Grinding and polishing method for gallium nitride single crystal substrate

Abstract

The invention provides a grinding and polishing method for a gallium nitride single crystal substrate. The grinding and polishing method comprises the steps that the Ga face of the gallium nitride single crystal substrate is fixed away from a grinding platform; measuring a Ga surface warping value and selecting a first grinding head to grind the Ga surface for the first time; the N surface of the gallium nitride single crystal substrate is fixed away from the grinding platform; measuring the warping value of the N surface, and selecting a second grinding head to grind the N surface for the first time; providing a third grinding head to perform secondary grinding on the N surface of the gallium nitride single crystal substrate; the Ga surface of the gallium nitride single crystal substrate is fixed away from the grinding platform; providing a fourth grinding head to perform secondary grinding on the Ga surface of the gallium nitride single crystal substrate; and performing chemical mechanical polishing on the gallium nitride single crystal substrate. When the Ga surface and the N surface of the gallium nitride single crystal substrate are ground for the first time, according to the warping condition of the Ga surface and the N surface, the grinding head with the difference between the central area and the edge position is selected for different grinding, the grinding and thinning efficiency of the protruding part can be improved, and meanwhile damage to the non-protruding part in the grinding process is reduced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxial processing technology, and in particular relates to a grinding and polishing method for gallium nitride single crystal substrates. Background Technology

[0002] Gallium nitride (GaN) single crystals are grown heteroepitaxially on sapphire substrates. Due to thermal and lattice mismatches between the sapphire substrate and GaN, warping occurs after epitaxial growth. After removing the sapphire substrate, the GaN single crystal tends to be flat, but some warping remains, primarily manifested as a slight convexity at the center of the Ga facet. The larger the GaN single crystal, the more pronounced the warping problem becomes. Under current grinding and polishing techniques, GaN single crystal warping negatively impacts grinding and polishing efficiency and product quality. Summary of the Invention

[0003] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a grinding and polishing method for gallium nitride single crystal substrates, which solves the problems of grinding and polishing efficiency and product quality caused by gallium nitride warping in the prior art.

[0004] To achieve the above and other related objectives, the present invention provides a grinding and polishing method for gallium nitride single crystal substrates, characterized in that the method includes the following steps: S01. A gallium nitride single crystal substrate is provided, the gallium nitride single crystal substrate having opposing Ga and N surfaces, the gallium nitride single crystal substrate is fixed to a polishing platform, and the Ga surface of the gallium nitride single crystal substrate faces away from the polishing platform; S02. Measure the Ga surface warpage value of the gallium nitride single crystal substrate, select a first polishing head based on the Ga surface warpage value, and use the first polishing head to perform a first polishing on the Ga surface; the first polishing head includes a first central region and a first edge region, and the particle size of the first central region is less than or equal to the particle size of the first edge region; S03. Re-fix the gallium nitride single crystal substrate to the polishing platform, with the N-side of the gallium nitride single crystal substrate facing away from the polishing platform; S04. Measure the N-plane warpage value of the gallium nitride single crystal substrate, select a second grinding head based on the N-plane warpage value, and use the second grinding head to perform the first grinding on the N-plane; the second grinding head includes a second central region and a second edge region, and the particle size of the second central region is greater than or equal to the particle size of the second edge region; S05. Provide a third grinding head to perform a second grinding on the N-side of the gallium nitride single crystal substrate; S06. Re-fix the gallium nitride single crystal substrate to the polishing platform, with the Ga surface of the gallium nitride single crystal substrate facing away from the polishing platform; S07. Provide a fourth grinding head to perform a second grinding on the Ga surface of the gallium nitride single crystal substrate; S08. Perform chemical mechanical polishing on the gallium nitride single crystal substrate.

[0005] Preferably, in step S02, the first grinding head is selected based on the Ga surface warpage value, specifically as follows: when the Ga surface warpage value is less than 50 μm, the particle size of the first central region is the same as that of the first edge region, and a particle size of 320 mesh or 400 mesh is selected; when the Ga surface warpage value is between 50 μm and 100 μm, the particle size of the first central region is 320 mesh, and the particle size of the first edge region is 400 mesh; when the Ga surface warpage value is greater than 100 μm, the particle size of the first central region is 320 mesh, and the particle size of the first edge region is 600 mesh or 800 mesh.

[0006] In step S03, the second grinding head is selected based on the N-surface warp value. Specifically, when the N-surface warp value is less than 50 μm, the particle size of the second central region is the same as that of the second edge region, and the particle size is 320 mesh or 400 mesh. When the N-surface warp value is between 50 μm and 100 μm, the particle size of the second central region is 400 mesh, and the particle size of the second edge region is 320 mesh. When the N-surface warp value is greater than 100 μm, the particle size of the second central region is 600 mesh or 800 mesh, and the particle size of the second edge region is 320 mesh.

[0007] Preferably, the Ga surface warpage value and the N surface warpage value of the gallium nitride single crystal substrate are measured using the moiré fringe method, X-ray diffraction method, optical interferometry method, or laser scanning method.

[0008] Preferably, in step S02, when the first grinding head is used to grind the Ga surface for the first time, the rotation speed of the first grinding head is 1500~2000 rpm, the rotation speed of the grinding platform is 150~200 rpm, the rotation direction of the first grinding head and the grinding platform are opposite, and the pressure is set at 220~350 g / cm².

[0009] Preferably, in step S04, when the second grinding head is used to perform the first grinding on the N-surface, the rotation speed of the second grinding head is 1500~2000 rpm, the rotation speed of the grinding platform is 150~200 rpm, the rotation direction of the second grinding head and the grinding platform are opposite, and the pressure is set at 200~300 g / cm².

[0010] Preferably, in step S05, the rotational speed of the third grinding head is 1800~2200 rpm, the rotational speed of the grinding platform is 200~250 rpm, and the pressure is set at 150~200 g / cm².

[0011] Preferably, in step S07, the rotational speed of the fourth grinding head is 2000~2500 rpm, the rotational speed of the grinding platform is 200~250 rpm, the rotational direction of the second grinding head is opposite to that of the grinding platform, and the pressure is set at 200~250 g / cm².

[0012] Preferably, in step S02, the thickness of the Ga surface thinned by the first grinding is 100~200um; Preferably, in step S04, the thickness of the N-side thinned by the first grinding is 100~150um; Preferably, in step S05, the thickness of the N-side thinned by the second grinding is 50~100um; Preferably, in step S07, the thickness of the Ga surface thinned by the second grinding is 50~150um.

[0013] Preferably, the gallium nitride single crystal substrate is fixed to the polishing platform by paraffin wax.

[0014] As described above, the grinding and polishing method for gallium nitride single crystal substrates of the present invention has the following beneficial effects: The present invention is applicable to grinding and polishing large-sized gallium nitride single crystal substrates with a certain warp. When grinding the Ga and N surfaces of the gallium nitride single crystal substrate for the first time, grinding heads with different positions in the center and edge are selected according to the warp of the gallium nitride single crystal substrate. This can improve the grinding and thinning efficiency of the protruding parts and reduce the damage to the non-protruding parts during the grinding process. Attached Figure Description

[0015] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of this application and to illustrate the implementation of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application.

[0016] Figure 1 This is a schematic diagram of the grinding and polishing process of the gallium nitride single crystal substrate of the present invention.

[0017] Figure 2 This is a schematic diagram of the first grinding of the Ga surface of the gallium nitride single crystal substrate in this invention.

[0018] Figure 3 This is a schematic diagram of the first grinding of the N-side of the gallium nitride single crystal substrate in this invention.

[0019] Figure 4 This is a schematic diagram of the second grinding of the N-side of the gallium nitride single crystal substrate in this invention.

[0020] Figure 5 This is a schematic diagram of the second grinding of the Ga surface of the gallium nitride single crystal substrate in this invention. Attached image description: 1-GaN single crystal substrate, 11-Ga facet, 12-N facet, 2-Grinding platform, 3-Paraffin wax, 4-First grinding head, 41-First central region, 42-First edge region; 5-Second grinding head, 51-Second central region, 52-Second edge region, 6-Third grinding head, 7-Fourth grinding head. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components.

[0024] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0025] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0026] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0027] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0028] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] like Figures 1-5 As shown, this embodiment provides a grinding and polishing method for gallium nitride single crystal substrates, the method comprising the following steps: like Figure 1 and Figure 2 As shown, proceed with steps S01 and S02.

[0030] Step S01: A gallium nitride single crystal substrate 1 is provided, the gallium nitride single crystal substrate 1 having opposing Ga surface 11 and N surface 12, the gallium nitride single crystal substrate 1 is fixed to a polishing platform 2, and the Ga surface 11 of the gallium nitride single crystal substrate 1 faces away from the polishing platform 2.

[0031] In this embodiment, paraffin wax 3 is used to fix the gallium nitride single crystal substrate 1 onto the polishing platform 2. In other embodiments, the gallium nitride single crystal substrate 1 can be directly fixed onto the polishing platform 2 using vacuum adsorption. Alternatively, the gallium nitride single crystal substrate 1 can be fixed onto a support plate using paraffin wax 3, and the support plate can then be fixed onto the polishing platform 2 via vacuum adsorption, thereby indirectly fixing the gallium nitride single crystal substrate 1 onto the polishing platform 2. The normals of the gallium nitride single crystal substrate 1 and the polishing platform 2 are centered.

[0032] Step S02: Provide a first grinding head 4 to perform the first grinding on the Ga surface 11.

[0033] Before the first grinding of the Ga surface 11, the Ga surface warpage value of the gallium nitride single crystal substrate 1 is measured. Based on the Ga surface warpage value, the first grinding head 4 is selected. The first grinding head 4 is used to grind the surface of the gallium nitride single crystal substrate 1, which includes a first central region 41 and a first edge region 42. The particle size of the first central region 41 is less than or equal to the particle size of the first edge region 42.

[0034] When the Ga surface 11 is polished for the first time, the first polishing head 4 is set parallel to the polishing platform 2, and the first polishing head 4 rotates coaxially with the gallium nitride single crystal substrate 1 and the polishing platform 2. The rotation direction of the first polishing head 4 is opposite to the rotation direction of the gallium nitride single crystal substrate 1 and the polishing platform 2.

[0035] Among them, the warpage value of the Ga surface of the gallium nitride single crystal substrate 1 can be measured by means of moiré fringe method, X-ray diffraction method, optical interferometry method or laser scanning method.

[0036] The specific logic for selecting the particle size of the first central region 41 and the first edge region 42 of the first grinding head 4 is as follows: When the Ga surface warpage value of the gallium nitride single crystal substrate 1 is less than 50 μm, the particle size of the first central region 41 is the same as that of the first edge region 42, and the particle size is selected as 320 mesh or 400 mesh. When the Ga surface warpage value of the gallium nitride single crystal substrate 1 is between 50um and 100um, the particle size of the first central region 41 is smaller than that of the first edge region 42. The particle size of the first central region 41 is 320 mesh, and the particle size of the first edge region 42 is 400 mesh. When the Ga surface warpage value of the gallium nitride single crystal substrate 1 is greater than 100 μm, the particle size of the first central region 41 is smaller than that of the first edge region 42. The particle size of the first central region 41 is 320 mesh, and the particle size of the first edge region 42 is 600 mesh or 800 mesh.

[0037] Preferably, when the Ga surface 11 is ground for the first time, the rotation speed of the first grinding head 4 is 1500~2000 rpm, the rotation speed of the grinding platform 2 is 150-200 rpm, the rotation direction of the first grinding head 4 is opposite to that of the grinding platform 2, and the pressure of the first grinding is set at 220~350 g / cm².

[0038] Based on the warping of the Ga surface 11 of the gallium nitride single crystal substrate 1, a first grinding head 4 with a particle size difference between the center and the edge is selected. This allows for targeted and efficient grinding of the relatively protruding central part due to warping, while reducing damage to the non-protruding parts at the edge during the first grinding of the Ga surface 11.

[0039] like Figure 3 As shown, proceed with steps S03 and S04.

[0040] Step S03: The gallium nitride single crystal substrate 1 is fixed back to the polishing platform 2, with the N-side 12 of the gallium nitride single crystal substrate 1 facing away from the polishing platform 2.

[0041] Similarly, in this embodiment, paraffin wax 3 is used to fix the gallium nitride single crystal substrate 1 onto the polishing platform 2. In other embodiments, the gallium nitride single crystal substrate 1 can be directly fixed onto the polishing platform 2 using vacuum adsorption, or the gallium nitride single crystal substrate 1 can be fixed onto a receiving plate using paraffin wax 3, and the receiving plate can then be fixed onto the polishing platform 2 via vacuum adsorption, thereby indirectly fixing the gallium nitride single crystal substrate 1 onto the polishing platform 2. In this case, the normals of the gallium nitride single crystal substrate 1 and the polishing platform 2 are centered.

[0042] Step S04: Provide a second grinding head 5 to perform the first grinding on the N-surface 12.

[0043] Before the first grinding of the N-surface 12, the N-surface warpage value of the gallium nitride single crystal substrate 1 is measured. Based on the N-surface warpage value, the second grinding head 5 is selected. The second grinding head 5 is used to grind the surface of the gallium nitride single crystal substrate 1, which includes a second central region 51 and a second edge region 52. The particle size of the second central region 51 is greater than or equal to the particle size of the second edge region 52.

[0044] When the N-side 12 is polished for the first time, the second polishing head 5 is arranged parallel to the polishing platform 2, and the second polishing head 5 rotates coaxially with the gallium nitride single crystal substrate 1 and the polishing platform 2. The rotation direction of the second polishing head 5 is opposite to the rotation direction of the gallium nitride single crystal substrate 1 and the polishing platform 2.

[0045] The warpage value of the N-plane of the gallium nitride single crystal substrate 1 can be measured, optionally by using the moiré fringe method, X-ray diffraction method, optical interferometry method or laser scanning method.

[0046] The specific logic for selecting the particle size of the second central region 51 and the second edge region 52 of the second grinding head 5 is as follows: When the N-plane warpage value of the gallium nitride single crystal substrate 1 is less than 50 μm, the particle size of the second central region 51 is the same as that of the second edge region 52, and the particle size is selected as 320 mesh or 400 mesh. When the N-plane warpage value of the gallium nitride single crystal substrate 1 is between 50um and 100um, the particle size of the second central region 51 is larger than that of the second edge region 52. The particle size of the second central region 51 is 400 mesh, and the particle size of the second edge region 52 is 320 mesh. When the N-plane warpage value of the gallium nitride single crystal substrate 1 is greater than 100 μm, the particle size of the second central region 51 is greater than that of the second edge region 52. The particle size of the second central region 51 is 600 mesh or 800 mesh, and the particle size of the second edge region 52 is 320 mesh.

[0047] Preferably, when the N-side 12 is ground for the first time, the rotation speed of the second grinding head 5 is 1500~2000 rpm, the rotation speed of the grinding platform 2 is 150-200 rpm, the rotation direction of the second grinding head 5 is opposite to that of the grinding platform 2, and the pressure of the first grinding is set at 200~300 g / cm².

[0048] Based on the warping of the N-side 12 of the gallium nitride single crystal substrate 1, a second grinding head 5 with a particle size difference between the center and the edge is selected. This allows for targeted and efficient grinding of the relatively protruding edge portion due to warping, while reducing damage to the non-protruding portion at the center during the first grinding of the N-side 12.

[0049] like Figure 4 As shown, in step S05, a third grinding head 6 is provided to perform a second grinding on the N-surface 12.

[0050] The third grinding head 6 does not need to divide the central and edge regions according to the first grinding head 4 and the second grinding head 5. The grinding surface of the third grinding head 6 has a uniform particle size. It is also not necessary to measure the N-surface warpage value of the gallium nitride single crystal substrate 1 before performing the second grinding on the N-surface 12.

[0051] Preferably, when the N-side 12 is ground for the second time, the particle size of the third grinding head 6 is 1500 mesh, the rotation speed of the third grinding head 6 is 1800~2200 rpm, the rotation speed of the grinding platform 2 is 200-250 rpm, the rotation direction of the second grinding head 5 is opposite to that of the grinding platform 2, and the pressure of the N-side 12 during the second grinding is set to 150~200 g / cm².

[0052] like Figure 5 As shown, proceed with steps S06 and S07.

[0053] Step S06: The gallium nitride single crystal substrate 1 is fixed to the polishing platform 2 again, with the Ga surface 11 of the gallium nitride single crystal substrate 1 facing away from the polishing platform 2.

[0054] Similarly, in this embodiment, paraffin wax 3 is used to fix the gallium nitride single crystal substrate 1 onto the polishing platform 2. In other embodiments, the gallium nitride single crystal substrate 1 can be directly fixed onto the polishing platform 2 using vacuum adsorption, or the gallium nitride single crystal substrate 1 can be fixed onto a receiving plate using paraffin wax 3, and the receiving plate can then be fixed onto the polishing platform 2 via vacuum adsorption, thereby indirectly fixing the gallium nitride single crystal substrate 1 onto the polishing platform 2. In this case, the normals of the gallium nitride single crystal substrate 1 and the polishing platform 2 are centered.

[0055] Step S07: Provide a fourth grinding head 7 to perform a second grinding on the Ga surface 11.

[0056] The fourth grinding head 7 does not need to divide the central and edge regions according to the first grinding head 4 and the second grinding head 5. The grinding surface of the fourth grinding head 7 has a uniform particle size. It is also not necessary to measure the Ga surface warpage value of the gallium nitride single crystal substrate 1 before performing the second grinding on the Ga surface 11.

[0057] Preferably, when the Ga surface 11 is ground for the second time, the fourth grinding head 7 has a particle size of 1500 mesh, the rotation speed of the fourth grinding head 7 is 2000~2500 rpm, the rotation speed of the grinding platform 2 is 200~250 rpm, the second grinding head 5 rotates in the opposite direction to the grinding platform 2, and the pressure of the second grinding of the Ga surface 11 is set at 200~250 g / cm².

[0058] To further explain, in the above steps S02 to S07, the thickness of Ga surface 11 during the first grinding and thinning is controlled at 100 to 200 μm, and the thickness of Ga surface 11 during the second grinding and thinning is controlled at 50 to 150 μm; the thickness of N surface 12 during the first grinding and thinning is controlled at 100 to 150 μm, and the thickness of N surface 12 during the second grinding and thinning is controlled at 50 to 100 μm.

[0059] Step S08: Perform chemical mechanical polishing on gallium nitride single crystal substrate 1.

[0060] A gallium nitride single crystal substrate 1 is fixed in a chemical mechanical polishing (CMP) apparatus. A polishing platform is provided, on which a polishing pad made of polyurethane material is disposed. Polishing slurry is continuously added to the polishing pad, and the gallium nitride single crystal substrate 1 is pressed against the polishing pad for chemical mechanical polishing. When an alkaline polishing slurry is used, the chemical mechanical polishing pressure is controlled at 200~250 g / cm²; when an acidic polishing slurry is used, the chemical mechanical polishing pressure is controlled at 220~350 g / cm², the polishing slurry temperature is kept constant at 40~50℃, and the polishing platform rotation speed is 800~1200 rpm. The chemical mechanical polishing in this embodiment is a conventional technical solution, and will not be described in detail in this patent.

[0061] In other possible embodiments, the division of the regions of the first grinding head and the second grinding head is not limited to the central region and the edge region. More regional conditions can be divided to achieve more precise zonal grinding. These will not be elaborated in detail in this invention.

[0062] As described above, the grinding and polishing method for gallium nitride single crystal substrates of the present invention has the following beneficial effects: This invention is applicable to the grinding and polishing of large-sized gallium nitride single crystal substrates 1 with a certain degree of warpage. When grinding the Ga surface 11 and N surface 12 of the gallium nitride single crystal substrate 1 for the first time, grinding heads with different positions in the central region and the edge are selected according to the warpage of the gallium nitride single crystal substrate 1. This can improve the grinding and thinning efficiency of the protruding parts, while reducing the damage to the non-protruding parts during the grinding process.

[0063] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A grinding and polishing method for gallium nitride single crystal substrates, characterized in that, The method includes the following steps: S01. A gallium nitride single crystal substrate is provided, the gallium nitride single crystal substrate having opposing Ga and N surfaces, the gallium nitride single crystal substrate is fixed to a polishing platform, and the Ga surface of the gallium nitride single crystal substrate faces away from the polishing platform; S02. Measure the Ga surface warpage value of the gallium nitride single crystal substrate, select a first polishing head based on the Ga surface warpage value, and use the first polishing head to perform the first polishing on the Ga surface; the first polishing head includes a first central region and a first edge region, and the particle size of the first central region is less than or equal to the particle size of the first edge region; S03. Re-fix the gallium nitride single crystal substrate to the polishing platform, with the N-side of the gallium nitride single crystal substrate facing away from the polishing platform; S04. Measure the N-plane warpage value of the gallium nitride single crystal substrate, select a second grinding head based on the N-plane warpage value, and use the second grinding head to perform the first grinding on the N-plane; the second grinding head includes a second central region and a second edge region, and the particle size of the second central region is greater than or equal to the particle size of the second edge region; S05. Provide a third grinding head to perform a second grinding on the N-side of the gallium nitride single crystal substrate; S06. Re-fix the gallium nitride single crystal substrate to the polishing platform, with the Ga surface of the gallium nitride single crystal substrate facing away from the polishing platform; S07. Provide a fourth grinding head to perform a second grinding on the Ga surface of the gallium nitride single crystal substrate; S08. Perform chemical mechanical polishing on the gallium nitride single crystal substrate.

2. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S02, the first grinding head is selected based on the Ga surface warpage value, specifically as follows: When the warpage value of the Ga surface is less than 50 μm, the particle size of the first central region is the same as that of the first edge region, and the particle size is selected as 320 mesh or 400 mesh. When the Ga surface warpage value is between 50 μm and 100 μm, the particle size of the first central region is 320 mesh, and the particle size of the first edge region is 400 mesh. When the Ga surface warpage value is greater than 100 μm, the particle size of the first central region is 320 mesh, and the particle size of the first edge region is 600 mesh or 800 mesh.

3. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S03, the second grinding head is selected based on the N-surface warp value, specifically as follows: When the N-surface warpage value is less than 50 μm, the particle size of the second central region is the same as that of the second edge region, and the particle size is selected as 320 mesh or 400 mesh. When the N-surface warpage value is between 50µm and 100µm, the particle size of the second central region is 400 mesh, and the particle size of the second edge region is 320 mesh. When the N-surface warpage value is greater than 100 μm, the particle size of the second central region is 600 mesh or 800 mesh, and the particle size of the second edge region is 320 mesh.

4. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: The Ga surface warpage value and the N surface warpage value of the gallium nitride single crystal substrate are measured using the moiré fringe method, X-ray diffraction method, optical interferometry method, or laser scanning method.

5. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S02, when the first grinding head is used to grind the Ga surface for the first time, the rotation speed of the first grinding head is 1500~2000 rpm, the rotation speed of the grinding platform is 150~200 rpm, the rotation direction of the first grinding head and the grinding platform are opposite, and the pressure is set at 220~350 g / cm².

6. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S04, when the second grinding head is used to grind the N-surface for the first time, the rotation speed of the second grinding head is 1500~2000 rpm, the rotation speed of the grinding platform is 150~200 rpm, the rotation direction of the second grinding head and the grinding platform are opposite, and the pressure is set at 200~300 g / cm².

7. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S05, the rotation speed of the third grinding head is 1800~2200 rpm, the rotation speed of the grinding platform is 200~250 rpm, and the pressure is set at 150~200 g / cm².

8. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S07, the rotation speed of the fourth grinding head is 2000~2500 rpm, the rotation speed of the grinding platform is 200~250 rpm, the rotation direction of the second grinding head is opposite to that of the grinding platform, and the pressure is set at 200~250 g / cm².

9. The grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: In step S02, the thickness of the Ga surface after the first grinding and thinning is 100~200um; in step S04, the thickness of the N surface after the first grinding and thinning is 100~150um. In step S05, the thickness of the N-side after the second grinding and thinning is 50~100um; in step S07, the thickness of the Ga-side after the second grinding and thinning is 50~150um.

10. A grinding and polishing method for gallium nitride single crystal substrates according to claim 1, characterized in that: The gallium nitride single crystal substrate is fixed to the polishing platform by paraffin wax.

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