A laser processing method for a quartz crystal oscillator wafer

Abstract

The application discloses a laser processing method of a quartz crystal wafer, which comprises the following steps: 1) thinning the wafer by using an ultrafast laser in a vacuum environment; 2) cutting the wafer by using the ultrafast laser to obtain a small wafer contour, the bottom of a cutting line of a small wafer combination area comprises a non-penetrating weakened layer, and the small wafer contour line surrounds a small wafer and a main wafer of the wafer to form a connecting point; 3) corroding the wafer by using a corrosion liquid to separate the small wafer combination area from the main wafer of the wafer; 4) vacuum sputtering a metal coating on the surface of the wafer; 5) etching an electrode pattern on the small wafer of the coated wafer by using the ultrafast laser; and 6) disconnecting the connecting point between the small wafer and the main wafer to obtain a single crystal wafer product. The application has the advantages of simple process, low cost, high precision and less environmental pollution.

Description

Technical Field

[0001] This invention relates to the processing technology of quartz crystal wafers, and more particularly to a laser processing method for quartz crystal wafers. Background Technology

[0002] Traditional quartz crystal wafers are manufactured primarily using a conventional photolithography-wet etching process. This method involves coating photoresist, exposure and development, wet etching to form a tuning fork structure, followed by coating and aging treatments. However, this process suffers from drawbacks such as severe chemical pollution, limited processing precision, complex procedures, significant wafer damage, long processing cycles, and high costs.

[0003] Application number CN202510122914.3 discloses a method for processing surface-mount wafers, relating to the field of surface-mount wafer production. It utilizes sandblasting and ultrasonic cutting to cut a complete board of surface-mount wafers from both sides of a wafer. Based on these methods, the cut surfaces are arc-shaped, increasing the electrode plating area and improving the quality of the surface-mount crystal oscillator. By performing electrode plating on a complete board of surface-mount wafers, this method eliminates the wet etching step essential in traditional processing. The invention also discloses a method for processing surface-mount crystal oscillators based on a complete board of surface-mount wafers. After quality inspection and marking of defective wafers, the information is uploaded to a server, and the entire board is positioned on a fixture. Then, based on the precise position of each surface-mount wafer and the location of defective wafers recorded by the server, a robotic arm picks up each wafer one by one and mounts it onto a substrate. The coordinate switching from a regular matrix to a matrix is ​​simple and accurate, and the repositioning step in processing individual surface-mount wafers is eliminated.

[0004] This invention still relies on a mask-blasting-wet process, with a V-shaped arc surface for the cut. The thickness / groove cannot be controlled at the micron level, resulting in numerous microcracks and a large amount of waste liquid, making it difficult to achieve sub-micron precision and frequency fine-tuning. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a laser processing method for high-precision quartz crystal wafers.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a laser processing method for quartz crystal wafers, comprising the following steps: 101) Thinning step: In a vacuum environment, ultrafast laser is used to thin large-size quartz wafers to remove microscopic defects on the surface of large-size quartz wafers and improve the uniformity of wafer thickness. 102) Small wafer outline cutting step: Use an ultrafast laser to cut the outline of a large-size quartz wafer into small wafers. The outlines of multiple small wafers are connected in series to form the outline of a combined area of ​​a small wafer. The bottom of the cutting line of the combined area of ​​the small wafers includes a weakening layer that is not penetrated. There are connection points between the small wafers surrounded by the outlines of the small wafers and the main wafer of the large-size quartz wafer. 103) Step to remove waste from the assembly area of ​​small wafers: In the etching tank, the large-size quartz wafer is etched with an etching solution to crack the weakened layer, and the assembly area of ​​small wafers is separated from the main wafer of the large-size quartz wafer as waste. 104) Coating step: Vacuum sputtering of a metal coating is performed on the surface of a large-size quartz wafer; 105) Circuit etching step: Electrode patterns are etched on the small wafers of the large-size quartz wafer after coating using an ultrafast laser; 106) Breaking and separating step: Disconnect the connection point between the small crystal and the main plate of the large-size quartz crystal to obtain a single crystal oscillator crystal product.

[0007] The laser processing method for quartz crystal wafers described above includes the following steps: 201) Tuning fork arm groove engraving step; After the small wafer contour cutting step in step 102, the tuning fork arm groove of the small wafer is engraved using an ultrafast ultraviolet laser; 202) Ultrasonic stress relief step; after the tuning fork arm groove engraving step in step 201 and before the waste removal step of the small wafer assembly area in step 103, dual-frequency ultrasonic waves are applied to the entire large-size quartz wafer plate to eliminate the residual stress of the large-size quartz wafer. 203) Cleaning and drying steps: After the waste material is removed by etching in step 103, clean the residual etching liquid and other residues on the large-size quartz wafer, and then dry it to remove the moisture and solvent from the surface of the large-size quartz wafer. 204) High-temperature aging step: After the large-size quartz wafer is coated in step 104, it is subjected to vacuum high-temperature aging.

[0008] The laser processing method for quartz crystal wafers described above, in step 101, involves thinning a large-size quartz wafer layer by layer using a picosecond laser with a pulse width of 5-20 ps on a vacuum laser thinning machine. The vacuum laser thinning machine includes a galvanometer, a first field mirror, a vacuum cavity, a first stage, a piezoelectric lifting and adjusting platform, a laser height sensor, and an XY moving platform. The first stage, piezoelectric lifting and adjusting platform, and XY moving platform are arranged in the vacuum cavity, with the piezoelectric lifting and adjusting platform mounted on the XY moving platform. The first stage is fixed to the top surface of the piezoelectric lifting and adjusting platform, and the top surface of the first stage includes a suction cup. The large-size quartz wafer is adsorbed by the suction cup on the top surface of the first stage and moves in the XY plane following the XY moving platform. The top plate of the vacuum cavity includes a first glass window and a second glass window, with the first field mirror arranged in the first glass window. Directly above, a laser height sensor is positioned above the second glass window. Before the laser thins the large-sized quartz wafer, the large-sized quartz wafer is moved to the area directly below the second glass window in the XY plane, and the laser height sensor measures the height of various positions on the upper surface of the large-sized quartz wafer. During laser thinning of the large-sized quartz wafer, the large-sized quartz wafer is located directly below the first glass window. During laser thinning of the large-sized quartz wafer, the first galvanometer reflects the incident laser light, and the reflected light enters the first field mirror for focusing. The focused light passes through the first glass window and enters the vacuum cavity, where it thins the large-sized quartz wafer.

[0009] The laser processing method for quartz crystal wafers described above, specifically step 102, involves small wafer contour cutting, performed on an ultrafast laser cutting machine. This ultrafast laser cutting machine includes a first vision system, at least one first cutting head, a second stage, a first light source, a first XY air-bearing module, and a second stage base. The second stage base is mounted on the first XY air-bearing module and moves within the XY plane, driven by the module. The first light source is installed inside the box-shaped second stage base. The second stage is fixed to the top of an opening on the second stage base. The top surface of the second stage includes at least one first protrusion for supporting large-sized quartz wafers. The four corners of the first protrusion have transparent square holes through which light from the first light source passes. A square aperture illuminates the edges and corners of a large-sized quartz wafer. The first vision system captures and positions the edges and corners of the large-sized quartz wafer. After capture and positioning, the large-sized quartz wafer moves along the XY plane to below the first cutting head. The first cutting head focuses its own incident light and then cuts the large-sized quartz wafer below, cutting a combination area of ​​multiple small wafers from one large-sized quartz wafer. The incident light of the first cutting head is an ultrafast laser. The parameters of the ultrafast laser include: laser wavelength 1064nm, pulse width 5-10ps, repetition frequency 50-200kHz, single pulse energy 20-50μJ, energy consistency ≤±5%, and the divergence angle of the optical path is adjusted to <1mrad using a 2-8x beam expander.

[0010] The laser processing method for quartz crystal wafers described above, specifically the tuning fork arm groove engraving step 201, is performed on an ultrafast laser engraving groove machine. A frequency-modulated microgroove with a tuning fork arm engraving depth of 0.02–0.07 mm is engraved on each small wafer. The ultrafast laser engraving groove machine includes a second vision system, a second galvanometer, a second field mirror, a third stage, a second light source, a second XY air-bearing module, and a third stage base. The third stage base is mounted on the second XY air-bearing module and is driven by the second XY air-bearing module to move within the XY plane. The second light source is installed inside the box-shaped third stage base, and the third stage is fixed to the top of the opening on the third stage base. The top surface of the third stage includes a second protrusion for supporting large-sized quartz wafers. Light-transmitting square holes are opened at the four corners of the second protrusion, allowing light from the second light source to pass through and illuminate the edges and corners of the large-sized quartz wafers. The second vision system... The system captures and positions the edges and corners of a large-sized quartz wafer. After capture and positioning, the large-sized quartz wafer moves along the XY plane below the second field mirror, so that the laser focused by the second field mirror can be precisely aligned with the corresponding position of the tuning fork arm for groove engraving. The second galvanometer reflects the incident laser light, and the second field mirror focuses the reflected light. The focused light engraves the grooves on the tuning fork arm of the large-sized quartz wafer. The incident laser light of the second galvanometer is an ultrafast ultraviolet laser. The ultrafast ultraviolet laser parameters include: wavelength 355nm, pulse width 500fs-10ps, single pulse energy 5-20μJ, and repetition frequency: 100-500kHz.

[0011] The laser processing method for quartz crystal wafers described above, in step 202, involves ultrasonic stress relief using low-frequency ultrasound at 15-25 kHz for coarse vibration, with a power density of 15-25 W / cm² and an amplitude of 80-120 μm; and high-frequency ultrasound at 0.8-1.2 MHz for fine vibration, with a power density of 0.5-2 W / cm² and an amplitude of 0.1-0.5 μm. The temporal superposition of coarse and fine vibrations achieves gradient elimination of internal stress in the quartz wafer. The low-frequency ultrasonic coarse vibration converts residual tensile stress in the wafer into compressive stress, while the high-frequency ultrasonic fine vibration promotes lattice dislocation slip and grain refinement. Furthermore, the microcrack interface is remelted and closed through localized high temperatures of 580-620°C. Power ramp start-stop control is used, and under the synergistic effect of 30-60 seconds of coarse vibration and 5-10 seconds of fine vibration, stress is eliminated and the stability of the wafer frequency is improved.

[0012] The laser processing method for quartz crystal wafers described above includes an etching solution containing hydrofluoric acid and an etching inhibitor in step 103. In step 102, an ultrafast laser forms a weakening layer with a triple structure including a modified layer, a microcrack network, and a residual stress zone at the bottom of the cutting line in the assembly area of ​​the small wafer. In step 103, the etching solution preferentially etches the weakening layer, and the synergistic stress achieves submicron-level precise separation between the assembly area of ​​the small wafer and the main body of the large-size quartz wafer.

[0013] In the laser processing method for quartz crystal wafers described above, in the coating step of step 104, a large-size quartz wafer is fixed in a coating fixture and placed in a magnetron sputtering coating machine. After the magnetron sputtering coating machine is evacuated, coating is performed at a coating temperature of 170℃-190℃ and an evaporation rate of 0.5–1.5 nm / s. After coating, the wafer is kept under vacuum and annealed at 180℃ for 1.5–2 hours. Nitrogen gas is introduced and the wafer is cooled to below 50℃ in the furnace before being removed. The coating thickness is 110nm-130nm, and the coating metals are chromium, nickel, silver, and gold in sequence.

[0014] The laser processing method for quartz crystal wafers described above, wherein the circuit etching step 105 is performed on an ultrafast laser engraving circuit machine, which includes a third vision system, a second cutting head, a fourth stage, a third light source, a third XY air-bearing module, and a fourth stage base; the fourth stage base is mounted on the third XY air-bearing module and is driven by the third XY air-bearing module to move in the XY plane; the third light source is installed inside the box-type fourth stage base, and the fourth stage is fixed to the top of the opening on the fourth stage base; the top of the fourth stage is covered with a third boss for supporting large-size quartz wafers, the third boss... The platform has square holes at its four corners for light transmission. Light from a third light source passes through these holes to illuminate the edges and corners of the large-sized quartz wafer. The third vision system captures and positions the edges and corners of the large-sized quartz wafer, enabling the focused laser to precisely etch the corresponding positions of the coating on the large-sized quartz wafer. During the circuit etching, the incident light entering the second cutting head is focused to etch the coating onto the smaller wafers on the large-sized quartz wafer. The incident light entering the second cutting head is an ultrafast laser. The parameters of the ultrafast laser include: laser wavelength 355nm, pulse width 10–30ps, repetition frequency 600–800 kHz, single pulse energy 10–30μJ, energy consistency ≤±5%, and the initial beam diameter is expanded to 20 mm using a 4-6x beam expander, with the divergence angle of the optical path adjusted to <0.8mrad.

[0015] The laser processing method for quartz crystal wafers of the present invention is simple in process, low in cost, high in precision, and causes less environmental pollution. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 This is a schematic diagram of the structure of the vacuum laser thinning machine according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the ultrafast laser cutting of a small wafer outline according to an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the structure of the ultrafast laser cutting machine according to an embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of an embodiment of the present invention using an ultrafast ultraviolet laser to carve grooves in a tuning fork arm.

[0021] Figure 5 This is a schematic diagram of the structure of the ultrafast laser engraving groove machine according to an embodiment of the present invention.

[0022] Figure 6 This is a schematic diagram of the corrosion / cleaning fixture according to an embodiment of the present invention.

[0023] Figure 7 This is a schematic diagram of the corrosion / cleaning tank in an embodiment of the present invention.

[0024] Figure 8 This is a perspective view of the coating fixture according to an embodiment of the present invention.

[0025] Figure 9 This is an exploded view of the coating fixture according to an embodiment of the present invention.

[0026] Figure 10 This is a schematic diagram of the structure of the high-temperature aging disc in an embodiment of the present invention.

[0027] Figure 11 This is a schematic diagram of ultrafast laser etching of circuits on a wafer according to an embodiment of the present invention.

[0028] Figure 12 This is a schematic diagram of the structure of the ultrafast laser engraving circuit machine according to an embodiment of the present invention.

[0029] Figure 13 This is a flowchart of a laser processing method for a quartz crystal wafer according to an embodiment of the present invention. In the diagram: 1. Large-size quartz wafer; 2. Assembly area of ​​small wafers; 3. Small wafer; 4. Trench; 5. Coating fixture; 6. High-temperature aging plate; 7. Circuit; 8. First galvanometer; 9. Incident light from the galvanometer; 10. First field mirror; 11. First glass window; 13. First stage; 14. Piezoelectric lifting adjustment platform; 15. Y-axis module; 16. X-axis module; 17. Laser height sensor; 18. Second glass window; 19. Vacuum cavity; 20. Y-axis module slider; 21. X-axis module slider; 22. Incident light from the first cutting head; 23. First cutting head; 24. First camera; 25. First lens; 26. Second stage base; 28. Second stage; 29. ​​First light source; 30. First Y-axis air-bearing module; 31. First X-axis air-bearing module; 32. Galvanometer incident light; 33. Second galvanometer; 34. Second camera; 35. Second lens; 36. Second light source; 37. Third stage base; 38. Second Y-axis air-bearing module; 39. Second field lens; 41. Third stage; 42. Second X-axis air-bearing module; 43. Handle; 44. Side plate; 45. Slot plate; 47. Etching / cleaning fixture; 48. Etching / cleaning tank; 49. Screw; 50. Top plate; 51. Upper pressure plate; 53. Positioning plate; 54. Lower pressure plate; 55. Base plate; 56. Second cutting head incident light; 57. Second cutting head; 58. Third camera; 59. Third lens; 61. Fourth stage; 62. Third light source; 63. Third Y-axis air-bearing module; 64. Third X-axis air-bearing module. Detailed Implementation

[0030] The laser processing method for quartz crystal wafers according to embodiments of the present invention is as follows: Figure 1 As shown, it includes the following steps: I. Laser Thinning: As a pre-cutting thinning process, laser thinning can vaporize microcracks and pores on the wafer surface, reduce stress concentration areas and damage layers of approximately 5μm, remove surface oxides or organic matter, and reduce frequency drift. Laser thinning results in good thickness uniformity, with a thickness tolerance of ±1 μm. Large-size quartz wafers 1 can be thinned in their entirety or in parts. Laser thinning enables precise thickness control of large-size quartz wafers 1, thereby improving cutting accuracy. Laser thinning uses a picosecond laser with a pulse width of 5-20 ps to thin large-size quartz wafers layer by layer. By uniformly removing material, internal stress is released, forming a low-damage surface to prevent wafer cracking due to stress concentration during the next laser cutting process.

[0031] The original thickness of the wafer is 0.15mm. The large-size quartz wafer 1 is thinned by 10μm on both sides by laser to remove the damaged layer generated during wafer grinding, improve the thickness uniformity of the wafer, facilitate subsequent laser cutting, and release internal stress to prevent the wafer from cracking during subsequent laser cutting.

[0032] like Figure 1 As shown, the vacuum laser thinning machine includes a first galvanometer 8, a first field mirror 10, a vacuum cavity 19, a first stage 13, a piezoelectric lifting and adjusting platform 14, a laser height sensor 17, and an XY moving platform.

[0033] The first stage 13, the piezoelectric lifting and adjusting platform 14, and the XY moving platform are arranged in the vacuum chamber 19. The XY moving platform includes a Y-axis module 15 and an X-axis module 16. The Y-axis module 15 is mounted on the X-axis module slider 21 of the X-axis module 16, and the piezoelectric lifting and adjusting platform 14 is mounted on the Y-axis module slider 20 of the Y-axis module 15. The first stage 13 is fixed to the top surface of the piezoelectric lifting and adjusting platform 14. The top surface of the first stage 13 includes a suction cup. The large-size quartz wafer 1 is attracted by the suction cup on the top surface of the first stage 13 and moves in the XY plane with the XY moving platform.

[0034] The top plate of the vacuum chamber 19 has a first glass window 11 and a second glass window 18. A first galvanometer 8 and a first field mirror 10 are arranged above the first glass window 11, and a laser height sensor 17 is arranged above the second glass window 18. During laser thinning of the large-size quartz wafer 1, the large-size quartz wafer 1 is located directly below the first glass window 11.

[0035] During laser thinning of the large-size quartz wafer 1, the incident light 9 from the first galvanometer 8 enters the first galvanometer 8, which reflects the incident laser light. The reflected light then enters the first field mirror 10 for focusing. The focused light passes through the first glass window 11 and enters the vacuum chamber 19. After passing through the first glass window 11, the light performs thinning processing on the large-size quartz wafer 1 on the first stage 13. The piezoelectric lifting adjustment platform 14 uses a compact precision Z-axis displacement stage, model L-306, from Puai Nano Displacement Technology Co., Ltd. Before the laser thinning of the large-size quartz wafer 1, the large-size quartz wafer 1 is moved to directly below the second glass window 18 in the XY plane, and the height of various positions on the upper surface of the large-size quartz wafer 1 is measured using a laser height sensor 17. During the laser thinning of the large-size quartz wafer 1, the piezoelectric lifting adjustment platform 14 adjusts the height of the large-size quartz wafer 1 to improve the flatness of the large-size quartz wafer 1 after laser thinning.

[0036] II. Ultrafast laser cutting: such as Figure 2As shown, an ultrafast laser is used to cut the contour of a small wafer (tuning fork wafer) 3 from a large-sized quartz wafer 1. The ultrafast laser parameters include a laser wavelength of 1064 nm, a pulse width of 5-10 ps, ​​a repetition rate of 50-200 kHz, a single pulse energy of 20-50 μJ, and energy uniformity ≤ ±5%. A 2-8x beam expander is used to adjust the divergence angle of the optical path to <1 mrad to ensure uniform energy density. Before cutting, the surface of the large-sized quartz wafer 1 is cleaned to remove processing residues from the previous process and avoid uneven laser absorption. The laser beam is emitted as a Gaussian circular spot, which passes through several mirrors and enters the beam expander for beam alignment. The beam expander enlarges the beam diameter and reduces the divergence angle, providing uniform input conditions for subsequent DOE shaping. Using a Holo / Or Top-Hat DOE (such as DOE-355-8-150) flat-top beam shaper, the circular Gaussian spot is shaped into a flat-top beam, reducing the edge energy gradient and achieving a near-rectangular intensity distribution, thus optimizing the beam energy distribution. The flat-top beam enters the first Bessel cutter 23 and is converted into a long focal depth Bessel beam, ensuring no overheating at the cut edges and improving the stability of the crystal oscillator frequency.

[0037] After laser thinning, the wafer surface is cleaned to remove processing residues. Then, an ultrafast laser is used to cut the contours of small wafers 3 from a large-size quartz wafer. The contour lines of multiple small wafers 3 are connected in series to form the contour lines of a combined region 2 of a small wafer. The bottom of the cutting line of the combined region 2 of the small wafer formed by the ultrafast laser is a weakened layer that is not penetrated. There is a break connection point between the small wafer 3 surrounded by the contour lines of the small wafer 3 and the main wafer of the large-size quartz wafer 1. In this embodiment, a combined region 2 of 5 small wafers is cut from one large-size quartz wafer 1. The width of the laser cut is 1μm. The combined region 2 of 5 small wafers cut from one large-size quartz wafer 1 is cut sequentially. Multiple small wafers (tuning fork wafers) 3 are cut out within each combined region 2 of the small wafer, with a certain distance between them.

[0038] The structure of an ultrafast laser cutting machine is as follows: Figure 3 As shown, the ultrafast laser cutting machine includes a first vision system, four first cutting heads 23, a second stage 28, a first light source 29, a first XY air-bearing module, and a second stage base 26. The first XY air-bearing module includes a first Y-axis air-bearing module 30 and a first X-axis air-bearing module 31. The second stage base 26 is mounted on the first XY air-bearing module and is driven by the first XY air-bearing module to move in the XY plane. The first light source 29 is installed inside the box-shaped second stage base 26. The second stage 28 is fixed to the top of the opening on the second stage base 26.

[0039] Four large-sized quartz wafers 1 can be placed on the second stage 28. The top surface of the second stage 28 includes four protrusions for supporting the large-sized quartz wafers 1. The four corners of the protrusions have light-transmitting square holes to allow light from the first light source 29 to pass through the square holes and illuminate the corners of the large-sized quartz wafers 1. The first vision system, consisting of the first camera 24 and the first lens 25, captures and positions the corners of the large-sized quartz wafers 1. After capture and positioning, the large-sized quartz wafers 1 move along the XY plane below the first cutting head 23. The incident light 22 of the first cutting head enters the cutting head from above the first cutting head 23. The first cutting head 23 focuses the incident light and cuts the large-sized quartz wafers 1. The four first cutting heads 23 can cut four large-sized quartz wafers 1 at a time (the structure can also be simplified to cut two or one wafer at a time).

[0040] III. Ultrafast laser engraving of grooves: such as Figure 4 As shown, an ultrafast ultraviolet laser and galvanometer system were used to carve the tuning fork arm groove. The ultrafast ultraviolet laser wavelength was 355nm, pulse width was 500fs-10ps, single pulse energy was 5-20μJ, and repetition rate was 100-500kHz, matched with the galvanometer scanning speed. The groove carving was performed using an ultrafast ultraviolet laser, and DOE flat-top beam shaping was still used, employing a Holo / Or Top-Hat DOE (such as DOE-355-8-150) flat-top beam shaper. The 355nm ultraviolet laser has a relatively large initial divergence angle. After passing through several mirrors, the laser beam is expanded by a 4x beam expander to increase the beam diameter by 4 times, reducing the divergence angle to 0.375mrad. Then, it enters a flat-top beam shaper to shape the circular Gaussian spot into a flat-top spot. A six-axis adjustment frame is used to calibrate the DOE angle to ensure that the optical axis coincides with the beam expander path and reduce zero-order diffraction interference. The flat-top beam enters a high-speed galvanometer, which focuses the spot for circuit processing. The galvanometer used is model APS-200, brand: Aerotech.

[0041] The structure of an ultrafast laser engraving groove machine is as follows: Figure 5 As shown, the system includes a second vision system, a second galvanometer 33, a second field lens 39, a third stage 41, a second light source 36, a second XY air-bearing module, and a third stage base 37. The second XY air-bearing module includes a second Y-axis air-bearing module 38 and a second X-axis air-bearing module 42. The third stage base 37 is mounted on the second XY air-bearing module and is driven by the second XY air-bearing module to move in the XY plane. The second light source 36 is installed inside the box-shaped third stage base 37, and the third stage 41 is fixed to the top of the opening on the third stage base 37. The second vision system includes a second camera 34 and a second lens 35.

[0042] The top surface of the third stage 41 includes a boss for supporting the large-size quartz wafer 1. The four corners of the boss have light-transmitting square holes to allow the light from the second light source 36 to pass through the square holes and illuminate the corners of the large-size quartz wafer 1, so that the second vision system can capture and position the corners of the large-size quartz wafer 1. The second vision system, consisting of the second camera 34 and the second lens 35, captures and positions the corners of the large-size quartz wafer 1. After capture and positioning, the large-size quartz wafer 1 moves along the XY plane to the bottom of the second field mirror 39, so that the laser focused by the second field mirror 39 can be aimed at the corresponding position of the tuning fork arm for precise groove engraving. At this time, the incident light 32 from the galvanometer enters the second galvanometer 33, which reflects the incident laser light. The second field mirror 39 focuses the reflected light, which then engraves the grooves 4 on the tuning fork arms of the large-size quartz wafer 1. One (or more) large-size quartz wafers 1 are placed on the third stage 41, and the laser processes one (or multiple) large-size quartz wafers 1 sequentially. This invention uses an ultrafast ultraviolet laser and a galvanometer system to carve the trench (frequency-modulated micro-groove) 4. The wafer thickness is 0.15mm, the trench depth of the trench 4 is 0.02-0.07mm, and the second galvanometer is model APS-200, brand: Aerotech.

[0043] IV. Ultrasonic Stress Relief: Ultrasonic vibration is used to eliminate internal stress in the wafer, preventing the internal stress from affecting the wafer's natural frequency and thus stabilizing the wafer's frequency stability. A 20kHz coarse ultrasonic vibration and a 1MHz fine ultrasonic vibration are used, superimposed to eliminate residual stress within the wafer through stress wave interference (elimination rate >90%), preventing the formation of surface microcracks. 20kHz is the coarse vibration mode, with a power density range of 15–25 W / cm², exceeding the quartz yield strength threshold (quartz critical stress ≈50MPa) but below the fracture limit (≈100MPa). Power densities <15W / cm² result in insufficient dislocation slip. Power densities >25W / cm² may induce microcracks at the wafer edges. Amplitude: 80–120μm, frequency: 20kHz±200Hz, duration: 30–60 seconds / wafer. 1MHz is the fine oscillation mode, with a power density range of 0.5–2 W / cm². At high frequencies, energy is concentrated per unit area; >2W / cm² easily induces surface cavitation pits, while <0.5W / cm² results in insufficient dislocation rearrangement dynamics. Amplitude: 0.1–0.5μm, frequency: 1MHz±10kHz, duration: 5–10 seconds / piece.

[0044] The formation of microcracks on the wafer surface can be reduced by controlling the vibration energy gradient, as follows: Power ramp start / stop: Coarse vibration start-up: linear increase from 0 to 25 W / cm² (3 seconds) to avoid step impact.

[0045] Fine-grained oscillation stop: exponential decay (time constant τ = 0.1 seconds) suppresses residual oscillations.

[0046] This step employs 20kHz coarse ultrasonic vibration and 1MHz fine ultrasonic vibration, with dual-frequency ultrasound superposition. The stress wave interference effect eliminates residual stress within the wafer, preventing the formation of surface microcracks. 20kHz is the coarse vibration mode, and 1MHz is the fine vibration mode; controlling the vibration energy gradient reduces the formation of microcracks on the wafer surface.

[0047] V. Remove waste from the assembly area of ​​small wafers: After the large-size quartz wafer 1 is laser-cut, it is placed in an etching fixture to etch the outline of the small wafer assembly area 2. The waste area in the small wafer assembly area 2 is a closed pattern. During the etching process, this closed pattern area falls into the etching solution. The fixed end of the small wafer (tuning fork wafer) 3 is still connected to the large-size quartz wafer 1, but it can be seen that the small wafer (tuning fork wafer) 3 is separated into a single piece, with only its fixed end connected to the large-size quartz wafer 1.

[0048] The etching solution uses a hydrofluoric acid composite solution, containing hydrofluoric acid (5% by mass), benzotriazole (0.5% by mass) as a corrosion inhibitor, and deionized water, achieving an etching rate of 10 μm / min. Ultrafast lasers form a weakening layer on the quartz wafer with a triple structure including a modified layer, a microcrack network, and a residual stress region. The etching solution preferentially etches the weakening layer, and the synergistic stress achieves sub-micron-level precise separation between the small wafer assembly's bonding region 2 and the large-size quartz wafer 1.

[0049] The structure of corrosion / cleaning fixture 47 is as follows: Figure 6 As shown, the device includes a handle 43, a side plate 44, and a slot plate 45. A large-size quartz wafer 1 is inserted into the slot of the slot plate 45. The handle 43 is used to place the etching / cleaning fixture 47 into the etching / cleaning tank 48 for etching or cleaning. The structure of the etching / cleaning tank 48 is as follows. Figure 7 As shown.

[0050] After the large-size quartz wafer 1 is laser-cut, it is placed in the etching fixture. The liftable basket can carry multiple etching fixtures. The etching tank contains etching liquid. The liftable basket is driven by a motor mechanism to lift and lower, and the etching fixtures are submerged and exposed in the etching liquid. This cycle is repeated until the set etching time is reached.

[0051] VI. Cleaning: After etching, the wafer is placed in a cleaning fixture to remove any remaining etching solution and other residues. This cleaning process needs to be repeated multiple times. The etching fixture and the cleaning fixture can be two types of fixtures with similar structures. The etching fixture is made of corrosion-resistant material, while the cleaning fixture can be made of corrosion-resistant material or metal. After etching, the wafer is removed from the etching fixture and then placed in the cleaning fixture for cleaning.

[0052] During the cleaning process, a large-sized quartz wafer 1 is inserted into the etching / cleaning fixture 47. The liftable basket can hold multiple cleaning fixtures. The cleaning tank contains cleaning fluid. The liftable basket is driven by a motor mechanism to perform lifting and lowering actions. The etching / cleaning fixture 47 is submerged in and exposed in the cleaning fluid. This cycle repeats until the set cleaning time is reached.

[0053] VII. Drying: After etching and cleaning, the wafer needs to be dried to remove surface moisture and solvents. This prevents pinholes and cracks from forming in the coating during the deposition process, which could affect the coating's adhesion. If the surface solvent is not dried, it will react with the coating material during the high-temperature deposition process, affecting the coating's electrical properties. Drying the surface solvent also prevents the high-temperature vaporization of the solvent during deposition from causing uneven thermal stress on the wafer surface, leading to wafer deformation or coating cracking. Nitrogen gas is introduced into the oven, the temperature is set to 100℃, and the drying time is 30 minutes.

[0054] 8. Coating: The dried large-size quartz wafer 1 is fixed in the coating fixture 5, which is then placed in a magnetron sputtering coating machine. A mechanical pump and a molecular pump combination is used to evacuate the vacuum to a degree of 1×10⁻⁶ in stages. -4 The coating temperature was 180℃, the coating thickness was approximately 120nm, and the evaporation rate was 0.5–1.5 nm / s. A molybdenum boat was resistance-heated with a stable current of 15–25A. The coating thickness was fed back in real-time by monitoring the wafer frequency. After coating, a vacuum annealing process was performed at 180℃ for 1.5–2 hours to relieve silver layer stress and improve conductivity. Nitrogen gas was then introduced, and the wafer was cooled to below 50℃ before removal to prevent thermal stress-induced wafer breakage. The coating metals were chromium, nickel, silver, and gold. A 10nm chromium layer was first deposited to enhance the adhesion between the metal and quartz, preventing the silver layer from peeling off. A 25nm nickel layer was then deposited to form a diffusion barrier layer, improving conductivity and inhibiting interpenetration between Cr and Ag, reducing Cr-Ag interface stress. An 80nm silver layer was then deposited as a low-resistance electrode. Finally, a 5nm gold layer was deposited to prevent silver oxidation and improve corrosion resistance.

[0055] The role of the chromium layer is to improve the bonding strength between the electrode and the wafer through mechanical interlocking and chemical bonding. The nickel layer has poor adhesion to the wafer, while the chromium layer has strong adhesion to the wafer. Therefore, chromium plating is performed first to increase the adhesion of the plating layer.

[0056] The nickel layer serves to improve the crystal's resistance to corrosion from external environments such as humidity and salt spray.

[0057] The silver layer is the main material of the electrode, and its high conductivity is used to reduce the equivalent series resistance of the crystal oscillator.

[0058] The gold layer prevents the electrodes from oxidizing in high temperature, high humidity or chemical environments.

[0059] The structure of the coating fixture 5 is as follows: Figure 8 and Figure 9 As shown, the system includes a rectangular top plate 50, a rectangular upper pressure plate 51, a rectangular positioning plate 53, a rectangular lower pressure plate 54, and a rectangular bottom plate 55. A large-size quartz wafer 1 is placed into the square hole of the positioning plate 53 for positioning. The upper pressure plate 51 and the lower pressure plate 54 cover the large-size quartz wafer 1 from the top and bottom of the positioning plate 53, respectively, to prevent the large-size quartz wafer 1 from coming out of the square hole of the positioning plate 53. The square holes of the upper pressure plate 51 and the lower pressure plate 54 allow the coating to adhere to the small wafer of the large-size quartz wafer 1. The top plate 50 presses down on the upper pressure plate 51, and the bottom plate 55 presses down on the lower pressure plate 54. Multiple screws 49 lock the top plate 50, the upper pressure plate 51, the positioning plate 53, the lower pressure plate 54, and the bottom plate 55 together.

[0060] 9. High-temperature aging: After the coating is completed, the large-size quartz wafer 1 is placed in... Figure 10 The high-temperature aging disk 6 shown is placed in a magnetron sputtering coating machine for vacuum high-temperature aging. The vacuum level is 1×10⁻⁶ in stages using a combination of mechanical and molecular pumps. -3 Pa, temperature 180℃, time 48 hours. A vacuum of 1×10⁻³ Pa is used to prevent silver layer oxidation and to prevent sulfide reactions between airborne sulfides and silver, which could lead to blackening of the silver layer and affect resonance characteristics. Due to the difference in thermal expansion coefficients between the coating layer and the quartz substrate, stress concentration is significant at 180℃. Under vacuum, fewer gas molecules reduce interference with the wafer, allowing for more uniform release of thermal stress and preventing wafer cracking. The vacuum level is maintained, and the wafer is removed after cooling in the furnace to below 50℃ to avoid thermal shock that could cause silver layer cracking.

[0061] 10. Ultrafast laser engraving circuit: such as Figure 11 As shown, an ultrafast laser is used to etch circuit 7 onto a large-sized quartz wafer after coating. The circuit linewidth etched by the second XY air-bearing module is 15μm. Because the coating material has a higher absorption rate for ultraviolet lasers, the ultraviolet laser eliminates the need for the 1064nm infrared laser and shorter pulse width (5–10ps) used in wafer cutting. High-precision circuit engraving can be achieved with a pulse width of 10–30ps, but the pulse width must be controlled within 30ps to suppress heat diffusion and avoid damage to the substrate. The laser emits a Gaussian circular spot, which passes through several mirrors and enters a 4–6x beam expander for beam alignment. The beam expander enlarges the beam diameter before it enters the Bezier cutting head and is converted into a long focal depth Bezier beam. A high repetition frequency is used, and the pulse overlap rate is adjusted to ensure a pulse overlap rate >80%, forming a continuous cutting line and avoiding short circuits at the circuit engraving point.

[0062] The structure of an ultrafast laser engraving circuit machine is as follows: Figure 12As shown, the system includes a third vision system, a second cutting head 57, a fourth stage 61, a third light source 62, a third XY air-bearing module, and a fourth stage base 65. The third XY air-bearing module includes a third Y-axis air-bearing module 63 and a third X-axis air-bearing module 64. The fourth stage base 65 is mounted on the third XY air-bearing module and is driven by the third XY air-bearing module to move in the XY plane. The third light source 62 is installed inside the box-shaped fourth stage base 65, and the fourth stage 61 is fixed to the top of the opening on the fourth stage base 65. The third vision system includes a third camera 58 and a third lens 59. The top surface of the fourth stage 61 includes a boss for supporting a large-size quartz wafer 1. The four corners of the boss have light-transmitting square holes to allow light from the third light source 62 to pass through the square holes and illuminate the corners of the large-size quartz wafer 1, facilitating the third vision system to capture and position the corners of the large-size quartz wafer 1. After capture and positioning, the large-size quartz wafer 1 moves along the XY plane below the second cutting head 57. The third vision system, consisting of the third camera 58 and the third lens 59, captures and positions the edges and corners of the large-size quartz wafer 1, enabling the focused laser to precisely etch the circuitry at the corresponding positions of the coating on the large-size quartz wafer 1. During circuit etching, the incident light 56 ​​from the second cutting head enters the second cutting head 57, which focuses the incident light 56. The focused light then etches the coating onto the smaller wafers of the large-size quartz wafer 1.

[0063] 11. Breaking and separating individual crystals: After the laser etching of the circuit is completed, individual crystals are broken. This can be done manually or by machine.

[0064] The beneficial effects of the above embodiments of the present invention are as follows: 1) It can be used to cut 32.768K 3215, 2012, and 1610 series wafers. The process is simple, the cost is low, the precision is high, and the environmental pollution is minimal.

[0065] 2) Laser thinning enables precise control over the thickness of large-sized quartz wafers.

[0066] 3) The Q value of large-size quartz wafers is significantly improved after laser thinning.

[0067] 4) The process of cutting wafers using ultrafast lasers is simple, the cutting precision can reach the submicron level, there is no heat-affected zone at the cutting edge, and the frequency stability is good.

[0068] 5) Using ultrafast laser engraving to create grooves results in low impedance of the crystal oscillator.

[0069] 6) Circuits engraved using ultrafast lasers are 50% more accurate than those formed using metal mask coating.

Claims

1. A laser processing method for a quartz crystal wafer, characterized in that, Includes the following steps: 101) Thinning step: In a vacuum environment, ultrafast laser is used to thin large-size quartz wafers to remove microscopic defects on the surface of large-size quartz wafers and improve the uniformity of wafer thickness. 102) Small wafer contour cutting steps: Use an ultrafast laser to cut the contours of small wafers into a large-size quartz wafer. The contour lines of multiple small wafers are connected in series to form the contour line of a combined area of ​​small wafers. The bottom of the cutting line of the combined area of ​​small wafers includes a weakening layer that is not penetrated. There are connection points between the small wafers surrounded by the small wafer contour lines and the main wafer of the large-size quartz wafer. The parameters of the ultrafast laser include: laser wavelength 1064nm, pulse width 5-10ps, repetition frequency 50-200kHz, single pulse energy 20-50μJ, energy consistency ≤±5%, and the divergence angle of the optical path is adjusted to <1mrad using a 2-8x beam expander. 103) Step for removing waste material from the assembly area of ​​small wafers: In the etching tank, the large-size quartz wafers are etched using an etching solution to crack the weakened layer. The waste material area in the assembly area of ​​the small wafers is a closed pattern. During the etching process, this closed pattern area falls into the etching solution. The etching solution is a hydrofluoric acid composite solution containing a composite solution of 5% hydrofluoric acid by mass + 0.5% benzotriazole corrosion inhibitor by mass + deionized water. 104) Coating step: Vacuum sputtering of a metal coating is performed on the surface of a large-size quartz wafer; 105) Circuit etching step: Electrode patterns are etched on the small wafers of the large-size quartz wafer after coating using an ultrafast laser; 106) Breaking and separating step: Disconnect the connection point between the small crystal and the main plate of the large-size quartz crystal to obtain a single crystal oscillator crystal product; 201) Tuning fork arm groove engraving step: After the small wafer outline cutting step in step 102, the tuning fork arm groove of the small wafer is engraved using an ultrafast ultraviolet laser. 202) Ultrasonic stress relief step: After the tuning fork arm groove engraving step in step 201 and before the waste removal step of the small wafer assembly area in step 103, dual-frequency ultrasonic waves are applied to the entire large-size quartz wafer board to eliminate the residual stress of the large-size quartz wafer.

2. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, Includes the following steps: 203) Cleaning and drying steps: After the waste material is removed by etching in step 103, clean the residual etching liquid and other residues on the large-size quartz wafer, and then dry it to remove the moisture and solvent from the surface of the large-size quartz wafer. 204) High-temperature aging step: Vacuum high-temperature aging is performed on the large-size quartz wafer after the coating is completed in step 104.

3. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, Step 101, the thinning step, uses a picosecond laser with a pulse width of 5-20 ps to thin a large-size quartz wafer layer by layer on a vacuum laser thinning machine. The vacuum laser thinning machine includes a first galvanometer, a first field mirror, a vacuum cavity, a first stage, a piezoelectric lifting and adjusting platform, a laser height sensor, and an XY moving platform. The first stage, the piezoelectric lifting and adjusting platform, and the XY moving platform are arranged in the vacuum cavity, with the piezoelectric lifting and adjusting platform mounted on the XY moving platform. The first stage is fixed to the top surface of the piezoelectric lifting and adjusting platform, and the top surface of the first stage includes a suction cup. The large-size quartz wafer is adsorbed by the suction cup on the top surface of the first stage and moves in the XY plane with the XY moving platform. The top plate of the vacuum cavity includes a first glass window and a second glass window, and the first field mirror is arranged in the first glass window. Directly above the first glass window, a laser height sensor is positioned above the second glass window. Before the laser thins the large-sized quartz wafer, the wafer is moved to the area directly below the second glass window in the XY plane. The laser height sensor measures the height of various positions on the upper surface of the wafer. During laser thinning, the wafer is positioned directly below the first glass window. The first galvanometer reflects the incident laser beam, which is then focused by the first field mirror. The focused beam passes through the first glass window and enters the vacuum chamber, where it thins the wafer.

4. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, Step 102, the small wafer contour cutting step, is performed on an ultrafast laser cutting machine. The ultrafast laser cutting machine includes a first vision system, at least one first cutting head, a second stage, a first light source, a first XY air-bearing module, and a second stage base. The second stage base is mounted on the first XY air-bearing module and is driven by the first XY air-bearing module to move in the XY plane. The first light source is installed inside the box-shaped second stage base. The second stage is fixed to the top of the opening on the second stage base. The top surface of the second stage includes at least one first protrusion for supporting a large-sized quartz wafer. The four corners of the first protrusion have light-transmitting square holes. The light from the first light source passes through the square holes to illuminate the edges and corners of the large-sized quartz wafer. The first vision system captures and positions the edges and corners of the large-sized quartz wafer. After capture and positioning, the large-sized quartz wafer moves along the XY plane to below the first cutting head. The first cutting head focuses its own incident light and cuts the large-sized quartz wafer below. One large-sized quartz wafer is cut into a combination area of ​​multiple small wafers. The incident light of the first cutting head is an ultrafast laser.

5. The laser processing method for quartz crystal wafers according to claim 2, characterized in that, Step 201, the tuning fork arm groove engraving step, is performed on an ultrafast laser engraving groove machine. Frequency-modulated microgrooves with a depth of 0.02–0.07 mm are engraved on the tuning fork arm of each small chip. The ultrafast laser engraving groove machine includes a second vision system, a second galvanometer, a second field mirror, a third stage, a second light source, a second XY air-bearing module, and a third stage base. The third stage base is mounted on the second XY air-bearing module and is driven by the second XY air-bearing module to move in the XY plane. The second light source is installed inside the box-shaped third stage base, and the third stage is fixed to the top of the opening on the third stage base. The top surface of the third stage includes a second protrusion for supporting a large-sized quartz wafer. The four corners of the second protrusion have light-transmitting square holes. The light from the second light source passes through the square holes to illuminate the edges and corners of the large-sized quartz wafer. The second vision system captures and positions the edges and corners of the large-sized quartz wafer. After capture and positioning, the large-sized quartz wafer moves along the XY plane below the second field mirror, so that the laser focused by the second field mirror can be precisely aligned with the corresponding position of the tuning fork arm for groove engraving. The second galvanometer reflects the incident laser light, and the second field mirror focuses the reflected light. The focused light engraves the grooves on the tuning fork arm of the large-sized quartz wafer. The incident laser light of the second galvanometer is an ultrafast ultraviolet laser. The ultrafast ultraviolet laser parameters include: wavelength 355nm, pulse width 500fs-10ps, single pulse energy 5-20μJ, and repetition frequency: 100-500kHz.

6. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, Step 202, the ultrasonic stress relief step, employs low-frequency ultrasound of 15-25 kHz for coarse vibration, with a power density of 15-25 W / cm² and an amplitude of 80-120 μm; and high-frequency ultrasound of 0.8-1.2 MHz for fine vibration, with a power density of 0.5-2 W / cm² and an amplitude of 0.1-0.5 μm. The temporal superposition of coarse and fine vibrations achieves gradient elimination of internal stress in the quartz wafer. The low-frequency ultrasonic coarse vibration converts the residual tensile stress in the wafer into compressive stress, while the high-frequency ultrasonic fine vibration promotes lattice dislocation slip and grain refinement. Furthermore, the microcrack interface is remelted and closed through localized high temperature of 580-620°C. Power ramp start-stop control is used, and under the synergistic effect of 30-60 seconds of coarse vibration and 5-10 seconds of fine vibration, stress is eliminated and the stability of the wafer frequency is improved.

7. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, The etching solution in step 103 contains hydrofluoric acid and an inhibitor. In step 102, the ultrafast laser forms a weakening layer with a triple structure, including a modified layer, a microcrack network, and a residual stress zone, at the bottom of the cutting line in the small wafer assembly area. In step 103, the etching solution preferentially etches the weakening layer, and the synergistic stress achieves submicron-level precise separation between the small wafer assembly area and the main wafer of the large-size quartz wafer.

8. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, In step 104, a large-size quartz wafer is fixed in a coating fixture and placed in a magnetron sputtering coating machine. After the magnetron sputtering coating machine is evacuated, coating is performed at a temperature of 170℃-190℃ and an evaporation rate of 0.5–1.5 nm / s. After coating, the wafer is kept under vacuum and annealed at 180℃ for 1.5–2 hours. Nitrogen gas is introduced and the wafer is cooled to below 50℃ in the furnace before being removed. The coating thickness is 110nm-130nm, and the coating metals are chromium, nickel, silver, and gold in sequence.

9. The laser processing method for quartz crystal wafers according to claim 1, characterized in that, The circuit etching step in step 105 is performed on an ultrafast laser engraving circuit machine, which includes a third vision system, a second cutting head, a fourth stage, a third light source, a third XY air-bearing module, and a fourth stage base. The fourth stage base is mounted on the third XY air-bearing module and is driven by the third XY air-bearing module to move in the XY plane. The third light source is installed inside the box-shaped fourth stage base, and the fourth stage is fixed to the top of the opening on the fourth stage base. The top of the fourth stage is covered with a third protrusion for supporting a large-sized quartz wafer. The four corners of the third protrusion have light-transmitting square holes. The light from the third light source passes through the square holes to illuminate the edges and corners of the large-sized quartz wafer. The third vision system captures and positions the edges and corners of the large-sized quartz wafer, so that the focused laser can accurately etch the circuit at the corresponding position of the coating on the large-sized quartz wafer. During circuit etching, the incident light entering the second cutting head is focused and then etches the coating on the small wafers on the large-sized quartz wafer. The incident light entering the second cutting head is an ultrafast laser. The parameters of the ultrafast laser include: laser wavelength 355nm, pulse width 10–30ps, repetition frequency 600–800 kHz, single pulse energy 10–30μJ, energy consistency ≤±5%, and a 4-6x beam expander is used to expand the initial beam diameter to 20 mm, and the divergence angle of the optical path is adjusted to <0.8mrad.

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