A method for quartz cutting using phase-modulated Bessel laser combined with chromium film protection

Abstract

This invention discloses a quartz cutting method combining phase-modulated Bessel laser cutting with chromium film protection. By modulating the wavefront phase of the incident Gaussian laser, the energy of the generated Bessel laser sidelobes is suppressed, reducing its damage to the material. A double-sided chromium film is applied to the quartz to protect the surface from etching damage. Ammonium bifluoride solution selectively etches the laser-modified areas. After etching, the chromium film is dissolved and removed, achieving high-quality quartz through-groove forming. This invention combines the high surface quality of traditional wet etching processes with the high perpendicularity of Bessel laser processing, demonstrating high-quality precision cutting capabilities for quartz and broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast laser application technology, and particularly relates to a method for quartz cutting using phase-modulated Bessel laser combined with chromium film protection. Background Technology

[0002] Quartz crystals, due to their piezoelectric effect and high quality factor, are often used to fabricate resonant beam structures. Changes in external force can cause changes in the resonant frequency of the beam, thus allowing the sensing of minute changes in external force by using the resonant frequency as the measured parameter. Quartz resonant beam structures are small in size, highly sensitive, and have high frequency stability. Quartz resonant beam sensors, with this structure as their core component, are widely used in sensing physical quantities such as acceleration, pressure, temperature, and humidity.

[0003] The fabrication of quartz resonant beams requires cutting through-slots into a quartz wafer to form the resonant beam structure. This process demands small dimensions, high precision, and the fact that quartz is a hard and brittle material, making traditional machining methods unsuitable. Therefore, a wet etching process based on photolithography is commonly used for cutting these through-slots. The basic steps are: obtaining a metal mask pattern on the quartz wafer surface using photolithography, followed by wet etching to obtain the through-slot structure. Specific steps include: sample cleaning, double-sided chromium / gold plating, double-sided spin-coating of photoresist, double-sided photolithography exposure, development and fixing, plasma etching of the metal film, wet etching of the quartz, and metal film removal. This process is complex and cumbersome. Furthermore, wet etching exhibits anisotropy, easily leading to side etching at the corners and sidewalls of the through-slots, resulting in crystal edges, poor etching uniformity and perpendicularity, and negatively impacting the resonant beam's performance.

[0004] Irradiating quartz crystals with a focused ultrafast laser alters the crystal structure of the irradiated area. The modified area exhibits a significantly higher etching rate in the etching solution than the unmodified area, enabling highly selective etching of quartz crystals. Ultrafast Bessel lasers, with their long focal depth and lack of diffraction, can achieve deep, efficient, and uniform modification of the quartz wafer, penetrating both the top and bottom surfaces. Combined with chemical etching, the modified area is thoroughly etched, achieving high-precision through-groove cutting of the quartz wafer. However, because the entire quartz wafer is immersed in the etching solution, etching causes thinning on both sides and pitting on the top and bottom surfaces, leading to decreased surface roughness and affecting resonator performance. Therefore, achieving high-quality, high-precision cutting of quartz wafers is one of the key factors restricting the manufacturing of high-quality quartz resonant beam sensors. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a quartz cutting method using phase-modulated Bessel laser combined with chromium film protection, which solves the problems of poor uniformity of etched crystal edges and resonator beams at corners and sidewalls due to the anisotropy of etching in traditional wet etching processes for quartz wafers, and the problem that ultrafast Bessel laser selective etching processes lead to overall thinning of quartz wafers, resulting in poor surface quality and reduced resonator performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for cutting quartz using phase-modulated Bessel laser combined with chromium film protection includes the following steps:

[0008] Step 1: Clean the Z-cut α-quartz wafer to be processed with acetone, anhydrous ethanol and deionized water respectively, and dry it with compressed air. Then, use electron beam evaporation to deposit chromium film on the upper and lower surfaces, with the upper surface chromium film thickness being 5-10nm and the lower surface thickness being 50-100nm.

[0009] Step 2: Establish a theoretical model for wavefront phase modulation Bessel optical field propagation, simulate optical field propagation, and obtain the wavefront modulation phase diagram corresponding to the Bessel optical field with optimal sidelobe suppression;

[0010] Step 3: Construct the phase-modulated Bessel laser processing optical path, load the wavefront modulation phase map corresponding to the Bessel light field with optimal sidelobe suppression onto the liquid crystal spatial light modulator, transport the modulated light to the front surface of the conical lens through the 4f lens system, and after the conical lens focuses, the phase-modulated Bessel laser is focused onto the translation stage surface through the 4f beam-shrinking system composed of a plano-convex lens and a focusing objective.

[0011] Step 4: Fix the quartz wafer with a chromium film on its surface onto a three-dimensional precision electronically controlled translation stage. Focus the phase-modulated Bessel laser onto the sample surface and control the movement of the translation stage so that the laser scans the quartz surface to obtain the designed contour. The contour trajectory is the laser-modified area.

[0012] Step 5: After cleaning the processed quartz wafer, immerse it in a saturated ammonium bifluoride solution and etch it thoroughly under water bath heating until the through-groove is etched and the designed contour structure is obtained.

[0013] Step 6: After cleaning the etched quartz wafer sample, immerse it in a chromium etching agent, cerium ammonium nitrate (NH4)2Ce(NO3)6 solution, to dissolve and remove the chromium protective layer; then clean the sample and dry it with compressed air to finally obtain the designed quartz through-channel structure.

[0014] Preferably, in step two, the incident Gaussian light is divided into two concentric beams by wavefront phase modulation, and the two beams are focused by a conical lens to produce interference in the Bessel region optical field, thereby suppressing the Bessel laser sidelobes. The interference optical field is modulated by a phase diagram, and the modulation parameters include the spot diameter R, the radius r of the inner circle, the number of phase rings n1 of the inner circle and the number of phase rings n2 of the outer circle, with the phase change range of 0-2π per ring. By optimizing the above three parameters and simulating the Bessel optical field, the phase diagram parameters under the optimal condition for suppressing the Bessel laser sidelobes are obtained.

[0015] Preferably, the chromium film thickness on the upper surface of the quartz wafer is 5-10 nm, and the thickness on the lower surface is 50-100 nm.

[0016] Preferably, in step three, the ultrafast laser emitted by the ultrafast laser in the phase-modulated Bessel laser processing optical path is limited by an aperture, attenuated by an attenuator group, and then reflected by an ultrafast mirror into a liquid crystal spatial light modulator to phase-modulate the incident Gaussian laser, generating a modulated light field. The light field is transported to the front surface of a conical lens by a 4f lens system consisting of a first lens and a second lens. The front surface of the conical lens and the liquid crystal screen of the spatial light modulator are conjugate surfaces. After the modulated light is focused by the conical lens, optical field interference occurs, generating a phase-modulated Bessel light field with suppressed side lobes. After being focused by a beam-shrinking system consisting of a plano-convex lens and a focusing objective, the beam is focused onto the surface of a quartz wafer sample, which is fixed on a three-dimensional precision electrically controlled translation stage. The illumination light from the illumination source is irradiated onto the sample surface by a beam splitter and a dichroic mirror. An imaging camera is located behind the beam splitter to image the sample surface, enabling real-time observation of the processing process.

[0017] As a preferred option, in step five, the processed sample is immersed in the etching solution, and a constant temperature water bath is used to ensure that the etching environment temperature is constant, controlled at 50°C, and the sample etching time is 2-3 hours until the through groove is etched and formed.

[0018] As a preferred embodiment, the incident light field radius is 3mm, the inner circle radius is 1.2mm, the number of inner annular phase regions n1=6, and the number of outer annular phase regions n2=3. Simulation results show that the minimum ratio of the first side lobe to the main lobe in the central region of the Bessel light field is 1.7%.

[0019] Preferably, in step three, the phase-modulated Bessel laser processing optical path uses an ultrafast laser, specifically a femtosecond laser or a picosecond laser.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention addresses the problem of overall corrosion and pitting defects in quartz wafers during ultrafast laser modification combined with chemical etching. This invention utilizes electron beam evaporation to deposit chromium films on both the upper and lower surfaces of the quartz wafer as protective layers during the etching process, effectively protecting the quartz surface from damage. The chromium film thickness on the upper surface (laser incident surface) is 5-10 nm to ensure high optical transmittance, while the thickness on the lower surface is 50-100 nm to minimize the ablation of the chromium film on the lower surface by the Bessel lobes passing through the quartz.

[0022] 2. This invention utilizes wavefront phase modulation to modulate the incident Gaussian laser into two concentric beams, and then focuses them through a conical lens to cause optical field interference in the Bessel region. By adjusting the phase diagram parameters, the sidelobe interference of the Bessel laser is canceled out, thereby suppressing the sidelobes. When processing chromium-plated quartz wafers, this effectively reduces the chromium film ablation zone on both sides of the scanning trajectory.

[0023] 3. This invention utilizes a liquid crystal spatial light modulator to perform phase modulation on the Gaussian light field in front of the conical lens. It offers high flexibility, enabling arbitrary modulation of the wavefront phase and thus arbitrary control of the energy distribution of the Bessel light field, thereby minimizing the sidelobe energy ratio.

[0024] 4. This invention utilizes the characteristic that the irradiated region of a Bessel laser has a faster etching rate in the etching solution compared to the intrinsic region, achieving highly selective etching. The Bessel laser has a long focal depth along its propagation direction, good optical field uniformity, and highly concentrated energy, enabling deep modification penetrating the upper and lower surfaces of the quartz wafer. The selective etching of the modified region results in cut sidewalls with good perpendicularity and low roughness (less than Ra0.1), effectively solving the problem of crystal edges and poor perpendicularity on the sidewalls caused by anisotropic etching in traditional wet etching processes.

[0025] 5. This invention utilizes a precision electronically controlled translation stage to move the sample relative to the laser, allowing for flexible control of the scanning trajectory and enabling the cutting of quartz wafers with arbitrary contour shapes. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 This is a process flow diagram of the quartz cutting method using phase-modulated Bessel laser combined with chromium film protection according to the present invention.

[0028] Figure 2This is a schematic diagram of the processing procedure of the quartz cutting method using phase-modulated Bessel laser combined with chromium film protection according to the present invention.

[0029] Figure 3 This is a schematic diagram illustrating the principle of optical field interference suppressing Bessel laser side lobes in the quartz cutting method of phase-modulated Bessel laser combined with chromium film protection according to the present invention.

[0030] Figure 4 The present invention compares the process of the present invention with that of the original Bessel process without protection. Figure (a) shows the simulation diagram of the light field distribution along the propagation direction and radial cross section of the original Bessel light field and the phase-modulated Bessel light field; Figure (b) shows the schematic diagram of the two processes for processing quartz crystals, where the former has no protective film and the latter has a chromium film protective layer on the upper and lower surfaces of the quartz crystal; Figure (c) shows the comparison of the morphology results of the two processes for cutting quartz wafers. The original Bessel process without protection results in a reduction of the thickness of the quartz wafer to 80 μm and pitting pits on the quartz surface. The phase-modulated Bessel process combined with chromium film protection does not reduce the thickness of the quartz wafer, which remains at the original thickness of 100 μm and the surface is undamaged.

[0031] Figure 5 This is a schematic diagram of the optical path of the overall processing system for the quartz cutting method using phase-modulated Bessel laser combined with chromium film protection according to the present invention.

[0032] Figure 6 This paper compares the process of the present invention with the traditional photolithography combined with wet etching process. Figures (a) and (b) show the etching schematic diagram, etched sidewall cross section and etched quartz surface result of the present invention and the traditional process, respectively; Figure (c) shows the process flow comparison of the two. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1:

[0036] The traditional fabrication process for quartz resonant beams is a wet etching process based on photolithography. First, a mask pattern is created on a Z-cut α-quartz wafer coated with a chromium / gold (Cr / Au) composite film using photolithography. Then, etching is performed using a saturated ammonium bifluoride (NH4HF2) solution to obtain the through-channel structure. This process leverages the anisotropic etching characteristic of quartz crystals in ammonium bifluoride solution, where the Z-axis etching rate is much higher than other crystal directions, to achieve through-channel formation. However, anisotropic etching occurs in different directions, which can easily lead to crystalline ridge structures on the beam sidewalls and at contour corners, resulting in poor uniformity and inconsistent sidewall perpendicularity, thus affecting resonant performance. Ultrafast Bessel laser selective etching leverages the deep, uniform modification capabilities of long-depth, diffraction-free Bessel lasers on quartz wafers, enabling modification processes that penetrate both the top and bottom surfaces. Combined with subsequent chemical etching, it overcomes the shortcomings of anisotropic etching in traditional processes, achieving high-precision, high-consistency, and high-perpendicularity through-slot cutting. However, this method requires the entire quartz wafer to be immersed in the etching solution, resulting in surface etching and overall wafer thinning, pitting, and impacting resonator performance. Therefore, there is an urgent need to develop improved processes to achieve high-quality, high-precision through-slot cutting of quartz wafers.

[0037] To address the significant issue of surface quality degradation caused by etching the upper and lower surfaces of the quartz wafer in the aforementioned ultrafast Bessel laser selective etching process, this invention utilizes electron beam evaporation to deposit a chromium film resistant to ammonium bifluoride solution corrosion on the upper and lower surfaces of the quartz wafer. This film serves as a protective layer during the wet etching process, preventing etching damage to the quartz wafer surface. Furthermore, due to the presence of Bessel laser side lobes, a relatively wide chromium film ablation zone exists on both sides of the scanning trajectory during the modification process of the chromium film-covered quartz wafer. This zone is not protected by the chromium film, resulting in a certain width of damage area on the quartz surface on both sides of the through-slot after wet etching. To minimize the etching damage area, this invention utilizes a liquid crystal spatial light modulator (SLM) to perform phase shaping on the Gaussian laser incident on the conical lens, generating optical field interference in the Bessel region behind the conical lens. This causes the sidelobe interference of the Bessel light field in a specific region to cancel each other out, minimizing the sidelobe energy ratio. Consequently, the width of the chromium film ablation zone after processing is reduced, the etching damage area is reduced, and the surface quality of the quartz resonant beam is further improved, thus enhancing the resonator performance.

[0038] This invention provides a method for cutting quartz using phase-modulated Bessel laser combined with chromium film protection, comprising the following steps:

[0039] Step 1: The Z-cut α-quartz wafer to be processed is cleaned with acetone, anhydrous ethanol and deionized water respectively, and dried with compressed air. Then, chromium film (Cr) is deposited on the upper and lower surfaces of the wafer by electron beam evaporation as a wet etching protective layer.

[0040] Step 2: Establish a theoretical model for wavefront phase modulation of the Bessel optical field transmission, simulate optical field propagation, and optimize to obtain a sidelobe-suppressed Bessel optical field. Wavefront phase modulation is applied to the Gaussian laser incident on a conical lens, splitting it into two concentric beams. After being focused by the conical lens, the two beams interfere in the Bessel region, achieving destructive interference of the sidelobes. The sidelobe energy ratio is evaluated, and the phase modulation parameters are optimized to obtain the wavefront modulation phase diagram corresponding to the optimal Bessel optical field for sidelobe suppression.

[0041] Step 3: Construct the phase-modulated ultrafast Bessel laser processing optical path. Load the phase map calculated in Step 2 onto the liquid crystal spatial light modulator to perform phase modulation on the incident Gaussian laser. The modulated light field is transported to the front surface of the conical lens through a 4f lens system. After being focused by the conical lens, a Bessel laser with suppressed side lobes is obtained. Then, it is further focused onto the translation stage surface by a 4f beam-shrinking system composed of a plano-convex lens and a focusing objective.

[0042] Step 4: Fix the quartz wafer sample with double-sided chromium-plated film described in Step 1 on a three-dimensional precision electronically controlled translation stage. Focus the optimal area for suppressing side lobes of the Bessel laser on the sample surface, and focus the other Bessel areas inside the quartz wafer. By controlling the movement of the translation stage, the Bessel laser scans the quartz surface to obtain the resonator profile. The profile trajectory is the laser-modified area.

[0043] Step 5: The laser-processed quartz wafer sample is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, and dried with compressed air. Then it is immersed in a saturated ammonium bifluoride solution and fully etched under water bath heating until the through groove is etched and the designed contour structure is obtained.

[0044] Step Six: The etched quartz wafer is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, and dried with compressed air. Then it is immersed in a chromium etching agent cerium ammonium nitrate ((NH4)2Ce(NO3)6) solution to dissolve and remove the chromium film protective layer. Subsequently, the quartz wafer is ultrasonically cleaned again with acetone, anhydrous ethanol and deionized water respectively, and dried with compressed air to finally obtain the designed quartz through-slot structure.

[0045] In one embodiment of the present invention, in step one, a chromium film of a specific thickness needs to be deposited on the upper and lower surfaces of the quartz crystal. The upper surface thickness is 5-10 nm to ensure high laser transmittance, thereby ensuring that the intensity of the Bessel light field focused into the quartz is sufficient to achieve effective modification of the quartz crystal. The lower surface thickness is 50-100 nm to reduce the ablation of the lower surface chromium film by the Bessel laser side lobes that pass through the quartz crystal, thereby reducing the chromium film ablation zone.

[0046] As one embodiment of the present invention, the wavefront modulation phase diagram in step two divides the incident Gaussian light field into two concentric annular regions, wherein the inner and outer regions are loaded with positive / negative conical lens phases with different equivalent tapers. The Bessel light field generated by focusing under different inner circle diameters and different inner and outer circle equivalent tapers is simulated, and the phase diagram parameters under the condition of minimizing the sidelobe energy ratio of the Bessel light field are selected. The specific parameters include: the diameter of the incident light field, the diameter of the central inner circle, and the number of annular phases corresponding to the inner and outer circle equivalent tapers.

[0047] As one embodiment of the present invention, the phase-modulated ultrafast Bessel laser processing system constructed in step three includes an ultrafast laser 1, an aperture 2, an attenuator group 3, an ultrafast mirror 4, a liquid crystal spatial light modulator 5, a first lens 6, a second lens 7, a mechanical switch 8, a conical lens 9, a plano-convex lens 10, a dichroic mirror 11, a beam splitter 12, an illumination source 13, an imaging camera 14, a focusing objective lens 15, a quartz wafer sample 16, a three-dimensional precision electrically controlled translation stage 17, and a computer system 18. The ultrafast laser generated by the ultrafast laser 1 is energy-controlled by the attenuator group 3, collimated by the aperture 2, and the laser spot is limited to a certain size by the aperture 2 before being incident on the liquid crystal spatial light modulator 5. The liquid crystal spatial light modulator 5 loads the phase diagram calculated in step two, performs wavefront modulation on the Gaussian beam, generates a modulated light field, and the light field is transported to the front surface of the conical lens 9 by a 4f lens system composed of lens 6 and lens 7. After being focused by a conical lens, the beam is further narrowed by a plano-convex lens 10 and a focusing objective lens 15, and then focused onto the surface of the quartz wafer sample 16. The quartz wafer sample 16 is fixed on a three-dimensional precision electrically controlled translation stage 17. A white light source passes through a beam splitter 12, a dichroic mirror 11, and a focusing objective lens 15, and is vertically irradiated onto the surface of the quartz wafer sample 16 from top to bottom. The white light is reflected back by the sample surface and then reflected back to the imaging tube and CCD camera at the beam splitter, realizing real-time imaging of the sample surface processing. The computer system 18 controls the movement of the three-dimensional precision electrically controlled translation stage 17, causing the focused laser to move relative to the sample surface, thereby processing the designed resonant beam contour structure.

[0048] Furthermore, in step three, the selected liquid crystal spatial light modulator is a phase-type modulation type, the liquid crystal type is reflective, and the pixel resolution is 3840*2160; the phase diagram loaded onto the liquid crystal spatial light modulator is the optimized phase diagram calculated in step two; the selected conical lens has a bottom angle of 2°, and for the beam contraction of the Bessel beam, the focal length of the plano-convex lens used is f=100mm, and the focusing objective lens used is a 50x objective lens.

[0049] As one embodiment of the present invention, in step four, the optimal area for suppressing Bessel laser side lobes should be focused on the upper surface of the quartz wafer sample, thereby reducing the size of the chromium film ablation area on both sides of the upper surface scanning trajectory.

[0050] As one embodiment of the present invention, the etching solution used in step five is a saturated ammonium bifluoride solution. The temperature of the etching solution is kept constant by a constant temperature water bath, with the temperature set at 30-50°C and the etching time at 2-3 hours, to ensure that the modified area is fully etched while the surface chromium film protective layer is not damaged.

[0051] As one embodiment of the present invention, the chromium etching agent selected in step six is ​​cerium ammonium nitrate solution with a mass fraction of 85%, the etching temperature is room temperature, and the etching time is about 15 minutes until the chromium film on the quartz surface is completely etched and dissolved.

[0052] It should be noted that the principle of the embodiments of the present invention also includes the application of other wavefront modulation phase shaping methods to achieve sidelobe suppression of Bessel lasers, and the application of this method to the modification of samples with anti-corrosion film protection on the surface, and finally selective etching with an etchant to achieve the forming and cutting of through grooves.

[0053] Example 2:

[0054] like Figure 1 and 2 As shown, this embodiment of the invention provides a quartz cutting method using phase-modulated Bessel laser combined with chromium film protection, comprising the following steps:

[0055] Step 1: Double-sided chrome plating of quartz wafers.

[0056] To protect the quartz wafer surface from corrosion by the etching solution during selective etching, this embodiment selects metallic chromium as the anti-corrosion protective layer. Electron beam evaporation is used to deposit a chromium film with a thickness of 5-10 nm on the upper surface of the quartz wafer and a chromium film with a thickness of 50-100 nm on the lower surface. The thickness of the upper surface film is selected based on the optical transmittance of the chromium film to the laser. During processing, the Bessel laser needs to pass through the upper surface of the quartz and be focused into the interior of the quartz crystal; therefore, the film thickness must ensure high transmittance. The thickness of the lower surface film depends on the ablation effect of the Bessel laser on the lower surface chromium film. Due to the inherent specificity of the Bessel laser light field distribution, the light field divergence range is larger on the lower surface; therefore, a thicker chromium film is selected to reduce the area of ​​laser damage to the chromium film. In this embodiment, the quartz wafer thickness is 0.1 mm.

[0057] Step 2: Establish a theoretical model for wavefront phase modulation Bessel optical field transmission, simulate optical field propagation, optimize phase shaping, and minimize the sidelobes of the Bessel optical field.

[0058] Due to the inherent sidelobe characteristics of Bessel lasers, when processing chromium-plated quartz wafers using conventional Bessel lasers, the sidelobes easily cause wide chromium film ablation zones on both sides of the scanning trajectory. During processing, the chromium film in these areas is ablated and removed, leaving them unprotected during subsequent etching with ammonium bifluoride solution. Therefore, this embodiment employs wavefront phase shaping to modulate the optical field interference, thereby suppressing Bessel laser sidelobes. A schematic diagram of the specific optical field modulation is shown below. Figure 3 As shown: A Gaussian ultrafast laser is incident on a liquid crystal spatial light modulator. A wavefront modulation phase diagram is applied, splitting the light field into two concentric beams. The modulated light field at the surface of the liquid crystal screen is transported to the front surface of a conical lens via a 4f lens system. After being focused by the conical lens, the two beams interfere in the Bessel region. This interference suppresses sidelobes. The interference field is modulated by the phase diagram, with modulation parameters including the spot diameter R, the radius r of the inner circle, the number of phase rings n1 of the inner circle, and the number of phase rings n2 of the outer circle. The phase change range for each ring is 0-2π. By optimizing these three parameters and simulating the Bessel light field, the phase diagram parameters under optimal Bessel laser sidelobe suppression can be obtained. In this embodiment, the preferred parameters are: incident light field radius 3mm, central inner circle radius 1.2mm, number of inner ring phase regions n1 = 6, number of outer ring phase regions n2 = 3. Simulation shows that the minimum ratio of the first sidelobe to the main lobe in the central region of the Bessel light field is 1.7%.

[0059] In this embodiment, the simulation of the original Bessel light field and the light field distribution of the phase-modulated Bessel laser along the propagation direction and radial direction is compared to... Figure 4 As shown in (a), the normalized intensity curve of radial light field energy distribution shows that the sidelobe energy of the latter is effectively suppressed. Figure 4 (b) is a schematic diagram of the unprotected processing of the original Bessel field and the phase-modulated Bessel field combined with chromium film protection processing of quartz crystals. Figure 4 (c) Comparison of the morphology of quartz wafers cut by two processes. Comparison of the processing results of quartz wafers with two light fields for chromium film and quartz. The original Bessel process without protection resulted in the quartz wafer thickness being reduced to 85μm and pitting pits on the quartz surface. The phase-modulated Bessel process combined with chromium film protection did not reduce the thickness of the quartz wafer, which remained at the original thickness of 100μm and the surface was undamaged.

[0060] Step 3: Construct the phase-modulated Bessel laser processing optical path, and load the phase map calculated above onto the liquid crystal spatial light modulator to obtain a phase-modulated Bessel laser with suppressed sidelobes.

[0061] The sidelobe-suppressing Bessel laser processing system constructed in this embodiment is as follows: Figure 5As shown, the system includes an ultrafast laser 1, an aperture 2, an attenuator group 3, an ultrafast mirror 4, a liquid crystal spatial light modulator 5, a first lens 6, a second lens 7, a mechanical switch 8, a conical lens 9, a plano-convex lens 10, a dichroic mirror 11, a beam splitter 12, an illumination source 13, an imaging camera 14, a focusing objective lens 15, a quartz wafer sample 16, a three-dimensional precision electrically controlled translation stage 17, and a computer system 18. The ultrafast laser emitted from the ultrafast laser 1 is limited by the aperture 2, attenuated by the attenuator group 3, and then reflected by the ultrafast mirror 4 into the liquid crystal spatial light modulator 5. This modulates the phase of the incident Gaussian laser, generating a modulated light field. This light field is transported to the front surface of the conical lens 9 by a 4f lens system consisting of the first lens 6 and the second lens 7. The front surface of the conical lens and the liquid crystal screen of the spatial light modulator are conjugate surfaces. After the modulated light is focused by the conical lens, optical field interference occurs, generating phase-modulated Bessel light with suppressed sidelobes. The light is focused onto the surface of the quartz wafer sample 16 after being focused by a beam-splitting system consisting of a plano-convex lens 10 and a focusing objective lens 15. The sample is fixed on a three-dimensional precision electronically controlled translation stage 17. In addition, the illumination light from the illumination source 13 is irradiated onto the sample surface after passing through a beam splitter 12 and a dichroic mirror 11. The imaging camera 14 is located behind the beam splitter 12 and can image the sample surface to realize real-time observation of the processing process. The on / off state of the optical path is controlled by a mechanical switch 8. The overall processing system and imaging system are controlled by a computer system 18.

[0062] In this embodiment of the invention, a Ti:sapphire femtosecond laser is used, with a center wavelength of 800nm, a pulse width of 35fs, and a repetition frequency of 1kHz. A pure phase-type liquid crystal spatial light modulator is selected, the liquid crystal type is emission-type, and the liquid crystal screen pixel resolution is 3840*2160. In the 4f system, both lenses have a focal length of 750mm, the plano-convex lens has a focal length of 100mm, the objective lens used is a 50x objective lens, and the conical lens has a base angle of 2°.

[0063] Step 4: Modify the quartz wafer using a phase-modulated Bessel laser.

[0064] A quartz wafer with a chromium coating is fixed on a three-dimensional precision electrically controlled translation stage. The optimal area for suppressing side lobes of a phase-modulated Bessel laser is focused on the sample surface, while other Bessel areas are focused inside the quartz wafer. The movement of the translation stage is controlled by a computer to allow the laser to process the designed quartz resonant beam profile structure on the quartz wafer.

[0065] Step 5: Selectively etch the processed sample using a saturated ammonium bifluoride solution.

[0066] After phase-modulated Bessel laser processing, a modified region is formed inside the quartz crystal wafer, penetrating the upper and lower surfaces. The quartz crystal in the modified region becomes amorphous, and the etching rate is faster in the saturated ammonium fluoride solution. The processed sample is immersed in the etching solution, and a constant temperature water bath is used to ensure that the etching environment temperature is constant, controlled at 50°C. The sample etching time is 2-3 hours until the through-groove is etched and formed.

[0067] Step 6: Remove the chromium film on the quartz surface using a chromium etchant.

[0068] After selective etching of the quartz wafer, the desired quartz resonator beam structure is obtained. Then, it is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, and dried with compressed air. After that, it is immersed in a chromium etchant solution of cerium ammonium nitrate ((NH4)2Ce(NO3)6) to dissolve and remove the chromium film protective layer on the surface. The ultrasonic cleaning steps are repeated to obtain the desired quartz resonator sample.

[0069] As can be seen from the embodiments of the present invention, by using a liquid crystal spatial light modulator to modulate the wavefront phase of the incident Gaussian laser, and then focusing it through a conical lens, the side lobes of the Bessel laser can be effectively suppressed by modulating the interference between the light fields. Furthermore, by optimizing the phase diagram parameters, the side lobes can be minimized. The method of double-sided chromium plating on the quartz wafer effectively protects the quartz surface from etching damage during the etching process in ammonium bifluoride solution. Combined with phase-modulated Bessel laser to suppress side lobes, the ablation area of ​​the surface chromium film can be effectively reduced, improving the final quartz wafer cutting quality. A comparison of this method with traditional photolithography combined with wet etching processes is provided. Figure 6 As shown, Figure 6 (a) and (b) show schematic diagrams of the etching morphology, cross-section of the etched sidewall, and comparison of the quartz surface results between the present method and the traditional process. Figure 6 (c) Comparison of process steps. Compared with traditional wet etching and traditional Bessel laser selective etching, this method can combine the high surface quality of the former with the high sidewall perpendicularity of the latter, achieving the advantages of both and significantly improving the precision cutting quality of quartz wafers, thus having broad application prospects.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for cutting quartz using phase-modulated Bessel laser combined with chromium film protection, characterized in that, Includes the following steps: Step 1: Clean the Z-cut α-quartz wafer to be processed with acetone, anhydrous ethanol and deionized water respectively, and dry it with compressed air. Then, use electron beam evaporation to deposit chromium film on the upper and lower surfaces, with the upper surface chromium film thickness being 5-10nm and the lower surface thickness being 50-100nm. Step 2: Establish a theoretical model for wavefront phase modulation Bessel optical field propagation, simulate optical field propagation, and obtain the wavefront modulation phase diagram corresponding to the Bessel optical field with optimal sidelobe suppression; Step 3: Construct the phase-modulated Bessel laser processing optical path, load the wavefront modulation phase map corresponding to the Bessel light field with optimal sidelobe suppression onto the liquid crystal spatial light modulator, transport the modulated light to the front surface of the conical lens through the 4f lens system, and after the conical lens focuses, the phase-modulated Bessel laser is focused onto the translation stage surface through the 4f beam-shrinking system composed of a plano-convex lens and a focusing objective. Step 4: Fix the quartz wafer with a chromium film on its surface onto a three-dimensional precision electronically controlled translation stage. Focus the phase-modulated Bessel laser onto the sample surface and control the movement of the translation stage so that the laser scans the quartz surface to obtain the designed contour. The contour trajectory is the laser-modified area. Step 5: After cleaning the processed quartz wafer, immerse it in a saturated ammonium bifluoride solution and etch it thoroughly under water bath heating until the through-groove is etched and the designed contour structure is obtained. Step 6: After cleaning the etched quartz wafer sample, immerse it in a chromium etching agent, cerium ammonium nitrate (NH4)2Ce(NO3)6 solution, to dissolve and remove the chromium protective layer; then clean the sample and dry it with compressed air to finally obtain the designed quartz through-channel structure.

2. The quartz cutting method using phase-modulated Bessel laser combined with chromium film protection as described in claim 1, characterized in that, In step two, the incident Gaussian light is divided into two concentric beams by wavefront phase modulation, and the two beams are focused by a conical lens to produce interference in the Bessel region optical field, thereby suppressing the sidelobes of the Bessel laser. The interference optical field is modulated by a phase diagram, and the modulation parameters include the spot diameter R, the radius r of the inner circle, the number of phase rings n1 of the inner circle and the number of phase rings n2 of the outer circle, with the phase change range of 0-2π per ring. By optimizing the above three parameters and simulating the Bessel optical field, the phase diagram parameters under the optimal condition for suppressing the sidelobes of the Bessel laser are obtained.

3. The quartz cutting method using phase-modulated Bessel laser combined with chromium film protection as described in claim 2, characterized in that, In step three, the ultrafast laser emitted by the ultrafast laser in the phase-modulated Bessel laser processing optical path is limited by an aperture, attenuated by an attenuator array, and then reflected by an ultrafast mirror into a liquid crystal spatial light modulator. The incident Gaussian laser is phase-modulated to generate a modulated light field. The light field is transported to the front surface of a conical lens by a 4f lens system consisting of a first lens and a second lens. The front surface of the conical lens and the liquid crystal screen of the spatial light modulator are conjugate surfaces. After the modulated light is focused by the conical lens, optical field interference occurs, generating a phase-modulated Bessel light field with suppressed side lobes. After being focused by a beam-shrinking system consisting of a plano-convex lens and a focusing objective, the beam is focused onto the surface of a quartz wafer sample. The sample is fixed on a three-dimensional precision electrically controlled translation stage. The illumination light from the illumination source is irradiated onto the sample surface by a beam splitter and a dichroic mirror. An imaging camera is located behind the beam splitter to image the sample surface, enabling real-time observation of the processing process.

4. The quartz cutting method using phase-modulated Bessel laser combined with chromium film protection as described in claim 3, characterized in that, In step five, the processed sample is immersed in the etching solution, and a constant temperature water bath is used to ensure that the etching environment temperature is constant, controlled at 50℃. The etching time is 2-3 hours until the through groove is etched and formed.

5. The quartz cutting method using phase-modulated Bessel laser combined with chromium film protection as described in claim 2, characterized in that, With an incident light field radius of 3 mm, a central inner circle radius of 1.2 mm, an inner ring phase region number n1=6, and an outer ring phase region number n2=3, the simulation shows that the minimum ratio of the first side lobe to the main lobe in the central region of the Bessel light field is 1.7%.

6. The quartz cutting method using phase-modulated Bessel laser combined with chromium film protection as described in claim 3, characterized in that, In step three, the phase-modulated Bessel laser processing optical path uses an ultrafast laser, either a femtosecond laser or a picosecond laser.

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