A method and system for laser cutting of quartz wafers

Abstract

The present invention discloses a method for laser cutting of quartz wafers, comprising the following steps: adsorbing the wafer onto a vacuum chuck serving as a cutting platform; using an ultrafast infrared laser to cut the wafer's outline, forming a weakened layer that does not penetrate the wafer; using an ultrafast ultraviolet laser to trim the edges of the cut outline; and treating the wafer with an etchant to crack the weakened layer, thereby separating the wafer into individual wafer units. The quartz wafer laser cutting method of the present invention utilizes an ultrafast infrared laser to precisely form the weakened layer, followed by atomic-level trimming of the cut edge using an ultraviolet laser. Combined with selective etching of the weakened layer using an etchant, this method achieves submicron cutting accuracy, improving the precision of traditional single-laser cutting by four times.

Description

Technical Field

[0001] The present invention relates to a quartz wafer cutting process, and in particular to a quartz wafer laser cutting method and system. Background Art

[0002] With the advancement of technology, crystal oscillators are becoming more widely used on PCBs. Traditionally, large wafers are cut into smaller wafers using mechanical wire cutting. This process is complex, costly, and has low precision, with an accuracy of ±5μm. This traditional process requires gluing, wire cutting, and repeated washing, which can lead to dust pollution and glue residue contamination.

[0003] The invention with patent number CN202410404634.7 discloses a low-loss all-laser processed wafer slicing method and wafer, which is applied to the field of semiconductor wafer processing technology, including: focusing a first laser on a preset depth of the wafer for heating, and then cooling the melted wafer area to form an amorphous amorphous region at a preset depth of the wafer; using a second laser to heat the amorphous region to separate the wafer from the preset depth; the energy density of the second laser is higher than the ablation threshold of the amorphous region and lower than the ablation threshold of the crystalline region other than the amorphous region in the wafer. The wafer is heated and melted using the first laser, and then cooled to produce microcracks in and around the amorphous region, and the laser-induced thermal stress will stretch the microcrack tips and form periodic microcracks inside the wafer silicon. The amorphous region is then heated specifically with a second laser. During this process, the microcracks will expand and connect to form a main crack layer, completely splitting the wafer and achieving wafer separation.

[0004] This invention is primarily targeted at cutting thicker wafers, such as silicon carbide wafers, but it still has certain limitations for miniaturized, high-precision wafer cutting. For example, its cutting accuracy, stress control, and etching process have not been specifically optimized, making it difficult to meet the special needs of miniaturization and high precision. Summary of the Invention

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

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for laser cutting of a quartz wafer, characterized in that it includes the following steps:

[0007] 101) The wafer is adsorbed onto a vacuum chuck serving as a cutting platform;

[0008] 102) Using ultrafast infrared laser to perform contour cutting of wafers, forming a weakened layer that does not penetrate the wafer;

[0009] 103) Using ultrafast UV laser to trim the edge of the cutting contour;

[0010] 104) The weakened layer of the wafer is cracked by treating it with a corrosive solution, thereby separating the wafer into independent wafer units.

[0011] The above-mentioned method for laser cutting of quartz wafers is characterized by comprising the following steps:

[0012] 201) In step 101, the cutting platform is made of a ceramic material with a thermal conductivity ≥ 150 W / (m·K);

[0013] 202) Using a laser rangefinder to measure the surface height of the quartz wafer in real time, in step 102, dynamically adjusting the height of the cutting platform using a piezoelectric ceramic fine-tuning mechanism to compensate for height errors caused by surface flatness of the quartz wafer surface;

[0014] 203) The etching solution in step 104 comprises hydrofluoric acid and a corrosion inhibitor;

[0015] 204) Before step 104, dual-frequency ultrasonic vibration is applied to the cut wafer to eliminate stress.

[0016] The above-mentioned method for laser cutting of quartz wafers is characterized by comprising the following steps:

[0017] 301) In step 101, the cutting platform is made of aluminum nitride ceramic material or sintered steel. The sintered steel cutting platform is used for production verification, and the aluminum nitride ceramic cutting platform is used for mass production.

[0018] 302) In step 102, the ultrafast infrared laser is a 1064 nm ultrafast infrared laser with a pulse width of ≤10 ps, ​​a single pulse energy of 50-100 μJ, and a scanning speed of 200-500 mm / s;

[0019] 303) In step 103, the ultrafast ultraviolet laser is a 355nm ultrafast ultraviolet laser that scans the edge twice along the same path, with a single pulse energy of 5-10 μJ and a scanning speed of 300-600 mm / s;

[0020] 304) In step 104, the wafer is placed in an etching solution containing 5 wt% hydrofluoric acid and 0.5 wt% benzotriazole at a temperature of 38-42°C for 3-5 minutes to achieve chipping;

[0021] 305) In step 204, a low-frequency ultrasonic wave of 15-25 kHz is used for coarse vibration, and a high-frequency ultrasonic wave of 0.8-1.2 MHz is used for fine vibration.

[0022] The above-described method for laser cutting of quartz wafers is characterized in that step 102 is performed by a cross-line cutting method: cutting is performed in sequence of crossing N lines each time, and then returning to the next line of the original line for cutting, and the cycle is repeated until the cutting is completed; wherein N≥1.

[0023] The above-described method for laser cutting of quartz wafers is characterized in that, in step 102, an ultrafast infrared laser forms a weakened layer on the quartz wafer comprising a triple structure of a modified layer, a microcrack network, and a residual stress zone. In step 104, an etching solution preferentially etches the weakened layer, and synergistic stress is used to achieve submicron-level precision separation of the wafers.

[0024] The above-described method for laser cutting of quartz wafers is characterized in that an air-floating XY motion platform is used to synchronously drive four independent workstations, each of which includes the cutting platform, the piezoelectric ceramic fine-tuning mechanism, a laser ranging sensor, and a dual-wavelength laser cutting head; the four workstations are respectively connected to four split light beams through a laser spectrometer system, the laser ranging sensors respectively monitor the height of the wafers at their respective workstations, and the upper computer controls each piezoelectric ceramic fine-tuning mechanism to achieve dynamic leveling. The four split light beams are respectively input into the corresponding dual-wavelength laser cutting head, and the wafers are dual-wavelength cut in a time sequence of infrared cutting first and then ultraviolet trimming; after the wafer cutting is completed, the wafers at the four workstations are collectively transferred to an ultrasonic fixture and a gauze etching tank for post-processing, thereby achieving four-station parallel processing.

[0025] The above-described method for laser cutting of quartz wafers is characterized in that, in step 305, coarse vibration is performed by low-frequency ultrasonic waves of 15-25 kHz, with a power density of 15-25 W / cm² and an amplitude of 80-120 μm, and fine vibration is performed by high-frequency ultrasonic waves of 0.8-1.2 MHz, with a power density of 0.5-2 W / cm² and an amplitude of 0.1-0.5 μm; the timing superposition of coarse vibration and fine vibration realizes gradient elimination of internal stress of the quartz wafer; low-frequency ultrasonic coarse vibration converts residual tensile stress of the wafer into compressive stress, and high-frequency ultrasonic fine vibration promotes lattice dislocation slip and grain refinement; and microcrack interface remelting and closure are achieved through local high temperature of 580-620°C, and power ramp start-stop control is adopted. Under the synergistic effect of 30-60 seconds of coarse vibration and 5-10 seconds of fine vibration, the stress elimination rate is improved and the frequency stability of the wafer is improved.

[0026] Using ultraviolet laser to perform atomic-level trimming of the cutting edge, combined with selective etching of the weakened layer by corrosive liquid, can achieve submicron cutting accuracy, which can be increased by 4 times compared to traditional single laser cutting. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 It is a three-dimensional diagram of the main structure of the quartz wafer laser cutting system according to an embodiment of the present invention.

[0029] Figure 2 It is a three-dimensional diagram of the combination of the cutting platform and the piezoelectric ceramic fine-tuning structure according to an embodiment of the present invention.

[0030] Figure 3 It is a three-dimensional diagram of a cutting platform according to an embodiment of the present invention.

[0031] Figure 4 Schematic diagram of cutting a large-size wafer according to an embodiment of the present invention.

[0032] Figure 5 2 is a perspective view of a clamp according to an embodiment of the present invention.

[0033] Figure 6 It is a three-dimensional diagram of the etching fixture according to an embodiment of the present invention.

[0034] Figure 7 It is a schematic diagram of the laser splitting path layout according to an embodiment of the present invention.

[0035] Figure 8 The figure is a flow chart of a quartz wafer laser cutting method according to an embodiment of the present invention.

[0036] The accompanying drawings include: 1, wafer; 2, cutting blade; 3, ultrasonic fixture; 4, etching fixture; 6, horizontal cutting line A; 7, horizontal cutting line B; 8, horizontal cutting line C; 9, horizontal cutting line D; 10, horizontal cutting line E; 11, horizontal cutting line F; 12, horizontal cutting line G; 13, vertical cutting line A; 14, vertical cutting line B; 15, vertical cutting line C; 16, vertical cutting line D; 17, vertical cutting line E; 18, vertical cutting line F; 19, vertical cutting line G; 20, cutting platform; 21, adsorption hole; 22, piezoelectric ceramic fine-tuning mechanism; 23, cutting head light input A; 24, cutting head input Light B; 25. Cutting head incident light C; 26. Cutting head incident light D; 27. Cutting head; 28. Laser distance sensor; 29. ​​Y-axis; 30. X-axis; 31. Laser A; 32. Outgoing light from laser A; 33. Quarter-wave plate A; 34. Reflector A; 35. Polarization beam splitter cube A; 36. Quarter-wave plate B; 37. Split light A; 38. Split light B; 39. Split light C; 40. Split light D; 41. Quarter-wave plate C; 42. Reflector B; 43. Polarization beam splitter cube B; 44. Quarter-wave plate D; 45. Outgoing light from laser B; 46. Laser B; DETAILED DESCRIPTION

[0037] The quartz wafer laser cutting method disclosed herein is primarily used for laser cutting of wafers, employing an ultrafast laser to perform wafer contour shaping. The objective is to place the wafer within the cutting window of the ultrafast laser, where the laser emits a laser beam of a specific frequency and pulse width to shape the wafer contour. Due to the specific laser frequency and pulse width, large wafers are merely separated into smaller pieces of a given size by laser points spaced at a certain distance, without being cracked. Therefore, the large wafers must be further loaded using an ultrasonic vibration fixture to perform ultrasonic vibration to eliminate internal stress in the wafers. The wafers must then be re-loaded using the fixture and etching solution to etch and crack the smaller pieces into smaller pieces of a given size.

[0038] The quartz wafer laser cutting method of the present invention is carried out in a quartz wafer laser cutting system, such as Figures 1 to 6 As shown, the quartz wafer laser cutting system is mainly composed of the following mechanisms:

[0039] 1. Cutting platform mechanism: The cutting platform is made of steel or aluminum nitride ceramics, and its top surface is a vacuum suction cup used to support and fix the wafer to prevent the wafer from being dislocated due to the high-speed movement of the cutting platform during the cutting process.

[0040] 2. Dynamic Leveling System: A piezoelectric ceramic fine-tuning mechanism is installed at the bottom of the cutting platform, and a laser interferometer, laser line scanner, or laser rangefinder is installed at the top of the cutting platform. The laser interferometer, laser line scanner, or laser rangefinder provides real-time feedback on the wafer surface flatness. The piezoelectric ceramic fine-tuning mechanism then fine-tunes the height based on this feedback, ensuring that the laser focal length remains within the same range, thereby ensuring a consistent cutting path width.

[0041] 3. Ultrafast laser sources, including ultrafast infrared laser sources and ultrafast ultraviolet laser sources.

[0042] 1) Ultrafast infrared laser source: This includes a 1064nm ultrafast infrared laser and an ultrafast infrared laser beam splitter. The ultrafast infrared laser is used for wafer contour cutting. The ultrafast infrared laser beam splitter includes a beam splitter prism or diffractive optical element (DOE), a half-wave plate, a quarter-wave plate, and a pre-beam expander. This single-ended 1064nm ultrafast infrared laser is split into multiple laser beams, enabling simultaneous processing of multiple wafers. The laser polarization state is adjusted using the half-wave plate and quarter-wave plate to optimize processing quality. The pre-beam expander expands and collimates the laser beam, reducing the divergence angle and ensuring uniform spot size for each split sub-beam.

[0043] When ultrafast infrared laser is used for wafer contour cutting, the laser wavelength is 1064nm, the pulse width is 5-10ps, the repetition frequency is 50-200kHz, the single pulse energy is 20-50μJ, a 2-8x beam expander is used, and the spot diameter is about 2μm.

[0044] 2) Ultrafast UV laser: This includes a 355nm ultrafast UV laser and an ultrafast UV laser beam splitter. The ultrafast UV laser is used to trim the cutting contour and improve cutting accuracy and quality.

[0045] 4. The laser beam splitter also includes a beam splitter prism or diffractive optical element (DOE), a half-wave plate, a quarter-wave plate, and a pre-beam expander. This splits the laser beam from a single source into multiple laser beams, enabling simultaneous processing of multiple wafers. The half-wave plate and quarter-wave plate adjust the laser polarization to optimize processing quality. The pre-beam expander expands and collimates the laser beam, reducing the divergence angle and ensuring uniform spot size for each sub-beam after splitting.

[0046] 5. Ultrasonic vibration device, including ultrasonic generator and ultrasonic fixture, is used to perform ultrasonic vibration on the cut wafer to eliminate the internal stress of the wafer, avoid the influence of internal stress on the natural frequency of the wafer, and stabilize the frequency of the wafer.

[0047] 6. The etching and cleaning device includes an etching fixture, an etching tank, and a cleaning tank. The etching fixture is used to load unfragmented wafers after dicing and place them into the etching tank for etching, breaking large wafers into smaller ones. The cleaning tank is used to clean the etched wafers.

[0048] 7. The motion control platform includes an air flotation module and an XY axis motion mechanism. The air flotation module provides a high-speed and stable motion platform, and the XY axis motion mechanism is used to accurately control the relative position of the cutting platform and the laser cutting head to achieve precise cutting path control. Figure 1 As shown, the lower axis of the air flotation module is the X-axis 30, and the upper axis is the Y-axis 29. There are several cutting platforms 20 above the air flotation module. In this embodiment, there are four cutting platforms 20. A laser ranging sensor 28 is provided above the large-size wafer 1 to measure the flatness of the wafer surface in real time and provide feedback to the piezoelectric ceramic fine-tuning mechanism 22. The piezoelectric ceramic fine-tuning mechanism 22 automatically rises and falls to compensate for the error in the surface flatness of the large-size wafer 1. A cutting head 27 is provided above the cutting platform 20. Cutting head input light A23, cutting head input light B24, cutting head input light C25, and cutting head input light D26 are respectively incident on the cutting head 27 from one end; the cutting head input light is indirectly transmitted by the light output of the laser spectrometer, and during the transmission process, it is also pressed through multiple sets of intermediate reflectors and beam expanders to adjust the beam angle and the roundness of the light spot.

[0049] 8. Cutting Head: The cutting head is a key component of the laser cutting system. Composed of optical lenses, focusing lenses, and a nozzle, it is responsible for precisely focusing the laser beam onto the wafer surface to achieve the cutting function. It can perform high-precision contour cutting and edge trimming on the wafer according to the set cutting path and process parameters.

[0050] The cutting head is connected to the ultrafast laser source through an optical path. The laser light generated by the ultrafast laser source is transmitted to the cutting head through an optical cable or a set of reflective mirrors. The cutting head is equipped with optical lenses and a focusing system to ensure that the laser beam is accurately focused on the wafer surface.

[0051] The cutting head is mounted on the cutting head bracket of the motion control platform, which precisely controls the position and movement trajectory of the cutting head through the XY axis motion mechanism.

[0052] In summary, the cutting platform provides a stable platform for supporting and securing the wafers. The dynamic leveling system beneath it ensures the flatness of the wafer surface during the cutting process. The laser light generated by the ultrafast laser source is split and path-optimized by a laser beam splitter before being applied to the wafer on the cutting platform to achieve the cutting process. After cutting, the cut disc is stress-relieved using an ultrasonic vibration device, followed by etching and cleaning using an etching and cleaning device, ultimately resulting in a finished wafer of the desired size. The motion control platform precisely controls the movement of each component in the entire system, ensuring cutting path accuracy and processing efficiency.

[0053] The principle of the quartz wafer laser cutting method of the present invention is described in further detail below. The process of the quartz wafer laser cutting method of the embodiment of the present invention is as follows: Figure 8 shown.

[0054] The cutting platform can be made of either a steel or aluminum nitride ceramic cutting platform. The cutting platform supports the wafer and features a vacuum chuck with a matrix of vacuum holes arranged on the top surface. These holes hold the wafer in place, preventing misalignment during high-speed movement. The cutting platform is made of steel or aluminum nitride ceramic. Steel is low-cost and has low water absorption and thermal expansion coefficient, resulting in minimal dimensional change at room temperature. It is suitable for rapid prototyping and production verification. Aluminum nitride ceramic has high thermal conductivity, minimizing heat-affected zones (HAZs) during ultrafast laser cutting, preventing cracking of quartz wafers and improving yield, making it suitable for mass production. Aluminum nitride ceramic has low reflectivity, improving laser energy utilization. Aluminum nitride is chemically stable and resists reaction with quartz wafers or cutting products at high temperatures, preventing secondary fusion and contaminant residue. Aluminum nitride's smooth surface allows for easy wafer separation after cutting, eliminating the need for complex cleaning procedures. Aluminum nitride ceramic's thermal expansion coefficient matches that of quartz, minimizing thermal deformation.

[0055] like Figure 2 and Figure 3As shown, the cutting platform 20 is made of SiC steel or aluminum nitride ceramics, and has distributed adsorption holes 21 for adsorbing products. The top of the piezoelectric ceramic fine-tuning mechanism 22 is connected to the cutting platform 20, and a large-size wafer 1 (general specification model is 32.768K, size is 2mm×6mm or 3mm×8mm) is placed on the cutting platform 20.

[0056] Aluminum nitride has a higher thermal conductivity than other materials, at 170–220 W / (m·K). Heat generated by wafer cutting can be more quickly dissipated through the aluminum nitride platform, preventing localized temperature rise. Heat from cutting can accumulate in the wafer, leading to carbonization at the edges. This high temperature can cause localized uneven thermal expansion, leading to lattice distortion, dislocations, or microcracks, thus reducing the Q value. Ultrafast laser cold processing reduces the heat-affected zone (HAZ) of wafers to less than 1μm, preventing thermal diffusion damage and reducing proximity effect losses, thereby improving the Q value by approximately 8%.

[0057] The dynamic leveling system features a piezoelectric ceramic fine-tuning mechanism installed at the bottom of the aluminum nitride ceramic cutting platform. (This mechanism can be a compact precision Z-axis translation stage (Model L-306) from Puai Nano Displacement Technology Co., Ltd.) This mechanism compensates for surface flatness errors in the wafer. A laser distance sensor installed above the aluminum nitride ceramic cutting platform measures the surface height of the quartz wafer in real time, providing real-time feedback on the wafer's surface flatness. This laser distance sensor can be a laser line scanner (Keyence, Model LJ-X8020, Line Laser Measuring Instrument) or a laser distance meter (ATES, Model CD33-85NA, Laser Displacement Sensor).

[0058] The laser cutting head and the laser line scanner need to be calibrated during machine adjustment. For example, the laser cutting head cuts the calibration pattern on the wafer or other calibration standard block. At this time, the lower motion platform moves the wafer or calibration standard block to the laser line scanner to measure the calibration pattern. After multiple calibrations, the relative position of the laser cutting head and the laser line scanner can be obtained. During normal production, the laser line scanner first measures each position of the wafer to obtain the height difference of each position of the wafer. The piezoelectric ceramic fine-tuning mechanism will adjust the height according to the height difference data obtained by the laser line scanner. During the height adjustment process, the bottom motion platform moves the same value according to the relative position of the laser cutting head and the laser line scanner.

[0059] Flatness values ​​are transmitted in real time to the piezoelectric ceramic fine-tuning mechanism for height fine-tuning. Both the laser line scanner and the piezoelectric ceramic fine-tuning mechanism are controlled by a host computer. This keeps the laser focal length in each area within the same range, ensuring a consistent laser cutting path width and precisely controlling the size of small 2×6 and 3×8 wafers.

[0060] Ultrafast laser processing, wherein the ultrafast laser has an output laser pulse width less than or equal to picosecond level, uses a 1064nm ultrafast infrared laser to cut the wafer contour, and uses a 355nm ultrafast ultraviolet laser to trim the edge of the cutting contour.

[0061] Laser beam splitting: Beam splitting is the process of splitting a single laser into two or more beams, enabling the simultaneous processing of one or more large wafers. Beam splitting is achieved using a beam splitter or diffractive optical element (DOE). Half-wave plates and quarter-wave plates are used to adjust the laser polarization state, converting linearly polarized light into circularly polarized light to optimize processing quality. A pre-beam expander expands and collimates the laser beam, reducing the divergence angle and ensuring uniform spot size for each sub-beam after splitting.

[0062] like Figure 7 As shown, the emitted light 32 of laser A31, the emitted light 32 of laser A passes through the quarter wave plate A33 to adjust the polarization state of the optical signal so that the two components of the emitted light 32 of laser A produce a phase difference of 1 / 4 wavelength. The two components of the emitted light 32 of laser A then pass through the polarization beam splitter cube A35 to separate into two components. The emitted light component reflected by the polarization beam splitter cube A35 is directly reflected by the reflector A34 to become the split light B38. The emitted light component transmitted by the polarization beam splitter cube A35 then enters the quarter wave plate B36 to adjust the polarization state and becomes Split light A37; the emitted light 45 of laser B46 passes through the quarter-wave plate D44 to adjust the polarization state of the optical signal so that the two components of the emitted light 45 of laser B produce a phase difference of 1 / 4 wavelength. The two components of the emitted light 45 of laser B are then separated into two components through the polarization beam splitter cube B43. The emitted light component reflected by the polarization beam splitter cube B43 is directly reflected by the reflector B42 to become the split light C39. The emitted light component transmitted by the polarization beam splitter cube B43 enters the quarter-wave plate C41 to adjust the polarization state and becomes the split light D40.

[0063] This invention utilizes a laser cross-line cutting path to improve cutting accuracy. Due to the small size of a 2×6 wafer, the distance between cutting lines is short, which can reduce cutting accuracy. Cross-line cutting improves accuracy by cutting across one line, two lines, or multiple lines, then returning to the next line and performing the same cross-line cutting again. This cycle continues until the cutting is complete. While traditional mechanical wire cutting achieves ±5µm accuracy, ultrafast laser cutting with an optimized cutting path achieves ±0.5µm.

[0064] like Figure 4As shown, the cutting sheet 2 after laser cutting has horizontal and vertical cutting lines, such as 6, 7, 8, 9, 10, 11, and 12 are horizontal cutting lines, and 13, 14, 15, 16, 17, 18, and 19 are vertical cutting lines. The general idea is to cut line 6 first, then line 7, and then line 8, etc., and such sequential cutting will reduce the cutting accuracy; the present invention proposes to cut line 6 first, then line 8, and then line 10, and then return to cut line 7, line 9, line 11, etc., and this method cuts across one line; or cuts across two lines, first cutting line 6, line 9, line 12, etc., and then cutting line 7, line 10, line 13, etc.

[0065] The improvement in precision brought by cross-line cutting has the following relationship with the number of cross-line cutting lines:

[0066] 1) Because large wafers are mostly around 50-100mm in size, the minimum spacing between cutting lines is around 1mm. The bottom platform is driven by a linear motor. The steep acceleration and deceleration curves during such small-pitch cutting result in significant motion errors. When cutting across lines, the spacing between lines increases, giving the linear motor more time to accelerate and decelerate, which in turn improves the platform's motion accuracy. Therefore, within the range of large wafer sizes, a greater number of line spans results in a greater improvement in accuracy.

[0067] 2) Another benefit of cross-line cutting is that the temperature generated during cutting can be exported in time. When the distance between two lines is close, the temperature next to them will affect the cutting of the adjacent lines.

[0068] Ultrasonic vibration is used to eliminate internal stress in the wafer, preventing it from affecting its natural frequency and stabilizing its frequency stability. Using 20kHz ultrasonic coarse vibration and 1MHz ultrasonic fine vibration, dual-frequency ultrasonic superposition eliminates residual stress within the wafer through the interference effect of stress waves (elimination rate >90%), while also preventing the formation of surface microcracks.

[0069] 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 ≈50 MPa) but below the fracture limit (≈100 MPa). Power densities below 15 W / cm² result in insufficient dislocation slip, while those above 25 W / cm² may induce microcracks at the wafer edge. Amplitude: 80–120 μm, frequency: 20 kHz ± 200 Hz, exposure time: 30–60 seconds per wafer.

[0070] 1MHz is the fine vibration mode, with a power density range of 0.5–2 W / cm². High frequencies concentrate the energy per unit area. Powers above 2W / cm² can easily induce surface cavitation pits, while those below 0.5W / cm² can lead to insufficient dislocation rearrangement. Amplitude: 0.1–0.5μm, frequency: 1MHz±10kHz, exposure time: 5–10 seconds per wafer.

[0071] Microcracks on the wafer surface are reduced by controlling the vibration energy gradient as follows:

[0072] Power ramp start and stop:

[0073] Coarse vibration start: 0→25W / cm² linear increase (3 seconds) to avoid step shock.

[0074] Fine vibration stop: exponential decay (time constant τ = 0.1 seconds) to suppress residual oscillations.

[0075] 20kHz ultrasound waves dominate macroscopic plastic deformation, while 1MHz ultrasound waves focus on microscopic lattice control. The 20kHz ultrasound waves transmit high-frequency mechanical vibrations (acceleration up to 30,000 times the acceleration of gravity) through the impactor, causing compressive plastic deformation on the surface of the quartz wafer, converting residual tensile stress (>100MPa) into compressive stress (-200 to -300MPa), eliminating the driving force for microcrack initiation.

[0076] High-frequency vibrations at 1 MHz promote dislocation slip and proliferation within the quartz lattice, reducing grain size by 30-50%. The refined grain boundaries increase density by 2–3 times, hindering dislocation accumulation and blocking the path for microcracks to propagate along grain boundaries. High-frequency stress waves induce local resonance at the microcrack interfaces, causing repeated opening and closing of the crack surfaces, generating frictional heat with transient temperatures reaching 600°C. This high temperature causes micromelting and recombination of the crack interfaces, achieving active closure of the microcracks (filling ratio >80%).

[0077] The etching fixture is used to load the wafers that have not been split after cutting so that the wafers can be etched and cleaned. After etching, the large-sized wafers are split into small wafers of 2×6 or 3×8 sizes.

[0078] After cutting and stress-relief, the quartz wafer is manually placed into a cleaning and etching fixture, which is then placed into a square tank filled with cleaning or etching fluid. Holes are cut into the cleaning fixture's four sides to facilitate the entry of the cleaning fluid for cleaning the wafers. The etching fixture is cylindrical and surrounded by a mesh screen. The mesh holes are smaller than the small wafers to prevent the large wafer from falling out of the fixture after etching.

[0079] The separation line formed on a quartz wafer after laser cutting is not a physical crack, but rather a non-penetrating weakened layer composed of three structures. Picosecond infrared laser light irradiates the quartz wafer, causing lattice distortion. This weakens intermolecular forces at the separation line, reduces SiO2 bond energy, and increases chemical activity, yet remains physically connected to the substrate. This is the modified layer. Laser thermal stress induces micron-scale cracks perpendicular to the cutting direction. However, limited by the toughness of quartz, the cracks do not penetrate the wafer and instead extend along the edges of the modified layer, forming a microcrack network. Laser processing causes residual tensile stress to accumulate around the modified layer, rendering this region metastable. This is another structure created around the quartz separation line during laser cutting. The corrosive solution preferentially attacks the loosely structured modified layer at the separation line, resulting in an etching rate 5–10 times faster than that of the unmodified area. This creates an occluded corrosive environment within the microcrack network, allowing for physical widening, thereby removing slag and connecting the crack network. Further corrosion propagates the cracks, causing the residual tensile stress to exceed the fracture toughness of quartz, enabling precise submicron separation.

[0080] The etching solution used in the present invention is a hydrofluoric acid composite solution, which contains a composite solution of hydrofluoric acid (5% by mass) + corrosion inhibitor benzotriazole (0.5% by mass) + deionized water, and the etching rate reaches 10 μm / min.

[0081] Table 1: Beneficial effects of the present invention compared with traditional processes

[0082]

[0083] The method for laser cutting of quartz wafers of the present invention has the following beneficial effects:

[0084] 1) Wafers that can be cut by ultrafast lasers.

[0085] 2) Ultrafast laser cutting of wafers has low cost, high precision and less environmental pollution. After the ultrafast infrared laser precisely forms the weakened layer, the ultraviolet laser is used to atomically trim the cutting edge. Combined with the selective etching of the weakened layer by corrosive liquid, submicron-level (±0.5μm) cutting accuracy is achieved, which is 4 times higher than the accuracy of traditional single laser cutting.

[0086] 3) Laser beam splitting processing can process multiple large-size wafers at the same time with high efficiency. The dynamic leveling system is used and the width of the wafer cutting line is controllable.

[0087] 4) Optimization of cutting platform materials to reduce thermal impact and improve wafer Q value. Dual-frequency ultrasonic stress relief increases the Q value from 100,000 in the reference document to 119,300, and the frequency temperature coefficient is optimized to ±0.6ppm / ℃ (the existing technology is ±3ppm / ℃).

[0088] 5) Ultrasonic wave can remove stress and reduce the generation of micro cracks.

Claims

1. A method for laser cutting of a quartz wafer, characterized in that: The following steps are involved: 101) The wafer is adsorbed on a vacuum chuck serving as a cutting platform, and the cutting platform is made of ceramic material with a thermal conductivity of ≥150W / (m·K); 102) Using a laser rangefinder to measure the surface height of a quartz wafer in real time, dynamically adjusting the height of the cutting platform through a piezoelectric ceramic fine-tuning mechanism to compensate for height errors on the quartz wafer surface caused by surface flatness; using an ultrafast infrared laser to contour cut the wafer, forming a non-penetrating weakened layer on the wafer; the ultrafast infrared laser is a 1064nm ultrafast infrared laser with a pulse width of ≤10ps, a single pulse energy of 50-100μJ, and a scanning speed of 200-500mm / s; 103) Ultrafast UV laser is used to trim the edge of the cutting contour; the ultrafast UV laser is a 355nm ultrafast UV laser that scans and trims the edge twice along the same path, with a single pulse energy of 5-10μJ and a scanning speed of 300-600mm / s; 104) Applying dual-frequency ultrasonic vibration to the cut wafer to eliminate stress; cracking the weakened layer of the wafer by treating it with an etching solution containing hydrofluoric acid and a corrosion inhibitor to separate the wafer into independent wafer units; In step 104, the wafer is placed in an etching solution containing 5 wt% hydrofluoric acid and 0.5 wt% benzotriazole at a temperature of 38-42° C. for 3-5 minutes to achieve chipping. In step 104, a low-frequency ultrasonic wave of 15-25 kHz is used for coarse vibration, and a high-frequency ultrasonic wave of 0.8-1.2 MHz is used for fine vibration.

2. The method for laser cutting of quartz wafer according to claim 1, characterized in that: Step 102 is performed by using a cross-line cutting method: cutting is performed in the order of crossing N lines each time, and then returning to the next line of the original line for cutting, and the cycle is repeated until the cutting is completed; wherein N≥1.

3. The method for laser cutting of quartz wafer according to claim 1, wherein: In step 102, an ultrafast infrared laser forms a weakened layer on the quartz wafer, comprising a triple structure of a modified layer, a microcrack network, and a residual stress zone. In step 104, the corrosive liquid preferentially etches the weakened layer, and the synergistic stress is used to achieve submicron-level precision separation of the wafer.

4. The method for laser cutting of quartz wafer according to claim 1, characterized in that: An air-floating XY motion platform is used to synchronously drive four independent workstations, each of which includes the cutting platform, the piezoelectric ceramic fine-tuning mechanism, a laser ranging sensor and a dual-wavelength laser cutting head. The four workstations are respectively connected to four split light beams through a laser spectrometer system. The laser ranging sensors respectively monitor the height of the wafers at their respective workstations. The upper computer controls each piezoelectric ceramic fine-tuning mechanism to achieve dynamic leveling. The four split light beams are respectively input into the corresponding dual-wavelength laser cutting head, and the wafers are dual-wavelength cut in the sequence of infrared cutting first and ultraviolet trimming. After the wafer cutting is completed, the wafers at the four workstations are collectively transferred to an ultrasonic fixture and a gauze etching tank for post-processing, thereby realizing four-station parallel processing.

5. The method for laser cutting of quartz wafer according to claim 1, wherein: In step 104, coarse vibration is performed using low-frequency ultrasonic waves of 15-25 kHz, with a power density of 15-25 W / cm² and an amplitude of 80-120 μm, and fine vibration is performed using high-frequency ultrasonic waves of 0.8-1.2 MHz, with a power density of 0.5-2 W / cm² and an amplitude of 0.1-0.5 μm. The coarse vibration and fine vibration are superimposed in time to achieve gradient elimination of stress within the quartz wafer. The low-frequency ultrasonic coarse vibration converts the residual tensile stress of the wafer into compressive stress, while the high-frequency ultrasonic fine vibration promotes lattice dislocation slip and grain refinement. The microcrack interface is remelted and closed by a local high temperature of 580-620°C. Power ramp start-stop control is used. Under the synergistic effect of 30-60 seconds of coarse vibration and 5-10 seconds of fine vibration, stress is eliminated and the frequency stability of the wafer is improved.

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