Anti-reflection film based on nano-laminated film material and design method thereof

Abstract

An anti-reflection film based on a nano-laminated thin film material and a design method thereof, comprising the following steps: obtaining a function of the refractive index of material A and material B, as well as the film thickness and wavelength; correcting the refractive index and thickness of each layer of the anti-reflection film based on a model of the interface layer between the two material sublayers in the nano-laminated thin film material; using the corrected refractive index and thickness to design the film structure, and then preparing and testing the film. The present invention utilizes a model of the gradient refractive index interface layer between the two material sublayers in the nano-laminated thin film material to design the film system, effectively reducing the error between experimental and theoretical spectra and improving the spectral performance of the anti-reflection film. This method is also applicable to the design of other films whose spectral performance is sensitive to the material's refractive index and thickness.

Description

Technical Field

[0001] The invention relates to a design method for an anti-reflection film, in particular to an anti-reflection film based on a nano-laminated film material and a design method thereof. Background Art

[0002] Nano-laminated thin film materials are thin film materials formed by alternating deposition of two sub-layer materials with thicknesses ranging from a few nanometers to tens of nanometers. Nano-laminated thin film materials have the advantage that the refractive index and optical band gap can be arbitrarily tuned within a certain range, and are suitable for a variety of thin film deposition technologies such as atomic layer deposition, electron beam evaporation, ion beam sputtering, and magnetron sputtering. They provide great flexibility in the design and preparation of optical thin films and are widely used in the design and preparation of various types of thin films such as anti-reflection and high-reflection. However, when the thickness of the sub-layer material in the nano-laminated thin film material is thin, its refractive index varies greatly with thickness; in addition, the diffusion between the two sub-layer materials will also affect the refractive index and thickness of the sub-layer material. The above two factors will cause the spectral performance of the actual prepared film to deviate from the designed spectral performance, especially for thin film structures whose spectral performance is sensitive to the refractive index and thickness of the material. The deviation between the prepared and designed spectral performance is even greater, and may even cause the spectral performance of the actual preparation to fail to meet the index requirements. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the above-mentioned existing technologies and provide an anti-reflection film based on a nano-laminated thin film material and a design method thereof. The method introduces a gradient refractive index interface layer model between two material sub-layers in the nano-laminated thin film material, effectively reducing the error between the experimental spectrum and the theoretical spectrum, and improving the optical performance of the anti-reflection film; the method is applicable to the design of other films whose spectral performance is sensitive to the refractive index and thickness of the material.

[0004] The technical solutions of the present invention are as follows:

[0005] In one aspect, the present invention provides an anti-reflection film based on a nano-laminated thin film material, characterized in that the anti-reflection film is obtained by randomly alternating deposition of a single-layer thin film of material A, a single-layer thin film of material B, and a nano-laminated thin film material C formed by alternating sub-layers of material A and material B;

[0006] The thickness of the sublayer of material A in the nano-laminated film material C is d A , the refractive index at wavelength λ is n A (λ); the thickness of the sublayer of material B in the nano-laminated film material C is d B , the refractive index at wavelength λ is n B (λ); the thickness of the interface diffusion layer between the material A sublayer and the material B sublayer is d I , the nano-laminated thin film material C satisfies the following interface layer model conditions:

[0007] When d A <d I , then n M (λ)=ρ M ×n B (λ)+(1-ρ M )×n A (λ), where n M (λ) is the refractive index at the middle point M of the diffusion layer, ρ M is the proportion of material B at the middle point M of the diffusion layer, The refractive index n of the interface diffusion layer I (λ) takes the middle point M of the diffusion layer as the extreme point in n M (λ) and n B (λ) linear gradient;

[0008] When d A >d I and d B >d I , the refractive index of the interface diffusion layer n I (λ) in n A (λ) and n B (λ) linear gradient;

[0009] When d B <d I , then n M (λ)=ρ M ×n B (λ)+(1-ρ M )×n A (λ), Refractive index of the interface diffusion layer n I (λ) takes the middle point M of the diffusion layer as the extreme point in n M (λ) and n A (λ) linear gradient.

[0010] On the other hand, the present invention also provides a method for designing an anti-reflection film based on a nano-laminated thin film material, which is characterized in that the design method comprises the following steps:

[0011] Step 1: Obtain the refractive index of material A and material B as a function of film thickness and wavelength n A (d A ,λ),n B (d B ,λ);

[0012] a) preparing a group N1 of monolayer thin films of material A with different thicknesses and a group N2 of monolayer thin films of material B with different thicknesses, with thicknesses ranging from 0 to 20 nm; N1 ≥ 4, N2 ≥ 4;

[0013] b) Transmission electron microscopy was used to characterize the thickness d of the single-layer thin films of material A and material B. A and d B , perform ellipsometric fitting or transmission spectrum fitting on the single-layer film to obtain the function n of the refractive index of material A and material B and the film thickness A (d A ,λ),n B (d B ,λ);

[0014] Step 2: Obtain the thickness d of the interface diffusion layer in the nano-laminated film material C I The thickness d of the sub-layer of material A A and the thickness of the material B sublayer film d B relationship;

[0015] a) preparing group N3 of nanolaminated thin film material C formed by alternating deposition of material A and material B sublayers with different thickness ratios, with a constant periodic thickness ranging from 15 to 40 nm; N3 ≥ 4;

[0016] b) Transmission electron microscopy was used to characterize the thickness d of the material A sublayer and the material B sublayer in the nano-laminated film material C. A and d B The thickness d of the interface diffusion layer between the material A sublayer and the material B sublayer in the nano-laminated film material C was obtained by using an energy spectrometer. I , obtain the thickness of the interface diffusion layer d I The relationship with the thickness of the sublayer.

[0017] Step 3: Use the interface layer model to correct the refraction and thickness of each layer in the anti-reflection film, perform film structure design, and carry out film preparation and testing.

[0018] Furthermore, material A includes but is not limited to HfO2 or Ta2O5, and material B includes but is not limited to SiO2 or Al2O3.

[0019] Furthermore, the preparation adopts one of electron beam evaporation deposition, atomic layer deposition or sputtering deposition.

[0020] Furthermore, the film structure of the nano-laminated material C is Sub / (BA) m / Air, m≥4, Sub is the substrate, and Air is air.

[0021] Technical effects of the present invention:

[0022] 1. The method of the present invention introduces a model of a gradient refractive index interface layer between two material sub-layers in a nano-laminated thin film material, which can effectively reduce the error between the experimental spectrum and the theoretical spectrum and improve the spectral performance of the anti-reflection film.

[0023] 2. The method of the present invention is applicable to the design of other thin films whose spectral properties are sensitive to the refractive index and thickness of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 .Refractive index curves of HfO2 material (left) and SiO2 material (right) in Example 1 of the present invention.

[0025] Figure 2 .The relationship between the refractive index of HfO2 material (left) and SiO2 material (right) at 510nm and the film thickness and the fitting curve in Example 1 of the present invention.

[0026] Figure 3 . Schematic diagram of the refractive index profile at a wavelength of 510nm obtained based on the interface layer model of the SiO2 / HfO2 nano-laminated film in Example 1 of the present invention.

[0027] Figure 4 .The measured spectrum and designed spectrum of the anti-reflection film in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] Example 1:

[0029] Taking materials HfO2 and SiO2 as an example, under normal incidence conditions, the reference wavelength is 510nm, and the average reflectivity in the wavelength range of 500nm to 900nm is set as the goal to be less than 1%. The present invention describes the anti-reflection film based on nano-laminated thin film materials and its design method. The specific steps are as follows.

[0030] Step 1. Using atomic layer deposition (ALD), four groups of HfO2 monolayer films with different thicknesses, six groups of SiO2 monolayer films with different thicknesses, and nine groups of SiO2 / HfO2 nanolaminated films with different sublayer thickness ratios were deposited on silicon substrates with a diameter of 25.4 mm and fused silica substrates with a diameter of 30 mm. The film structure was Sub / (SiO2 / HfO2). 4 / Air, Sub base, Air is air.

[0031] Step 2. Use transmission electron microscopy to characterize the actual thickness of 4 groups of HfO2 monolayer films and 6 groups of SiO2 monolayer films prepared on silicon substrates and The transmission spectrum of the sample prepared on the fused silica substrate was measured using a spectrophotometer, and the refractive index was calculated; the refractive index function of HfO2 material and SiO2 material was obtained. like Figure 1 . Figure 2 The relationship between the refractive index of HfO2 and SiO2 materials and the actual film thickness at a wavelength of 510nm and the fitting curve are given. Figure 1 and Figure 2It can be seen that the refractive index of the HfO2 material is greatly affected by the film thickness; the refractive index of the SiO2 material is less affected by the film thickness. In this embodiment, the refractive index of the SiO2 material at a wavelength of 510 nm is set to a constant of 1.455.

[0032] Step 3. Use an energy spectrometer to characterize the thickness of the interface diffusion layer in the SiO2 / HfO2 nano-laminated film, as shown in Table 1. It can be seen that when the thickness of the sub-layers is relatively thick, the thickness of the interface diffusion layer tends to be stable.

[0033] Table 1. Sublayer thickness and interface diffusion in nanolaminated thin film materials

[0034]

[0035] The gradient refractive index interface layer model is established at a reference wavelength of 510 nm as follows:

[0036] (1) Thickness of HfO2 sublayer in samples 1 and 2 Less than the thickness of the interface diffusion layer d I , the refractive index n of the middle point M of the diffusion layer M Calculated by formulas (1) and (2), they are 1.572 and 1.643 respectively. The refractive index of the HfO2 sublayer and the SiO2 sublayer and According to step 2, the refractive index of the HfO2 sublayer in samples 1 and 2 is 1.734 and 1.759, respectively, and the refractive index of the SiO2 sublayer is 1.455.

[0037]

[0038]

[0039] Among them, ρ M is the proportion of material SiO2 at the middle point M of the diffusion layer.

[0040] (2) Thickness of HfO2 sublayer and SiO2 sublayer in samples 3-6 and are both greater than the thickness of the interface diffusion layer d I , the refractive index of the HfO2 sublayer and the SiO2 sublayer and All are obtained according to step 2, as shown in the following table.

[0041] Table 2. Refractive index of HfO2 sublayer and SiO2 sublayer in samples 3-6

[0042]

[0043] (3) SiO2 sublayer thickness in samples 7-9 Less than the thickness of the interface diffusion layer dI , the refractive index n of the middle point M of the diffusion layer M Calculated by formulas (3) and (4), they are 1.467, 1.575 and 1.648 respectively. The refractive index of HfO2 sublayer and SiO2 sublayer and According to step 2, the refractive index of the HfO2 sublayer in samples 7-9 is 1.845, 1.856 and 1.866, respectively, and the refractive index of the SiO2 sublayer is 1.455.

[0044]

[0045]

[0046] Among them, ρ M is the proportion of material SiO2 at the middle point M of the diffusion layer.

[0047] Figure 3 Schematic diagram of the refractive index profile at a wavelength of 510 nm obtained according to the above model.

[0048] Step 4. Design an anti-reflection film based on nano-laminated thin film material with a reference wavelength of 510nm. The film structure is Sub / M1LM2HL / Air, where Sub is the substrate, Air is air, and M1 represents the structure (L N1 H N1 ) 4 Nano-laminated, M2 represents the structure (L N2 H N2 ) 4 of nano-laminated layers.

[0049] Based on the preliminary design of the film thickness, the interface layer thickness was determined to be 6 nm according to step 3. First, the thickness of each layer in the anti-reflection film was corrected, and then the refractive index of each layer was corrected based on the corrected film thickness. Specific design information is shown in Table 2.

[0050] Table 2 Refractive index and thickness information of each layer of the anti-reflection film in the embodiment

[0051]

[0052] Step 5. Prepare the designed anti-reflection film on a K9 substrate with a diameter of 30 mm using atomic layer deposition technology.

[0053] The prepared anti-reflection film was subjected to a spectrum test using a spectrophotometer. The measured average reflectivity within the wavelength range of 500 nm to 900 nm was 0.61%. Figure 4 The figure shows a comparison of the measured spectrum with the traditional design spectrum and the corrected design spectrum. It can be seen that after the refractive index and thickness corrections, the error between the measured spectrum and the design spectrum is significantly reduced.

[0054] Other embodiments:

[0055] Example Material A Material B Material C Average reflectivity from 500nm to 900nm 2 <![CDATA[HfO2]]> <![CDATA[Al2O3]]> <![CDATA[HfO2 / Al2O3 nano-laminate]]> ≤1％ 3 <![CDATA[Ta2O5]]> <![CDATA[SiO2]]> <![CDATA[Ta2O5 / SiO2 nano - laminated layers]]> ≤2％ 4 <![CDATA[Ta2O5]]> <![CDATA[Al2O3]]> <![CDATA[Ta2O5 / Al2O3 nano-laminate]]> ≤2％

Claims

1. An anti-reflection film based on a nano-laminated thin film material, characterized in that: The anti-reflection film is obtained by randomly and alternately depositing a single-layer film of material A, a single-layer film of material B, and a nano-laminated film material C formed by alternating sub-layers of material A and material B; The thickness of the sublayer of material A in the nano-laminated film material C is d A , the refractive index at wavelength λ is n A (λ); the thickness of the sublayer of material B in the nano-laminated film material C is d B , the refractive index at wavelength λ is n B (λ); the thickness of the interface diffusion layer between the material A sublayer and the material B sublayer is d I , the nano-laminated thin film material C satisfies the following interface layer model conditions: When d A <d I , then n M (λ)=ρ M ×n B (λ)+(1-ρ M )×n A (λ), where n M (λ) is the refractive index at the middle point M of the diffusion layer, ρ M is the proportion of material B at the middle point M of the diffusion layer, The refractive index n of the interface diffusion layer I (λ) takes the middle point M of the diffusion layer as the extreme point in n M (λ) and n B (λ) linear gradient; When d A >d I and d B >d I , the refractive index of the interface diffusion layer n I (λ) in n A (λ) and n B (λ) linear gradient; When d B <d I , then n M (λ)=ρ M ×n B (λ)+(1-ρ M )×n A (λ), Refractive index of the interface diffusion layer n I (λ) takes the middle point M of the diffusion layer as the extreme point in n M (λ) and n A (λ) linear gradient.

2. A method for designing an anti-reflection film based on a nano-laminated thin film material, for designing the anti-reflection film based on a nano-laminated thin film material according to claim 1, characterized in that: The design method comprises the following steps: Step 1: Obtain the refractive index of material A and material B as a function of film thickness and wavelength n A (d A ,λ),n B (d B ,λ); a) preparing a group N1 of monolayer thin films of material A with different thicknesses and a group N2 of monolayer thin films of material B with different thicknesses, with thicknesses ranging from 0 to 20 nm; N1 ≥ 4, N2 ≥ 4; b) Transmission electron microscopy was used to characterize the thickness d of the single-layer thin films of material A and material B. A and d B , perform ellipsometric fitting or transmission spectrum fitting on the single-layer film to obtain the function n of the refractive index of material A and material B and the film thickness A (d A ,λ),n B (d B ,λ); Step 2: Obtain the thickness d of the interface diffusion layer in the nano-laminated film material C I The thickness d of the sub-layer of material A A and the thickness of the material B sublayer film d B relationship; a) preparing group N3 of nanolaminated thin film material C formed by alternating deposition of material A and material B sublayers with different thickness ratios, with a constant periodic thickness ranging from 15 to 40 nm; N3 ≥ 4; b) Transmission electron microscopy was used to characterize the thickness d of the material A sublayer and the material B sublayer in the nano-laminated film material C. A and d B The thickness d of the interface diffusion layer between the material A sublayer and the material B sublayer in the nano-laminated film material C was obtained by using an energy spectrometer. I , obtain the thickness of the interface diffusion layer d I Relationship with sublayer thickness; Step 3: Use the interface layer model to correct the refraction and thickness of each layer in the anti-reflection film, perform film structure design, and carry out film preparation and testing.

3. The method for designing an anti-reflection film based on nano-laminated thin film materials according to claim 2, characterized in that: Material A includes but is not limited to HfO2 or Ta2O5, and material B includes but is not limited to SiO2 or Al2O3.

4. The method for designing an anti-reflection film based on nano-laminated thin film materials according to claim 2, characterized in that: In the step 1, the preparation is carried out by electron beam evaporation deposition, atomic layer deposition or sputtering deposition.

5. The method for designing an anti-reflection film based on nano-laminated thin film materials according to claim 2, characterized in that: In the step 1, the film structure of the nano-laminated material C is Sub / (BA) m / Air, m≥4, Sub is the substrate, and Air is air.

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