Method for measuring thickness and optical properties of multi-layer film

Abstract

A method for measuring a thickness and optical constants of a multi-layer film comprises the following steps: 1: depositing films on a substrate to form a multi-layer film; 2: measuring an ellipsometric spectrum of the multi-layer film; 3: when the film layer of the multi-layer film is the diamond film, step 41 is executed; when the film layer of the multi-layer film is the diamond-like film, steps 42, 5, and 6 are executed; 41: obtaining optical constants and a thickness of the film layer of the multi-layer film; 42: selecting a spectral region defining a transparent section of the film layer of the multi-layer film, and obtaining optical constants and a thickness of the film layer of the multi-layer film; 5: adjusting an amplitude and a width of an oscillator model according to the ellipsometric spectrum; and 6: evaluating a difference between an experimental value and a fitted value.

Claims

1. A method for measuring a thickness and optical properties of a multi-layer film, comprising: step 1: depositing films on a substrate to form a multi-layer film in sequence, wherein the films of the multi-layer film are classified into a diamond-like film and a diamond film; step 2: measuring an ellipsometric spectrum of the multi-layer film; step 3: judging whether each film layer of the multi-layer film is the diamond film or the diamond-like film; when the film layer of the multi-layer film is the diamond film, step 41 is executed; when the film layer of the multi-layer film is the diamond-like film, steps 42, 5, and 6 are executed; step 41: obtaining optical constants and a thickness of the film layer of the multi-layer film by calculating using Cauchy model in a full spectral region; step 42: selecting a spectral region defining a transparent section of the film layer of the multi-layer film, and obtaining optical constants and a thickness of the film layer of the multi-layer film by calculating using Cauchy model in the spectral region; step 5: adding an oscillator model for dielectric constants to an absorption spectrum region of the diamond-like film, and adjusting an amplitude and a width of the oscillator model according to the ellipsometric spectrum; and step 6: evaluating a difference between an experimental value and a fitted value by using an evaluation function mean squared error (MSE) to determine a structure of the multi-layer film and optical constants and a thickness of each film layer of the multi-layer film, wherein the optical constants comprise refractive index n and extinction coefficient k.

2. The method according to claim 1, wherein: in the step 42, a calculation formula of the Cauchy model is: $\begin{array}{cc}n=An+\frac{Bn}{{}^2}+\frac{Cn}{{}^4},& \left(1\right)\end{array}$
k()=A.sub.ke.sup.B.sup.k.sup.(EE.sup.b.sup.)(2), An, Bn, and Cn are parameters of the Cauchy model, is wavelength, the extinction coefficient k is described by three parameters A.sub.k, B.sub.k and E.sub.b, E.sub.b=1240/.sub.b, and E.sub.b relates to a material of the substrate.

3. The method according to claim 1, wherein: in the step 5, the oscillator model for the dielectric constants is a Lorentz oscillator, and a calculation formula of the Lorentz oscillator is: $\begin{array}{cc}n=\frac{A{E}_n}{E_n^2-E^2-iBrE},& \left(3\right)\end{array}$ A is an amplitude of parameters of the oscillator model, E.sub.n is a center position of the parameters of the oscillator model, and Br is a half wave width of the parameters of the oscillator model.

4. The method according to claim 1, wherein: in step 6, a calculation formula of the evaluation function MSE is: $\begin{array}{cc}{\mathrm{MSE}}^2=\frac{1}{2N-M}\underset{i=1}{\overset{n}{.Math.}}\left[{\left(\frac{{}_i^{mod}-{}_i^{\exp }}{{}_{,i}^{\exp }}\right)}^2+{\left(\frac{{}_i^{mod}-{}_i^{\exp }}{{}_{,i}^{\exp }}\right)}^2\right],& \left(4\right)\end{array}$ mod is a fitted value, exp is a measured value, is a measurement error, N is a total logarithm of and measured by an ellipsometer at a same time, and M is a logarithm of a selected fitted parameter.

5. The method according to claim 1, wherein: a bottom layer of the multi-layer film is a base, the base is the diamond-like film or the diamond film, a top layer of the multi-layer film is the diamond film, one or more layers between the bottom layer and the top layer are one or more intermediate layers, the one or more intermediate layers comprise the diamond-like film or a film with adjustable refractive index, and the film with the adjustable refractive index is different from the diamond film and the diamond-like film.

6. The method according to claim 1, wherein the multi-layer film comprises at least three layers.

7. The method according to claim 1, wherein: in the step 3, judging whether each film layer of the multi-layer film is the diamond film or the diamond-like film comprises judging whether the film layer of the multi-layer film is the diamond film or the diamond-like film according to characteristics of a material of the film layer of the multi-layer film.

8. The method according to claim 1, wherein the substrate is a diamond substrate, a Si substrate, or a Ge substrate.

9. The method according to claim 1, wherein the multi-layer film is an infrared window, a detector, or a protective film for glass.

10. The method according to claim 1, wherein: the measuring an ellipsometric spectrum of the multi-layer film comprises measuring the ellipsometric spectrum of the multi-layer film using a broad-spectrum ellipsometer, the broad-spectrum ellipsometer comprises a broad-spectrum light source, a collimating lens, a polarizer, a first compensator, a sample of the multi-layer film to be tested, a collimating lens group, a second compensator, an analyzer, and a detector, light emitted from the broad-spectrum light source irradiates the sample of the multi-layer film to be tested through the collimating lens, the polarizer, and the first compensator, and after the light is reflected, the light is transmitted to the detector through the collimating lens group, the second compensator, and the analyzer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a measurement method of an embodiment.

(2) FIG. 2 is a schematic view of a measurement system in the embodiment.

(3) FIG. 3 is a structural view of a multi-layer film measured in the embodiment.

REFERENCE NUMBERS IN THE DRAWINGS

(4) Broad-spectrum light source 11, collimating lens 12, polarizer 13, first compensator 14, a sample 15 of the multi-layer layer to be tested, collimating lens group 16, second compensator 17, analyzer 18, and detector 19.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) In order to explain the objective, the technical solution, and the features of the present disclosure, a method for measuring a thickness and optical properties of a multi-layer film will be further described below in combination with the accompanying embodiments and drawings.

(6) The method for measuring the thickness and the optical properties of the multi-layer film comprises: Step 1. Films are deposited on a substrate to form a multi-layer film in sequence, and films of the multi-layer film are classified into diamond-like films and diamond films. The substrate is a diamond substrate, a Si substrate (e.g., a Si glass), or a Ge substrate (e.g., a Ge glass), but other substrates can be selected as required. The multi-layer film has at least three layers, as shown in FIG. 3. A bottom layer of the multi-layer film is a base, and the base is a diamond-like film or a diamond film. A top layer of the multi-layer film is the diamond film and functions as a protective layer, and one or more layers between the bottom layer and the top layer are one or more intermediate layers. The one or more intermediate layers comprise a diamond-like film or a film with an adjustable refractive index, and the film with the adjustable refractive index is different from the diamond film and the diamond-like film; Step 2. Ellipsometric spectrum of the multi-layer film is measured; Step 3. Whether each film layer of the multi-layer film is the diamond film or the diamond-like film is judged according to characteristics of a material of the multi-layer film. When the film layer of the multi-layer film is the diamond film, step 41 is executed; when the film layer of the multi-layer film is the diamond-like film, steps 42, 5, and 6 are executed. Whether the film layer of the multi-layer film is the diamond film or the diamond-like film is judged to select an appropriate optical model, that is, the optical model is established. A composition (sp.sup.2, sp.sup.3, etc.) of the material of the diamond film or the diamond-like film is different, resulting in an absorption difference (one of the characteristics of the material). The film layer of the multi-layer film is judged by the absorption difference in combination with the ellipsometric spectrum; Step 41. Optical constants and a thickness of the film layer of the multi-layer film are determined by calculation using Cauchy model in a full spectral region; Step 42. A spectral region defining a transparent section of the film layer of the multi-layer film is selected, and the optical constants and the thickness of the film layer of the multi-layer film are calculated using Cauchy model in the spectral region; Step 5. An oscillator model for dielectric constants is added to an absorption spectrum region of the diamond-like film, and an amplitude and a width of the oscillator model is adjusted according to the ellipsometric spectrum; and Step 6. A difference between an experimental value and a fitted value is evaluated using an evaluation function mean squared error (MSE) to determine a structure of the multi-layer film and the optical constants and the thickness of each film layer of the multi-layer film.

(7) The optical constants comprise refractive index n and extinction coefficient k. A fitted effect is better when the evaluation function MSE is smaller.

(8) In Step 42, a calculation formula of the Cauchy model is as follows:

(9) $\begin{array}{cc}n=An+\frac{Bn}{{}^2}+\frac{Cn}{{}^4},& \left(1\right)\end{array}$
k()=A.sub.ke.sup.B.sup.k.sup.(EE.sup.b.sup.)(2),

(10) wherein An, Bn, and Cn are parameters of the Cauchy model, is wavelength, the extinction coefficient k is described by three parameters A.sub.k, B.sub.k, and E.sub.b, E.sub.b=1240/.sub.b, and E.sub.b relates to a material of the substrate.

(11) In Step 5, the oscillator model for the dielectric constants is the Lorentz oscillator, and a calculation formula of the Lorentz oscillator is as follows:

(12) $\begin{array}{cc}n=\frac{A{E}_n}{E_n^2-E^2-iBrE},& \left(3\right)\end{array}$
wherein A is an amplitude of parameters of the oscillator model, E.sub.n is a center position of the parameters of the oscillator model, and Br is a half wave width of the parameters of the oscillator model.

(13) In Step 6, a calculation formula of the evaluation function MSE is as follows:

(14) $\begin{array}{cc}{\mathrm{MSE}}^2=\frac{1}{2N-M}\underset{i=1}{\overset{n}{.Math.}}\left[{\left(\frac{{}_i^{mod}-{}_i^{\exp }}{{}_{,i}^{\exp }}\right)}^2+{\left(\frac{{}_i^{mod}-{}_i^{\exp }}{{}_{,i}^{\exp }}\right)}^2\right],& \left(4\right)\end{array}$
wherein mod is the fitted value, exp is a measured value, is a measurement error, N is a total logarithm of and measured by an ellipsometer at a same time, and M is a logarithm of a selected fitted parameter.

(15) The multi-layer film of the embodiment can be used as an infrared window, a detector, a protective film for glass, etc., and the refractive index of the multi-layer film can be adjusted to increase light transmittance as required.

(16) The ellipsometric spectrum of the multi-layer film is measured by a test system. Referring to FIG. 2, the test system comprises a broad-spectrum ellipsometer. The broad-spectrum ellipsometer comprises a broad-spectrum light source 11, a collimating lens 12, a polarizer 13, a first compensator 14, a sample 15 of the multi-layer film to be tested, a collimating lens group 16, a second compensator 17, an analyzer 18, and a detector 19. Light emitted from the broad-spectrum light source 11 irradiates the sample 15 of the multi-layer film to be tested through the collimating lens 12, the polarizer 13, and the first compensator 14. After the light is reflected, the light is transmitted to the detector 19 through the collimating lens group 16, the second compensator 17, and the analyzer 18. A spectral range of the broad-spectrum ellipsometer covers ultraviolet light, visible light, and near-infrared light.

(17) The aforementioned embodiments are merely some embodiments of the present disclosure, and the scope of the disclosure is not limited thereto. Thus, it is intended that the present disclosure cover any non-substantive modifications of the presently presented embodiments provided they are made without departing from the appended claims and the specification of the present disclosure by person skilled in the art.