Wafer grinding method

Abstract

The invention discloses a wafer grinding method, the wafer comprises a sapphire substrate and a gallium nitride epitaxial layer epitaxially growing on the sapphire substrate, the grinding method comprises the following steps: S1, the wafer is fixed on a grinding table, and the gallium nitride epitaxial layer is arranged close to the grinding table; s2, obtaining the morphology of the sapphire substrate; s3, according to the morphology of the sapphire substrate, at least one grinding head is selected for grinding; s4, the connection between the wafer and the grinding table is relieved, and standing is carried out; and repeating the steps S1 to S4 until the sapphire substrate is thinned to a preset thickness or completely removed. According to the embodiment of the invention, targeted grinding is carried out in a multi-time grinding manner, so that thinning or removal of the sapphire substrate of the large-size wafer with relatively large warpage is realized, the grinding effect is good, and the wafer cracking risk is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the field of wafer manufacturing, and particularly relates to a method for grinding a wafer. Background Art

[0002] After growing a gallium nitride epitaxial layer on a sapphire substrate, due to the combined action of thermal mismatch stress and lattice mismatch stress, when the thickness of the gallium nitride epitaxial layer reaches a certain value, the whole wafer will warp. After epitaxially growing gallium nitride single crystals on a large-size sapphire substrate, the warping of the wafer is more serious, which will significantly increase the difficulty of using Laser Lift-Off (LLO). For example, when the height difference between the center and the edge of the wafer is 200 μm, while the laser depth of focus (DOF) of a typical excimer laser system is only about ±20 μm, resulting in a significant decrease in the proportion of the effective peeling area; in addition to laser peeling, grinding can also be used to remove the sapphire substrate, but the current grinding methods are usually applied to wafers with flat or insignificant warping, and it is difficult to apply them to the substrate peeling process of large-size warped wafers. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for grinding a wafer to solve the problem that it is difficult to thin or remove the sapphire substrate of a large-size warped wafer.

[0004] To achieve the above purpose, the present invention provides a method for grinding a wafer, where the wafer includes a sapphire substrate and a gallium nitride epitaxial layer epitaxially grown on the sapphire substrate. The grinding method includes: S1, fixing the wafer on a grinding table with the gallium nitride epitaxial layer close to the grinding table; S2, obtaining the topography of the sapphire substrate; S3, selecting at least one grinding head for grinding according to the topography of the sapphire substrate; S4, releasing the connection between the wafer and the grinding table and standing still; repeating steps S1 to S4 until the sapphire substrate is thinned to a preset thickness or completely removed.

[0005] Preferably, when the topography of the sapphire substrate is a bowl-shaped structure symmetric about its center axis, the number of grinding heads is one, and the grinding head is a bowl-shaped structure symmetric about its center corresponding to the topography. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the grinding head.

[0006] Preferably, when the topography of the sapphire substrate is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of grinding heads is at least three, and at least three grinding heads are arranged corresponding to the topography of the sapphire substrate. During grinding, the grinding table does not rotate and the grinding heads rotate for grinding.

[0007] Preferably, the grinding method specifically includes the following steps: S1. Fix the wafer on the grinding table with the gallium nitride epitaxial layer of the wafer close to the grinding table; S2. Obtain the first topography of the sapphire substrate; S3. Select at least one first grinding head corresponding to the first topography to perform a first grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S4. Disconnect the wafer from the grinding table and let it stand; S5. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S6. Obtain the second topography of the sapphire substrate; S7. Select at least one second grinding head corresponding to the second topography to perform a second grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S8. Disconnect the wafer from the grinding table again and let it stand; S9. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S10. Obtain the third topography of the sapphire substrate; S11. Select at least one third grinding head corresponding to the third topography to perform a third grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer to thin the sapphire substrate to a preset thickness or completely remove the sapphire substrate.

[0008] Preferably, the grinding method specifically includes the following steps: S1. Fix the wafer on the grinding table with the gallium nitride epitaxial layer of the wafer close to the grinding table; S2. Obtain the first topography of the sapphire substrate; S3. Select one first grinding head to perform a first grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S4. Disconnect the wafer from the grinding table and let it stand;

[0009] S5. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S6. Obtain the second topography of the sapphire substrate; S7. Determine a fourth topography according to the first topography and the second topography, and select at least one second grinding head corresponding to the fourth topography to perform a second grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S8. Disconnect the wafer from the grinding table again and let it stand; S9. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S10. Obtain the third topography of the sapphire substrate; S11. Select at least one third grinding head corresponding to the third topography to perform a third grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer to thin the sapphire substrate to a preset thickness or completely remove the sapphire substrate.

[0010] Preferably, the first grinding head is of a flat plate structure or the first grinding head is of a bowl-shaped structure symmetric about its center. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the first grinding head.

[0011] Preferably, when the fourth morphology is a bowl-shaped structure symmetric about its central axis, the number of the second grinding heads is one, and the second grinding head is a bowl-shaped structure symmetric about its center; during grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the second grinding head; when the fourth morphology is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of the second grinding heads correspondingly is at least three, and at least three grinding heads grind according to the morphology of the sapphire substrate. During grinding, the grinding table does not rotate and the second grinding heads rotate for grinding.

[0012] Preferably, when the third morphology is a bowl-shaped structure symmetric about its central axis, the number of the third grinding heads is one, and the third grinding head is a bowl-shaped structure symmetric about its center. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the grinding head; when the third morphology is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of the third grinding heads correspondingly is at least three, and at least three grinding heads grind according to the morphology of the sapphire substrate. During grinding, the grinding table does not rotate and the third grinding heads rotate for grinding.

[0013] Preferably, the particle size of the second grinding head is larger than the particle size of the first grinding head, and the particle size of the third grinding head is larger than the particle size of the first grinding head.

[0014] Preferably, the thickness of the sapphire substrate removed by the second grinding is less than the thickness of the sapphire substrate removed by the first grinding, and the thickness of the sapphire substrate removed by the third grinding is less than the thickness of the sapphire substrate removed by the second grinding.

[0015] Compared with the prior art, the embodiments of the present invention perform grinding in a targeted manner through multiple grindings, realizing the thinning or removal of the sapphire substrate of a large-size wafer with a large warpage. The grinding effect is good and the risk of chipping is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a front view of a wafer of the first structure in the embodiments of the present invention, wherein the sapphire substrate is a bowl-shaped structure symmetric about its central axis.

[0017] Figure 2 It is a top view of a wafer of the first structure in the embodiments of the present invention, wherein the sapphire substrate is a bowl-shaped structure symmetric about its central axis.

[0018] Figure 3 is Figure 2 a sectional view taken along the A-A direction of

[0019] Figure 4 a structural diagram of the first structure in the embodiment of the present invention, where a wafer is mounted on a grinding table and docked with a matching grinding head.

[0020] Figure 5 a front view of the wafer of the second structure in the embodiment of the present invention, where the sapphire substrate is an arch structure with mirror symmetry.

[0021] Figure 6 a top view of the wafer of the second structure in the embodiment of the present invention, where the sapphire substrate is an arch structure with mirror symmetry.

[0022] Figure 7 is Figure 6 a sectional view taken along the B-B direction of

[0023] Figure 8 a structural diagram of the wafer of the second structure in the embodiment of the present invention, where the wafer is mounted on a grinding table and docked with three matching grinding heads.

[0024] Figure 9 a structural diagram of the wafer of the third structure in the embodiment of the present invention, where the sapphire substrate is a saddle-shaped structure. Detailed Embodiments

[0025] To describe in detail the technical content, structural features, and achieved effects of the present invention, the following is a detailed description in conjunction with the embodiments and with reference to the accompanying drawings.

[0026] Embodiment 1

[0027] As Figures 1 to 9 shown, the embodiment of the present invention provides a grinding method for a wafer 10. The wafer 10 includes a sapphire substrate 1 and a gallium nitride epitaxial layer 2 epitaxially grown on the sapphire substrate 1. The grinding method includes:

[0028] S1. Fix the wafer 10 on the grinding table 4 with the gallium nitride epitaxial layer 2 disposed close to the grinding table 4; specifically, as Figure 4 or Figure 8 shown, after epitaxial growth, the wafer 10 has a warped morphology. The size of the wafer 10 is greater than or equal to 6 inches. The thickness of the sapphire substrate 1 is greater than or equal to 850 microns and less than or equal to 1000 microns. The thickness of the gallium nitride epitaxial layer 2 is greater than or equal to 300 microns and less than or equal to 500 microns. It should be noted that in the embodiment of the present invention, the gallium nitride epitaxial layer 2 being disposed close to the grinding table 4 means that the gallium nitride epitaxial layer 2 is relatively closer to the grinding table 4 than the sapphire substrate 1 so that the sapphire substrate 1 faces outward for grinding.

[0029] S2. Obtain the topography of the sapphire substrate 1; specifically, the topography of the sapphire substrate 1 can be obtained by means such as the moiré fringe method, X-ray diffraction method, optical interference method, or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained. By obtaining the specific thickness of the sapphire substrate 1, the grinding time can be controlled.

[0030] S3. Select at least one grinding head 5 for grinding according to the topography of the sapphire substrate 1; specifically, select a suitable grinding head 5 for grinding. The grinding can be divided into rough grinding and fine grinding. For example, the first grinding can be rough grinding, and the subsequent grindings can be fine grinding.

[0031] S4. Disconnect the wafer 10 from the grinding table 4 and let it stand; specifically, as the sapphire substrate 1 thins, the warpage condition of the wafer 10 may change. To avoid excessive errors during grinding, after grinding, disconnect the wafer 10 from the grinding table 4, so that the wafer 10 can adjust its own warpage condition to a certain extent under the action of stress, and at the same time release the stress to reduce the risk of grinding chipping.

[0032] Repeat steps S1 to S4 until the sapphire substrate 1 is thinned to a preset thickness or completely removed. Specifically, according to actual needs, perform the third grinding, fourth grinding, etc. on the sapphire substrate 1 to thin the sapphire substrate 1 to the preset thickness or completely remove the sapphire substrate 1.

[0033] It should be noted that the order of the above steps S1 and S2 can be exchanged, and the specific selection is based on actual needs.

[0034] In the embodiment of the present invention, targeted grinding is carried out by means of multiple grindings, realizing the thinning or removal of the sapphire substrate 1 of the large-size wafer 10 with large warpage. The grinding effect is good and the risk of chipping is effectively reduced.

[0035] In the embodiment of the present invention, when the topography of the sapphire substrate 1 is a bowl-shaped structure symmetric about its center axis, the number of grinding heads 5 is one, and the grinding head 5 is a bowl-shaped structure symmetric about its center corresponding to the topography. During grinding, the grinding table 4 rotates and the rotation direction of the grinding table 4 is opposite to the rotation direction of the grinding head 5. Specifically, when the obtained topography of the sapphire substrate 1 is a bowl-shaped structure symmetric about its center axis, only one grinding head 5 with a bowl-shaped structure corresponding to the topography of the sapphire substrate 1 can be used for grinding. At this time, in step S3, there is no need to design multiple grinding heads 5, and the grinding of the sapphire substrate 1 can be realized only by one grinding head 5, and the structure is more concise. During grinding, both the grinding head 5 and the grinding platform rotate and the rotation directions are opposite, which can further increase the grinding speed. The rotation speed of the grinding table 4 can be, for example, 100 rpm.

[0036] In an embodiment of the present invention, when the topography of the sapphire substrate 1 is a mirror-symmetric arched structure or a saddle-shaped structure, the number of polishing heads 5 is at least three. At least three polishing heads 5 are arranged corresponding to the topography of the sapphire substrate 1. During polishing, the polishing table 4 does not rotate, and the polishing heads 5 rotate for polishing. Specifically, when the topography of the sapphire substrate 1 is a mirror-symmetric arched structure or a saddle-shaped structure, in step S3, at least three polishing heads 5 are correspondingly designed, and the structures of at least three polishing heads 5 can be different to correspond to different regions of the topography of the sapphire substrate 1, so as to achieve curved surface polishing. In order to avoid interference, in this case, only the polishing heads 5 rotate and the polishing table 4 does not rotate.

[0037] In an embodiment of the present invention, the sapphire substrate 1 can be thinned to a preset thickness or completely removed by three times of polishing. The polishing method of the wafer 10 specifically includes the following steps:

[0038] S1. Fix the wafer 10 on the polishing table 4 and arrange the gallium nitride epitaxial layer 2 of the wafer 10 close to the polishing table 4. Specifically, as Figure 4 or Figure 8 shown, after epitaxial growth, the wafer 10 has a warped topography. The size of the wafer 10 is greater than or equal to 6 inches. The thickness of the sapphire substrate 1 is greater than or equal to 850 microns and less than or equal to 1000 microns. The thickness of the gallium nitride epitaxial layer 2 is greater than or equal to 300 microns and less than or equal to 500 microns.

[0039] S2. Obtain the first topography of the sapphire substrate 1. Specifically, the first topography is the surface topography of the side of the sapphire substrate 1 far from the gallium nitride epitaxial layer 2. The first topography can be obtained by selecting methods such as the moiré fringe method, X-ray diffraction method, optical interference method or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained. As Figure 1 、 Figures 3 to 5 and Figure 7 shown, the surface topography of the side of the sapphire substrate 1 far from the gallium nitride epitaxial layer 2 is the first surface topography 11.

[0040] S3. Select at least one first polishing head corresponding to the first topography to perform the first polishing on the side of the sapphire substrate 1 far from the gallium nitride epitaxial layer 2. Specifically, when the first topography is a bowl-shaped structure symmetric about its central axis, the number of the first polishing heads is one, and the first polishing head is a bowl-shaped structure symmetric about its center corresponding to the first topography; when the first topography is a mirror-symmetric arched structure or a saddle-shaped structure, the number of the first polishing heads is at least three. The first polishing can be rough grinding, and the rotation speed of the first polishing can be set relatively fast.

[0041] S4. Disconnect the wafer 10 from the polishing table 4 and let it stand still; specifically, the wafer 10 can stand still for a preset time, which can be greater than or equal to 5 seconds and less than or equal to 60 seconds. The specific standing time is uncertain and can be set according to actual needs.

[0042] S5. Fix the wafer 10 on the polishing table 4 again and arrange the gallium nitride epitaxial layer 2 of the wafer 10 close to the polishing table 4.

[0043] S6. Obtain the second topography of the sapphire substrate 1; specifically, since the first polishing has been carried out, the topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 may change compared with the topography before polishing. For example, it may change from a bowl-shaped structure to a saddle-shaped structure. Therefore, it is necessary to obtain the second topography, and the second topography is the surface topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. The second topography can be obtained by selecting methods such as the moiré fringe method, X-ray diffraction method, optical interference method or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained.

[0044] S7. Select at least one second polishing head corresponding to the second topography to polish the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 for the second time. Specifically, during the second polishing, the sapphire substrate 1 is relatively thin. To avoid polishing the gallium nitride epitaxial layer 2 during the polishing process, the second polishing can be fine polishing. The rotation speed of the second polishing can be less than that of the first polishing. The precision of fine polishing is higher and the polishing effect is better. In addition, by obtaining the specific thickness of the sapphire substrate 1, the polishing time can be controlled. Similarly, when the second topography is a bowl-shaped structure symmetric about its center axis, the number of second polishing heads is one, and the second polishing head is a bowl-shaped structure symmetric about its center corresponding to the second topography; when the second topography is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of second polishing heads is at least three.

[0045] S8. Disconnect the wafer 10 from the polishing table 4 again and let it stand still; specifically, disconnect the wafer 10 from the polishing table 4 again and let it stand still for a preset time, which can be greater than or equal to 5 seconds and less than or equal to 60 seconds. The specific standing time is uncertain and can be set according to actual needs.

[0046] S9. Fix the wafer 10 on the polishing table 4 again and arrange the gallium nitride epitaxial layer 2 of the wafer 10 close to the polishing table 4.

[0047] S10. Obtain the third morphology of the sapphire substrate 1; specifically, after the second grinding, the morphology of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 may change relative to the second morphology. For example, it may change from a bowl-shaped structure to a saddle-shaped structure. Therefore, it is necessary to obtain the third morphology, which is the surface morphology of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. The third morphology can be obtained by selecting methods such as the moiré fringe method, X-ray diffraction method, optical interference method, or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained.

[0048] S11. Select at least one third grinding head corresponding to the third morphology to perform a third grinding on the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 to thin the sapphire substrate 1 to a preset thickness or completely remove the sapphire substrate 1. Specifically, the third grinding can be fine grinding, and the grinding effect is better. When the third morphology is a bowl-shaped structure symmetric about its center axis, the number of third grinding heads is one, and the third grinding head is a bowl-shaped structure symmetric about its center corresponding to the third morphology; when the third morphology is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of third grinding heads is at least three. The rotation speed of the third grinding can be less than the rotation speed of the first grinding. By performing three grindings, the sapphire substrate 1 is thinned to a preset thickness or completely removed. On the basis of ensuring the grinding accuracy, the grinding time can be shorter.

[0049] In the embodiment of the present invention, the thickness of the sapphire substrate 1 removed by the second grinding is less than the thickness of the sapphire substrate 1 removed by the first grinding, and the thickness of the sapphire substrate 1 removed by the third grinding is less than the thickness of the sapphire substrate 1 removed by the second grinding. Specifically, before grinding, the thickness of the sapphire substrate 1 is greater than or equal to 850 microns and less than or equal to 1000 microns. After the first grinding, the thickness of the sapphire substrate 1 is greater than or equal to 200 microns and less than or equal to 250 microns. After the second grinding, the thickness of the sapphire substrate 1 is greater than or equal to 50 microns and less than or equal to 100 microns. After the third grinding, the thickness of the sapphire substrate 1 is greater than or equal to 0 microns and less than or equal to 50 microns.

[0050] In the embodiment of the present invention, the particle size of the second polishing head is larger than that of the first polishing head, and the particle size of the third polishing head is larger than that of the first polishing head, so as to ensure higher precision and better polishing effect in the second polishing and the third polishing. Specifically, the polishing speed of the first polishing head can be set relatively high. For example, the rotation speed of the first polishing head can be set to 3000 rpm, the particle size of the first polishing head can be set to 320 mesh, and the polishing pressure of the first polishing head is greater than or equal to 0.3 MPa and less than or equal to 0.5 MPa. The rotation speed of the second polishing head can be set lower than that of the first polishing head. For example, the rotation speed of the second polishing head can be set to 1500 rpm, the particle size of the second polishing head is 2000 mesh, and the polishing pressure of the second polishing head is greater than or equal to 0.1 MPa and less than or equal to 0.15 MPa. The rotation speed of the third polishing head can be set lower than that of the first polishing head. For example, the rotation speed of the third polishing head can be set to 1500 rpm, the particle size of the third polishing head is 2000 mesh, and the polishing pressure of the third polishing head is greater than or equal to 0.1 MPa and less than or equal to 0.15 MPa.

[0051] In the embodiment of the present invention, the wafer 10 is adhesively fixed to the polishing table 4 by wax 3. Specifically, as Figure 4 and Figure 8 shown, the wax 3 is applied to the curved surface of the gallium nitride epitaxial layer 2 until the curved surface of the gallium nitride epitaxial layer 2 is filled and exceeds to stably fix the wafer 10 to the polishing table 4. Of course, in some other embodiments, the wafer 10 can also be adsorbed and fixed to the polishing table 4, or the wafer 10 can be fixed to the polishing table 4 by a temporary bonding adhesive, which can be specifically selected according to actual needs.

[0052] In the embodiments of the present invention, after each step of disconnecting the wafer 10 from the polishing table 4, a step of cleaning the wafer 10 is further included. Specifically, the cleaning method can be one or more of ultrasonic cleaning, chemical cleaning, and ultrapure water cleaning. Among them, ultrasonic cleaning is used for cleaning large particulate abrasives that are loosely attached, such as diamond or SiC, etc. The solution for ultrasonic cleaning is a mixture of deionized water and 0.1% surfactant (such as Triton X-100). The cleaning frequency is greater than or equal to 40 kHz and less than or equal to 60 kHz, the cleaning temperature is greater than or equal to 25 °C and less than or equal to 40 °C, and the cleaning time is greater than or equal to 5 minutes and less than or equal to 10 minutes; Chemical cleaning is used to remove organic residues and slightly oxidize the GaN surface. Specifically, a mixed solution with a volume ratio of H2O:NH4OH:H2O2 of 5:1:1 can be selected. The cleaning temperature is greater than or equal to 70 °C and less than or equal to 80 °C, and the cleaning time is greater than or equal to 5 minutes and less than or equal to 10 minutes; Ultrapure water rinsing is used to thoroughly rinse chemical residues. The resistivity of the ultrapure water is greater than 18 MΩ·cm, the flow rate of the ultrapure water is greater than or equal to 10 L / min and less than or equal to 20 L / min, and the duration is greater than or equal to 3 minutes and less than or equal to 5 minutes.

[0053] It should be noted that the morphology of the sapphire substrate 1 in each step of the above embodiments is a regular morphology, that is, the surface morphology of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 is the same as the surface morphology of the side of the sapphire substrate 1 close to the gallium nitride epitaxial layer 2.

[0054] Embodiment 2

[0055] In some other specific embodiments of the present invention, the sapphire substrate 1 can also be thinned to a preset thickness or completely removed by other three polishing methods. The wafer 10 polishing method can specifically further include the following steps:

[0056] S10. Fix the wafer 10 on the polishing table 4 and arrange the gallium nitride epitaxial layer 2 of the wafer 10 close to the polishing table 4; As Figure 4 or Figure 8 shown, after epitaxial growth, the wafer 10 has a warped morphology. The size of the wafer 10 is greater than or equal to 6 inches, the thickness of the sapphire substrate 1 is greater than or equal to 850 microns and less than or equal to 1000 microns, and the thickness of the gallium nitride epitaxial layer 2 is greater than or equal to 300 microns and less than or equal to 500 microns.

[0057] S20. Obtain the first topography of the sapphire substrate 1; specifically, the first topography is the surface topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. The first topography can be obtained by methods such as the moiré fringe method, X-ray diffraction method, optical interference method, or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained.

[0058] S30. Select a first grinding head to perform the first grinding on the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2; specifically, only one grinding head is selected for grinding in this step. The first grinding head can directly adopt a flat structure. The size of the first grinding head with a flat structure can be set to be larger than the size of the wafer 10, without the need to set a complex grinding head structure, and the cost is lower. During grinding, the grinding table 4 rotates and the rotation direction of the grinding table 4 is opposite to the rotation direction of the first grinding head, thereby accelerating the grinding speed. In some other specific embodiments, when the first topography is a mirror-symmetric arched structure or a saddle-shaped structure, the first grinding head is a bowl-shaped structure symmetric about its center.

[0059] S40. Disconnect the wafer 10 from the grinding table 4 and let it stand; specifically, the wafer 10 can stand for a preset time. The preset time can be greater than or equal to 5 seconds and less than or equal to 60 seconds. The specific standing time is not fixed and can be set according to actual needs.

[0060] S50. Fix the wafer 10 on the grinding table 4 again and arrange the gallium nitride epitaxial layer 2 of the wafer 10 close to the grinding table 4.

[0061] S60. Obtain the second topography of the sapphire substrate 1; specifically, the second topography is the surface topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. The second topography can be obtained by methods such as the moiré fringe method, X-ray diffraction method, optical interference method, or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained.

[0062] S70. Determine the fourth topography based on the first topography and the second topography, and select at least one second grinding head corresponding to the fourth topography to perform a second grinding on the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. Specifically, since the first grinding uses a first grinding head with a flat structure, the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 after the first grinding is an irregular shape and remains irregular even after releasing stress in step S80. If the grinding head is set in an irregular shape, it is easy to grind the gallium nitride epitaxial layer 2 during the second grinding, causing damage to the gallium nitride epitaxial layer 2. Therefore, in order to achieve a better grinding effect, select the fourth topography, that is, the surface topography of the side of the sapphire substrate 1 close to the gallium nitride epitaxial layer 2, to design the second grinding head. The second grinding can be fine grinding, which has a higher precision and a better grinding effect. When the fourth topography is a bowl-shaped structure symmetric about its center axis, the number of second grinding heads is one, and the second grinding head is a bowl-shaped structure symmetric about its center corresponding to the fourth topography. When the second topography is a mirror-symmetric arched structure or a saddle-shaped structure, the number of second grinding heads is at least three. The second grinding can be fine grinding, and the rotation speed of the second grinding can be less than that of the first grinding. The fourth topography can be directly obtained by fitting the first topography and the second topography through a detection device. For example, there is a trained fitting data model in the detection device. For the case where the first topography is a mirror-symmetric arched structure or a saddle-shaped structure and the first grinding head is a bowl-shaped structure symmetric about its center, the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 after the first grinding is also an irregular shape, and the fourth topography also needs to be determined.

[0063] S80. Disconnect the wafer 10 from the grinding table 4 again and let it stand still. Specifically, disconnect the wafer 10 from the grinding table 4 again and let it stand still for a preset time. The preset time can be greater than or equal to 5 seconds and less than or equal to 60 seconds. The specific standing time is uncertain and can be set according to actual needs.

[0064] S90. Fix the wafer 10 on the grinding table 4 again with the gallium nitride epitaxial layer 2 of the wafer 10 close to the grinding table 4.

[0065] S100. Obtain the third topography of the sapphire substrate 1. Specifically, after the second grinding, the sapphire substrate 1 is restored to a regular topography, that is, the surface topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 is the same as the surface topography of the side of the sapphire substrate 1 close to the gallium nitride epitaxial layer 2. The third topography is the surface topography of the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2. The third topography can be obtained by selecting methods such as the moiré fringe method, X-ray diffraction method, optical interference method, or laser scanning method. In this step, the specific thickness of the sapphire substrate 1 can also be obtained.

[0066] S110. Select at least one third grinding head corresponding to the third morphology to perform a third grinding on the side of the sapphire substrate 1 away from the gallium nitride epitaxial layer 2 to thin the sapphire substrate 1 to a preset thickness or completely remove the sapphire substrate 1. Specifically, when the third morphology is a bowl-shaped structure symmetric about its central axis, the number of third grinding heads is one, and the third grinding head is a bowl-shaped structure symmetric about its central axis corresponding to the third morphology; when the third morphology is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of third grinding heads is at least three. The rotation speed of the third grinding can be less than that of the first grinding, and the third grinding can be fine grinding, with better grinding effect.

[0067] The difference between this embodiment and Embodiment 1 lies in that in this embodiment, the first grinding head in step S30 is a flat structure or the first grinding head is a bowl-shaped structure symmetric about its central axis, and the acquisition of the fourth morphology and the design of the second grinding head in step S70. The remaining steps are the same as those in Embodiment 1 and will not be elaborated here.

[0068] The above-disclosed are only the preferred examples of the present invention. Of course, the scope of the rights of the present invention cannot be limited by this. Therefore, equivalent changes made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention.

Claims

1. A grinding method for a wafer, the wafer comprising a sapphire substrate and a gallium nitride epitaxial layer epitaxially grown on the sapphire substrate, characterized in that, The grinding method includes: S1. Fix the wafer on the grinding table with the gallium nitride epitaxial layer close to the grinding table; S2. Obtain the topography of the sapphire substrate; S3. Select at least one grinding head for grinding according to the topography of the sapphire substrate; S4. Disconnect the wafer from the grinding table and let it stand; Repeat steps S1 - S4 until the sapphire substrate is thinned to a preset thickness or completely removed.

2. The grinding method of the wafer as described in claim 1, characterized in that, When the topography of the sapphire substrate is a bowl-shaped structure symmetric about its center axis, the number of grinding heads is one, and the grinding head is a bowl-shaped structure symmetric about its center corresponding to the topography. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to that of the grinding head.

3. The grinding method of the wafer as described in claim 1, characterized in that, When the topography of the sapphire substrate is a mirror-symmetric arched structure or a saddle-shaped structure, the number of grinding heads is at least three. At least three grinding heads are arranged corresponding to the topography of the sapphire substrate. During grinding, the grinding table does not rotate and the grinding heads rotate for grinding.

4. The grinding method of the wafer according to claim 1, wherein The grinding method specifically includes the following steps: S1. Fix the wafer on the grinding table with the gallium nitride epitaxial layer of the wafer close to the grinding table; S2. Obtain the first topography of the sapphire substrate; S3. Select at least one first grinding head corresponding to the first topography to perform the first grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S4. Disconnect the wafer from the grinding table and let it stand; S5. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S6. Obtain the second topography of the sapphire substrate; S7. Select at least one second grinding head corresponding to the second topography to perform the second grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S8. Disconnect the wafer from the grinding table again and let it stand; S9. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S10. Obtain the third topography of the sapphire substrate; S11. Select at least one third grinding head corresponding to the third topography to perform the third grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer to thin the sapphire substrate to a preset thickness or completely remove the sapphire substrate.

5. The grinding method of the wafer according to claim 1, characterized in that, The grinding method specifically includes the following steps: S1. Fix the wafer on the grinding table with the gallium nitride epitaxial layer of the wafer close to the grinding table; S2. Obtain the first topography of the sapphire substrate; S3. Select one first grinding head to perform the first grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S4. Disconnect the wafer from the grinding table and let it stand; S5. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer close to the grinding table; S6. Obtain the second topography of the sapphire substrate; S7. Determine a fourth topography based on the first topography and the second topography, and select at least one second grinding head corresponding to the fourth topography to perform a second grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer; S8. Disconnect the wafer from the grinding table again and let it stand still; S9. Fix the wafer on the grinding table again with the gallium nitride epitaxial layer of the wafer facing the grinding table; S10. Obtain the third topography of the sapphire substrate; S11. Select at least one third grinding head corresponding to the third topography to perform a third grinding on the side of the sapphire substrate away from the gallium nitride epitaxial layer to thin the sapphire substrate to a preset thickness or completely remove the sapphire substrate.

6. The grinding method of the wafer according to claim 5, characterized in that, The first grinding head is of a flat structure or the first grinding head is a bowl-shaped structure symmetric about its center. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the first grinding head.

7. The grinding method of the wafer as described in claim 5, characterized in that, When the fourth topography is a bowl-shaped structure symmetric about its center axis, the number of the second grinding heads is one, and the second grinding head is a bowl-shaped structure symmetric about its center; during grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the second grinding head; When the fourth topography is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of the second grinding heads correspondingly is at least three, and at least three grinding heads grind according to the topography of the sapphire substrate. During grinding, the grinding table does not rotate and the second grinding heads rotate for grinding.

8. The grinding method of the wafer as described in claim 5, characterized in that, When the third topography is a bowl-shaped structure symmetric about its center axis, the number of the third grinding heads is one, and the third grinding head is a bowl-shaped structure symmetric about its center. During grinding, the grinding table rotates and the rotation direction of the grinding table is opposite to the rotation direction of the grinding head; When the third topography is an arch-shaped structure with mirror symmetry or a saddle-shaped structure, the number of the third grinding heads correspondingly is at least three, and at least three grinding heads grind according to the topography of the sapphire substrate. During grinding, the grinding table does not rotate and the third grinding heads rotate for grinding.

9. The grinding method of a wafer according to claim 4 or 5, characterized in that, The particle size of the second grinding head is larger than the particle size of the first grinding head, and the particle size of the third grinding head is larger than the particle size of the first grinding head.

10. The grinding method of the wafer according to claim 4 or 5, characterized in that, The thickness of the sapphire substrate removed by the second grinding is less than the thickness of the sapphire substrate removed by the first grinding, and the thickness of the sapphire substrate removed by the third grinding is less than the thickness of the sapphire substrate removed by the second grinding.

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