Infrared optical window processing method

Abstract

The invention relates to an infrared optical window processing method in the technical field of infrared optical windows. The infrared optical window processing method comprises the following steps: preparing a sapphire material; laser cutting is adopted to assist liquid nitrogen injection to cut the sapphire material, liquid nitrogen covers a cutting area along with laser, and the injection flow of the liquid nitrogen is adjusted in stages according to the laser cutting process; and after the sapphire wafer is obtained after cutting is completed, the sapphire wafer is subjected to grinding, chamfering, polishing, annealing and cleaning treatment in sequence, and finally the infrared optical window is obtained. According to the machining method, the staged liquid nitrogen flow control mode is adopted in the laser cutting process, the requirement for the cooling performance of the sapphire material in different cutting stages can be better met, the heat influence possibly brought in the cutting process is effectively reduced, it is ensured that no stress concentration exists in the wafer, and the crack risk in the subsequent machining process is reduced; and the high transmittance and the structural stability of the product in an infrared band are ensured.

Description

Technical Field

[0001] This application relates to the technical field of infrared optical windows, and particularly to a processing method for infrared optical windows. Background Art

[0002] Infrared Optical Windows are crucial components in optical and sensor technologies and are widely used in fields such as infrared imaging, spectral analysis, laser systems, and communications. Currently, the existing infrared optical windows are mainly obtained by initially cutting sapphire materials with a wire cutting machine and then undergoing processes such as grinding, polishing, and cleaning. However, micro-cracks are easily generated at the edges of the sapphire wafers obtained by wire cutting, and there are defects such as wire marks on the cutting surface. This not only affects the quality of the sapphire wafers, making it difficult to ensure high transmittance and structural stability of the product in the infrared band, but also increases the difficulty of subsequent processing. Summary of the Invention

[0003] In view of the problems in the background art, this application provides a processing method for infrared optical windows, which can improve the cutting accuracy, cutting efficiency, and cutting quality of sapphire wafers, reduce micro-cracks at the edges of sapphire wafers, enhance the quality of infrared optical windows, and adopt a method of controlling the liquid nitrogen flow in stages, which can better meet the cooling performance requirements of sapphire materials in different cutting stages, effectively reduce the thermal influence that may be brought during the cutting process, ensure no stress concentration inside the wafer, reduce the crack risk during subsequent processing, and ensure high transmittance and structural stability of the product in the infrared band.

[0004] According to one aspect of the present invention, there is provided a processing method for infrared optical windows, including the following steps: preparing sapphire materials; cutting the sapphire materials by laser cutting assisted with liquid nitrogen injection, wherein the liquid nitrogen covers the cutting area along with the laser, the liquid nitrogen injection flow rate is adjusted in stages according to the laser cutting process, and the auxiliary liquid flow control during the laser cutting process is divided into three stages; after the cutting is completed to obtain sapphire wafers, the sapphire wafers are successively subjected to grinding, chamfering, polishing, annealing, and cleaning processes, and finally an infrared optical window is obtained.

[0005] By using the processing method in this technical solution, especially by adopting the method of controlling the liquid nitrogen flow rate in stages during laser cutting, it can better meet the cooling performance requirements of sapphire materials in different cutting stages, effectively reduce the thermal influence that may be brought during the cutting process, ensure no stress concentration inside the wafer, reduce the crack risk during subsequent processing, and ensure high transmittance and structural stability of the product in the infrared band.

[0006] In some embodiments of the present invention, the laser cutting assisted liquid nitrogen injection technology, wherein the liquid nitrogen covers the cutting area in the form of atomization or laminar flow through a high-pressure nozzle, and the pressure of the high-pressure nozzle is 0.5 - 2 MPa.

[0007] In some embodiments of the present invention, the laser cutting assisted liquid nitrogen injection for cutting the sapphire material includes: first, adjusting the liquid nitrogen flow rate to a first preset flow rate, and using a laser to perform a first-stage cutting on the sapphire material; then, adjusting the liquid nitrogen flow rate to a second preset flow rate, and using a laser to perform a second-stage cutting on the sapphire material; finally, adjusting the liquid nitrogen flow rate to a third preset flow rate, and using a laser to perform a third-stage cutting on the sapphire material.

[0008] In this embodiment, the first stage is the initial stage of cutting, the second stage is the stable cutting process, and the third stage is the final stage of cutting; according to the respective conditions of the initial stage of cutting, the stable cutting process, and the final stage of cutting, the present invention sets the adjusted liquid nitrogen flow rate to the first preset flow rate for the initial stage of cutting, which can be used to quickly reduce the surface temperature of the sapphire material, thereby inhibiting the expansion of the heat affected zone, reducing the attachment of slag and the generation of microcracks; setting the adjusted liquid nitrogen flow rate to the second preset flow rate for the stable cutting process, which can be used to maintain the temperature stability of the cutting area and balance the cooling efficiency and cutting speed; setting the adjusted liquid nitrogen flow rate to the third preset flow rate for the final stage of cutting, which can be used to avoid the lattice stress imbalance caused by sudden temperature changes.

[0009] In some embodiments of the present invention, during the laser cutting process, phased flow control is performed. The first preset flow rate is 10 - 15 L / min, the second preset flow rate is 8 - 10 L / min, and the third preset flow rate is 5 - 8 L / min.

[0010] In some embodiments of the present invention, during the laser cutting process, the liquid nitrogen injection flow rate is dynamically adjusted, and the liquid nitrogen flow rate is dynamically adjusted from the first preset flow rate to the second preset flow rate and from the second preset flow rate to the third preset flow rate according to the temperature of the laser cutting area.

[0011] In some embodiments of the present invention, the liquid nitrogen flow rate is dynamically adjusted within the respective intervals of the first stage or the second stage or the third stage of laser cutting according to the temperature of the laser cutting area.

[0012] In some embodiments of the present invention, the adjustment error of the liquid nitrogen flow rate is controlled within ±0.5 L / min.

[0013] In some embodiments of the present invention, the temperature of the laser cutting area is monitored in real time by an infrared thermal imager.

[0014] In some embodiments of the present invention, the liquid nitrogen injection is precisely synchronized with the laser in time sequence, and the delay of the liquid nitrogen injection compared to the laser is less than 1 ms.

[0015] In some embodiments of the present invention, the laser light source is an ultraviolet picosecond laser, the wavelength of the laser light source is 355 nm, and the pulse width is < 10 ps. The diameter of the focused light spot is 10 - 30 μm, and the power density is > 10 10 W / cm 2 , the single - pulse energy is 50 - 200 μJ, and the repetition frequency is 100 kHz - 1 MHz.

[0016] In some embodiments of the present invention, the laser cutting speed is 3 mm / s. Description of the Drawings

[0017] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. In the drawings:

[0018] Figure 1 is a process flow chart of the method for processing an infrared optical window of the invention. Detailed Embodiments

[0019] The present invention will be further described below with reference to specific embodiments. It should be clear that the described embodiments are only a part of the embodiments of the present application, and are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0020] For those not specified in the embodiments in terms of specific techniques or conditions, they shall be in accordance with the techniques or conditions described in the literature in the field or in accordance with the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through regular channels. The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The test materials used in the following embodiments are all commercially available products unless otherwise specified.

[0021] In the description of this application, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances. In addition, in the description of this application, unless otherwise specified, "a plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0022] An embodiment of this application discloses a method for processing an infrared optical window on the surface of a high-quality wafer. As Figure 1 shown, the infrared optical window processing method includes the following steps:

[0023] First, prepare sapphire material, and then use laser cutting assisted by liquid nitrogen injection to cut the sapphire material. Among them, liquid nitrogen covers the cutting area along with the laser, and the liquid nitrogen injection flow rate is adjusted in stages according to the laser cutting process. And the control of the auxiliary liquid flow rate during the laser cutting process is mainly divided into three stages; after the cutting is completed to obtain a sapphire wafer, the sapphire wafer is successively ground, chamfered, polished, annealed and cleaned to finally obtain an infrared optical window.

[0024] By using the processing method in this technical solution, using a laser to cut sapphire material and assisting with liquid nitrogen injection cooling during the laser cutting process can not only improve the cutting accuracy, cutting efficiency and cutting quality of the sapphire wafer based on laser cutting, reduce the micro-cracks on the edge of the sapphire wafer, and improve the quality of the infrared optical window, but also adopt the method of controlling the liquid nitrogen flow rate in stages, which can better adapt to the cooling performance requirements of different cutting stages of sapphire material, effectively reduce the thermal influence that may be brought during the cutting process, ensure no stress concentration inside the wafer, reduce the crack risk during the subsequent processing process, and ensure high transmittance and structural stability of the product in the infrared band.

[0025] In some embodiments of the present invention, using laser cutting assisted by liquid nitrogen injection to cut sapphire material includes the following steps: First, adjust the liquid nitrogen flow rate to the first preset flow rate, and use a laser to perform the first-stage cutting on the sapphire material; then adjust the liquid nitrogen flow rate to the second preset flow rate, and use a laser to perform the second-stage cutting on the sapphire material; finally, adjust the liquid nitrogen flow rate to the third preset flow rate, and use a laser to perform the third-stage cutting on the sapphire material.

[0026] In this embodiment, the first stage is the initial stage of cutting, the second stage is the stable cutting process, and the third stage is the final stage of cutting. According to the respective conditions of the initial cutting stage, the stable cutting process, and the final cutting stage, the present invention sets the regulated liquid nitrogen flow rate to a first preset flow rate for the initial cutting stage, which can be used to quickly reduce the surface temperature of the sapphire material, thereby inhibiting the expansion of the heat affected zone, reducing the adhesion of slag and the generation of microcracks; sets the regulated liquid nitrogen flow rate to a second preset flow rate for the stable cutting process, which can be used to maintain the temperature stability of the cutting area and balance the cooling efficiency and cutting speed; sets the regulated liquid nitrogen flow rate to a third preset flow rate for the final cutting stage, which can be used to avoid the lattice stress imbalance caused by sudden temperature changes.

[0027] Further, the first preset flow rate can be 10 - 15 L / min, the second preset flow rate can be 8 - 10 L / min, and the third preset flow rate can be 5 - 8 L / min.

[0028] In the initial cutting stage, a high flow rate of liquid nitrogen with a flow rate of 10 - 15 L / min can quickly reduce the surface temperature of the sapphire material to below -150°C, effectively inhibiting the expansion of the heat affected zone and reducing the adhesion of slag and the generation of microcracks; during the cutting process, it is adjusted to a medium flow rate of 8 - 10 L / min, which can effectively maintain the temperature stability of the cutting area, control the temperature rise ≤ 50°C, and balance the cooling efficiency and cutting speed of 50 - 100 mm / s (the moving speed of the focused spot); at the end of cutting, it is reduced to 5 - 8 L / min, which can effectively avoid the lattice stress imbalance caused by sudden temperature changes.

[0029] In some embodiments of the present invention, the liquid nitrogen flow rate is dynamically adjusted from the first preset flow rate to the second preset flow rate and from the second preset flow rate to the third preset flow rate according to the temperature of the laser cutting area.

[0030] In this embodiment, based on the temperature of the laser cutting area, controlling the multi-stage dynamic adjustment of the liquid nitrogen flow rate can make the stage flow rate of liquid nitrogen match well with the laser cutting process, so that the cooling effect requirements in the initial cutting stage, during the cutting process, and at the end of cutting can all reach their ideal states.

[0031] In some embodiments of the present invention, the liquid nitrogen flow rate is dynamically adjusted within the respective intervals of the first stage, the second stage, or the third stage of laser cutting according to the temperature of the laser cutting area.

[0032] In this embodiment, based on the temperature of the laser cutting area, controlling the dynamic adjustment of the liquid nitrogen flow rate within each stage can make the liquid nitrogen flow rate match well with the laser stage within the stage, and further make the cooling effect requirements in the initial cutting stage, during the cutting process, and at the end of cutting reach their ideal states respectively.

[0033] In some embodiments of the present invention, a laser cutting assisted liquid nitrogen injection technique is provided, wherein liquid nitrogen covers the cutting area in the form of atomization or laminar flow through a high-pressure nozzle, and the pressure of the high-pressure nozzle is 0.5 - 2 MPa.

[0034] In some embodiments of the present invention, the error control of the liquid nitrogen flow rate is within ±0.5 L / min.

[0035] Furthermore, the temperature of the laser cutting area is monitored in real time by an infrared thermal imager.

[0036] During the laser cutting assisted liquid nitrogen cooling process, a dynamic regulation and closed-loop monitoring system is adopted to enable the linked control of temperature and flow rate. An infrared thermal imager is integrated to monitor the temperature of the cutting area in real time, and the liquid nitrogen injection flow rate is dynamically adjusted, with the error controlled within ±0.5 L / min, thus achieving precise temperature control.

[0037] Furthermore, the liquid nitrogen injection is precisely synchronized with the laser in terms of timing, and the delay of the liquid nitrogen injection compared to the laser is less than 1 ms; ensuring immediate cooling after the laser action, suppressing heat accumulation, and the liquid nitrogen during the laser cutting process isolates oxygen, which can also reduce oxidation by-products.

[0038] In some embodiments of the present invention, the laser is an ultraviolet picosecond laser.

[0039] Furthermore, the laser cutting speed can be 3 mm / s (cutting depth).

[0040] Preferably, the laser wavelength is 355 nm, the pulse width is <10 ps, the focused spot diameter is 10 - 30 μm, the power density is >10 10 W / cm 2 , the single pulse energy is 50 - 200 μJ, and the repetition frequency is 100 kHz - 1 MHz.

[0041] The present invention can achieve precise cutting of sapphire materials through a high-precision laser cutting machine. During the laser cutting process, liquid nitrogen is used for cooling, which can effectively reduce the temperature of the processing area, thereby reducing the thermal affected zone of the material and improving the cutting quality and efficiency. After the sapphire cutting is completed, the chipping width is <5 μm, the surface roughness Ra is <0.5 μm, the depth of the thermal affected zone (HAZ) is <2 μm, and the cutting precision error is ±1 μm.

[0042] In some embodiments of the present invention, the grinding step adopts a fine grinding process. Specifically, a high-purity diamond suspension can be used for grinding with a double-sided or single-sided precision grinding machine. Preferably, the particle size of the diamond suspension can be 3 - 4 μm, and the grinding machine can adopt the Peter Wolters AC series. Through the fine grinding treatment, the surface roughness of the sapphire wafer can be further reduced to ≤5 nm, while ensuring no residual processing stress on the surface.

[0043] In some embodiments of the present invention, chamfering can be performed using a high-precision automatic chamfering machine, such as the NAGASE CNC series. The chamfering angle is controlled at 45° according to the design requirements, and the grinding wheel grit is increased to 1000# - 2000#. The chamfering quality requires no chipping or microcracks at the edge, and the fillet radius error is controlled within ≤±0.01 mm to ensure a smooth edge transition and improve the durability of the component.

[0044] In some embodiments of the present invention, the polishing process includes a rough polishing step and a fine polishing step performed in sequence. Among them, rough polishing uses chemical mechanical polishing equipment, such as the NTS series, with an alumina polishing liquid of pH 10 - 12 and a non-woven polishing pad, such as SUBA600. Through rough polishing, the surface roughness is reduced to Ra≤1 nm, and the processing damage layer is completely removed.

[0045] In the fine polishing stage, a high-precision single-sided polishing machine, such as the NTS series, is used with a silica polishing liquid of a particle size of 100 nm, and the polishing pressure is set at 0.1 - 0.3 kg / cm 2 , and the time is 20 - 40 minutes. Through fine polishing, the surface roughness is finally reduced to Ra≤0.3 nm, micro-scratches are eliminated, and stress residues are reduced.

[0046] In some embodiments of the present invention, the annealing treatment can be carried out in a high-temperature annealing furnace, such as CarboliteGero; during annealing, the temperature is raised to 1200 - 1300 °C, which is 100 °C higher than the original standard upper limit. Through the annealing treatment, the internal stress of the sapphire is fully released. During the annealing process, 99.999% high-purity argon gas is used as the protective gas, and the flow rate is controlled at 10 L / min to ensure that there is no oxidation or contamination on the crystal surface. After annealing, the cooling rate is controlled at 3 °C / min to avoid microcracks caused by thermal stress.

[0047] Furthermore, an X-ray diffraction (XRD) test is added after annealing to confirm that there are no lattice defects inside the crystal, meeting the requirements of a high-precision optical window.

[0048] In some embodiments of the present invention, the cleaning treatment can select the RCA cleaning process, such as the KPD pickling machine series. Through multi-stage cleaning, mainly using solutions such as sulfuric acid, hydrofluoric acid, and hydrogen peroxide, the ultrasonic frequency is increased to 950 kHz to completely remove micro-particles and surface contaminants.

[0049] After cleaning, it is dried with nitrogen of 99.999% purity to avoid secondary particle attachment. The surface contamination density requirement after cleaning and drying is controlled within ≤2 pieces / cm 2 , without water stains or cleaner residues, ensuring that the surface cleanliness meets the high requirements of an infrared optical window.

[0050] The above infrared optical window processing method in the present application will be further described below in conjunction with specific embodiments.

[0051] Embodiment 1

[0052] (1) Laser cutting:

[0053] Use an ultraviolet laser cutting machine, adopt an ultraviolet picosecond laser light source, with a wavelength of 355 nm, a pulse width < 10 ps, a focused spot diameter of 10 - 30 μm, a power density > 10 10 W / cm 2 , a single pulse energy of 50 - 200 μJ, a repetition frequency of 100 kHz - 1 MHz, and a cutting speed of 3 mm / s.

[0054] Meanwhile, during the laser cutting process, auxiliary liquid nitrogen injection cooling is used, and staged liquid nitrogen flow control is adopted. -196 °C liquid nitrogen covers the cutting area in the form of atomization or laminar flow through a high-pressure nozzle at a pressure of 0.5 - 2 MPa.

[0055] In the high-flow stage (at the initial stage of cutting), the liquid nitrogen flow rate is increased to 10 - 15 L / min to rapidly cool the surface layer of the material; in the medium-flow stage (during the stable cutting process), the flow rate is reduced to 8 - 10 L / min to maintain the temperature stability of the cutting area, control the temperature rise ≤ 50 °C, and balance the cooling efficiency and cutting speed (50 - 100 mm / s). In the low-flow stage (at the later stage of cutting), the flow rate is reduced to 5 - 8 L / min to maintain a stable temperature field and avoid lattice stress imbalance caused by sudden temperature changes.

[0056] Furthermore, the laser and liquid nitrogen injection timings are precisely synchronized with a delay < 1 ms to ensure immediate cooling after the laser action and suppress heat accumulation. The auxiliary liquid nitrogen during the laser cutting process isolates oxygen and can also reduce oxidation by-products.

[0057] The method of the present invention uses a picosecond laser cutting assisted liquid nitrogen injection technology for effective cutting. After sapphire cutting is completed, the chipping width < 5 μm, the surface roughness Ra < 0.5 μm, the depth of the heat affected zone (HAZ) < 2 μm, and the cutting accuracy error is ±1 μm. The bow is controlled within Bow ≤ 10, the warp is controlled within Warp ≤ 15, and the thickness deviation is controlled within TTV ≤ 5. Using liquid nitrogen for cooling during the cutting process can effectively reduce the temperature of the processing area, thereby reducing the heat affected zone of the material and improving the cutting quality and efficiency.

[0058] (2) Precision grinding process: Precision grinding uses a high-purity diamond suspension with a particle size of 3 - 4 μm and is ground through a Morinaga series single-sided precision grinding machine. The pressure is controlled at 2 - 8 kg / cm 2 , the time is 15 - 20 minutes, the surface roughness requirement is ≤ 5 nm, and at the same time, it is ensured that there is no residual processing stress on the surface.

[0059] (3) Chamfering process: It is processed by using a NAGASE CNC series high-precision automatic chamfering machine. The chamfering angle is controlled at 45° according to the design requirements. The grinding wheel grit is increased to 1000# - 2000#. After chamfering, ultrasonic cleaning is used to remove the inducement of microcracks and machining debris. The chamfering quality requirements are that there is no chipping or microcracks at the edge, and the fillet radius error is controlled within ≤±0.01 mm to ensure a smooth edge transition and improve the durability of the component.

[0060] (4) Polishing process: In the rough polishing stage, NTS series chemical mechanical polishing equipment is used, with a pH10 - 12 alumina polishing liquid and a SUBA600 non-woven polishing pad. The polishing pressure is controlled at 0.3 - 0.5 kg / cm 2 , and the time is 20 - 40 minutes. Finally, the surface roughness is reduced to Ra≤1 nm. In the fine polishing stage, a NTS series high-precision single-sided polishing machine is used, with a 100 nm silica polishing liquid. The polishing pressure is set at 0.1 - 0.3 kg / cm 2 , and the time is 20 - 40 minutes to ensure that the surface roughness is reduced to Ra≤0.3 nm, completely removing the machining damage layer. Eliminate micro-scratches and ensure no stress residue. At the same time, an interferometer is introduced to detect the surface topography after polishing, and the surface shape accuracy reaches λ / 4 or higher, which is adjusted according to the specific design requirements.

[0061] (5) Annealing: Annealing treatment is carried out using a Carbolite Gero high-temperature annealing furnace. The temperature is raised to 1200 - 1300 °C, which is 100 °C higher than the original standard upper limit, fully releasing the internal stress of the sapphire. The cooling rate is controlled at 3 °C / min to avoid microcracks caused by thermal stress. During the annealing process, 99.999% high-purity argon gas is used as the protective gas, and the flow rate is controlled at 10 L / min to ensure that there is no oxidation or contamination on the crystal surface. After annealing, an X-ray diffraction (XRD) test is added to confirm that there are no lattice defects inside the crystal, meeting the requirements of a high-precision optical window.

[0062] (6) RCA cleaning process: The RCA cleaning process is adopted, and multi-stage cleaning is carried out using a KPD pickling machine series. Mainly sulfuric acid, hydrofluoric acid, hydrogen peroxide and other solutions are used, and the ultrasonic frequency is increased to 950 kHz to completely remove micro-particles and surface contaminants. After cleaning, it is dried with 99.999% pure nitrogen to avoid secondary particle attachment. The surface contamination density requirement after cleaning is controlled within ≤2 pieces / cm 2 , without water marks or cleaner residues, ensuring that the surface cleanliness meets the high requirements of an infrared optical window.

[0063] (7) Finally, clean again to complete the processing. Use an infrared transmittance tester to detect the transmittance of the product in the infrared band. In the wavelength range of 3 - 5 μm / 8 - 12 μm, the infrared band transmittance ≥95%.

[0064] Comparative Example 1

[0065] (1) Cutting process: High-quality sapphire crystal material is used. The cutting is performed using a high-bird single-wire cutting machine, and the cutting speed is about 0.5 mm / s (cutting depth). After cutting, the chipping width > 20 μm, the depth of the heat-affected zone (HAZ) > 10 μm, the bow is controlled within 15 ≤ |bow| ≤ 35, the warp is controlled within 25 ≤ warp ≤ 50, and the thickness tolerance is controlled within TTV ≤ 10. There are micro-cracks at the edge of the sapphire wafer, and defects such as wire marks exist on the cutting surface.

[0066] (2) Grinding process: Grinding is divided into rough grinding and fine grinding. For rough grinding, a Morinaga double-sided grinding machine series is used, with diamond abrasive, and the particle size is controlled within 6 - 9 μm. The grinding parameters are set as pressure 2 - 8 kg / cm 2 , the disc rotation speed is 20 - 40 rpm. After grinding, the thickness error of the wafer is controlled within ≤ ±3 μm, the surface roughness (Ra) ≤ 5 nm, and there are no obvious scratches or cracks. In the fine grinding stage, a high-purity diamond suspension with a particle size of 3 - 4 μm is used, and the grinding is carried out through a Morinaga single-sided precision grinding machine series. The pressure is controlled within 2 - 8 kg / cm 2 , the time is 15 - 20 minutes, and the surface roughness requirement is ≤ 5 nm. At the same time, it is ensured that there is no residual processing stress on the surface.

[0067] (3) Chamfering process: A NAGASE CNC series high-precision automatic chamfering machine is used for processing. The chamfering angle is controlled at 45° according to the design requirements. The grinding wheel grain size is increased to 1000# - 2000#. After chamfering, ultrasonic cleaning is used to remove the inducement of micro-cracks and processing debris. The chamfering quality requirement is that there is no chipping or micro-cracks at the edge, and the fillet radius error is controlled within ≤ ±0.01 mm, ensuring a smooth edge transition and improving the durability of the component.

[0068] (4) Polishing process: In the rough polishing stage, an NTS series chemical mechanical polishing equipment is used, with an alumina polishing liquid with pH 10 - 12 and a SUBA600 non-woven polishing pad. The polishing pressure is controlled within 0.3 - 0.5 kg / cm 2 , the time is 20 - 40 minutes, and finally the surface roughness is reduced to Ra ≤ 1 nm. In the fine polishing stage, an NTS series high-precision single-sided polishing machine is used, with a silica polishing liquid with a particle size of 100 nm. The polishing pressure is set at 0.1 - 0.3 kg / cm 2 , the time is 20 - 40 minutes, ensuring that the surface roughness is reduced to Ra ≤ 0.3 nm, and completely removing the processing damage layer. Micro-scratches are eliminated and it is ensured that there is no stress residue. At the same time, an interferometer is introduced to detect the surface topography after polishing, and the surface shape accuracy reaches λ / 4 or higher, which is adjusted according to the specific design requirements.

[0069] (5) Annealing: Annealing treatment is carried out using a Carbolite Gero high-temperature annealing furnace. The temperature is raised to 1200 - 1300 °C to fully release the internal stress of the sapphire. The cooling rate is controlled at 3 °C / min to avoid microcracks caused by thermal stress. During the annealing process, 99.999% high-purity argon gas is used as the protective gas, and the flow rate is controlled at 10 L / min to ensure that there is no oxidation or contamination on the crystal surface. After annealing, X-ray diffraction (XRD) testing is added to confirm that there are no lattice defects inside the crystal, meeting the requirements of a high-precision optical window.

[0070] (6) RCA cleaning process: The RCA cleaning process is adopted, and multi-stage cleaning is carried out using a KPD pickling machine series. Solutions such as sulfuric acid, hydrofluoric acid, and hydrogen peroxide are mainly used, and the ultrasonic frequency is increased to 950 kHz to thoroughly remove micro-particles and surface contaminants. After cleaning, it is dried with nitrogen gas with a purity of 99.999% to avoid secondary particle attachment. The surface contamination density requirement after cleaning is controlled at ≤ 2 per cm 2 , without water marks or residual cleaning agents, ensuring that the surface cleanliness meets the high requirements of an infrared optical window.

[0071] (7) Finally, cleaning is carried out again to complete the processing. An infrared transmittance tester is used to detect the transmittance of the product in the infrared band. In the wavelength range of 3 - 5 μm / 8 - 12 μm, the infrared band transmittance ≥ 95%.

[0072] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0073] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An infrared optical window processing method, characterized in that Including the following steps: Prepare sapphire material; Cut the sapphire material by using laser cutting assisted with liquid nitrogen injection, wherein the liquid nitrogen covers the cutting area along with the laser, the liquid nitrogen injection flow rate is adjusted in stages according to the laser cutting process, and the control of the auxiliary liquid flow rate during the laser cutting process is divided into three stages. After the cutting is completed to obtain a sapphire wafer, the sapphire wafer is successively subjected to grinding, chamfering, polishing, annealing and cleaning treatments, and finally an infrared optical window is obtained.

2. The infrared optical window processing method according to claim 1, characterized in that For the laser cutting assisted liquid nitrogen injection technology, the liquid nitrogen covers the cutting area in the form of atomization or laminar flow through a high-pressure nozzle, and the pressure of the high-pressure nozzle is 0.5 - 2 MPa.

3. The infrared optical window processing method according to claim 1, characterized in that, The cutting of the sapphire material by using the laser cutting assisted with liquid nitrogen injection includes: First, adjust the liquid nitrogen flow rate to a first preset flow rate, and use a laser to perform the first-stage cutting on the sapphire material; Then, adjust the liquid nitrogen flow rate to a second preset flow rate, and use a laser to perform the second-stage cutting on the sapphire material; Finally, adjust the liquid nitrogen flow rate to a third preset flow rate, and use a laser to perform the third-stage cutting on the sapphire material.

4. The infrared optical window processing method according to claim 3, characterized in that, The first preset flow rate is 10 - 15 L / min, the second preset flow rate is 8 - 10 L / min, and the third preset flow rate is 5 - 8 L / min.

5. The infrared optical window processing method according to claim 4, characterized in that The liquid nitrogen flow rate is dynamically adjusted from the first preset flow rate to the second preset flow rate and from the second preset flow rate to the third preset flow rate according to the temperature of the laser cutting area.

6. The infrared optical window processing method according to claim 4, characterized in that, The liquid nitrogen flow rate is dynamically adjusted within the respective intervals of the first stage or the second stage or the third stage of the cutting according to the temperature of the laser cutting area.

7. The infrared optical window processing method according to claim 5 or 6, characterized in that The adjustment error of the liquid nitrogen flow rate is controlled within ±0.5 L / min.

8. The infrared optical window processing method according to claim 5 or 6, characterized in that The temperature of the laser cutting area is monitored in real time by an infrared thermal imager.

9. The infrared optical window processing method according to claim 2, wherein, The liquid nitrogen injection is precisely synchronized with the laser in time sequence, and the delay of the liquid nitrogen injection compared with the laser is less than 1 ms.

10. The infrared optical window processing method according to claim 1, characterized in that The laser is an ultraviolet picosecond laser, with a laser light source wavelength of 355 nm, a pulse width < 10 ps, a focused spot diameter of 10 - 30 μm, and a power density > 10 10 W / cm 2 , a single pulse energy of 50 - 200 μJ, a repetition frequency of 100 kHz - 1 MHz, and a cutting speed of 3 mm / s.

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