin optical thin films using a spectrophotometer is characterized in that, in step 3, the ultrathin thin film B to be tested is deposited on the optically transparent glass substrate S to prepare the sample S. B The material of the ultrathin film B to be tested is the same as that of the reference film A, and the thickness d of the ultrathin film B is characterized by this. B The sample S was tested using a spectrophotometer. B Transmission spectrum under normal incidence conditions. Assume the extinction coefficient k of the ultrathin film B under test at each wavelength. B (λ j Given that ) is 0, calculate the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j ). and use n A (λ j ) for n B (λ j Corrections are made to obtain the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j The specific steps are as follows:

[0027] a. Deposit the ultrathin optical film B to be tested on the optically transparent glass substrate S, and test the sample S using a spectrophotometer. B The transmission spectrum of the sample S under normal incidence conditions was obtained. B At the minimum wavelength λ min up to the maximum wavelength λ max Transmittance T at each wavelength point λ between SB (λ);

[0028] b. Characterizing the thickness d of the ultrathin film B to be tested B ;

[0029] c. Calculate the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j The details are as follows:

[0030] 1) Let j = 0, calculate the ultrathin film B under test in λ j =λ min The refractive index n at the wavelength point +j·Δλ B (λ j The formula is as follows:

[0031]

[0032]

[0033]

[0034]

[0035]

[0036] In the formula, T B (λ j R refers to the surface transmittance of the ultrathin film B under test. B (λ j The reflectance refers to the surface reflectance of the ultrathin film B under test. The characteristic matrix is ​​denoted by i, where i represents the imaginary unit.

[0037] 2) Calculate the reference coefficient f(λ) using any one of formulas (10) to (15). j );

[0038]

[0039]

[0040]

[0041] n B (λ j )=f(λ j )·n A (λ j )+[1-f(λ j )]·n 水 (13)

[0042]

[0043]

[0044] Where, n 水 The refractive index of water;

[0045] 3) Let j = j + 1, and repeat steps 1) and 2) above until λ. j =λ max ; to all f(λ) j Connect them to form a curve;

[0046] 4) Let j = 0, calculate the wavelength point λ. j =λ min The slope of the curve at +j·Δλ;

[0047] 5) Let j = j + 1, repeat step 4) until the wavelength point λ is reached. j The slope at point is 0 or λ j =λ max When, let f = f(λ) j );

[0048] 6) Let j = 0, calculate the wavelength point λ of the ultrathin film B to be tested. j =λ min The corrected refractive index n at +j·Δλ B (λ j The following formula is used according to the following rules:

[0049]

[0050]

[0051]

[0052] n B (λ j )=f·n A (λ j )+(1-f)·n 水 (19)

[0053]

[0054]

[0055] The rules are as follows:

[0056] When the reference coefficient f(λ) is calculated using formula (10) in step 2), j Then, the refractive index n can be calculated using formula (16). B (λ j The reference coefficient f(λ) is calculated using formula (11). j Then, the refractive index n can be calculated using formula (17). B (λ j The reference coefficient f(λ) is calculated using formula (12). j Then, the refractive index n can be calculated using formula (18).B (λ j The reference coefficient f(λ) is calculated using formula (13). j Then, the refractive index n can be calculated using formula (19). B (λ j The reference coefficient f(λ) is calculated using formula (14). j Then, the refractive index n can be calculated using formula (20). B (λ j The reference coefficient f(λ) is calculated using formula (15). j Then, the refractive index n can be calculated using formula (21). B (λ j );

[0057] 7) Let j = j + 1, and repeat step 6) until λ. j =λ max ;

[0058] The method described above for characterizing the optical constants of ultrathin optical films using a spectrophotometer is characterized in that step 4, calculating the extinction coefficient k of the ultrathin film B to be tested, is... B (λ j The specific steps are as follows:

[0059] a. Let j = 0, calculate the wavelength point λ of the ultrathin film B to be tested. j =λ min Extinction coefficient k at +j·Δλ B (λ j The formula is as follows:

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] b. Let j = j + 1, and repeat step a until λ. j =λ max .

[0066] Technical effects of the present invention:

[0067] This invention utilizes the transmission spectra of a glass substrate and a reference thin film sample under normal incidence conditions measured by a spectrophotometer to obtain the refractive index dispersion curve of the reference thin film using the envelope method; it calculates the refractive index of the ultrathin thin film at a longer wavelength where the extinction coefficient is 0 based on the transmittance of the ultrathin thin film at that wavelength, calculates the relationship between the refractive index of the ultrathin thin film and the refractive index of the reference thin film, and obtains the refractive index and extinction coefficient of the ultrathin thin film within the wavelength range of interest.

[0068] This invention utilizes the transmission spectrum measured by a spectrophotometer to characterize the refractive index and extinction coefficient of ultrathin optical films. This method is applicable to both optically transparent and weakly absorbing films. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of a physical embodiment of the present invention, which uses a spectrophotometer to characterize the optical constants of ultrathin optical films.

[0070] Figure labeling: 1-Optically transparent glass substrate S; 2-Reference thin film A; 3-Ultra-thin thin film to be tested B.

[0071] Figure 2 The transmission spectrum curves of the optically transparent glass substrate and the sample under test in an embodiment of the present invention are shown.

[0072] Figure 3 The curves representing the refractive index and extinction coefficient obtained in the embodiments of the method of the present invention are shown. Detailed Implementation

[0073] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0074] Please refer to Figure 1 , Figure 1 This is a schematic diagram of a physical embodiment of the present invention, which uses a spectrophotometer to characterize the optical constants of ultrathin optical films.

[0075] This embodiment sets the minimum wavelength λ. min =300nm, maximum wavelength λ max =800nm, the wavelength interval Δλ = 1nm, the refractive index of water n 水 =1.33, air refractive index n0 = 1.0. Taking fused silica glass as the optical glass substrate, this invention illustrates the method for characterizing the optical constants of ultrathin Al2O3 films in the wavelength range of 300 nm to 800 nm using a spectrophotometer as an example. The method includes the following steps:

[0076] ① Test the transmission spectrum of an optically transparent glass substrate and calculate its refractive index:

[0077] a. The transmission spectrum of an optically transparent glass substrate S under normal incidence conditions was measured using a spectrophotometer to obtain the minimum wavelength λ of the optically transparent glass substrate S. min up to the maximum wavelength λ max Transmittance T at each wavelength point λ 0S (λ), with the interval between each wavelength point being Δλ;

[0078] b. Eliminate the influence of the back surface of the optically transparent glass substrate S according to formula (1), and obtain the transmittance T of the front surface of the optically transparent glass substrate S at each wavelength point λ. S (λ);

[0079]

[0080] c. According to formula (2), calculate the optically transparent glass substrate S at wavelength λ when j = 0. j =λ min The refractive index n at +j·Δλ S (λ j );

[0081]

[0082] Where n0 refers to the refractive index of air;

[0083] d. Let j = j + 1, and repeat step c until λ. j =λ max .

[0084] ② Test the transmission spectrum of the reference thin film and calculate its refractive index:

[0085] a. An optically transparent glass substrate S is ultrasonically cleaned. A reference thin film A is deposited on the cleaned optically transparent glass substrate S. The optical thickness of the reference thin film A is...

[0086] b. Using a spectrophotometer to test the reference sample S A The transmission spectrum of the reference sample S was obtained under normal incidence conditions. A At the minimum wavelength λ min up to the maximum wavelength λ max Transmittance T at each wavelength point λ between SA (λ); the reference sample S A By connecting the transmittance maxima and transmittance minima respectively, two envelope lines are drawn to obtain the minimum wavelength λ. min up to the maximum wavelength λ max Maximum transmittance T at each wavelength λ max (λ) and the minimum transmittance T min (λ).

[0087] c. Calculate the wavelength point λ of the reference thin film A when j = 0 according to formula (3). j =λ min The refractive index n at +j·Δλ A (λ j );

[0088]

[0089] In the formula,

[0090]

[0091] d. Let i = i + 1, and repeat step c until λ. j =λ max .

[0092] ③ Test the transmission spectrum of the sample to be tested and calculate the refractive index of the ultrathin film to be tested:

[0093] a. An ultrathin optical film B to be tested is deposited on the optically transparent glass substrate S. The ultrathin film B to be tested is made of the same material as the reference film A. The sample S to be tested is then tested using a spectrophotometer. B The transmission spectrum of the sample S under normal incidence conditions was obtained. B At the minimum wavelength λ min up to the maximum wavelength λ max Transmittance T at each wavelength point λ between SB (λ).

[0094] b. Characterize the thickness of the ultrathin film B under test using transmission electron microscopy. B =32nm;

[0095] c. Calculate the refractive index n of the ultrathin film B under test at various wavelengths. B (λ j The details are as follows:

[0096] 1) Let j = 0, the ultrathin film B to be measured at wavelength λ j =λ min The extinction coefficient k at +j·Δλ is B (λ j If the value is 0, calculate the wavelength point λ of the ultrathin film B to be tested according to formulas (5) to (9). j The refractive index n at that point B (λ j );

[0097]

[0098]

[0099]

[0100]

[0101]

[0102] In the formula, T B (λ j R refers to the surface transmittance of the ultrathin film B under test. B (λ j The reflectance refers to the surface reflectance of the ultrathin film B under test. The characteristic matrix is ​​denoted by i, where i represents the imaginary unit.

[0103] 2) Calculate the reference coefficient f(λ) using formula (11). j );

[0104]

[0105] Where, n 水 The refractive index of water;

[0106] 3) Let j = j + 1, and repeat steps 1) and 2) above until λ. j =λ max . All f(λ) j Connect them to form a curve;

[0107] 4) Calculate the wavelength point λ when j = 0. j =λ min The slope of the curve at +j·Δλ;

[0108] 5) Let j = j + 1, repeat step 4) until the wavelength point λ is reached. j The slope at point is 0 or λ j =λ max When, let f = f(λ) j );

[0109] 6) Let j = 0, calculate the wavelength point λ of the ultrathin film B to be tested. j =λ min The corrected refractive index n at +j·Δλ B (λ j The formula is as follows;

[0110]

[0111] 7) Let j = j + 1, and repeat step 6) until λ. j =λ max ;

[0112] ④ Calculate the extinction coefficient of the ultrathin film B to be tested:

[0113] a. Based on formulas (5), (6), (7), (8), and (13), calculate the wavelength point λ of the ultrathin film B to be tested when j = 0. j =λ min The extinction coefficient k at +j·Δλ is B (λ j );

[0114]

[0115] b. Let j = j + 1, and repeat step a until λ. j =λ max .

[0116] Figure 2 The figure shows the transmission spectrum curves of an optically transparent glass substrate and the sample under test in an embodiment of the method of the present invention. Figure 3 The figures shown are the refractive index and extinction coefficient curves obtained in the embodiments of the method of the present invention. It can be seen that the present invention overcomes the shortcomings of the prior art and provides a method for characterizing the optical constants of ultrathin optical films using a spectrophotometer. This method can characterize the optical constants of ultrathin films deposited on optically transparent glass substrates, and is applicable to both transparent ultrathin films and ultrathin films with weak absorption.

Claims

1. A method for characterizing the optical constants of an ultrathin optical thin film, characterized in that, The method comprises the following steps: Step 1. Test the transmission spectrum of the optically transparent glass substrate S under normal incidence condition by using a spectrophotometer, and calculate the refractive index n of the optically transparent glass substrate S at each wavelength λ S (λ j ) from λ min to λ max , with each wavelength point interval of Δλ. Step 2. Calculate the average refractive index n of the optically transparent glass substrate S at each wavelength point, and calculate the average refractive index n of the optically transparent glass substrate S at each wavelength point interval Δλ. Step 3. Calculate the average refractive index n of the optically transparent glass substrate S at each wavelength point interval Δλ, and calculate the average refractive index n of the optically transparent glass substrate S at each wavelength point interval Δλ. Step 4. Calculate the average refractive Step 2. Preparing a reference sample S by depositing a reference thin film A on said optically transparent glass substrate S A , the optical thickness d of the reference thin film A A is not less than Testing the reference sample S with a spectrophotometer A in transmission at normal incidence, and calculating the refractive index n of the reference thin film A at each wavelength A (λ j ) Step 3. Depositing the ultra-thin film B to be measured on the optically transparent glass substrate S to prepare a sample S to be measured B , the material of the ultra-thin film B to be measured is the same as that of the reference film A, and the thickness d of the ultra-thin film B to be measured is characterized B , testing the sample S to be measured by using a spectrophotometer B The transmission spectrum under normal incidence condition; assuming that the extinction coefficient k B (λ j ) of the ultra-thin film B to be measured at each wavelength is 0, calculating the refractive index n B (λ j ) of the ultra-thin film B to be measured at each wavelength; and correcting n A (λ j ) with n B (λ j ) to obtain the corrected refractive index n B (λ j ) of the ultra-thin film B to be measured at each wavelength; The specific steps are as follows: a. Depositing the ultra-thin optical film B to be measured on the optically transparent glass substrate S, testing the sample S to be measured with a spectrophotometer B Transmission spectrum under normal incidence, obtaining the sample S to be measured B The transmission T(λ) at each wavelength point λ between the minimum wavelength λ min and the maximum wavelength λ max is obtained SB ​ b. Characterizing the thickness d of the ultra-thin film B under test B ; c. Calculate the refractive index n of the ultra-thin film B to be tested at each wavelength B (λ j ), specifically as follows: 1) Let j = 0, calculate the ultrathin film B under test in λ j =λ min The refractive index n at the wavelength point +j·Δλ B (λ j The formula is as follows: In the formula, T B (λ j ) refers to the film surface transmittance of the ultra-thin film B to be measured, R B (λ j ) refers to the film surface reflectance of the ultra-thin film B to be measured, refers to a characteristic matrix, i refers to an imaginary unit; n0 refers to the refractive index of air; T S (λ j ) refers to the transmittance of the front surface of the optically transparent glass substrate S; 2) using any one of equations (6) to (11) to calculate the reference factor f(λ j ); n B (λ j )=f(λ j )·n A (λ j )+[1-f(λ j )]·n 水 (9) wherein n 水 n is the refractive index of water; 3) let j = j + 1, repeat steps 1) and 2) above until λ j = λ max ; connect all f(λ j ) into a curve; 4) Let j = 0, calculate the curve slope at the wavelength point λ j = λ min + j-Δλ; 5) let j = j + 1, repeat step 4) until the slope at the wavelength point λ j is 0 or λ j = λ max , let f = f(λ j ); 6) Let j = 0, calculate the wavelength point λ of the ultrathin film B to be tested. j =λ min The corrected refractive index n at +j·Δλ B (λ j The following formula is used according to the following rules: n B (λ j )=f·n A (λ j )+(1-f)·n 水 (15) The rule is: When the reference coefficient f(λ j ) is calculated in step 2) using formula (6), the refractive index n B (λ j ) is calculated using formula (12); when the reference coefficient f(λ j ) is calculated using formula (7, the refractive index n B (λ j ) is calculated using formula (13); when the reference coefficient f(λ j ) is calculated using formula (8), the refractive index n B (λ j ) is calculated using formula (14); when the reference coefficient f(λ j ) is calculated using formula (9), the refractive index n B (λ j ) is calculated using formula (15); when the reference coefficient f(λ j ) is calculated using formula (10), the refractive index n B (λ j ) is calculated using formula (16); when the reference coefficient f(λ j ) is calculated using formula (11), the refractive index n B (λ j ) is calculated using formula (17). 7) Let j = j + 1, repeat step 6) until λ j = λ max ; Step 4. Calculate the extinction coefficient k of the ultra-thin film B to be tested B (λ j ).

2. The method of characterizing optical constants of an ultrathin optical film according to claim 1, wherein, Said step 1. uses a spectrophotometer to test the transmission spectrum of the optically transparent glass substrate S under normal incidence conditions, and calculates the refractive index n of the optically transparent glass substrate S at each wavelength S (λ j ), the wavelength being λ min ~ λ max , each wavelength point interval being Δλ, the specific steps being as follows: a. The transmission spectrum of an optically transparent glass substrate S under normal incidence conditions was measured using a spectrophotometer to obtain the minimum wavelength λ of the optically transparent glass substrate S. min up to the maximum wavelength λ max Transmittance T at each wavelength point λ 0S (λ), with the interval between each wavelength point being Δλ; b. The transmittance T of the front surface of the optically transparent glass substrate S at each wavelength point λ is obtained by eliminating the influence of the back surface of the optically transparent glass substrate S according to formula (18) S (λ); c. According to equation (19), the refractive index n j (λ S ) of the optically transparent glass substrate S at the wavelength point λ j + j- Δλ for j = 0 is calculated. min ​ d. Let j = j + 1, repeat step c until λ j = λ max .

3. The method of ultra-thin optical film optical constant characterization of claim 1, wherein, Step 2 involves depositing a reference thin film A on the optically transparent glass substrate S to prepare a reference sample S. A The optical thickness d of the reference thin film A A Not less than Using a spectrophotometer to test reference sample S A The transmission spectrum under normal incidence conditions is obtained, and the refractive index n of the reference thin film A at each wavelength is calculated. A (λ j The specific steps are as follows: a. ultrasonic cleaning of the optically transparent glass substrate S, deposition of a reference film A on the surface-cleaned optically transparent glass substrate S, optical thickness d of the reference film A A not less than b. The reference sample S is tested with a spectrophotometer A The transmission spectrum under normal incidence is obtained for the reference sample S A At each wavelength point λ between the minimum wavelength λ min and the maximum wavelength λ max The transmittance T SA (λ) is obtained The transmission maximum points and the transmission minimum points of the reference sample S A are connected to obtain two envelope lines, and the transmission maximum T min (λ) and the transmission minimum T max (λ) of each wavelength point λ between the minimum wavelength λ max and the maximum wavelength λ min are obtained. c. Calculate the refractive index n j (λ min ) of reference film A at the wavelength point λ A j-Δλ for j = 0 according to equation (20) j ; In the formula, In the formula, d. Let j = j + 1, repeat step c until λ j = λ max .

4. The method of ultra-thin optical film optical constant characterization of claim 1, wherein, The step 4. calculates the extinction coefficient k of the ultra-thin film B to be tested B (λ j ), and the specific steps are as follows: a. Let j = 0, calculate the extinction coefficient k(λ) of the ultra-thin film B to be tested at the wavelength point λ j = λ min + j-Δλ, the formula is as follows: B (λ j ) b. Let j = j + 1, repeat step a until λ j = λ max .

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