Large-size gallium nitride crystal slicing method

Abstract

The invention discloses a slicing method of a large-size gallium nitride crystal, and relates to the technical field of micro-jet laser processing, and the method comprises the following steps: fixing a gallium nitride crystal to be cut on a rotating tool, installing a first nozzle to calibrate the verticality of micro-jet laser, and adjusting the angle between the micro-jet laser and the rotating tool; setting a first cutting parameter, and performing seam-expanding cutting on the gallium nitride crystal to be cut by adopting a first nozzle to form a seam-expanding cutting groove; a second nozzle is replaced, the perpendicularity of the micro-jet laser is calibrated, a second cutting parameter is set, the second nozzle is adopted to cut the gallium nitride crystal to be cut along the seam expanding cutting groove, and crystal slicing is completed; the diameter of the first nozzle is smaller than that of the second nozzle, and the diameter of the second nozzle does not exceed the width of the seam expanding cutting groove. According to the method, the surface quality of the sliced gallium nitride crystal is guaranteed, meanwhile, the problem of edge breakage in the slicing process is avoided, and high-quality cutting of the inch-level gallium nitride crystal is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-jet laser processing, and particularly relates to a slicing method for large-size gallium nitride crystals. Background Art

[0002] Gallium nitride crystal is one of the most attractive third-generation semiconductor materials at present, and it has good physical and chemical properties and thermal stability. At present, single-crystal gallium nitride materials are mainly epitaxially grown on heterogeneous substrates such as Si (silicon), sapphire, and SiC (silicon carbide), which makes the development of gallium nitride single-crystal substrates and homoepitaxial devices lag behind the applications based on heteroepitaxial devices. Therefore, how to cut single-crystal gallium nitride wafers from high-quality gallium nitride crystal blocks has become a key issue.

[0003] The traditional slicing processing method is to use a diamond wire to saw the crystal into crystal slices of the same thickness, and then perform surface grinding and chemical mechanical polishing for processing. Gallium nitride, as a representative of hard and brittle materials, has a wide diamond wire during sawing, which will cause large losses during the cutting process, and the surface quality after sawing is poor, resulting in large losses and long time consumption in subsequent grinding and polishing. The cumulative loss of sawing, grinding and polishing for cutting one wafer is about 0.4 - 0.6 mm, almost losing a complete substrate wafer. The production cost of gallium nitride is high, and excessive losses will further increase the production cost.

[0004] Micro-jet laser processing technology is a precision processing technology that uses a water jet to guide a laser beam to cut a workpiece to be processed. Compared with the traditional laser processing technology, it has the characteristics of a flat processing surface, no need for focusing, large cutting depth, and small processing loss. It is especially suitable for the cutting processing of high-precision devices of the third-generation semiconductor materials, and has great advantages for gallium nitride slicing processing. However, there are still some problems in the current micro-jet laser technology during the slicing process of gallium nitride. For example, there are many surface defects after cutting, such as a large number of pits and microcracks, and the surface quality is poor. The main reason for the large number of surface defects on the crystal is the nozzle water pressure. The greater the water pressure, the worse the surface quality, and the smaller the water pressure, the better the surface quality. However, for micro-jet lasers, the smaller the water pressure, the shorter the coupled water column, and the smaller the processing depth, resulting in limited processing dimensions of gallium nitride crystals. At the same water pressure, the larger the nozzle size, the longer the coupled water column, and large-size crystals can be sliced. However, when a large-size nozzle cuts a large-size gallium nitride crystal, it is easy to cause chipping at the crystal edge, resulting in the failure of the cut wafer, especially at the beginning of the cutting stage, the chipping phenomenon is particularly serious. Therefore, the current micro-jet laser technology can only process small-size gallium nitride crystals, that is, crystals within 1 inch, and it cannot effectively complete the slicing processing of large-size crystals, such as 2 inches and above. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a slicing method for large-size gallium nitride crystals. The technical problems to be solved by the present invention are realized through the following technical solutions: The present invention provides a slicing method for large-size gallium nitride crystals, comprising: Step 1: Fix the gallium nitride crystal to be cut on a rotating tooling, install the first nozzle to calibrate the perpendicularity of the micro-jet laser and adjust the angle between the micro-jet laser and the rotating tooling; Step 2: Set the first cutting parameters, and use the first nozzle to perform a slot-expanding cut on the gallium nitride crystal to be cut to form a slot-expanding cutting groove; Step 3: Replace the second nozzle and calibrate the perpendicularity of the micro-jet laser, set the second cutting parameters, and use the second nozzle to cut the gallium nitride crystal to be cut along the slot-expanding cutting groove to complete crystal slicing; Wherein, the diameter of the first nozzle is smaller than the diameter of the second nozzle, the diameter of the second nozzle does not exceed the width of the slot-expanding cutting groove, the diameter of the second nozzle is not less than 100 μm, and the nozzle water pressure in the first cutting parameters and the second cutting parameters is not greater than 150 bar.

[0006] In an embodiment of the present invention, before the step 1, it further includes: performing a rounding operation on the grown gallium nitride crystal to obtain the gallium nitride crystal to be cut.

[0007] In an embodiment of the present invention, the gallium nitride crystal to be cut includes a seed crystal and a first grown crystal and a second grown crystal located on both sides of the seed crystal surface.

[0008] In an embodiment of the present invention, the step 1 includes: Step 1.1: Install the first nozzle to adjust the perpendicularity of the micro-jet laser to make the micro-jet laser perpendicular to the XOY plane; Step 1.2: Fix one side of the gallium nitride crystal to be cut on the rotating tooling by bonding, so that the seed crystal surface of the gallium nitride crystal to be cut is perpendicular to the center line of the rotating tooling; Step 1.3: Adjust the motor shaft of the rotating tooling to make the motor shaft horizontal in the horizontal plane and the pitching plane; Step 1.4: Adjust the micro-jet laser to be perpendicular to the center line of the motor shaft.

[0009] In an embodiment of the present invention, the first cutting parameters and the second cutting parameters include: the rated power, wavelength and pulse frequency of the laser, the nozzle diameter, the nozzle water pressure, the flow rate and coupling power of the protective gas.

[0010] In one embodiment of the present invention, the protective gas is helium with a purity greater than 99.999%.

[0011] In one embodiment of the present invention, the diameter of the first nozzle does not exceed 60 μm.

[0012] In one embodiment of the present invention, the jet length generated by the first nozzle is not less than 15 mm.

[0013] In one embodiment of the present invention, the jet length generated by the second nozzle is not less than 35 mm.

[0014] In one embodiment of the present invention, the depth of the slit cutting groove is 5 - 10 mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The slicing method of large-size gallium nitride crystals of the present invention uses a first nozzle and a second nozzle to perform staged cutting on gallium nitride crystals. The diameter of the first nozzle is smaller than that of the second nozzle. First, a low-water-pressure small nozzle is used to perform slit cutting on the gallium nitride crystal to be cut, and then a large nozzle with low water pressure is used for slicing processing. After slicing, there are no defects such as pit points and cracks on the crystal surface, ensuring the surface quality of the gallium nitride crystal after slicing. At the same time, the problem of chipping during slicing is avoided, improving the finished product quality of the gallium nitride wafer, reducing the polishing cost of the wafer, and achieving high-quality cutting of inch-level gallium nitride crystals.

[0016] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present invention more obvious and understandable, the following preferred embodiments are specifically given, and in conjunction with the drawings, the details are described as follows. Description of the Drawings

[0017] Figure 1 is a flowchart of a slicing method for large-size gallium nitride crystals provided by an embodiment of the present invention; Figure 2 is a process schematic diagram of step S2 provided by an embodiment of the present invention; Figure 3 is a process schematic diagram of step S3 provided by an embodiment of the present invention; Figure 4 is a process schematic diagram of step S5 provided by an embodiment of the present invention; Figure 5 is a process schematic diagram of step S6 provided by an embodiment of the present invention; Figure 6 is a process schematic diagram of step S7 provided by an embodiment of the present invention; Figure 7It is a process schematic diagram of step S8 provided by an embodiment of the present invention; Figure 8 It is a process schematic diagram of step S10 provided by an embodiment of the present invention; Figure 9 It is a process schematic diagram of step S11 provided by an embodiment of the present invention; Figure 10 It is a process schematic diagram of step S12 provided by an embodiment of the present invention; Figure 11 It is a process schematic diagram of step S13 provided by an embodiment of the present invention.

[0018] Icons: 1 - Gallium nitride crystal to be cut; 11 - Seed crystal; 12 - First grown crystal; 13 - Second grown crystal; 2 - Microjet laser; 3 - Rotating tooling; 4 - First slitting cutting groove; 5 - Second slitting cutting groove; 6 - Third slitting cutting groove; 7 - Fourth slitting cutting groove. Detailed implementation manners

[0019] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in combination with the accompanying drawings and specific implementation manners, details a slicing method for a large-size gallium nitride crystal according to the present invention.

[0020] Regarding the foregoing and other technical contents, features and effects of the present invention, they can be clearly presented in the following detailed description of the specific implementation manners in conjunction with the accompanying drawings. Through the description of the specific implementation manners, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the predetermined purpose can be obtained. However, the accompanying drawings are only for reference and illustration purposes, and are not used to limit the technical solutions of the present invention.

[0021] An embodiment of the present invention provides a slicing method for a large-size gallium nitride crystal. Please refer to Figure 1 , Figure 1 which is a process schematic diagram provided by an embodiment of the present invention. As Figure 1 shown, the slicing method for a large-size gallium nitride crystal in this embodiment includes the following steps: Step 1: Fix the gallium nitride crystal to be cut on the rotating tooling, install the first nozzle to calibrate the perpendicularity of the microjet laser and adjust the angle between the microjet laser and the rotating tooling; Step 2: Set the first cutting parameters, and use the first nozzle to perform slitting cutting on the gallium nitride crystal to be cut to form a slitting cutting groove; Step 3: Replace the second nozzle and calibrate the perpendicularity of the micro-jet laser. Set the second cutting parameters, and use the second nozzle to cut the gallium nitride crystal to be cut along the slit cutting groove to complete crystal slicing. Among them, the diameter of the first nozzle is smaller than that of the second nozzle, the diameter of the second nozzle does not exceed the width of the slit cutting groove, the diameter of the second nozzle is not less than 100 μm, and the nozzle water pressure in the first cutting parameters and the second cutting parameters is not greater than 150 bar.

[0022] In this embodiment, the gallium nitride crystal to be cut includes a seed crystal and a first growth crystal and a second growth crystal located on both sides of the seed crystal surface.

[0023] Specifically, Step 1 includes: Step 1.1: Install the first nozzle and adjust the perpendicularity of the micro-jet laser so that the micro-jet laser is perpendicular to the XOY plane. Step 1.2: Fix one side of the gallium nitride crystal to be cut on the rotating fixture by bonding, so that the seed crystal surface of the gallium nitride crystal to be cut is perpendicular to the center line of the rotating fixture.

[0024] Step 1.3: Adjust the motor shaft of the rotating fixture so that the motor shaft is horizontal in the horizontal plane and the pitching plane.

[0025] In this embodiment, by adjusting the motor shaft of the rotating fixture, the angles between the motor shaft and the horizontal XOZ plane and the pitching YOZ plane are both 0°.

[0026] Step 1.4: Adjust the micro-jet laser to be perpendicular to the center line of the motor shaft.

[0027] In this embodiment, by adjusting the angle between the micro-jet laser and the motor shaft, the micro-jet laser is perpendicular to the center line of the motor shaft.

[0028] In this embodiment, the first cutting parameters include: the rated power, wavelength and pulse frequency of the laser, the nozzle diameter, the nozzle water pressure, the flow rate and coupling power of the protective gas.

[0029] Optionally, the laser uses a green nanosecond pulsed laser, the rated power of the laser is 120 W, the wavelength is 532 nm, and the pulse frequency is 8 KHZ. The diameter of the first nozzle does not exceed 60 μm, the nozzle water pressure does not exceed 150 bar. Exemplarily, the diameter of the first nozzle is 50 μm and the nozzle water pressure is 100 bar. The resistivity of pure water is greater than 15 ΩM / cm 3 , the protective gas can be helium with a purity greater than 99.999%, the flow rate of helium is not less than 0.06 L / min. Exemplarily, the flow rate of helium is 0.1 L / min. The coupling power is 25 - 30 W.

[0030] It should be noted that by setting the above cutting parameters, the jet length generated by the first nozzle is ensured to be not less than 15 mm.

[0031] In this embodiment, when using the first nozzle to perform slotting cutting on the gallium nitride crystal to be cut, four slotting cutting grooves can be formed at the interface between the seed crystal and the first grown crystal, the interface between the seed crystal and the second grown crystal, the growth surface of the first grown crystal, and the growth surface of the second grown crystal. Optionally, the depth of the slotting cutting groove is 5 - 10 mm.

[0032] In this embodiment, the second cutting parameters include: the rated power, wavelength, and pulse frequency of the laser, the nozzle diameter, the nozzle water pressure, the flow rate and coupling power of the protective gas.

[0033] Optionally, the laser uses a green nanosecond pulse laser, the rated power of the laser is 120 W, the wavelength is 532 nm, and the pulse frequency is 8 KHZ. The diameter of the second nozzle is not less than 100 μm, the nozzle water pressure does not exceed 150 bar. Exemplarily, the diameter of the second nozzle is 100 μm and the nozzle water pressure is 150 bar. The resistivity of pure water is greater than 15 ΩM / cm 3 , the protective gas can be helium with a purity greater than 99.999%, the flow rate of helium is not less than 0.06 L / min. Exemplarily, the flow rate of helium is 0.1 L / min. The coupling power is 50 - 55 W.

[0034] It should be noted that by setting the above cutting parameters, the jet length generated by the second nozzle is ensured to be not less than 35 mm.

[0035] It should be noted that after replacing the first nozzle with the second nozzle, it is necessary to readjust the angle between the micro-jet laser and the motor shaft so that the micro-jet laser is perpendicular to the center line of the motor shaft.

[0036] It can be understood that the outer surface of the gallium nitride crystal obtained by epitaxial growth is irregular. Therefore, before step 1, it also includes: performing a rounding operation on the grown gallium nitride crystal to obtain the gallium nitride crystal to be cut. Specifically, the grown gallium nitride crystal is placed horizontally, and the peripheral irregular parts of the gallium nitride crystal are removed by using a micro-jet laser to form a regular circular plate-shaped gallium nitride crystal to be cut.

[0037] In this embodiment, first, a low-water-pressure small nozzle is used to perform slit cutting on the gallium nitride crystal to be cut, and then a large nozzle with low water pressure is used for slicing. Through the staged composite cutting process, that is, "low-water-pressure small nozzle slit cutting + large nozzle low-water-pressure slicing", the wafer processing quality is significantly improved. The low-water-pressure slicing process is adopted throughout the process to reduce the jet impact force, reduce the lateral wall shear force in the process of crystal material removal, achieve "soft contact" slicing, avoid the formation of surface pits and microcracks, and the surface roughness can be controlled at the nanometer level. In the stage of slit cutting with the small nozzle, due to the short jet length, a pre-cut micro-slit is formed inside the crystal to form a cutting groove as a stress buffer zone, dispersing the thermal stress at the cutting edge to avoid excessive coupling power during subsequent main cutting, which may cause the wafer edge to crack. In the stage of slicing with the large nozzle, the micro-jet laser enters the cutting groove along the prefabricated cutting slit, and the jet energy is directly transmitted to the bottom of the cutting groove, preventing the wafer edge from cracking. At the same time, the jet length of the large nozzle increases, and the cutting depth is further improved, which can effectively complete the cutting of large-size crystals.

[0038] The slicing method of the large-size gallium nitride crystal according to the embodiment of the present invention solves the core contradiction of "insufficient cutting depth with a small nozzle at low water pressure" and "easy edge cracking during cutting with a large nozzle due to large coupling power" in the slicing of large-size gallium nitride crystals by the "pre-release stress + gentle removal" synergistic process. After slicing, there are no defects such as pits and cracks on the crystal surface, which ensures the surface quality of the gallium nitride crystal after slicing. At the same time, the problem of edge cracking during slicing is avoided, the finished product quality of the gallium nitride wafer is improved, the polishing cost of the wafer is reduced, and high-quality cutting of inch-level gallium nitride crystals is achieved.

[0039] Further, please refer to Figures 2 - 11 , and the slicing method of the large-size gallium nitride crystal of the present invention is described by specific examples.

[0040] The grown gallium nitride crystal is a hexagonal crystal with an inscribed circle of Ф56×1.8 mm, where the seed crystal thickness is 0.4 mm, and the planned slicing thickness t = 0.5 mm. After peeling off the seed crystal, two two-inch wafers are formed to illustrate the slicing method of the large-size gallium nitride crystal of the present invention. The specific slicing process is as follows: S1: Place the grown gallium nitride crystal horizontally, and use the micro-jet laser to remove the irregular parts around the gallium nitride crystal to form a 2-inch gallium nitride crystal 1 to be cut with a diameter of 50.8 mm. The gallium nitride crystal 1 to be cut includes a seed crystal 11 and first growth crystals 12 and second growth crystals 13 on both sides of the seed crystal surface. After rounding, the interface between the seed crystal 11 and the growth crystals (first growth crystal 12 and second growth crystal 13) can be clearly observed on the circumferential surface.

[0041] S2: Fix one side of the gallium nitride crystal 1 to be cut on the rotating tooling 3 by bonding, making the seed crystal surface of the gallium nitride crystal 1 to be cut perpendicular to the center line of the rotating tooling 3, as Figure 2 shown.

[0042] S3: Adjust the motor shaft of the rotating tooling 3 so that the angles between the motor shaft and both the horizontal XOZ plane and the pitching YOZ plane are 0°, and adjust the micro-jet laser 2 to be perpendicular to the center line of the motor shaft, as Figure 3 shown.

[0043] S4: Set the first cutting parameters. Among them, the laser is a green nanosecond pulsed laser, the rated power of the laser is 120W, the wavelength is 532nm, and the pulse frequency is 8KHZ. The diameter of the first nozzle is 50μm, the nozzle water pressure is 100bar. The resistivity of pure water is greater than 15ΩM / cm 3 , and the helium gas flow rate is 0.1L / min. The coupling power is 25W.

[0044] S5: Align the center of the micro-jet laser 2 with the interface between the seed crystal 11 and the first grown crystal 12 for rotary cutting. Stop cutting when the cutting depth reaches 5mm; then offset the micro-jet laser 2 by 0.05mm in the direction of the seed crystal 11 and continue rotary cutting. Stop cutting when the cutting depth reaches 5mm; at this time, a first widened slot cutting groove 4 with a width of 0.1mm and a depth of 5mm is formed at the interface between the seed crystal 11 and the first grown crystal 12, as Figure 4 shown.

[0045] S6: Move the micro-jet laser 2 0.6mm in the direction of the growth surface of the first grown crystal 12 and continue rotary cutting. Stop cutting when the cutting depth reaches 5mm; then offset the micro-jet laser 2 by 0.05mm in the direction of the growth surface of the first grown crystal 12. Stop cutting when the rotary cutting depth reaches 5mm; at this time, a second widened slot cutting groove 5 with a width of 0.1mm and a depth of 5mm is formed at the growth surface of the first grown crystal 12, as Figure 5 shown.

[0046] S7: Align the center of the micro-jet laser 2 with the interface between the seed crystal 11 and the second grown crystal 13 for rotary cutting. Stop cutting when the cutting depth reaches 5mm; then offset the micro-jet laser 2 by 0.05mm in the direction of the seed crystal 11 and continue rotary cutting. Stop cutting when the cutting depth reaches 5mm; at this time, a third widened slot cutting groove 6 with a width of 0.1mm and a depth of 5mm is formed at the interface between the seed crystal 11 and the second grown crystal 13, as Figure 6 shown.

[0047] S8: Move the micro-jet laser 2 0.6 mm towards the growth surface of the second growth crystal 13, and continue rotational cutting. Stop cutting when the cutting depth reaches 5 mm. Then offset the micro-jet laser 2 0.05 mm towards the growth surface of the second growth crystal 13, and stop cutting when the rotational cutting depth reaches 5 mm. At this time, a fourth slotted cutting groove 7 with a width of 0.1 mm and a depth of 5 mm is formed at the growth surface of the second growth crystal 13, as Figure 7 shown.

[0048] S9: Replace the first nozzle with the second nozzle, and readjust the angle between the micro-jet laser 2 and the motor shaft so that the micro-jet laser 2 is perpendicular to the center line of the motor shaft. Set the second cutting parameters. Among them, the laser uses a green nanosecond pulsed laser, the rated power of the laser is 120 W, the wavelength is 532 nm, and the pulse frequency is 8 KHZ. The diameter of the second nozzle is 100 μm, the nozzle water pressure is 150 bar. The resistivity of pure water is greater than 15 ΩM / cm 3 , and the helium gas flow rate is 0.1 L / min. The coupling power is 50 W.

[0049] S10: Adjust the micro-jet laser 2 into the second slotted cutting groove 5, and start rotational cutting until the growth surface of the first growth crystal 12 is completely separated from the first growth crystal 12, as Figure 8 shown.

[0050] S11: Adjust the micro-jet laser 2 into the first slotted cutting groove 4, and start rotational cutting until the first growth crystal 12 is completely separated from the seed crystal 11, obtaining the first growth crystal 12 with a thickness of 0.5 mm, as Figure 9 shown.

[0051] S12: Adjust the micro-jet laser 2 into the third slotted cutting groove 6, and perform rotational cutting until the second growth crystal 13 is completely separated from the seed crystal 11, thereby completely removing the seed crystal 11, as Figure 10 shown.

[0052] S13: Adjust the micro-jet laser 2 into the fourth slotted cutting groove 7, and perform rotational cutting until the growth surface of the second growth crystal 13 is completely separated from the second growth crystal 13, obtaining the second growth crystal 13 with a thickness of 0.5 mm, as Figure 11 shown.

[0053] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant are intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the article or device comprising said element. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0054] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not have to be directed to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0055] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for slicing a large-size gallium nitride crystal, characterized in that: include: Step 1: Fix the gallium nitride crystal to be cut on the rotating fixture, install the first nozzle to calibrate the verticality of the microjet laser and adjust the angle between the microjet laser and the rotating fixture; Step 2: setting the first cutting parameters, and using the first nozzle to perform seam expansion cutting on the gallium nitride crystal to be cut to form a seam expansion cutting groove; Step 3: Replace the second nozzle and calibrate the verticality of the microjet laser, set the second cutting parameters, and use the second nozzle to cut the gallium nitride crystal to be cut along the expanded cutting groove to complete crystal slicing; Among them, the diameter of the first nozzle is smaller than the diameter of the second nozzle, the diameter of the second nozzle does not exceed the width of the expanded cutting groove, the diameter of the second nozzle is not less than 100μm, and the nozzle water pressure in the first cutting parameter and the second cutting parameter is not greater than 150bar.

2. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: Before step 1, the method further includes: performing a rounding operation on the grown gallium nitride crystal to obtain the gallium nitride crystal to be cut.

3. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The gallium nitride crystal to be cut includes a seed crystal and a first growing crystal and a second growing crystal located on two sides of the seed crystal.

4. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The step 1 comprises: Step 1.1: Install the first nozzle and adjust the verticality of the microjet laser so that the microjet laser is perpendicular to the XOY plane; Step 1.2: fixing one side of the gallium nitride crystal to be cut on the rotating fixture by bonding, so that the seed crystal surface of the gallium nitride crystal to be cut is perpendicular to the center line of the rotating fixture; Step 1.3: Adjust the motor shaft of the rotating fixture so that the motor shaft remains level in the horizontal plane and the pitch plane; Step 1.4: Adjust the microjet laser to be perpendicular to the center line of the motor shaft.

5. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The first cutting parameter and the second cutting parameter include: rated power, wavelength and pulse frequency of the laser, nozzle diameter, nozzle water pressure, flow rate and coupling power of the protective gas.

6. The method for slicing a large-size gallium nitride crystal according to claim 5, characterized in that: The protective gas is helium with a purity greater than 99.999%.

7. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The diameter of the first nozzle does not exceed 60 μm.

8. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The jet length generated by the first nozzle is not less than 15 mm.

9. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The jet length generated by the second nozzle is not less than 35 mm.

10. The method for slicing a large-size gallium nitride crystal according to claim 1, characterized in that: The depth of the expansion cutting groove is 5-10 mm.

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