Multi-field coupling high-precision etching method and device for optical element

Abstract

The invention provides a multi-field coupling high-precision etching method and device for an optical element, and belongs to the technical field of optical manufacturing, and the method comprises the steps: preparing a to-be-etched optical element and an etching solution; carrying out acid pickling pretreatment; putting the optical element which is dried after acid pickling pretreatment into a hydrofluoric acid etching tank, adding an etching solution, and starting an etching program, the required etching depth is accurately matched by adjusting the megasonic frequency of a megasonic controller, the pH value is collected in real time through an acidimeter, hydrofluoric acid is supplemented when the concentration is reduced to ensure the concentration of the etching liquid, and temperature control is realized through a constant-temperature circulating water temperature control system and a temperature sensor; and carrying out acid pickling post-treatment to obtain a dry etched optical element. The device comprises a pickling pretreatment system, a megasonic wet etching system and a pickling aftertreatment system. Through multi-field cooperative controlled etching and megasonic, temperature and concentration field coupling regulation and control, the etching precision reaches + / -0.1 mu m, and the uniformity error is less than or equal to + / -0.05%, which is far better than that in the prior art.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical manufacturing technology, and particularly relates to a multi-field coupling high-precision etching method and device for optical elements. BACKGROUND

[0002] With the modern optical system, especially the high-energy laser device and space-to-ground observation, etc. The caliber and surface shape accuracy of optical elements are unprecedentedly required. The caliber of optical elements is increasing, and at the same time, the surface shape accuracy requirement has reached nanometer or even sub-nanometer level. Such high-precision optical elements are the key to realize high performance and high resolution of the system.

[0003] Laser-driven inertial confinement fusion device is an important national defense scientific research project facing the frontiers of strategic needs. Its construction scale and technical level mark the comprehensive strength of the country in the field of high-energy density physics research and advanced laser system development. In the megajoule level laser-driven device, the optical elements of optical transmission are used as core components to realize the efficient and consistent transmission of high-energy and large-size light beams, which requires them to have very high wavefront precision and laser damage resistance.

[0004] In order to meet the needs of optical transmission type optical elements, megasonic wet etching technology has become a key link to improve the surface quality of the elements and improve the damage resistance.

[0005] However, the existing megasonic wet etching technology mostly relies on single process parameter control, and lacks the synergistic control mechanism of megasonic field, temperature field and concentration field. On the one hand, the megasonic parameters are fixed or the adjustment range is limited, which cannot accurately match the different etching depth requirements, resulting in uneven etching rate, and the uniformity error is generally more than ±0.1 μm; and the existing post-processing process is simple, mostly using single pure water rinsing or normal temperature drying, which cannot effectively remove the residual hydrogen fluoride etching liquid and nanoscale reaction residues on the surface of the element. The residual liquid residue is usually higher than 10PPM. SUMMARY

[0006] The purpose of the present application is to solve the technical problems of single etching process, uneven etching rate and high residual amount of element surface residues, and to provide a multi-field coupling high-precision etching method for optical elements, comprising the following steps: S1: preparing the optical element to be etched and the etching liquid; S2: performing acid pickling pretreatment on the optical element to be etched to obtain a dry optical element with impurity particle number less than or equal to 0.03 / mm 2 ​S3: Put the dried optical element after the acid pickling pretreatment into the hydrofluoric acid etching tank, add etching solution, start the etching program, and precisely match the required etching depth by adjusting the megasonic frequency of the megasonic controller, collect the pH value in real time by the acidimeter, and supplement the hydrofluoric acid to ensure the concentration of the etching solution when the concentration decreases, realize temperature control by the constant temperature circulating water temperature control system and the temperature sensor; S4: Perform acid pickling post-treatment on the optical element after etching to obtain a dried etched optical element.

[0007] Further, in S1, the etching solution is a solution obtained by mixing hydrofluoric acid and ammonium fluoride at a ratio of 1:8.

[0008] Further, in S2, the acid pickling pretreatment includes the following steps: S21: In the first ultrasonic cleaning tank, complex cavitation effects are excited in the alkaline cleaning solution by ultrasonic waves to strip and disperse the residues attached to the surface of the optical element and its clamp; S22: In the ultrapure water spraying tank, ultrapure water is used to strip the alkaline cleaning solution from the surface of the optical element and its clamp; S23: In the second ultrasonic cleaning tank, ultrasonic waves are used to clean nanoscale residues and trace particles and cleaning agent ions remaining in the ultrapure water spraying tank; S24: In the ultrapure water rinsing tank, ultrapure water is used to further strip and disperse the residues attached to the optical element and its clamp; S25: In the hot water rinsing tank, the optical element and its clamp are pulled up and washed in hot water to evenly drain the water from their surfaces, and then dried after rinsing.

[0009] Further, in S3, the megasonic controller has a working power of 1kW-5kW, a power density of 1W / cm 2 -5W / cm 2 , a continuous adjustment supporting a 5W step, a megasonic frequency of 0.65MHz-1MHz, and ensures that the etching uniformity error is less than or equal to ±0.05μm; The constant temperature circulating water temperature control system ensures that the etching temperature is stable in the range of 20-25℃ with a control accuracy of ±0.5℃; The acidimeter and hydrofluoric acid ensure that the etching solution concentration fluctuation error is less than or equal to ±0.5%; The multi-field coupling high-precision etching method ensures that the etching precision reaches ±0.1μm during the etching process by the cooperation of the megasonic controller, the constant temperature circulating water temperature control system, and the acidimeter and hydrofluoric acid.

[0010] Further, in S4, the acid pickling post-treatment specifically includes the following steps: S41: After the etched optical element and its clamp are placed in the spray tank for spraying, the etching residue on the surface of the optical element is removed after being taken out; S42: In the pure water rinsing tank, the residual hydrofluoric acid on the surface of the etched optical element is preliminarily removed by using the physical dilution mechanism of ultrapure water; S43: In the ultrapure water megasonic rinsing tank, the surface of the optical element is disturbed and peeled off by using cold water and megasonic in the rinsing liquid; S44: In the hot water lifting tank, the residual hydrofluoric acid on the surface of the optical element is further diluted to the PPM level by using high-temperature pure water through the effects of reducing the surface tension and temperature difference driving, and the wall droplets and water marks are reduced by lifting. S45: The optical element is dried in the drying tank to obtain a dried etched optical element.

[0011] A multi-field coupling high-precision etching device for an optical element and a multi-field coupling high-precision etching method for an optical element, comprising an acid pickling pretreatment system, a megasonic wet etching system and an acid pickling post-treatment system; The acid pickling pretreatment system comprises a first ultrasonic cleaning tank, an ultrapure water spraying tank, a second ultrasonic cleaning tank, an ultrapure water rinsing tank and a hot water rinsing tank. The optical element and its clamp clean the residual substances attached to the surface through the acid pickling pretreatment system, ensure the dryness of the surface of the optical element, and the number of impurity particles is less than or equal to 0.03 / mm 2 ; The megasonic wet etching system comprises a hydrofluoric acid etching tank, a megasonic controller and a constant-temperature circulating water temperature control system. The hydrofluoric acid etching tank is provided with a temperature sensor and an acidity meter. The optical element is etched by the megasonic wet etching system, and the etching control precision is ensured to be ±0.1 μm; The acid pickling post-treatment system comprises a spraying tank, a pure water rinsing tank, an ultrapure water megasonic rinsing tank, a hot water lifting tank and a drying tank. The optical element removes the surface impurities after etching, dilutes the residual hydrofluoric acid on the surface to the PPM level and dries, to obtain a dried etched optical element Further, the constant-temperature circulating water temperature control system is uniformly distributed with cooling pipes on the tank body of the hydrofluoric acid etching tank. The cooling liquid is circulated through the cooling pipes by the compressor refrigeration and the heat exchanger to uniformly cool the etching liquid in the hydrofluoric acid etching tank.

[0012] Further, the tank body of the hydrofluoric acid etching tank is uniformly distributed with a plurality of temperature sensors. The plurality of temperature sensors are signal connected with the constant-temperature circulating water temperature control system. The constant-temperature circulating water temperature control system collects the temperature in the tank body through the plurality of temperature sensors, and automatically starts and stops the refrigeration and the circulation of the cooling liquid according to the preset temperature threshold.

[0013] Compared with the prior art, the beneficial effects of the present application mainly include: Multi-field synergistic etching, through megasonic, temperature, and concentration field coupling regulation, etching precision reaches ±0.1 μm, and uniformity error is ≤±0.05%, far exceeding existing technologies.

[0014] After five acid pickling pretreatment, the number of impurity particles on the surface of the element is ≤0.03 / mm 2 , and secondary pollution is eliminated.

[0015] Through the adjustable frequency megasonic controller and the large-size megasonic vibration source built-in the hydrofluoric acid etching tank, the diffusion of reaction products is accelerated, and the adhesion of the reaction products on the surface of the element is prevented; in combination with precise temperature and concentration control, the generation of products is further reduced.

[0016] In the application, after the optical element is treated by five acid pickling, the residual liquid is diluted to PPM level, the zero metal residue of the subsurface layer is realized, and long-term stability is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is the process and each system schematic diagram of the multi-field coupling high-precision etching method of the optical element of the application.

[0018] Figure 2 It is the process schematic diagram of the acid pickling pretreatment in the application; Figure 3 It is the process schematic diagram of the megasonic wet etching in the application; Figure 4 It is the process schematic diagram of the acid pickling post-treatment in the application DETAILED DESCRIPTION

[0019] The multi-field coupling high-precision etching method and device for optical elements of the application will be described in more detail below in conjunction with the schematic diagram, wherein the preferred embodiments of the application are represented, and it should be understood that the application described herein can be modified by those skilled in the art, and the advantageous effects of the application can still be achieved, therefore, the following description should be understood as extensive knowledge for those skilled in the art, and not as a limitation on the application.

[0020] As Figure 1 shown, a multi-field coupling high-precision etching method for optical elements comprises the following steps: Step 1: preparing the optical element to be etched and the etching liquid.

[0021] The optical element to be etched and its clamp are prepared, and the etching liquid is a solution prepared by mixing hydrofluoric acid and ammonium fluoride in a proportion of 1:8.

[0022] Step 2: pretreating the optical workpiece to be etched by the acid pickling pretreatment system to remove the surface contaminants of the workpiece, as Figure 2 shown.

[0023] The acid pickling pretreatment system comprises a first ultrasonic cleaning tank, an ultrapure water spraying tank, a second ultrasonic cleaning tank, an ultrasonic pure water rinsing tank and a hot water rinsing tank. The tank body material is 316 stainless steel, the tank body is designed without dead angle, and the appearance is treated with corrosion-resistant coating. According to the need, 304 stainless steel can also be selected as the tank body material.

[0024] Step 2.1: The first ultrasonic cleaning tank is the first process of the system. Through high energy density and multi-frequency ultrasonic waves in the alkaline cleaning solution, complex cavitation effect is excited to realize efficient stripping and dispersion of particles, oil stains and surface attached residues on the surface of optical elements and clamps.

[0025] Step 2.2: The ultrapure water spraying tank is the second process. Its main function is to quickly strip the cleaning solution attached to the optical elements and clamps after the first tank cleaning to prevent further reaction or secondary pollution in the subsequent process. The pure water spraying tank adopts a conical nozzle design, and the water jet can spray the entire surface of the workpiece. The pressure pump uses a high-pressure water pump and a large-flow water pump without damaging the filter core structure.

[0026] Step 2.3: The second ultrasonic cleaning tank is the third process. It uses ultrasonic waves to clean small particles and remove nanoscale residues and micro-particles or cleaning agent ions remaining in the ultrapure water spraying tank.

[0027] Step 2.4: The ultrasonic pure water rinsing tank uses high-frequency single-frequency ultrasonic waves to efficiently strip and disperse the residues attached to the optical elements and clamps. The single frequency is 150 KHZ.

[0028] Step 2.5: The hot water rinsing tank is the fifth processing unit. By slowly lifting the optical elements and clamps and keeping the hot water above 45 degrees Celsius, the excess water on the surface of the clamps and optical elements is uniformly and naturally drained, significantly reducing the amount of water carried into the hydrofluoric acid etching tank with the workpiece, and reducing the risk of interference with the acid concentration and etching uniformity of the subsequent hydrofluoric acid etching tank. After cleaning and drying, the impurity particle count is less than or equal to 0.03 / mm 2 .

[0029] Step 3: The dry and clean optical workpiece is fixed by a clamp and placed in the hydrofluoric acid etching tank. The etching process is started by adding etching solution. The required etching depth is accurately matched by adjusting the megasonic controller. The working power range is 1 kW-2 kW, supporting continuous adjustment with a step size of 5 W, and it is equipped with a 0.65-1 MHz adjustable high-frequency megasonic. The etching tank is equipped with a temperature sensor, and the constant temperature circulating water temperature control system realizes a temperature control accuracy of ±0.5°C, ensuring that the etching temperature is stable in the range of 20-25°C. During the etching process, the pH value of the solution is collected in real time by the acidity meter. When the concentration of the etching solution is detected to be reduced, the system automatically supplements high-concentration hydrofluoric acid solution, so that the concentration fluctuation error of the etching solution is controlled to be ≤±0.5%. Through the synergistic regulation of megasonic field, temperature field and concentration field, high-precision control of the etching process is realized, and the precision can reach ≤±0.1 μm, as shown in Figure 3 .

[0030] Specifically, the etching depth reaches 4 μm. During the etching process, megasonic waves are introduced to accelerate the diffusion of fluorosilicate through megasonic microjet action and prevent the deposition of chemical reaction products. The large-size megasonic vibration source in the tank body of the hydrofluoric acid etching tank prevents the deposition of chemical reaction products and ensures the final damage performance and wavefront accuracy of the optical element.

[0031] The constant temperature circulating water temperature control system controls the 3 high-precision temperature sensors uniformly arranged in the tank body of the hydrofluoric acid etching tank, measures the real-time monitoring with an accuracy of ±0.1°C, strictly limits the etching temperature in the range of 20-25°C, realizes the adjustment accuracy of ±0.5°C by means of the constant temperature circulating water temperature control system, and prevents the etching rate from being uneven due to temperature fluctuations. Using the acidity meter, the solution pH value is collected in real time with an accuracy of ±0.01 pH. When the concentration of hydrofluoric acid is reduced due to reaction consumption, high-concentration hydrofluoric acid solution is supplemented to ensure that the concentration fluctuation error of the etching solution is ≤±0.5%. After etching, the particle density is ≤0.02 / mm 2 , and after etching the element surface to a depth of 5 μm, the wavefront accuracy of the element satisfies PV degradation ≤30 nm.

[0032] The constant temperature circulating water temperature control system provides hydrofluoric acid cooling, which realizes timely balance of the heat generated in the megasonic working process through refrigeration and heat exchange. The core of the constant temperature circulating water temperature control system adopts a high-performance compressor to provide guarantee for the heat balance of the device. The constant temperature circulating water temperature control system integrates a high-efficiency plate heat exchanger, which can utilize the cold provided by the compressor.

[0033] The start and stop of the constant temperature circulating water temperature control system depends on the intelligent temperature control mechanism. A temperature sensor is arranged in the tank body of the hydrofluoric acid etching tank. The probe of the sensor monitors the temperature of the hydrofluoric acid in real time and feeds back the signal to the control system. The control system automatically judges and starts or stops the refrigeration cycle according to the preset temperature threshold, realizing accurate temperature control.

[0034] Step 4: The acid post-treatment system is used for rinsing and drying the optical element after etching is completed, and the acid post-treatment system comprises a spraying tank, a pure water rinsing tank, an ultrapure water megasonic rinsing tank, a hot water lifting tank and a drying tank. Since the acid post-treatment needs to deal with the residual hydrofluoric acid medium, the tank body, filter element and pump valve must have strong HF corrosion resistance, such as that shown in Fig. Figure 4 .

[0035] Step 4.1: The spraying tank is used as the first process of the post-treatment to remove the surface impurities after etching.

[0036] Step 4.2: The pure water rinsing tank is used as the second process of the post-treatment to rapidly and preliminarily remove the residual hydrofluoric acid on the surface of the element after etching through a physical dilution mechanism, which adopts pure water to rapidly reduce the concentration of the residual hydrofluoric acid.

[0037] Step 4.3: In order to prevent local enrichment of the nano-chemical reactants, the ultrapure water megasonic rinsing tank is used as the third process of the post-treatment, and the rinsing liquid adopts cold water to perform micro-disturbance and stripping on the surface of the optical element. The working frequency is required to be greater than or equal to 0.65 MHz megasonic frequency, and the power should reach greater than or equal to 1 kW.

[0038] Step 4.4: The hot water slow lifting tank is used as the fourth process of the post-treatment to perform further purification and liquid removal. The high-temperature pure water in the hot water tank body can further dilute the residual trace acid liquid to the ppm level through the effects of reducing the surface tension and temperature difference driving.

[0039] Step 4.5: The drying tank is used as the fifth process of the post-treatment to reduce the vaporization temperature of water in a low-pressure negative pressure environment, so that rapid drying is realized under the condition of no heating or low temperature. The whole process is in a closed environment to prevent interference of external pollution sources such as air particles and ions.

[0040] Step 4.6: The etched optical element after the post-treatment cleaning and drying is output According to the present application, the size of the hydrofluoric acid etching tank is set to 570mm*400mm*100mm, so that high uniformity and high cleanliness etching of the 400mm size optical element can be realized.

[0041] The present application can be used for various types of cross-scale pollutants generated in the optical element processing process, including particulate matter, organic pollutants and etching pollutants, which have different attachment mechanisms and adsorption states. According to the properties of the pollutants, the optimized combination cleaning and etching process is selected to realize effective control of the multi-scale pollutants above the submicron level.

[0042] The present application forms a closed-loop pure, uniform and controllable etching environment through the cooperation of each system and component, and finally realizes the goal of completely removing the subsurface layer and zero metal residue, and meets the stringent requirements of the super high energy laser system on the optical element. The device provides strong early-stage guarantee for the process stability and finished product quality of hydrofluoric acid etching, and realizes nanoscale precision etching of the element through multi-field coupling high-precision control.

[0043] The above are only preferred embodiments of the present application, and do not have any limiting effect on the present application. Any person skilled in the art can make any form of equivalent replacement or modification of the technical solutions and technical contents disclosed by the present application without departing from the scope of the technical solutions of the present application, and still belongs to the protection scope of the present application.

Claims

1. A high-precision etching method for multi-field coupling of optical components, characterized in that, Includes the following steps: S1: Prepare the optical components to be etched and the etching solution; S2: Perform acid pickling pretreatment on the optical components to be etched to obtain an impurity particle count of less than or equal to 0.03 particles / mm. 2 Dry optical components; S3: Place the dried optical components after pickling into the hydrofluoric acid etching tank, add etching solution, start the etching program, and accurately match the required etching depth by adjusting the megohm frequency of the megohm controller, collect the pH value in real time by the pH meter and add hydrofluoric acid to ensure the concentration of etching solution when the concentration drops, and achieve temperature control by the constant temperature circulating water temperature control system and temperature sensor. S4: After etching, the optical element is acid-washed to obtain a dry etched optical element.

2. The high-precision etching method for multi-field coupling of optical components according to claim 1, characterized in that, In S1, the etching solution is a solution of hydrofluoric acid and ammonium fluoride mixed in a ratio of 1:

8.

3. The high-precision etching method for multi-field coupling of optical components according to claim 1, characterized in that, In step S2, the pre-acid pickling treatment includes the following steps: S21: In the first ultrasonic cleaning tank, ultrasonic waves are excited in an alkaline cleaning solution to create a complex cavitation effect, which peels off and disperses the residues attached to the surface of the optical components and their fixtures. S22: In an ultrapure water spray tank, ultrapure water is used to peel off the alkaline cleaning solution from the surface of the optical components and their fixtures. S23: In the second ultrasonic cleaning tank, ultrasonic cleaning is used to clean nanoscale residues as well as trace particles and cleaning agent ions remaining in the ultrapure water spray tank of optical components and their fixtures. S24: In an ultrasonic pure water rinsing tank, ultrapure water is used to further peel off and disperse the residues attached to the optical components and their fixtures. S25: In a hot water rinsing tank, the optical components and their fixtures are lifted and rinsed in hot water to ensure that the surface moisture is evenly discharged. After rinsing, they are dried.

4. The high-precision etching method for multi-field coupling of optical components according to claim 1, characterized in that, In S3, the operating power of the megaphone controller is 1kW-5kW and the power density is 1W / cm³. 2 -5W / cm 2 It supports continuous adjustment in 5W steps and has a megaphone frequency of 0.65MHz-1MHz, ensuring that the etching uniformity error is less than or equal to ±0.05μm; A temperature control accuracy of ±0.5℃ is achieved through a constant temperature circulating water temperature control system, ensuring that the etching temperature remains stable in the range of 20-25℃. By using a pH meter in conjunction with hydrofluoric acid, the concentration fluctuation error of the etching solution is ensured to be less than or equal to ±0.5%. The multi-field coupling high-precision etching method ensures an etching accuracy of ±0.1μm during the etching process by using a megohmmeter controller, a constant temperature circulating water control system, a pH meter, and hydrofluoric acid.

5. The high-precision etching method for multi-field coupling of optical components according to claim 1, characterized in that, In step S4, the post-pickling treatment specifically includes the following steps: S41: After etching, the optical components and their fixtures are placed in a spray tank for spraying. After etching, the remaining impurities on the surface of the optical components are removed. S42: In a pure water rinsing tank, hydrofluoric acid residue on the surface of the etched optical components is initially removed by using ultrapure water and a physical dilution mechanism. S43: In an ultrapure water megasonic rinsing tank, the surface of the optical components is disturbed and peeled off by using cold water and megasonic rinsing solution in conjunction with the rinsing fluid. S44: In the hot water lifting tank, high-temperature pure water is used to further dilute the residual hydrofluoric acid liquid of the optical components to the PPM level by reducing surface tension and temperature difference driving effect, and the lifting reduces the residue of wall droplets and water marks. S45: The optical element is dried in a drying tank to obtain a dried etched optical element.

6. A multi-field coupling high-precision etching apparatus for optical elements, used in the multi-field coupling high-precision etching method for optical elements as described in any one of claims 1-5, characterized in that, This includes a pre-acid pickling treatment system, a mega-acoustic wet etching system, and a post-acid pickling treatment system; The pre-acid pickling treatment system includes a first ultrasonic cleaning tank, an ultrapure water spray tank, a second ultrasonic cleaning tank, an ultrapure water rinsing tank, and a hot water rinsing tank. Optical components and their fixtures are cleaned of surface residues by the pre-acid pickling treatment system, ensuring the surface of the optical components is dry and the number of impurity particles is less than or equal to 0.03 particles / mm. 2 ; The mega-acoustic wet etching system includes a hydrofluoric acid etching tank, a mega-acoustic controller, and a constant temperature circulating water temperature control system. The hydrofluoric acid etching tank has a built-in temperature sensor and pH meter. The optical components are etched by the mega-acoustic wet etching system, and the etching control accuracy is ensured to reach ±0.1μm. The pickling post-treatment system includes a spray tank, a pure water rinsing tank, an ultrapure water megasonic rinsing tank, a hot water lifting tank, and a drying tank. The optical element is treated by the pickling post-treatment system to remove surface impurities after etching, and the residual hydrofluoric acid on the surface is diluted to the PPM level and dried to obtain a dry etched optical element.

7. The high-precision etching apparatus for multi-field coupling of optical components according to claim 6, characterized in that, The constant temperature circulating water temperature control system has cooling pipes evenly distributed on the body of the hydrofluoric acid etching tank. The cooling liquid is circulated through the cooling pipes by a compressor and a heat exchanger to uniformly cool the etching liquid in the hydrofluoric acid etching tank.

8. The high-precision etching apparatus for multi-field coupling of optical components according to claim 7, characterized in that, The hydrofluoric acid etching tank has multiple temperature sensors evenly distributed inside. These temperature sensors are connected to a constant temperature circulating water control system. The constant temperature circulating water control system collects the temperature inside the tank through the multiple temperature sensors and automatically starts and stops the cooling and coolant circulation according to a preset temperature threshold.

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