Large-size wide-spectrum infrared color separation film with controllable surface precision and manufacturing method of large-size wide-spectrum infrared color separation film

Abstract

The invention relates to a large-size wide-spectrum infrared color separation film with controllable surface precision and a manufacturing method thereof, the color separation film takes a silicon plain film as a substrate, a color separation film is designed on a light incident surface of the silicon substrate, germanium and zinc sulfide are used as high and low refractive index materials of a reflecting film stack, ytterbium fluoride is added in a matching layer, the film thickness ratio is regulated and controlled, and a thin film deposition process is optimized. The surface type change caused by the film layer is reduced; a thickness compensation film layer is added when the antireflection film is designed on the light transmission surface of the silicon substrate, so that the stress of the antireflection film and the stress of the color separation film are mutually counteracted, and the surface type is controlled. Appropriate substrate temperature, deposition rate and local film layer ion auxiliary deposition are adopted in the preparation of the color separation film, and the environmental reliability is good. The prepared large-size color separation sheet is controllable in surface type, the surface type precision RMS of the color separation surface is 0.028 lambda, the surface type precision RMS of the anti-reflection surface is 0.042 lambda, the large-size color separation sheet can highly reflect a broadband of 2-3.95 microns and highly transmit a broadband of 4.2-5.1 microns, and the large-size color separation sheet can be used for spectrum color separation of a large-view-field infrared optical system.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, and specifically to a large-size broadband infrared color filter with controllable surface shape precision and its fabrication method. Background Technology

[0002] Wide field-of-view infrared cameras (WFRs) offer broad field-of-view coverage and all-weather operation, finding wide applications in space remote sensing and Earth observation, security and search and rescue, astronomical and scientific research. These applications include tracking forest fires, volcanic activity, urban heat island effects, analyzing the atmospheric composition of exoplanets, capturing faint celestial bodies, and distinguishing asteroids. One of the core components of a WFR is a large-size broadband infrared dichroic film. Besides ensuring optical transmission efficiency meets system imaging requirements, the surface accuracy of the dichroic film directly impacts the imaging quality of the optical system.

[0003] For large-size broadband infrared dichroic films, to meet the bandwidth requirements of the reflection band, two or even more reflective film stacks are needed in the dichroic film. The high- and low-refractive-index materials used typically number in the dozens. Stress mismatch between the film layers can cause significant surface shape changes, leading to wavefront distortion during transmission, reducing the modulation transfer function (MTF), and ultimately severely impacting the system's detection performance. Therefore, surface shape control during thin film deposition is a key technology in the manufacturing of large-size dichroic films, requiring solutions to problems such as film stress introduced after depositing dozens of thin films, thermal effects on the substrate and film layers, and the uniformity of stress distribution on large-size substrates. To meet the spectral requirements of large-size broadband dichroic films while simultaneously achieving precise control over the dichroic film surface shape, these problems need to be addressed through new film system design and optimized manufacturing processes. Summary of the Invention

[0004] The purpose of this invention is to provide a large-size broadband infrared color separator with controllable surface shape accuracy and its manufacturing method. It addresses the problems that need to be solved in large-size broadband infrared color separators by performing spectral modulation on the 2-5.1μm short-wave infrared to mid-wave infrared spectrum and achieving surface shape accuracy control to meet the spectral color separation requirements of large field-of-view infrared systems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A large-size broadband infrared dichroic film with controllable surface shape precision includes a silicon substrate, a dichroic film disposed on the light incident surface of the silicon substrate, and an anti-reflection film disposed on the light transmission surface of the silicon substrate. The dichroic film has two reflective film stacks, and matching layers are disposed on the upper and lower surfaces of the reflective film stacks. The front matching layer is disposed on the lower surface of the reflective film stack facing the silicon substrate, and the rear matching layer is disposed on the upper surface of the reflective film stack facing the air.

[0007] The reflective film stack of the dichroic film is composed of alternating layers of germanium and zinc sulfide; ytterbium fluoride is added to the matching layer;

[0008] The antireflective coating includes a thickness compensation layer and an antireflective coating layer sequentially disposed on the light transmission surface of a silicon substrate; the thicknesses of the germanium film layer and the zinc sulfide film layer in the thickness compensation layer are periodically superimposed.

[0009] The color separation film is S0 / 1.259M 0.387H (0.81H 1.69M 0.81H). 7 (0.55H 1.16M 0.55H) 6 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M / air, of which (0.81H 1.69M 0.81H) 7 (0.55H 1.16M 0.55H) 6 For the reflective film stack, 1.259M 0.387H is the front matching layer, and 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M is the rear matching layer;

[0010] S0 represents the silicon substrate, M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integers 6 and 7 are the number of cycles of the two reflective film stacks, and the values ​​before M, H and L are the film layer scaling factors.

[0011] The antireflective coating is S0 / (0.71H 0.87M 0.65H). 7 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M / air, of which (0.71H 0.87M 0.65H) 7 For thickness compensation film, 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M is for antireflection film;

[0012] S0 represents the silicon substrate, M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integer 7 is the number of cycles of the thickness compensation film, and the values ​​before M, H and L are the film scaling factors.

[0013] The specific steps of the aforementioned method for fabricating large-size broadband infrared color filters with controllable surface shape accuracy are as follows:

[0014] Step 1: Heat and maintain the temperature of the silicon substrate in a box-type vacuum coating equipment with a molecular pump system. The heating process adopts a step-by-step heating method. The silicon substrate is kept at the coating temperature for 2 to 3 hours. The temperature of the silicon substrate is selected from 170℃ to 190℃.

[0015] Step 2: Before depositing the thin film, the silicon substrate is bombarded with an ion beam using a Hall ion source; the anode voltage is 150V and the anode current is 4A.

[0016] Step 3: Electron beam evaporation is used to deposit germanium and ytterbium fluoride, and resistance heating is used to deposit zinc sulfide.

[0017] In step one, the temperature of the silicon substrate is set to 180℃.

[0018] The step-by-step heating method in step one is to heat the silicon substrate from room temperature to 100°C, hold it at that temperature for 0.5 hours, then continue heating it to 130°C, hold it at that temperature for 0.5 hours, and finally heat it to 180°C, hold it at that temperature for 2 hours.

[0019] In step three, the zinc sulfide deposition rate is 2.8–3.5 nm / s.

[0020] The advantages of this invention are as follows: 1. The dichroic film adopts the structure of a long-pass filter. Based on the optical and stress characteristics of germanium, zinc sulfide, and ytterbium fluoride, different reflective film stacks are formed by alternating superposition of germanium and zinc sulfide. Matching layers are set on the upper and lower surfaces of the reflective film stacks, and ytterbium fluoride is added to the matching layers. By optimizing the matching layers and controlling the thickness ratio, the transmittance of the transmission channel is improved while minimizing the surface shape changes caused by the dichroic film. 2. During the baking of large-size silicon substrates, the temperature is gradually increased through a stepped heating process to ensure uniform heating of the substrate and prevent significant surface shape changes before film deposition. 3. Based on the surface shape changes caused by the dichroic film, a thickness compensation film layer is added when designing the antireflective film on the light transmission surface of the silicon substrate. The local antireflective film layer is optimized to obtain high transmittance while minimizing the mutual cancellation of stress between the antireflective film and the dichroic film, achieving precise surface shape control. After double-sided coating, the dichroic film has high surface shape accuracy, good reliability, and stable product performance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the film structure of the color separation film.

[0022] Figure 2 The measured reflectance spectrum curves of the reference film under the same cover as the color separation film are shown.

[0023] Figure 3 The measured transmittance spectrum curves of the reference film under the same cover as the color separation film are shown.

[0024] Figure 4 This is a test diagram of the color separation surface of the color separation film.

[0025] Figure 5 Test diagram of the translucent surface of the color separation film.

[0026] In the diagram: 1-Dial separator; 2-Substrate; 3-Antireflective coating; 4-Incident beam; 5-Reflected beam; 6-Transmitted beam. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings. The drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0028] To simplify the description of this embodiment, some components that are well-known to those skilled in the art but are not related to the main content of this invention may be omitted in the accompanying drawings or description. Additionally, for ease of description, some components in the drawings may be omitted, enlarged, or reduced, but these do not represent the actual product dimensions or the complete structure.

[0029] This invention discloses a large-size broadband infrared color filter with controllable surface shape precision, such as... Figure 1 As shown, it includes a silicon substrate 2, a dichroic film 1 disposed on the light incident surface of the silicon substrate 2, and an antireflective film 3 disposed on the light transmission surface of the silicon substrate 2; the incident light beam 4 enters from the dichroic film 1, part of which is reflected to form a reflected light beam 5, and part of which is transmitted from the silicon substrate 2 and the antireflective film 3 as a transmitted light beam 6.

[0030] The color separation film 1 has two reflective film stacks. Matching layers are provided on the upper and lower surfaces of the reflective film stacks. The front matching layer is provided on the lower surface of the reflective film stack facing the silicon substrate 2, and the rear matching layer is provided on the upper surface of the reflective film stack facing the air. The reflective film stacks of the color separation film 1 are composed of germanium and zinc sulfide stacked alternately. Ytterbium fluoride is added to the matching layer.

[0031] According to technical requirements, a broadband dichroic film 1 is fabricated on the light incident surface of a silicon substrate 2, and an antireflection film 3 is fabricated on the light transmission surface of the silicon substrate 2. A stack of reflective films is constructed based on the requirements of the reflection band and the center wavelength. The dichroic film 1 adopts the structure of a long-pass filter, and two stacks of reflective films are designed to expand the bandwidth of the reflection band. Based on the optical and stress characteristics of germanium, zinc sulfide, and ytterbium fluoride, different reflective film stacks are constructed by alternating layers of germanium and zinc sulfide. Ytterbium fluoride is added to the matching layer. By optimizing the ratio of the matching layer and the film thickness, the transmittance of the transmission channel is improved, while the surface shape change caused by the dichroic film 1 is reduced. The feasibility of process control was considered in the film system design.

[0032] Color separation film 1 is SO / 1.259M 0.387H (0.81H 1.69M 0.81H). 7(0.55H 1.16M 0.55H) 6 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M / air, of which (0.81H 1.69M 0.81H) 7 (0.55H 1.16M 0.55H) 6 For the reflective film stack, 1.259M 0.387H is the front matching layer, and 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M is the rear matching layer;

[0033] S0 represents silicon substrate 2, M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integers 6 and 7 are the number of cycles of the two reflective film stacks, and the values ​​before M, H and L are the film layer ratio coefficients.

[0034] The antireflective coating 3 includes a thickness compensation film layer and an antireflective film layer sequentially disposed on the light transmission surface of the silicon substrate 2;

[0035] Based on the requirements of the transmission band and the surface shape changes caused by the dichroic film 1, when designing the antireflection film 3 on the light transmission surface of the silicon substrate 2, germanium and zinc sulfide are used as high and low refractive index materials, respectively. A thickness compensation film layer is designed on the side close to the silicon substrate 2. The thickness compensation film layers of germanium and zinc sulfide are periodically superimposed. After the thickness compensation film layer, there is an antireflection film layer. Optimizing the local film layer thickness obtains high transmittance of the transmission channel.

[0036] The antireflective coating 3 has a composition of S0 / (0.71H 0.87M 0.65H). 7 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M / air, of which (0.71H 0.87M 0.65H) 7 For thickness compensation film, 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M is for antireflection film;

[0037] S0 represents silicon substrate 2, M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integer 7 is the number of cycles of the thickness compensation film, and the values ​​before M, H and L are the film scaling factors.

[0038] The specific steps for fabricating the large-size broadband infrared color filter with controllable surface shape accuracy are as follows:

[0039] Step 1: Heat and maintain the temperature of silicon substrate 2 in a box-type vacuum coating equipment with a molecular pump system. The heating process adopts a step-by-step heating method. At the coating temperature, the silicon substrate 2 is kept at the temperature for 2 to 3 hours. The temperature of silicon substrate 2 is selected from 170℃ to 190℃.

[0040] Preferably, the temperature of the silicon substrate 2 is 180°C.

[0041] The stepwise heating method involves heating the silicon substrate 2 from room temperature to 100°C and holding it at that temperature for 0.5 hours, then continuing to heat it to 130°C and holding it at that temperature for 0.5 hours, and finally heating it to 180°C and holding it at that temperature for 2 hours.

[0042] Step 2: Before depositing the thin film, the silicon substrate 2 is bombarded with an ion beam using a Hall ion source; the anode voltage is 150V and the anode current is 4A.

[0043] Step 3: Germanium and ytterbium fluoride are deposited by electron beam evaporation, and zinc sulfide is deposited by resistance heating evaporation. Preferably, the zinc sulfide deposition rate is 2.8–3.5 nm / s.

[0044] In the specific fabrication process, germanium and ytterbium fluoride thin films were prepared by electron beam evaporation deposition. By adjusting the pre-melting process and deposition rate, the sputtering of the coating material was reduced. Zinc sulfide thin films were prepared by resistance evaporation deposition. Ion beam-assisted deposition was used for local film layers to improve the film density and achieve film stress control.

[0045] The color separation film prepared using the method of the present invention was tested, and the test results are as follows:

[0046] Test 1: An adhesion test was conducted on the reference film coated with the same color separation film. A 12.7mm (i.e. 1 / 2 inch) wide polyester transparent adhesive tape was firmly attached to the film surface without leaving any air bubbles or gaps. The tape was held for 15 minutes, and then one end of the adhesive tape was quickly pulled up. The film surface was intact and there was no film detachment.

[0047] Test 2: A temperature and humidity test was conducted on the reference film coated with the same color separation film. The sample was placed in a constant temperature and humidity chamber, and the temperature and humidity inside the chamber were set. The temperature was gradually increased to 45±2℃ and the relative humidity was ≥95%, and it was maintained for 24 hours. After that, it was cooled to room temperature and taken out. The film surface was intact and there was no film peeling.

[0048] Test 3 involved a temperature cycling test on a reference film coated with the same coating as the color separation film. The sample was placed in a constant temperature and humidity chamber (Hitachi EC-16MHHP), and the chamber temperature was slowly raised to 50±1℃ and maintained for 1 hour; then slowly lowered to -25±1℃ and maintained for another hour. After completing three temperature cycles, the sample was removed after being heated to room temperature. The film surface was intact, with no film peeling.

[0049] Test 4: Immersion test was conducted on the reference film coated with the same color separation film. The sample was immersed in a container filled with pure water, and then the container was placed in a constant temperature and humidity chamber with the temperature set at 45±2℃. The water-immersed sample was observed every hour. After immersion for 8 to 10 hours, the film surface was intact and there was no film peeling.

[0050] Test 5: A surface cleaning test is performed on the color separation films. After removing residual dust and particles from the sample surface, the film surface is lightly wiped with a cotton ball soaked in cleaning solution. The liquid evaporates without leaving any traces on the surface, and the film surface remains intact after wiping, with no film peeling. The cleaning solution is a mixture of anhydrous ethanol and anhydrous diethyl ether (analytical grade, conforming to GB678-78).

[0051] from Figure 2 It can be seen that this dichroic filter has high reflectivity in the 2–3.95 μm wavelength range, and its average reflectivity is calculated to be 95%; from Figure 3 It can be seen that the dichroic filter has high transmittance in the 4.2–5.1 μm wavelength range, and its average transmittance is calculated to be 92%. From... Figure 4 It can be seen that the surface accuracy RMS of the color separation surface of this color separation film is 0.028λ; Figure 5 It can be seen that the surface accuracy (RMS) of the anti-reflection surface of this dichroic film is 0.042λ. The large-size broadband infrared dichroic film of this invention has good reliability and stable optical and physical properties, and can be used for spectral color separation in large field-of-view infrared systems.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. All equivalent changes and modifications made within the scope of the claims of this invention should be considered within the technical scope of this invention.

Claims

1. A large-size wide-spectrum infrared dichroic plate with controllable surface accuracy, characterized in that: It includes a silicon substrate (2), a dichroic film (1) disposed on the light incident surface of the silicon substrate (2), and an anti-reflection film (3) disposed on the light transmission surface of the silicon substrate (2); the dichroic film (1) has two reflective film stacks, and matching layers are disposed on the upper and lower surfaces of the reflective film stacks, namely a front matching layer disposed on the lower surface of the reflective film stack facing the silicon substrate (2) and a rear matching layer disposed on the upper surface of the reflective film stack facing the air; The reflective film stack of the color separation film (1) is composed of alternating layers of germanium and zinc sulfide; ytterbium fluoride is added to the matching layer; The antireflective coating (3) includes a thickness compensation film and an antireflective film layer sequentially disposed on the light transmission surface of the silicon substrate (2); the thicknesses of the germanium film layer and the zinc sulfide film layer in the thickness compensation film layer are periodically superimposed.

2. The face precision controllable large size wide spectrum infrared dichroic plate according to claim 1, characterized in that: Dichroic film (1) is S0 / 1.259M 0.387H (0.81H 1.69M 0.81H) 7 (0.55H 1.16M 0.55H) 6 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M / air; wherein, (0.81H 1.69M 0.81H) 7 (0.55H 1.16M 0.55H) 6 is a reflective film stack, 1.259M 0.387H is a front matching layer, 0.33M 1.098L 0.697M 0.67L 0.505M 1.049L 0.576M 1.617L 0.33M is a back matching layer; S0 represents the silicon substrate (2), M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integers 6 and 7 are the number of cycles of the two reflective film stacks, and the values ​​before M, H and L are the film layer ratio coefficients.

3. The face precision controllable large size wide spectrum infrared dichroic filter according to claim 1, characterized in that: The anti-reflective film (3) is S0 / (0.71H 0.87M 0.65H) 7 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M / air; wherein, (0.71H 0.87M 0.65H) 7 is a thickness compensation film layer, and 2.598M 0.867H 0.485M 3.373H 1.786M 4.909H 2.141M 3.595H 1.852M is an anti-reflective film layer; S0 represents silicon substrate (2), M represents zinc sulfide with an optical thickness of λ0 / 4, H represents germanium with an optical thickness of λ0 / 4, L represents ytterbium fluoride with an optical thickness of λ0 / 4, λ0 is the center wavelength, the integer 7 is the number of cycles of the thickness compensation film, and the values ​​before M, H and L are the film ratio coefficients.

4. The method for making large-size wide-spectrum infrared dichroic filter with controllable surface accuracy according to any one of claims 1-3, characterized in that: The specific steps are as follows: Step 1: Heat and keep the silicon substrate (2) at a constant temperature in a box-type vacuum coating equipment with a molecular pump system. The heating process adopts a step-by-step heating method. At the coating temperature, the silicon substrate (2) is kept at a constant temperature for 2 to 3 hours. The temperature of the silicon substrate (2) is selected as 170℃ to 190℃. Step 2: Before depositing the thin film, the silicon substrate is bombarded with an ion beam (2). The ion source is a Hall ion source; the anode voltage is 150V and the anode current is 4A. Step 3: Electron beam evaporation is used to deposit germanium and ytterbium fluoride, and resistance heating is used to deposit zinc sulfide.

5. The method according to claim 4, wherein: In step one, the temperature of the silicon substrate (2) is selected as 180°C.

6. The method for manufacturing face-type precision-controllable large-size wide-spectrum infrared dichroic filter according to claim 5, characterized in that: The step-by-step heating method in step one is to heat the silicon substrate (2) from room temperature to 100°C, hold it at that temperature for 0.5 hours, then continue heating it to 130°C, hold it at that temperature for 0.5 hours, and finally heat it to 180°C, hold it at that temperature for 2 hours.

7. The method according to claim 4, wherein the method is characterized by: In step three, the zinc sulfide deposition rate is 2.8–3.5 nm / s.

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