Preparation method of multilayer film plane window reflector film system

Abstract

The invention provides a preparation method of a multilayer film plane window reflector film system, which adopts a vacuum evaporation method, the structure of the film system is G (Hf-SiO2) n (A), a reflecting film takes HfO2 as a high-refractive-index material and takes SiO2 as a low-refractive-index material, and the HfO2 layer is completed by evaporating Hf deposition in an oxygen-containing vacuum environment. According to the method disclosed by the invention, the TOLLING value parameters are captured for multiple times in stages in the coating process, so that the performance of the prepared plane window reflecting mirror can be remarkably improved, the plane window reflecting mirror is closer to a design value, and the method has important application in preparation of a high-performance beam splitting film.

Description

Technical Field

[0001] The present invention relates to the technical field of ultraviolet mirrors, and particularly to a method for preparing a film system of a planar window mirror. Background Art

[0002] The planar window mirror in the ultraviolet band is an optical element for reflecting ultraviolet light (wavelength range approximately 100 nm to 400 nm), and is widely used in fields such as lithography technology, space exploration, synchrotron radiation light sources, gas monitoring, etc.

[0003] Among them, the multi-layer film planar window mirror enhances the reflectivity of a specific wavelength by alternately stacking high-refractive-index and low-refractive-index materials as the reflective film and utilizing the interference effect.

[0004] To meet the requirements of high reflectivity in the deep ultraviolet and visible light, designing a high-performance reflective film needs to meet the following principles: (1) Select a material combination with a large difference in high and low refractive indices, reduce the number of deposited film layers, and reduce the preparation difficulty and production cost; (2) From the perspective of the spectral curve of the thin film, the film layer material should have extremely low absorption performance in the deep ultraviolet to ensure its reflectivity. SiO2 has a very small absorption coefficient at the working wavelength, grows in a uniform particulate form, the film layer structure is amorphous, and it has a high laser damage threshold, and is an ideal low-refractive-index material. Considering the possible high and low refractive index differences and the absorption problem in the deep ultraviolet, the available high-refractive-index materials are very limited. For example, Ta2O5, TiO2, Nb2O5, etc. are generally low-melting-point materials, and their absorption rate in the deep ultraviolet is relatively large, and the energy accumulation during laser irradiation has an obvious ablation effect on the thin film. High-refractive-index materials with low absorption in the deep ultraviolet, such as HfO2, Al2O3, CaF2, etc., often have a relatively low refractive index. To meet the high reflectivity requirements, there are problems such as a large number of required layers, difficult plating, long plating time, and easy curve deviation. Summary of the Invention

[0005] The present invention provides a method for preparing a film system of a multi-layer film planar window mirror to solve the problem of easy curve deviation when HfO2 is used as a high-refractive-index material in the prior art, and to achieve the stable production of a high-reflectivity multi-layer film planar window mirror film system.

[0006] In a first aspect, the present invention provides a method for preparing a film system of a multi-layer film planar window mirror. The preparation method uses a vacuum evaporation method, and the film system structure of the reflective film is G丨(HfO2-SiO2) n 丨A, where G is the substrate, A is the external medium, the reflective film is composed of HfO2 and SiO2 deposited in sequence, and is cycled n times. During the plating process of the reflective film, the TOLLING value is evenly grabbed x times to correct the plating process, where x is 2 to 4.

[0007] The TOLLING value is the ratio of the actual coating thickness to the designed thickness. This value can be used to correct for discrepancies between the actual and designed film thicknesses. The present invention has discovered that using the same process parameters from start to finish can alter the film material's refractive index or the tooling used during the coating process, leading to shifts in the spectral curve, either left or right, or in height, affecting the spectral yield. Therefore, the present invention improves upon the traditional "single parameter" approach by employing variable process parameters to adjust the material's refractive index, bringing the final reflector's refractive index closer to the designed value.

[0008] Preferably, in the above preparation method, x is 3.

[0009] Preferably, the number of layers n of the reflective film in the above preparation method is 80-160, preferably 100-140.

[0010] When there are more reflective film layers, the coating time increases significantly, the TOLLING value is more likely to change, and it is also more likely to cause the film coating to deviate from the design during the entire coating process.

[0011] Preferably, the TOLLING value capture in the above preparation method is carried out by using a refractive index comparison method, the steps of which are: coating a certain thickness of the film material on a glass substrate, measuring the residual reflectivity of the corresponding band, and determining the difference between the design value and the actual value by designing a comparison reflectivity curve, thereby determining the TOLLING value.

[0012] It takes a certain amount of time to capture the TOLLING value, so the more corrections the better. Multiple captures of TOLLING will also increase the entire plating time. The TOLLING value does not change much in a short period of time. It will only change after a long period of multi-layer plating.

[0013] Preferably, in the above preparation method, the thickness of the HfO2 layer is 150~200nm, and the thickness of the SiO2 layer is 150~200nm.

[0014] Preferably, the high refractive material layer in the above preparation method is deposited by evaporating Hf in an oxygen-containing vacuum environment, and the vacuum degree of the oxygen-containing vacuum environment is 2×10 -3 ~6×10 -4 Pa, oxygen supply volume is 80~100SCCM.

[0015] Preferably, the high-refractive material layer and the low-refractive material layer of the reflective film in the above preparation method are both formed by electron gun evaporation, and the deposition rate is controlled to be 0.6-0.8A / s when coating the high-refractive material layer, and the deposition rate is controlled to be 5-6A / s when coating the low-refractive material layer.

[0016] Since the Hf coating rate is very slow, the machine takes a long time to coat multi-layer films, usually more than 10 hours, while the vacuum system is constantly pumping vacuum. Excessive time will cause slight changes in the material's refractive index and TOOLING, thereby affecting the spectral curve.

[0017] Preferably, the deposition temperature of the reflective film during the coating process is 200-250°C, the substrate 1 is etched for 10-15 min using a Hall ion source before coating, and the vacuum degree is lower than 2×10 -3 Pa, keep constant temperature at 200~250℃ for 10-20 min.

[0018] Preferably, the above preparation method also includes the preparation of an antireflection film, which is located on the other side of the substrate. The preparation method is not particularly limited. For example, the preparation steps may be: using HFO2 and MGF2 as a combination of film materials, and maintaining the background vacuum degree below 2×10 -3 The film was formed by electron gun evaporation at a temperature of 250-280°C for 20-30 minutes. Each HFO2 film was deposited at a rate of 0.3-0.5 nm / s, with an oxygen supply of 10-20 sccm. The equipment used was a Cathay Pacific GTV-1350. The MGF2 film was deposited at a rate of 0.5-0.8 nm / s.

[0019] In a second aspect, the present invention provides a plane window reflector, which is prepared by the above-mentioned preparation method.

[0020] In a third aspect, the present invention provides an application of the above-mentioned preparation method in improving the preparation accuracy of a multilayer beam splitter film.

[0021] The above method can be used not only for the preparation of reflective films, but also for the preparation of other multilayer beam splitting films.

[0022] The present invention provides a method for fabricating a multilayer flat window reflector film system. By capturing the TOLLING parameters multiple times during the coating process, this method solves the problems of requiring many layers, long coating times, and easily deviated curves when fabricating high-refractive-index UV multilayer flat window reflectors using Hf as the high-refractive-index material. This method allows the resulting reflective parameters of the reflector to more closely approximate the designed values. In an embodiment of the present invention, the reflectivity at 40° is 98.264% and the transmittance is 0.563% at a wavelength of 260-450nm; the reflectivity at 45° is 98.029% and the transmittance is 0.543%; and the reflectivity at 50° is 97.557% and the transmittance is 0.505%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is the design value curve of the residual reflectivity of the antireflection film layer at 40° provided by the present invention.

[0025] Figure 2 This is the design value curve of the residual reflectivity of the antireflection film layer at 45° provided by the present invention.

[0026] Figure 3 This is the design value curve of the residual reflectivity of the antireflection film layer at 50° provided by the present invention.

[0027] Figure 4 This is the design value curve of the residual reflectivity of the multilayer reflective film layer at 40° provided by the present invention.

[0028] Figure 5 This is the design value curve of the residual reflectivity of the multilayer reflective film layer at 45° provided by the present invention.

[0029] Figure 6 This is the design value curve of the residual reflectivity of the multilayer reflective film layer at 50° provided by the present invention.

[0030] Figure 7 These are the measured results of the reflectivity of the reflector prepared by the present invention at 50°-40°, wherein pink to green represent the measured reflectivity at 50°-40°, respectively. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0032] Example 1 This embodiment provides a method for preparing a multilayer film flat window reflector, including the deposition of an antireflection film and a multilayer reflective film.

[0033] The film layer is coated using a Cathay vacuum coating machine, model GTV1350.

[0034] Anti-reflection coating deposition: The film system materials of the anti-reflection coating use HfO2 and MgF2 in combination. It is designed using the film system design software TFC, and its design curve is as shown in Figure 1 , Figure 2 , Figure 3 . It can be seen from the figure that the average values of the residual reflectance at three angles are 0.488%, 0.744%, and 1.218% respectively in terms of design. Before plating, the background vacuum degree is maintained below 2×10 -3 Pa, the deposition temperature is 250 - 280 °C, and it is kept at a constant temperature for 20 - 30 minutes. The film is formed by electron gun evaporation; when plating each HfO2 film layer, the deposition rate is controlled at 0.3 - 0.5 nm / s, and the oxygen filling amount is 10 - 20 SCCM. When plating the MgF2 film layer, the deposition rate is controlled at 0.5 - 0.8 nm / s.

[0035] Multi-layer reflective film system design: According to the film system indicators, the present invention designs a multi-material film system structure of G|HfO2-SiO2|A. The specific film system structure is as follows: 0.88(HL)^13, 0.77(HL)^13, 0.66(HL)^13, 0.56(HL)^11, 0.48(HL)^10. The central wavelength is 550 nm, where H is the high refractive index material metal HfO2, L is the low refractive index material SiO2, and (HL)^S is the classic high reflection film system. The reflective film system in the 260 - 450 nm band is made using the characteristics of the film materials metal HfO2 and SiO2. The film system designed by the original film stack cannot directly meet the requirements of the drawing and needs to be optimized using the film system design software TFC to obtain the design values. The optimized design curves are as shown in Figure 4 , Figure 5 , Figure 6 . They are the spectral curves at 40°, 45°, and 50° respectively. Through the software, the design values at 40° can be calculated: Ravg = 98.61%, Tavg = 1.39% @ 260 - 450 nm; the design values at 45°; Ravg = 98.21%, Tavg = 1.79% @ 260 - 450 nm; the design values at 50°: Ravg = 97.53%, Tavg = 2.47% @ 260 - 450 nm.

[0036] The plating method of the multi-layer reflective film is: First, use a Hall ion source to etch the substrate film layer for 10 - 15 minutes, and before plating, the background vacuum degree is maintained below 2×10 -3Pa, deposition temperature 200-250°C, constant temperature for 10-20 minutes to ensure the firmness of the base film layer during HfO2 vapor deposition. Film formation is achieved by electron gun evaporation. When depositing each HfO2 film layer, the deposition rate is controlled at 0.6-0.8A / s. When depositing the SiO2 film layer, the deposition rate is controlled at 5-6A / s. Simultaneously, optimization is performed using film system design software to obtain the design thickness of the reflective film. The actual thickness is obtained based on TOOLING information, as shown in Table 6. Due to the slow metal HF deposition rate, the machine takes a long time to deposit multiple layers. Since the vacuum system is constantly evacuating, excessive time can cause slight changes in the material's refractive index and TOOLING, thereby affecting the spectral curve. Therefore, the parameters of this 119-layer film system were captured in three stages. The TOLLING values of the three captures are shown in Tables 1, 2, and 3.

[0037] The partial correction results of the coating using the TOLLING value of the grab are shown in Table 4, where different colors represent different TOLLING value partitions, green for the first grab, blue for the second grab, and purple for the third grab.

[0038] The transmittance of the reflector after coating was measured at 40°-50° using the spectrophotometer Lambda1050+. The results are as follows: Figure 7 As shown, the pink to green curves are the measured reflectivity at 50°-40°, and the transmittance at 40°-50° is 40deg: Ravg=98.264%, Tavg=0.563%@260-450nm; 45deg; Ravg=98.029%, Tavg=0.543%@260-450nm; 50deg: Ravg=97.557%, Tavg=0.505%@260-450nm.

[0039] Compared with the design value, the transmittance deviations at 40°-50° are -0.35%, -0.18% and +0.03% respectively, all of which meet the requirements.

[0040] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that only one TOLLING grab is performed at the beginning of plating. The TOLLING value of the metal HF is 0.765, and the TOLLING value of SiO2 is 1.095.

[0041] The transmittance of the reflector after coating was measured at 40°~50°. 40deg: Ravg=97.983%, Tavg=0.735%@260-450nm; 45deg; Ravg=97.235%, Tavg=0.675%@260-450nm; 50deg: Ravg=96.669%, Tavg=0.603%@260-450nm.

[0042] Compared with the design value, the transmittance deviations at 40°-50° are -0.64%, -0.99% and -0.88% respectively.

[0043] It can be seen that when a process with a single parameter is used for film coating, the overall reflectivity will deviate significantly from the designed value.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method for a multilayer film planar window mirror film system, the film system structure of the reflective film being G丨(HfO2 - SiO2) n 丨A, characterized in that The preparation method adopts a vacuum evaporation method, and during the reflective film plating process, x TOLLING values are captured on average to correct the plating process, where x is 2-4.

2. The preparation method according to claim 1, characterized in that The x is 3.

3. The preparation method according to claim 2, characterized in that The number n of layers of the reflective film is 80-160, preferably 100-140.

4. The preparation method according to claim 3, characterized in that The TOLLING value is captured by using a refractive index comparison method, which includes the following steps: coating a certain thickness of the film material on a glass substrate, measuring the residual reflectivity of the corresponding band, and determining the difference between the design value and the actual value by designing a comparison reflectivity curve to determine the TOLLING value.

5. The preparation method according to claim 4, characterized in that The thickness of the HfO2 single layer is 150-200 nm, and the thickness of the SiO2 single layer is 150-200 nm.

6. The preparation method according to claim 5, characterized in that The high refractive material layer is deposited by evaporating Hf in an oxygen-containing vacuum environment, and the vacuum degree of the oxygen-containing vacuum environment is 2×10 -3 ~6×10 -4 Pa, oxygen supply volume is 80~100SCCM.

7. The preparation method according to claim 6, characterized in that The high-refractive material layer and the low-refractive material layer of the reflective film are both formed by electron gun evaporation. The deposition rate is controlled to be 0.6-0.8A / s when depositing the high-refractive material layer, and the deposition rate is controlled to be 5-6A / s when depositing the low-refractive material layer.

8. The preparation method according to claim 7, characterized in that The deposition temperature of the reflective film is 200~250℃. The substrate 1 is etched for 10~15 min using a Hall ion source before plating, and the vacuum degree is less than 2×10 -3 Pa, keep constant temperature at 200~250℃ for 10-20 min.

9. Plane window reflector, characterized in that, The flat window reflector is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the preparation method according to any one of claims 1 to 8 in improving the preparation accuracy of a multilayer beam splitter film.

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