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, it is found that the time of a coating system is extremely long, the actual thickness of a coating film deviates from the designed thickness due to the change of the vacuum degree in the coating process, TOLLING values need to be grabbed for multiple times through pre-coating, correction needs to be conducted according to the grabbed TOLLING values during formal coating, the performance of the manufactured plane window reflecting mirror can be remarkably improved through the method, and the production efficiency of the plane window reflecting mirror is improved. Therefore, the method has important application in the preparation of the high-performance beam splitting film.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet reflector technology, and in particular to a method for preparing a planar window reflector film system. Background Technology

[0002] Ultraviolet (UV) plane window mirrors are optical elements used to reflect UV light (wavelength range of approximately 100 nm to 400 nm) and are widely used in fields such as photolithography, space exploration, synchrotron radiation sources, and gas monitoring.

[0003] Among them, multilayer film planar window reflectors use alternating stacks of high-refractive-index and low-refractive-index materials as reflective films to enhance the reflectivity of specific wavelengths through interference effects.

[0004] To achieve the requirements of high reflectivity in deep ultraviolet and visible light, the design of high-performance reflective films must meet the following principles: (1) Select a combination of materials with a large difference between high and low refractive indices to reduce the number of coating layers, thereby reducing the difficulty of preparation and production costs; (2) From the perspective of the spectral curve of the thin film, the film material should have extremely low absorption performance in deep ultraviolet light to ensure its reflectivity. SiO2 has a very small absorption coefficient at the working wavelength, exhibits uniform particle growth, and has an amorphous film structure with a high laser damage threshold, making it an ideal low refractive index material. Considering the achievable difference between high and low refractive indices and the absorption problem in deep ultraviolet light, the high refractive index materials that can be selected are very limited. For example, Ta2O5, TiO2, and Nb2O5 are generally low melting point materials with relatively high absorption rates in deep ultraviolet light. During laser irradiation, the energy accumulation has a significant ablation effect on the thin film. Deep ultraviolet light uses high refractive index materials with low absorption rates, such as HfO2, Al2O3, and CaF2. However, their refractive indices are often low, and achieving high reflectivity requires multiple layers, is difficult to fabricate, takes a long time, and can easily cause the reflectivity curve to deviate. Summary of the Invention

[0005] This invention provides a method for preparing a multilayer planar window reflector system, which solves the problem that the curve is easily deviated when HfO2 is used as a high refractive index material in the prior art, and realizes the stable production of high reflectivity multilayer planar window reflector systems.

[0006] In a first aspect, the present invention provides a method for preparing a multilayer planar window reflective film system, wherein the reflective film system has a structure of G|(HfO2-SiO2). n |A, the preparation method adopts vacuum evaporation deposition. During the deposition of the reflective film, a predicted TOLLING value is used to correct the deposition process. The predicted TOLLING value is obtained by performing x captures on average according to the deposition thickness when the same technical parameters as the actual deposition process are used, where x is 2~4.

[0007] The tolling value is the ratio of the actual coating thickness to the designed thickness. This value can be used to correct the difference between the actual and designed film thickness. This invention reveals that if the same process parameters are used from start to finish, the refractive index of the film material or the tolling value will change, leading to left-right or high-low shifts in the spectral curve, affecting the pass rate. This shift may be mainly related to changes in vacuum level caused by continuous vacuum extraction. Therefore, this invention improves upon the traditional "one parameter throughout" approach by using variable process parameters to adjust the material's refractive index, making the final reflector's refractive index closer to the design value.

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

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

[0010] When there are more reflective film layers, the deposition time increases significantly, the tolling value is more likely to change, and the film deposition is more likely to deviate from the design throughout the deposition process.

[0011] Preferably, the TOLLING value is determined by the refractive index comparison method in the above preparation method. The steps are as follows: before the formal coating, a certain thickness of the film is pre-coated on the glass substrate, the residual reflectance of the corresponding band is measured, and the difference between the design value and the actual value is determined by designing a curve of the comparative reflectance, thereby determining the TOLLING value.

[0012] Preferably, the thickness of the HfO2 layer and the thickness of the SiO2 layer in the above preparation method are 150~200nm.

[0013] Preferably, the high-refractive-index material layer in the above preparation method is deposited by evaporation of Hf in an oxygen-containing vacuum environment, wherein the vacuum degree of the oxygen-containing vacuum environment is 2 × 10⁻⁶. -3 ~6×10 -4 Pa, oxygenation capacity is 80~100 SCCM.

[0014] Preferably, in the above preparation method, both the high-refractive-index material layer and the low-refractive-index material layer of the reflective film are formed by electron gun evaporation. When depositing the high-refractive-index material layer, the deposition rate is controlled to be 0.6-0.8 A / s, and when depositing the low-refractive-index material layer, the deposition rate is controlled to be 5-6 A / s.

[0015] Because the Hf deposition rate is very slow, the time required for the machine to deposit multilayer films is long, usually more than 10 hours. During this time, the vacuum system is constantly evacuating the vacuum. The excessive time will cause slight changes in the material's refractive index and tooling, which in turn will affect the spectral curve.

[0016] Preferably, in the above preparation method, the deposition temperature of the reflective film is 200~250℃, the substrate 1 is etched with a Hall ion source for 10~15 min before deposition, and the vacuum degree is below 2×10⁻⁶ before deposition. -3 Pa, constant temperature at 200~250℃ for 10-20 min.

[0017] Preferably, the above preparation method further includes the preparation of an antireflection membrane, which is located on the other side of the substrate. The preparation method is not particularly limited; for example, the preparation steps may include: using HFO2 and MGF2 as a combination of membrane materials, and maintaining a base vacuum level below 2 × 10⁻⁶ before deposition. -3 The deposition temperature was 250-280℃, held at that temperature for 20-30 minutes, and the film was formed by electron gun evaporation. When depositing each HFO2 film layer, the deposition rate was controlled at 0.3-0.5 nm / s, the oxygen charge was 10-20 SCCM, and the equipment used was a Guotai GTV-1350. When depositing the MGF2 film layer, the deposition rate was controlled at 0.5-0.8 nm / s.

[0018] Secondly, the present invention provides a planar window reflector, which is prepared by the above-described preparation method.

[0019] Thirdly, the present invention provides the application of the above-mentioned preparation method in improving the preparation accuracy of multilayer beam splitting films.

[0020] 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.

[0021] The method for fabricating a multilayer planar window reflector system provided by this invention solves the problems of numerous coating layers, long deposition time, and easy deviation of the deposition curve when using Hf as a high refractive index material to prepare a high refractive index ultraviolet multilayer planar window reflector. This is achieved by repeatedly capturing TOLLING parameters before the formal deposition process to correct the deposition. As a result, the final reflector parameters are closer to the design values. In the embodiments of this invention, at wavelengths of 260-450 nm, the reflectivity at 40° is 98.264%, and the transmittance is 0.563%; at 45°, the reflectivity is 98.029%, and the transmittance is 0.543%; and at 50°, the reflectivity is 97.557%, and the transmittance is 0.505%. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is the design value curve of the residual reflectance of the antireflection film layer at 40° provided by the present invention.

[0024] Figure 2 This is the design value curve of the residual reflectance of the antireflection film layer at 45° provided by the present invention.

[0025] Figure 3 This is the design value curve of the residual reflectance of the antireflection film layer at 50° provided by the present invention.

[0026] Figure 4 This is the design value curve of the residual reflectivity of the multilayer reflective film at 40° provided by the present invention.

[0027] Figure 5 This is the design value curve of the residual reflectivity of the multilayer reflective film at 45° provided by the present invention.

[0028] Figure 6 This is the design value curve of the residual reflectivity of the multilayer reflective film at 50° provided by the present invention.

[0029] Figure 7 These are the measured reflectance results of the reflector prepared by this invention at 50°-40°, where pink to green represent the measured reflectance at 50°-40° respectively. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] Example 1 This embodiment provides a method for preparing a multilayer planar window reflector, including the deposition of an antireflective coating and a multilayer reflective coating.

[0032] The film coating was applied using a Cathay vacuum coating machine, model GTV1350.

[0033] Antireflection Coating Fabrication: The antireflection coating material system uses HFO2 and MGF2 in combination, and is designed using the film system design software TFC. The design curve is shown below. Figure 1 , Figure 2 , Figure 3 As shown in the figure, the average residual reflectivity at the three angles is 0.488%, 0.744%, and 1.218%, respectively, in terms of design. The base vacuum level is maintained below 2 × 10⁻⁶ before plating. -3 The deposition temperature is 250-280℃, held at this temperature for 20-30 minutes, and the film is formed by electron gun evaporation. When depositing each HFO2 film, the deposition rate is controlled at 0.3-0.5 nm / s, and the oxygen content is 10-20 SCCM. When depositing the MGF2 film, the deposition rate is controlled at 0.5-0.8 nm / s.

[0034] Multilayer Reflective Film System Design: Based on the film system specifications, this invention designs a G|HfO2-SiO2|A multi-material film system structure, specifically as follows: 0.88(HL)^13, 0.77(HL)^13, 0.66(HL)^13, 0.56(HL)^11, 0.48(HL)^10. The center wavelength is 550nm, where H is the high-refractive-index material HfO2, L is the low-refractive-index material SiO2, and (HL)^S represents the classic high-reflectivity film system. The reflective film system in the 260-450nm wavelength band is created by utilizing the characteristics of the HfO2 and SiO2 materials. The original film stack design cannot directly meet the requirements of the drawings; it needs to be optimized using the film system design software TFC to obtain the design values. The optimized design curve is shown below. Figure 4 , Figure 5 , Figure 6 The figures show the spectral curves at 40°, 45°, and 50°, respectively. The design values ​​at 40° can be calculated using software: Ravg=98.61%, Tavg=1.39%@260-450nm; at 45°: Ravg=98.21%, Tavg=1.79%@260-450nm; and at 50°: Ravg=97.53%, Tavg=2.47%@260-450nm.

[0035] The deposition method for the multilayer reflective film is as follows: first, the base film layer is etched using a Hall ion source for 10-15 minutes, and the base vacuum level is maintained below 2×10⁻⁶ before deposition. -3 Pa, deposition temperature 200-250℃, held at this temperature for 10-20 minutes to ensure the adhesion of the substrate film during HfO2 evaporation. Film formation is achieved via electron gun evaporation. For each HfO2 film, the deposition rate is controlled at 0.6-0.8 A / s. For SiO2 film deposition, the deposition rate is controlled at 5-6 A / s.

[0036] TOLLING value pre-capture: The coating is carried out according to the above multilayer reflective film system design and method. After the coating is completed, the reflectivity of the coated multilayer reflective film is tested by a spectrophotometer. The reflectivity is analyzed by the film system design software to obtain the actual film thickness. The TOLLING value of the two film materials at each stage is compared with the design thickness. The TOLLING values ​​of the three stages are shown in Tables 1, 2 and 3.

[0037] Actual production coating: The design thickness of the reflective film was obtained through optimization using film system design software. The actual thickness was calculated based on the previously captured TOOLING values, as shown in Table 4. Due to the slow coating rate of HF metal, the coating time for multiple layers was long. Because the vacuum system was constantly evacuating, the excessive time would cause slight changes in the material's refractive index and TOOLING, thus affecting the spectral curve. Therefore, the parameters of this 119-layer film system were captured in three stages. The TOOLING values ​​from the three captures are shown in Tables 1, 2, and 3.

[0038] The partial correction results of the coating using the captured TOLLING value are shown in Table 4. Different green colors represent different TOLLING value zones, with green being the first capture, blue the second capture, and purple the third capture.

[0039] The transmittance of the coated mirror was measured at 40°-50° using a Lambda 1050+ spectrophotometer. The results are as follows: Figure 7 As shown, the pink to green curves represent the measured reflectance 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.

[0040] 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.

[0041] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that only one tolling grab was performed at the beginning of the plating process, with a tolling value of 0.765 for metal HF and a tolling value of 1.095 for SiO2.

[0042] The transmittance of the coated mirror was measured at an angle of 40° to 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.

[0043] Compared with the design value, the transmittance deviations at 40°-50° are -0.64%, -0.99% and -0.88%, respectively.

[0044] It can be seen that using a single parameter for film deposition will result in a significant deviation in overall reflectivity from the design value.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a multilayer planar window reflective film system, wherein the reflective film system has a structure of G|(HfO2-SiO2). n |A, characterized in that, The preparation method adopts vacuum evaporation deposition. During the deposition of the reflective film, a predicted TOLLING value is used to correct the deposition process. The predicted TOLLING value is obtained by performing x captures on average according to the deposition thickness when the same technical parameters as the actual deposition process are used, where x is 2~4.

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

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

4. The preparation method according to claim 3, characterized in that, The TOLLING value is determined using the refractive index comparison method. The steps are as follows: before the formal coating, a certain thickness of the film is pre-coated on the glass substrate, the residual reflectance of the corresponding band is measured, and the difference between the design value and the actual value is determined by designing a curve to compare the reflectance, thereby determining the TOLLING value.

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

6. The preparation method according to claim 5, characterized in that, The high-refractive-index material layer was deposited by evaporating Hf in an oxygen-containing vacuum environment with a vacuum level of 2 × 10⁻⁶. -3 ~6×10 -4 Pa, oxygenation capacity is 80~100 SCCM.

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

8. The preparation method according to claim 7, characterized in that, The deposition temperature for the reflective film is 200~250℃. Before deposition, the substrate 1 is etched with a Hall ion source for 10~15 min, and the vacuum level is below 2×10⁻⁶ before deposition. -3 Pa, constant temperature at 200~250℃ for 10-20 min.

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

10. The application of the preparation method according to any one of claims 1-8 in improving the preparation accuracy of multilayer beam splitting films.

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