Method for preparing secondary aspherical microstructure of glass substrate

Abstract

The application discloses a kind of preparation methods of glass substrate secondary aspheric surface microstructure, comprising the following steps: S1, optical glass substrate is pretreated;S2, preparation secondary gradually variable thickness gray scale mask, mask is adhered to glass substrate surface;S3, using picosecond ultrafast laser etching is combined with ultrasonic vibration auxiliary and high-pressure optical cooling liquid chip removal composite etching process, control etching posture, using layered etching strategy is processed to glass substrate;S4, etching depth and secondary aspheric surface profile accuracy are monitored in real time during etching, form closed-loop control, automatically adjust etching parameter;S5, after etching is completed, in proper order post-processing and detection acceptance are carried out, and secondary aspheric surface microstructure is obtained.The preparation method of glass substrate secondary aspheric surface microstructure of the application, through mask optimization, glass special composite etching process is combined with the closed-loop control of surface profile and depth, realizes the high-precision, high-efficiency preparation of secondary aspheric surface small-caliber, large-depth microstructure on glass substrate.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication technology. Specifically, this invention relates to a method for preparing secondary aspherical microstructures on glass substrates. Background Technology

[0002] As optical imaging technology advances towards miniaturization, high precision, and high integration, secondary aspherical microstructures, due to their excellent light focusing, homogenization, and aberration correction capabilities, are increasingly widely used in fields such as lidar homogenizers, miniature optical lenses, and fiber optic coupling devices. Among these, the secondary aspherical microstructures required for lidar large diffusion angle homogenizers must simultaneously meet the requirements of a small aperture design (≤30μm) to ensure uniform light homogenization, a large depth requirement (≥50μm) to achieve large diffusion angle output, and be fabricated on a glass substrate (to ensure high transmittance, high hardness, and optical stability). Furthermore, the microstructures must possess high surface accuracy, smooth hole walls, and be free of edge chipping and cracks to avoid affecting optical transmission and homogenization effects.

[0003] Currently, microstructure processing methods are mainly divided into two categories: mechanical processing and special processing. For the secondary aspherical microstructure processing of glass substrates, existing technologies face significant bottlenecks: mechanical processing, such as micro-milling and grinding, is limited by the high brittleness and hardness of glass, easily resulting in edge chipping and cracking during processing, and cannot achieve small-diameter processing below 30μm, making it even more difficult to guarantee the surface accuracy of the secondary aspherical surface; special processing, such as traditional laser processing, reactive ion etching, and wet etching, while capable of small-diameter processing, suffers from many adaptability defects: traditional laser processing utilizes high-energy beams to melt and erode glass materials, resulting in a large heat-affected zone, which is prone to... This can lead to crystallization and cracking on the glass surface, damaging light transmittance. Furthermore, increasing the depth during small-diameter processing can easily cause surface distortion, failing to meet the precision requirements of secondary aspherical surfaces. While reactive ion etching can achieve high processing precision, its etching rate is slow, and when the aperture is reduced to below 30μm, the etching depth is difficult to exceed 50μm, limiting the aspect ratio. It is also difficult to precisely control the surface profile of secondary aspherical surfaces. Wet etching, based on the anisotropic etching of glass, can lead to chip removal difficulties and problems such as aperture deformation and sidewall roughness when the depth is increased at small diameters. Moreover, the surface control precision is extremely low, making it unsuitable for the processing requirements of secondary aspherical microstructures.

[0004] In the existing technology, there is no preparation method that can take into account the compatibility with glass substrate, small aperture of ≤30μm, large depth of ≥50μm and secondary aspherical surface accuracy, while ensuring the light transmittance and surface quality of the microstructure. This cannot meet the application requirements of optical imaging devices such as lidar light homogenizers.

[0005] Therefore, developing a preparation method that can be adapted to glass substrates, stably realize the secondary aspherical microstructure processing with small diameter and large depth, and ensure the light transmittance and surface quality of the microstructure has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for preparing secondary aspherical microstructures on a glass substrate, with the goal of achieving high-precision and high-efficiency preparation of small-diameter, deep-depth secondary aspherical microstructures on a glass substrate.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing secondary aspherical microstructures on a glass substrate, comprising the following steps: S1. Pre-treat the optical glass substrate; S2. Prepare a secondary gradient thickness grayscale mask that is adapted to the secondary aspherical surface shape, and attach and fix the mask to the surface of the pretreated glass substrate. S3. A composite etching process combining picosecond ultrafast laser etching with ultrasonic vibration assistance and high-pressure optical coolant chip removal is adopted. The etching posture is controlled by a five-axis linkage platform, and a layered etching strategy is used to process the glass substrate. S4. During the etching process, the etching depth and the accuracy of the secondary aspherical surface shape are monitored in real time to form a dual closed-loop control of depth and surface shape, and the etching parameters are automatically adjusted. S5. After etching, post-processing and testing are carried out sequentially to obtain secondary aspherical microstructures with a diameter of 10-30μm and a depth of 50-200μm.

[0008] In step S1, the pretreatment includes ultrasonic cleaning, vacuum drying and annealing performed sequentially; the ultrasonic cleaning is performed sequentially using deionized water, anhydrous ethanol and optical glass cleaning agent, with each cleaning step taking 15-20 minutes; the vacuum drying temperature is 80-100℃ and the drying time is 20-30 minutes.

[0009] In step S1, the annealing process involves placing the dried glass substrate in an annealing furnace, holding it at 450-550℃ for 2-3 hours, cooling it in the furnace to 200℃, and then air-cooling it to room temperature. The surface flatness of the pretreated glass substrate is ≤0.3μm, and the light transmittance is ≥90%. The optical glass substrate is any one of quartz glass, borosilicate glass, or soda glass.

[0010] In step S2, the secondary gradient thickness grayscale mask is prepared using grayscale photolithography combined with projection mask moving filter technology; the opening size of the mask is 10-30μm, the flatness of the opening edge is ≤0.1μm, the mask thickness is distributed in a secondary gradient from the center of the opening to the edge, the gradient is 0.5-2μm / mm, and the total thickness of the mask is 4-6μm.

[0011] In step S3, the picosecond ultrafast laser has a pulse width of 10-50 ps, ​​a laser power of 80-200 mW, a laser focusing spot diameter of 5-10 μm, and a laser scanning trajectory adapted to the contour of a quadratic aspherical surface.

[0012] In step S3, the frequency of the ultrasonic vibration is 20-40kHz and the amplitude is 1-2μm; the high-pressure optical coolant is a residue-free coolant with added nano-SiO2 particles, the coolant pressure is 5-8MPa, the flow rate is 10-15L / min, and the coolant nozzle is oriented towards the etching area.

[0013] In step S3, the layered etching strategy involves controlling the etching depth of each layer to 2-4 μm. After each layer is etched, ultrasonic cleaning at a frequency of 20-30 kHz for 3-5 minutes is used to remove residual debris before proceeding to the next layer. During the etching process, the five-axis linkage platform adjusts the relative posture of the laser focusing position and the glass substrate in real time to control the perpendicularity deviation between the etching direction and the substrate surface to ≤0.5°.

[0014] In step S4, laser interferometry endpoint detection technology is used to monitor the etching depth in real time, with a depth detection accuracy of ±0.1μm; a phase-shifting interferometer is used to detect the surface accuracy of the secondary aspherical surface in real time; the depth data and surface data are synchronously fed back to the etching control system, and the laser power, etching speed, ultrasonic vibration parameters and five-axis linkage attitude are automatically adjusted after being compared with preset parameters.

[0015] In step S5, the post-processing sequentially includes mask removal, plasma cleaning, low-temperature vacuum drying, and optical precision polishing; the mask removal uses an optical glass release agent or plasma etching, with a removal time of 8-12 min; the plasma cleaning time is 8-10 min; the low-temperature vacuum drying temperature is 60-80℃, and the drying time is 30-60 min; the optical precision polishing uses chemical mechanical polishing combined with robotic automatic polishing, and after polishing, the surface roughness Ra of the inner wall of the microstructure is ≤0.03μm, and the light transmittance of the substrate remains ≥90%.

[0016] In step S5, the inspection and acceptance includes: A laser diameter gauge was used to detect the aperture size and uniformity of the microstructure. Laser interferometer was used to detect the depth and perpendicularity of microstructures; The surface roughness of the inner wall of the microstructure was detected using atomic force microscopy. The accuracy of the surface profile of a secondary aspherical surface is measured using a phase-shifting interferometer. The transmittance of the substrate was measured using a transmittance tester.

[0017] The method for preparing secondary aspherical microstructures on glass substrates of the present invention achieves high-precision and high-efficiency preparation of secondary aspherical microstructures with small diameter and large depth on glass substrates by combining mask optimization, glass-specific composite etching process with closed-loop control of surface shape and depth. Detailed Implementation

[0018] The following description of the embodiments further illustrates the specific implementation of the present invention in detail, with the aim of helping those skilled in the art to have a more complete, accurate, and in-depth understanding of the concept and technical solution of the present invention, and facilitating its implementation.

[0019] It should be noted that in the following embodiments, the terms "first," "second," and "third" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution; they are merely for the convenience of description.

[0020] This invention provides a method for preparing secondary aspherical microstructures on a glass substrate, comprising the following steps: S1. Pre-treat the optical glass substrate; S2. Prepare a secondary gradient thickness grayscale mask that is adapted to the secondary aspherical surface shape, and attach and fix the mask to the surface of the pretreated glass substrate. S3. A composite etching process combining picosecond ultrafast laser etching with ultrasonic vibration assistance and high-pressure optical coolant chip removal is adopted. The etching posture is controlled by a five-axis linkage platform, and a layered etching strategy is used to process the glass substrate. S4. During the etching process, the etching depth and the accuracy of the secondary aspherical surface shape are monitored in real time to form a dual closed-loop control of depth and surface shape, and the etching parameters are automatically adjusted. S5. After etching, post-processing and testing are carried out sequentially to obtain secondary aspherical microstructures with a diameter of 10-30μm and a depth of 50-200μm.

[0021] Specifically, the method for preparing secondary aspherical microstructures on glass substrates according to the present invention can realize the preparation of high-precision secondary aspherical microstructures with a diameter of 10-30μm and a depth of 50-200μm on glass substrates, which can meet the application requirements of various devices in the field of optical imaging.

[0022] In step S1 above, the optical glass substrate undergoes pretreatment to eliminate internal stress and surface impurities, providing a stable substrate foundation for subsequent microstructure processing. The optical glass substrate can be any of quartz glass, borosilicate glass, or soda glass, and the selection can be flexible based on actual optical performance requirements.

[0023] In step S1 above, the pretreatment includes ultrasonic cleaning, vacuum drying and annealing in sequence; ultrasonic cleaning is performed sequentially using deionized water, anhydrous ethanol and optical glass cleaning agent, with each cleaning step taking 15-20 minutes; vacuum drying temperature is 80-100℃ and drying time is 20-30 minutes.

[0024] Furthermore, during ultrasonic cleaning, deionized water, anhydrous ethanol, and optical glass-specific cleaning agent are used sequentially to ultrasonically clean the glass substrate. The cleaning time for each step is controlled to be 15-20 minutes. By using multiple media and step-by-step cleaning, dust, organic contaminants, and oxide layers on the substrate surface can be effectively removed, avoiding impurities from affecting the accuracy of subsequent photolithography and etching.

[0025] After cleaning, place the glass substrate in a vacuum drying device and dry it at a temperature of 80-100℃ for 20-30 minutes to remove the residual cleaning solution on the surface of the glass substrate and ensure that the surface of the glass substrate is dry and clean.

[0026] The dried glass substrate is then placed in an annealing furnace, heated to 450-550℃ and held for 2-3 hours, followed by furnace cooling to 200℃. After removal, it is air-cooled to room temperature. Annealing effectively eliminates residual stress inside the glass substrate, preventing defects such as substrate cracking and surface distortion caused by stress concentration during subsequent laser etching, while also improving the optical uniformity of the substrate.

[0027] After the above pretreatment, the surface flatness of the glass substrate is ≤0.3μm, and the transmittance in the visible light band is ≥90%, which meets the substrate requirements for high-precision microstructure processing.

[0028] In step S2 above, a secondary gradient thickness grayscale mask matching the target secondary aspherical surface needs to be prepared and bonded to the pretreated glass substrate surface to provide a pattern reference and etching mask for subsequent etching processing. The secondary gradient thickness grayscale mask is prepared using grayscale photolithography combined with projection mask moving filtering technology; the mask opening size is 10-30μm, the opening edge flatness is ≤0.1μm, the mask thickness is distributed in a secondary gradient from the opening center to the edge, the gradient is 0.5-2μm / mm, and the total mask thickness is 4-6μm. During the etching process, the etching rate of different areas can be controlled by the gradient difference in film thickness to realize the reproduction of the curved surface contour of the secondary aspherical surface.

[0029] In step S2 above, the secondary gradient thickness grayscale mask is fabricated using grayscale lithography combined with projection mask moving filter technology. Based on the theoretical surface data of the secondary aspherical surface, a grayscale distribution map is digitally generated. Projection mask moving filter is used to eliminate diffraction and step errors at the lithographic edges. The mask film layer achieves a continuous gradient thickness through grayscale lithography, ultimately obtaining a dedicated grayscale mask that precisely matches the surface shape of the secondary aspherical surface. This provides a preliminary pattern reference for subsequent pattern transfer and etching depth control. Specifically, the complete fabrication process of the secondary gradient thickness grayscale mask includes the following steps: S201. Surface Data Analysis and Gray-Scale Mapping Modeling: Import the surface equation, aperture size, depth distribution, and curvature parameters of the target quadratic aspherical surface, and linearly convert the axial etching depth difference at various points on the glass substrate into photolithographic gray-scale levels. Based on the required etching depth at each location of the surface, divide it into 256 continuous gray levels, and establish a one-to-one correspondence between etching depth, gray-scale level, and mask film thickness; for areas with greater depth, the corresponding mask gray-scale value is higher and the film thickness is greater, providing a quantitative basis for subsequent pattern transfer; S202. Mask substrate pretreatment: High flatness quartz glass is selected as the mask substrate. It is subjected to ultrasonic cleaning, plasma resist removal and drying in sequence to ensure that the surface roughness of the substrate is <5nm and that there are no impurities, scratches and other defects, so as to avoid the distortion of photolithography pattern caused by substrate defects. S203. Photoresist spin coating and pre-baking: A grayscale photoresist is uniformly spin-coated onto the surface of the mask substrate, and the thickness uniformity deviation of the photoresist layer is controlled to be <±10nm; after spin coating, a constant temperature pre-baking is performed to remove organic solvents in the photoresist layer and improve the adhesion between the photoresist layer and the substrate and the photosensitivity stability. S204. Grayscale photolithography pattern exposure: Using a high-precision grayscale photolithography device, the secondary aspherical grayscale pattern generated in step S201 is loaded, and zoned quantitative exposure is performed according to the zoned grayscale parameters. Different grayscale regions receive corresponding doses of exposure energy, causing the photoresist to produce differentiated photochemical reactions, forming a latent image pattern that matches the surface shape of the secondary aspherical surface; S205. Simultaneous implementation of projection mask moving filter: During the exposure process, a small-amplitude reciprocating movement filter mechanism of the projection mask is activated to control the mask to perform micron-level uniform translation and micro-amplitude oscillation within the exposure optical path, thereby offsetting problems such as edge diffraction, line burrs, and gray-level step transitions caused by traditional fixed masks; moreover, the filtering effect is strengthened for aspherical curvature change regions, weakening local light field inhomogeneity and ensuring continuous gray-level transition without jumps; S206. Development, Fixing and Post-Baking: A constant temperature and uniform speed development process is adopted, which utilizes the difference in the dissolution rate of photoresist in different grayscale regions to form a photoresist pattern with a continuous gradient thickness. After development, fixing, pure water cleaning, and strong air drying are performed in sequence, followed by high temperature post-baking to solidify the photoresist layer structure and improve the etching resistance of the photoresist layer. S207. Mask Coating and Pattern Transfer: Using a photoresist pattern of varying thickness as a protective layer, a metal light-shielding film is deposited on the mask surface using magnetron sputtering. Then, the varying thickness structure of the photoresist is transferred to the light-shielding film layer by dry etching. After stripping off the residual photoresist, a grayscale mask semi-finished product with continuously varying film thickness and matching secondary aspherical surface shape is obtained. S208. Accuracy Inspection and Correction: The film thickness and grayscale uniformity of each region of the grayscale mask semi-finished product are detected by using a profilometer and a spectrometer. The theoretical surface data are compared, and the deviation areas are locally repaired. The final finished mask has a film thickness error of <10nm, and the grayscale transition is continuous, meeting the accuracy requirements of secondary aspherical pattern transfer.

[0030] After the secondary gradient thickness grayscale mask is prepared, it is bonded and fixed to the surface of the pretreated glass substrate using optical photoresist to ensure that the mask opening is aligned with the preset processing position and the alignment deviation is <1μm.

[0031] In step S3 above, a composite etching process combining picosecond ultrafast laser etching with ultrasonic vibration assistance and high-pressure optical coolant chip removal is employed. The etching posture is controlled by a five-axis linkage platform, and a layered etching strategy is used to process the glass substrate layer by layer, achieving the formation of secondary aspherical microstructures. The composite etching system used in this step mainly includes a picosecond ultrafast laser etching subsystem, an ultrasonic vibration assistance subsystem, a high-pressure coolant supply subsystem, and a five-axis linkage platform.

[0032] In step S3 above, a picosecond-level ultrafast laser is selected as the etching energy source to achieve cold processing of the glass material, significantly reducing the heat-affected zone and preventing crystallization and cracking on the glass surface. The picosecond ultrafast laser has a pulse width of 10-50 ps, ​​a laser power of 80-200 mW, a laser focused spot diameter of 5-10 μm, and a laser scanning trajectory adapted to the curved contour of the quadratic aspherical surface, ensuring that the etching contour is consistent with the target surface shape.

[0033] In step S3 above, the ultrasonic vibration provided by the ultrasonic vibration-assisted subsystem has a frequency of 20-40 kHz and an amplitude of 1-2 μm. Ultrasonic vibration promotes the removal of etching debris from the processing area, avoiding surface scratches and uneven etching caused by debris accumulation. At the same time, it can improve the etching characteristics of the glass material to a certain extent and reduce the risk of cracking.

[0034] In step S3 above, the high-pressure optical coolant is supplied by a high-pressure coolant supply subsystem. This high-pressure optical coolant is a residue-free coolant containing nano-SiO2 particles, with a pressure of 5-8 MPa and a flow rate of 10-15 L / min. The coolant nozzles of the high-pressure coolant supply subsystem are directed towards the etching area. The high-pressure coolant quickly washes away the debris and molten material generated during etching. Combined with the lubricating and polishing effects of the nano-SiO2 particles, it prevents debris residue from scratching the inner walls of the microstructure. Simultaneously, it provides real-time cooling to the processing area, further suppressing the formation of a heat-affected zone.

[0035] To address the challenges of processing small-diameter, deep-depth glass microstructures, this invention abandons the one-time deep etching approach and adopts a stepped layer etching strategy, which divides the total etching depth into multiple etching layers for processing one by one, adapting to the brittle characteristics of glass and the continuous curvature variation of secondary aspherical surfaces.

[0036] In step S3 above, the layered etching strategy involves controlling the etching depth of each layer to 2-4 μm. After each layer is etched, residual debris is removed by ultrasonic cleaning at a frequency of 20-30 kHz for 3-5 minutes before proceeding to the next layer. The complete layered etching process includes the following steps: S301. Etching Layer Planning: Layering is performed based on the target total etching depth, the rate of change of curvature of the secondary aspherical surface, and the maximum depth of a single laser etching layer. For areas with gentle curvature, thicker etching layers are used to improve processing efficiency; for areas with abrupt curvature changes and structural edges, thinner etching layers are used to improve surface shape control accuracy. The theoretical etching depth, processing area range, and corresponding surface shape coordinates for each layer are recorded to generate a layered etching process table. S302. Substrate clamping and initial alignment: Fix the cleaned and dried glass substrate in the tooling of the five-axis linkage platform. Use visual positioning and laser focusing dual alignment methods to calibrate the center of the glass substrate and the reference axis of the secondary aspherical surface to ensure that the initial position deviation between the center of the glass substrate and the reference axis of the secondary aspherical surface is <1μm. S303. First layer reference etching: The pattern transfer is completed by a secondary gradient thickness grayscale mask. The picosecond ultrafast laser etching subsystem is started to etch each layer according to the preset etching. After etching is completed, the processing is paused and the surface shape, depth and sidewall verticality data of the current layer are collected by an online contour detection device as the reference for subsequent layer processing. S304. Layered Iterative Etching and Real-time Surface Shape Verification: Processing is carried out strictly according to the layered sequence. The processing flow for a single layer is as follows: parameter call → laser etching → online detection → deviation correction → processing of the next layer. After each layer is etched, the theoretical surface shape parameters of that layer are compared. If depth deviation or curvature offset occurs, the etching trajectory, laser energy, and etching speed of the next layer are immediately fine-tuned. Accumulated errors are eliminated through layer-by-layer closed-loop processing. S305. Layer transition area optimization: For the stepped transition positions between layers, a trajectory smoothing interpolation method is used to weaken the interlayer steps; for the quadratic aspherical surface area, the curvature fitting degree of the etching path is finely adjusted layer by layer to ensure that the overall surface is continuous and smooth after multiple layers are stacked, without obvious layering marks. S306. Final layer finishing etching: When processing to the penultimate layer, reduce the single layer etching depth and laser scanning speed, carry out final layer finishing etching, and perform overall calibration of the surface shape, depth and sidewall perpendicularity of the entire diameter to further improve the surface shape accuracy; S307. Post-etching cleaning: After all layer processing is completed, a combination of ultrasonic and organic solvent cleaning is used to thoroughly remove etching residues and dust from the surface of the glass substrate, completing the entire process of step-by-step layer etching.

[0037] During the etching process, the relative posture of the laser focusing position and the glass substrate is adjusted in real time using a five-axis linkage platform to ensure that the perpendicularity deviation between the etching direction and the substrate surface is ≤0.5°, thus ensuring the surface accuracy of the secondary aspherical surface. The five-axis linkage platform consists of X / Y / Z linear axes and A / B rotary axes, and is equipped with a laser focusing module, an online surface shape detection module, a secondary aspherical surface parameter database, and a motion control closed-loop system. Specifically, the attitude control logic of the five-axis linkage is as follows: 1. Preset parameter loading and coordinate system binding: The surface equation, radius of curvature, theoretical depth of each point, and normal angle of the target quadratic aspherical surface are all entered into the control system in advance. A unified coordinate system is established for the glass substrate, laser focus, and five-axis linkage platform, and the theoretical attitude parameters corresponding to each processing coordinate point are bound.

[0038] 2. Dynamic laser focus tracking control: The Z-axis serves as the laser focusing axis. During the processing, the Z-axis position is dynamically adjusted in real time. Based on the surface undulations of the secondary aspherical surface, the laser focus is kept on the glass surface to be etched throughout the entire process, eliminating uneven etching depth and spot distortion caused by focus shift. The focus positioning repeatability is <0.1μm.

[0039] 3. Real-time five-axis attitude matching with surface normal: Rotary axes A and B are responsible for adjusting the substrate attitude, and the laser etching direction is always perpendicular to the tangent plane of the current point on the secondary aspherical surface. The control system reads the etching trajectory coordinates in real time, retrieves the theoretical normal angle of the surface at that point, and synchronously drives the A and B rotary axes to fine-tune the substrate attitude, so that the laser beam remains perpendicular to the tangent plane of the glass surface; it dynamically compensates for minute displacements and mechanical vibrations of the substrate throughout the process, controlling the perpendicularity deviation between the etching direction and the substrate surface to ≤0.5°.

[0040] 4. Layered Etching Trajectory Planning and Execution: Combining the contour of each layer in the stepped etch, the control system plans the laser scanning trajectory point by point and line by line based on the radial coordinates of the quadratic aspherical surface. The trajectory strictly fits the theoretical surface contour, avoiding trajectory deviation, repeated etching, and missed etching. During each etching process, X / Y axis linkage achieves high-precision scanning, with motion interpolation accuracy <0.1μm.

[0041] 5. Depth Closed-Loop Detection and Error Correction: After each trajectory segment or entire etching layer is completed, the online laser profilometer collects the actual depth and actual surface profile in real time, comparing them with theoretical parameters to calculate the deviation. When the surface profile error is <0.2μm, normal processing continues; when the surface profile error approaches or exceeds the threshold, trajectory operation is immediately paused, and the attitude is finely adjusted and the etching depth and trajectory for the next segment are corrected through a five-axis linkage platform, forcing the final surface profile error of the entire process to be stabilized at ≤0.2μm.

[0042] 6. Full-range continuous machining guarantee: For small-diameter, deep structures, the five-axis linkage platform adopts a continuous motion mode to avoid attitude jitter caused by start-stop; the attitude of curved edges and curvature extreme points is pre-adjusted in advance to ensure that the perpendicularity and surface accuracy meet the standards throughout the entire diameter range.

[0043] In step S4 above, during the etching process, the etching depth and the surface accuracy of the secondary aspherical surface are monitored in real time to form a closed-loop control of depth and surface accuracy, and the etching parameters are automatically adjusted to ensure processing accuracy. Laser interferometry endpoint detection technology is used to monitor the etching depth in real time, with a depth detection accuracy of ±0.1μm; a phase-shifting interferometer is used to detect the surface accuracy of the secondary aspherical surface in real time; the depth data and surface data are synchronously fed back to the etching control system, and after comparison with preset parameters, the laser power, etching speed, ultrasonic vibration parameters, and five-axis linkage attitude are automatically adjusted. The specific control and adjustment process includes the following steps: S401. Multi-parameter calibration and process library establishment: Complete the process calibration test in advance. For different glass materials, different etching depths, and different surface curvatures, test and establish a parameter matching process library, which includes four major categories of parameters: laser power range, scanning etching speed range, ultrasonic vibration frequency and amplitude, and five-axis attitude compensation amount. These parameters correspond one-to-one with the characteristics of each region of the secondary aspherical surface, providing data support for automatic control. S402. Deployment of multiple sensing units for real-time data acquisition: The depth detection unit employs laser interferometry endpoint detection technology to acquire etching depth data in real time, with a detection accuracy of ±0.1μm; the surface shape detection unit uses a phase-shifting interferometer to detect the surface shape accuracy of the secondary aspherical surface in real time; simultaneously, supporting vibration sensors and speed / position sensors acquire the real-time vibration state of the glass substrate and the motion speed and attitude angle of the five-axis platform. All acquired data is uploaded to the upper control system at millisecond-level frequency; S403. Automatic Laser Power Matching by Zone: The control system automatically adjusts the laser power based on the local depth, curvature, and etching difficulty of the aspherical surface. For areas with great depth and high curvature, the laser output power is automatically increased to ensure that the etching rate and depth meet the requirements. For shallow depth, gently curved surfaces, and areas with fine edges, the laser power is automatically reduced to prevent over-etching and sidewall ablation. The power adjustment is continuously stepless, with a response time of <10ms.

[0044] S404. Dynamic Adaptive Adjustment of Etching Speed: The etching scanning speed is adjusted in conjunction with laser power and surface curvature. For areas with abrupt curvature changes or high precision requirements, the scanning speed is automatically reduced, the laser action time is extended, and the contour accuracy is improved. For flat, large-area areas, the etching speed is automatically increased to improve processing efficiency. Speed ​​adjustment and trajectory interpolation are performed synchronously to ensure uniform scanning without stuttering.

[0045] S405. Automatic Control of Ultrasonic Vibration Parameters: The system automatically adjusts the frequency and amplitude of ultrasonic vibration based on the etching depth and the difficulty of residue removal. For deep etching stages, the ultrasonic amplitude is increased and the frequency is optimized to accelerate the removal of etching debris and melt, preventing residue from adhering to the surface and causing surface defects. For shallow finishing stages, the ultrasonic amplitude is reduced to minimize the impact of vibration on the substrate's posture and surface accuracy. Ultrasonic parameters are synchronously linked with five-axis posture and laser parameters.

[0046] S406. Five-axis attitude linkage correction: When the laser power, etching speed, and ultrasonic parameters are adjusted, the control system synchronously pre-compensates the five-axis linkage attitude to offset the slight position and angle shifts caused by power changes and vibrations, and always maintains the verticality and trajectory accuracy of the laser beam; if the sensor detects an attitude deviation, it immediately corrects the A / B rotation axis angle in a closed loop.

[0047] S407. Abnormal self-tuning and parameter reset: When conditions such as excessive depth, attitude deviation, or abnormal vibration are detected, the system automatically locks the current trajectory temporarily and rematches the optimal power, speed, ultrasonic, and attitude combination; after a single layer of processing is completed, all parameters are automatically reset to the initial process parameters of the next layer and the process is repeated.

[0048] S408. Full-process parameter recording and traceability: Automatically records the laser power, etching speed, ultrasonic parameters, and five-axis attitude data at every coordinate point throughout the process, forming a complete process log, which is convenient for process review and mass production reuse.

[0049] By implementing the closed-loop control described above, it can be ensured that the final fabricated microstructure has a depth accuracy of ≤ ±1 μm and a surface shape error of ≤ 0.2 μm.

[0050] In step S5 above, after etching is completed, post-processing and inspection are performed sequentially to obtain the final glass substrate secondary aspherical microstructure product. The post-processing sequentially includes mask removal, plasma cleaning, low-temperature vacuum drying, and optical precision polishing.

[0051] Specifically, the mask is removed using an optical glass release agent or plasma etching, with a removal time of 8-12 minutes. This process thoroughly removes the mask while avoiding damage to the glass surface, thus ensuring the light transmittance of the substrate.

[0052] Plasma cleaning technology is used to clean residual mask material and etching debris from the surface of the substrate and the interior of the microstructure. The cleaning time is 8-10 minutes, achieving clean treatment of the interior of the deep holes of the microstructure.

[0053] After cleaning, place the substrate in a vacuum drying device and dry it at 60-80℃ for 30-60 minutes to completely remove moisture and avoid water stains affecting optical performance.

[0054] A combination of chemical mechanical polishing (CMP) and robotic polishing is used to precisely polish the inner walls of the microstructure and the surface of the substrate, eliminating micro-scratches and burrs generated during etching. After polishing, the surface roughness Ra of the inner wall of the microstructure is ≤0.03μm, and the overall light transmittance of the substrate remains ≥90%, ensuring optical transmission performance.

[0055] In step S5 above, the inspection and acceptance process includes: A laser diameter gauge was used to detect the aperture size and uniformity of the microstructure. Laser interferometer was used to detect the depth and perpendicularity of microstructures; The surface roughness of the inner wall of the microstructure was detected using atomic force microscopy. The accuracy of the surface profile of a secondary aspherical surface is measured using a phase-shifting interferometer. The transmittance of the substrate was measured using a transmittance tester.

[0056] After passing the inspection, a high-precision glass substrate secondary aspherical microstructure with an aperture of 10-30μm and a depth of 50-200μm is obtained. Its aperture accuracy is ≤±0.5μm, depth accuracy is ≤±1μm, perpendicularity deviation is ≤0.5°, surface shape error is ≤0.2μm, inner wall surface roughness Ra is ≤0.03μm, and substrate transmittance is ≥90%. It can be directly applied to optical imaging devices such as large diffusion angle homogenizers for lidar, miniature imaging lenses, and optical sensors.

[0057] The method for preparing secondary aspherical microstructures on glass substrates according to the present invention has the following advantages compared with the prior art: 1. Overcoming the processing contradictions of glass substrates, small apertures, large depths, and secondary aspherical surface shapes, this technology is specifically adapted to the needs of the optical imaging field. Through high-precision gradient grayscale masks (adapted to secondary aspherical surface shapes) and glass-specific composite etching processes, it enables the processing of secondary aspherical microstructures with small apertures of 10-30μm and large depths of 50-200μm on glass substrates, with an aspect ratio of 5-20:1. This solves the core bottlenecks in existing technologies, such as the difficulty in breaking through the 50μm depth of small-aperture microstructures, insufficient accuracy of secondary aspherical surface shapes, and easy cracking of glass substrates. It can be directly adapted to optical imaging devices such as large diffusion angle homogenizers for lidar.

[0058] 2. Excellent optical performance and high processing precision: Picosecond-level ultrafast lasers are used for cold processing of glass, effectively suppressing the heat-affected zone and avoiding crystallization and cracking on the glass surface, ensuring that the light transmittance of the substrate is ≥90%; ultrasonic vibration-assisted chip removal combined with high-pressure special coolant completely solves the problem of chip removal difficulties in small-diameter etching, reducing the scraping of the inner wall of the microstructure by debris, and optical precision polishing makes the surface roughness Ra of the inner wall of the microstructure Ra≤0.03μm; through dual closed-loop control of depth and surface shape, the secondary aspherical surface shape error is ensured to be ≤0.2μm, the diameter accuracy is ≤±0.5μm, the depth accuracy is ≤±1μm, and the perpendicularity deviation is ≤0.5°, fully meeting the stringent requirements of optical imaging for microstructures.

[0059] 3. High processing efficiency and wide applicability: The layered etching strategy combined with dual closed-loop control ensures both processing accuracy and the optical performance of the glass substrate, while avoiding repeated processing. Compared with traditional reactive ion etching, the processing efficiency is improved by more than 40%. It is applicable to the processing of various optical glass substrates such as quartz glass and borosilicate glass, and can prepare various types of microstructures such as secondary aspherical micropores and microgrooves. It is suitable for various optical imaging scenarios such as lidar light homogenizers, miniature imaging lenses, and optical sensors, and has strong practicality.

[0060] 4. Strong process stability and good repeatability: The substrate pretreatment is specifically designed to remove residual stress inside the glass, avoiding processing cracks; the mask preparation adopts high-precision photolithography technology, which is suitable for secondary aspherical surface shapes; during the etching process, real-time depth and surface shape dual closed-loop control is used to ensure the consistency of size, surface shape and optical performance of each batch and each microstructure. The yield rate has been increased from about 60% in the existing technology to more than 95%, which reduces production costs, facilitates industrial mass production, and meets the needs of large-scale application of optical imaging devices.

[0061] The feasibility and technical effectiveness of the method of the present invention are further verified through three sets of examples with different parameters.

[0062] Example 1: Preparation of secondary aspherical microstructures in quartz glass This embodiment prepares a secondary aspherical microstructure of quartz glass with an aperture of 25 μm and a depth of 60 μm, adapted to a large diffusion angle homogenizer for lidar. The specific steps are as follows: 1. Substrate Pretreatment: Quartz glass sheets with a light transmittance ≥92% were selected as the substrate. They were ultrasonically cleaned sequentially using deionized water, anhydrous ethanol, and a quartz glass-specific cleaning agent, with each step lasting 15 minutes. After cleaning, the substrate was vacuum-dried at 90℃ for 25 minutes. Subsequently, it was placed in an annealing furnace and held at 500℃ for 2.5 hours, then cooled in the furnace to 200℃ and finally air-cooled to room temperature. After treatment, the surface flatness of the substrate was 0.2 μm, and the light transmittance remained at 92%.

[0063] 2. Mask Fabrication and Bonding: A grayscale mask with secondary gradient thickness was fabricated using silicon oxide as the mask material, employing grayscale photolithography combined with projection mask moving filtering technology. The mask aperture size was 25 μm, the aperture edge flatness was 0.08 μm, the thickness gradient was 1 μm / mm, and the total thickness was 5 μm. The mask was then bonded and fixed to the surface of a quartz glass substrate using optically specific photoresist.

[0064] 3. Composite Etching Process: The picosecond laser pulse width was set to 30 ps, ​​the power to 120 mW, and the focused spot diameter to 8 μm; the ultrasonic vibration frequency was 30 kHz, and the amplitude to 1.5 μm; the coolant used was a residue-free coolant specifically for quartz glass, with added nano-SiO2 particles, at a pressure of 7 MPa and a flow rate of 12 L / min. A layered etching strategy was adopted, with a single layer etching depth of 3 μm, for a total of 20 layers. After each layer was etched, it was ultrasonically cleaned at 25 kHz for 4 minutes to remove debris. During the etching process, the attitude was adjusted in real time using a five-axis linkage platform to control the verticality deviation to 0.3°.

[0065] 4. Dual closed-loop control: The depth is monitored by laser interferometry endpoint detection technology and the surface shape is monitored by phase-shifting interferometer, and the etching parameters are adjusted in real time. When the depth reaches 60μm and the surface shape error is 0.18μm, the control system automatically stops etching.

[0066] 5. Post-processing and testing: The mask was removed using a quartz glass-specific release agent and immersed for 10 minutes; plasma cleaning for 8 minutes; vacuum drying at 70℃ for 45 minutes; and chemical mechanical polishing combined with robotic polishing for 15 minutes. Testing revealed that the microstructure had an aperture of 25±0.3μm, a depth of 60±0.8μm, a perpendicularity deviation of 0.3°, an inner wall surface roughness Ra of 0.02μm, a surface shape error of 0.18μm, and a substrate transmittance of 91.5%. All indicators met the application requirements.

[0067] Example 2: Fabrication of secondary aspherical microstructures in borosilicate glass This embodiment prepares a borosilicate glass secondary aspherical microstructure with a diameter of 15 μm and a depth of 80 μm to be adapted to a miniature optical imaging lens. The specific steps are as follows: 1. Substrate Pretreatment: Borosilicate glass sheets with a light transmittance ≥90% were selected as the substrate. They were ultrasonically cleaned sequentially using deionized water, anhydrous ethanol, and a borosilicate glass-specific cleaning agent, with each step lasting 20 minutes. After cleaning, the substrate was vacuum-dried at 100℃ for 20 minutes. Subsequently, it was placed in an annealing furnace and held at 480℃ for 3 hours, then cooled in the furnace to 200℃ and finally air-cooled to room temperature. After treatment, the surface flatness of the substrate was 0.3 μm, and the light transmittance remained at 90%.

[0068] 2. Mask Fabrication and Bonding: A grayscale mask with secondary gradient thickness was fabricated using silicon nitride as the mask material, employing grayscale photolithography combined with projection mask moving filtering technology. The mask aperture size was 15 μm, the aperture edge flatness was 0.07 μm, the thickness gradient was 0.8 μm / mm, and the total thickness was 4 μm. The mask was then bonded and fixed to the surface of a borosilicate glass substrate.

[0069] 3. Composite Etching Process: The picosecond laser pulse width was set to 20 ps, ​​the power to 90 mW, and the focused spot diameter to 6 μm; the ultrasonic vibration frequency was 25 kHz, and the amplitude to 1.2 μm; the coolant used was a borosilicate glass-specific residue-free coolant with added nano-SiO2 particles, at a pressure of 6 MPa and a flow rate of 11 L / min. A layered etching strategy was adopted, with a single layer etching depth of 2 μm, for a total of 40 layers. After each layer was etched, ultrasonic cleaning was performed for 5 minutes to remove debris. During the etching process, the posture was adjusted in real time using a five-axis linkage platform to control the verticality deviation to 0.4°.

[0070] 4. Dual closed-loop control: The etching parameters are adjusted in real time through a dual closed-loop system of depth and surface shape; when the depth reaches 80μm and the surface shape error is 0.19μm, etching is stopped and the depth deviation is +0.9μm.

[0071] 5. Post-processing and inspection: The silicon nitride mask was removed by plasma etching for 12 minutes; plasma cleaning for 10 minutes; vacuum drying at 80℃ for 30 minutes; and optical precision polishing for 20 minutes. Inspection revealed that the microstructure had an aperture of 15±0.4μm, a depth of 80±0.9μm, a perpendicularity deviation of 0.4°, an inner wall surface roughness Ra of 0.03μm, a surface shape error of 0.19μm, and a substrate transmittance of 89.8%. All indicators met the requirements.

[0072] Example 3: Preparation of secondary aspherical microstructures in soda glass This embodiment prepares a secondary aspherical microstructure of soda glass with a diameter of 30 μm and a depth of 50 μm, which is adapted to a lidar-assisted light homogenizing device. The specific steps are as follows: 1. Substrate Pretreatment: Soda glass sheets with a light transmittance ≥91% were selected as the substrate. They were ultrasonically cleaned sequentially using deionized water, anhydrous ethanol, and a special soda glass cleaner, with each step lasting 18 minutes. After cleaning, the substrate was vacuum dried at 80℃ for 30 minutes. Subsequently, it was placed in an annealing furnace and held at 550℃ for 2 hours, then cooled in the furnace to 200℃ and finally air-cooled to room temperature. After treatment, the surface flatness of the substrate was 0.2 μm, and the light transmittance remained at 91%.

[0073] 2. Mask fabrication and bonding: A grayscale mask with secondary gradient thickness was fabricated using photoresist as the mask material, employing grayscale photolithography combined with projection mask moving filtering technology. The mask opening size was 30 μm, the opening edge flatness was 0.1 μm, the thickness gradient was 2 μm / mm, and the total thickness was 6 μm. The mask was then fixed onto the surface of a soda ash glass substrate.

[0074] 3. Composite Etching Process: The picosecond laser pulse width was set to 50 ps, ​​and the power to 200 mW; the ultrasonic vibration frequency was set to 40 kHz, and the amplitude to 2 μm; the coolant pressure was set to 8 MPa, and the flow rate to 15 L / min. A layered etching strategy was adopted, with a single layer etching depth of 4 μm, for a total of 13 layers. Through dual closed-loop control of depth and surface shape, the depth was guaranteed to reach 50 μm, and the surface shape error was ≤0.2 μm.

[0075] 4. Post-processing and inspection: After mask removal, plasma cleaning for 8 min; vacuum drying at 70℃ for 40 min; optical precision polishing for 10 min. Inspection revealed that the microstructure aperture was 30±0.5μm, depth was 50±0.7μm, perpendicularity deviation was 0.2°, inner wall surface roughness Ra was 0.02μm, surface shape error was 0.17μm, and substrate transmittance was 90.5%. All indicators met the requirements.

[0076] The present invention has been described above by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention; or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for preparing secondary aspherical microstructures on a glass substrate, characterized in that, Includes the following steps: S1. Pre-treat the optical glass substrate; S2. Prepare a secondary gradient thickness grayscale mask that is adapted to the secondary aspherical surface shape, and attach and fix the mask to the surface of the pretreated glass substrate. S3. A composite etching process combining picosecond ultrafast laser etching with ultrasonic vibration assistance and high-pressure optical coolant chip removal is adopted. The etching posture is controlled by a five-axis linkage platform, and a layered etching strategy is used to process the glass substrate. S4. During the etching process, the etching depth and the accuracy of the secondary aspherical surface shape are monitored in real time to form a dual closed-loop control of depth and surface shape, and the etching parameters are automatically adjusted. S5. After etching, post-processing and testing are carried out sequentially to obtain secondary aspherical microstructures with a diameter of 10-30μm and a depth of 50-200μm.

2. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S1, the pretreatment includes ultrasonic cleaning, vacuum drying and annealing performed sequentially; the ultrasonic cleaning is performed sequentially using deionized water, anhydrous ethanol and optical glass cleaning agent, with each cleaning step taking 15-20 minutes; the vacuum drying temperature is 80-100℃ and the drying time is 20-30 minutes.

3. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 2, characterized in that, In step S1, the annealing process involves placing the dried glass substrate in an annealing furnace, holding it at 450-550℃ for 2-3 hours, cooling it in the furnace to 200℃, and then air-cooling it to room temperature. The surface flatness of the pretreated glass substrate is ≤0.3μm, and the light transmittance is ≥90%. The optical glass substrate is any one of quartz glass, borosilicate glass, or soda glass.

4. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S2, the secondary gradient thickness grayscale mask is prepared using grayscale photolithography combined with projection mask moving filter technology; the opening size of the mask is 10-30μm, the flatness of the opening edge is ≤0.1μm, the mask thickness is distributed in a secondary gradient from the center of the opening to the edge, the gradient is 0.5-2μm / mm, and the total thickness of the mask is 4-6μm.

5. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S3, the picosecond ultrafast laser has a pulse width of 10-50 ps, ​​a laser power of 80-200 mW, a laser focusing spot diameter of 5-10 μm, and a laser scanning trajectory adapted to the contour of a quadratic aspherical surface.

6. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S3, the frequency of the ultrasonic vibration is 20-40kHz and the amplitude is 1-2μm; the high-pressure optical coolant is a residue-free coolant with added nano-SiO2 particles, the coolant pressure is 5-8MPa, the flow rate is 10-15L / min, and the coolant nozzle is oriented towards the etching area.

7. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S3, the layered etching strategy involves controlling the etching depth of each layer to 2-4 μm. After each layer is etched, ultrasonic cleaning at a frequency of 20-30 kHz for 3-5 minutes is used to remove residual debris before proceeding to the next layer. During the etching process, the five-axis linkage platform adjusts the relative posture of the laser focusing position and the glass substrate in real time to control the perpendicularity deviation between the etching direction and the substrate surface to ≤0.5°.

8. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S4, laser interferometry endpoint detection technology is used to monitor the etching depth in real time, with a depth detection accuracy of ±0.1μm; a phase-shifting interferometer is used to detect the surface accuracy of the secondary aspherical surface in real time; the depth data and surface data are synchronously fed back to the etching control system, and the laser power, etching speed, ultrasonic vibration parameters and five-axis linkage attitude are automatically adjusted after being compared with preset parameters.

9. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S5, the post-processing sequentially includes mask removal, plasma cleaning, low-temperature vacuum drying, and optical precision polishing; the mask removal uses an optical glass release agent or plasma etching, with a removal time of 8-12 min; the plasma cleaning time is 8-10 min; the low-temperature vacuum drying temperature is 60-80℃, and the drying time is 30-60 min; the optical precision polishing uses chemical mechanical polishing combined with robotic automatic polishing, and after polishing, the surface roughness Ra of the inner wall of the microstructure is ≤0.03μm, and the light transmittance of the substrate remains ≥90%.

10. The method for preparing secondary aspherical microstructures on a glass substrate according to claim 1, characterized in that, In step S5, the inspection and acceptance includes: A laser diameter gauge was used to detect the aperture size and uniformity of the microstructure. Laser interferometer was used to detect the depth and perpendicularity of microstructures; The surface roughness of the inner wall of the microstructure was detected using atomic force microscopy. The accuracy of the surface profile of a secondary aspherical surface is measured using a phase-shifting interferometer. The transmittance of the substrate was measured using a transmittance tester.