Method for reducing warpage of gallium nitride substrate

Abstract

The present application provides a method for reducing the warpage of a gallium nitride substrate, including: providing a gallium nitride substrate; performing a first gallium surface grinding on the gallium surface of the gallium nitride substrate using a first grinding wheel; performing a first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate using a second grinding wheel, wherein the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel; performing a second nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate using a third grinding wheel, wherein the maximum particle size of the abrasive in the third grinding wheel is smaller than the minimum particle size of the abrasive in the second grinding wheel; performing a second gallium surface grinding on the gallium surface of the gallium nitride substrate using a fourth grinding wheel, wherein the maximum particle size of the abrasive in the fourth grinding wheel is smaller than the minimum particle size of the abrasive in the third grinding wheel; performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step. The above method for reducing the warpage of a gallium nitride substrate can reduce the warpage of the gallium nitride substrate and improve the yield of grinding and polishing.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor technologies, and particularly to a method for reducing the warpage of a gallium nitride substrate. Background Art

[0002] Gallium nitride semiconductor materials have unique excellent properties such as a large bandgap width, a high electron saturation drift velocity, a small dielectric constant, a strong radiation resistance, and high chemical stability. Therefore, gallium nitride has broad application prospects in the fields of optoelectronic devices and microelectronic devices.

[0003] Before being applied to optoelectronic devices, gallium nitride needs to be ground and polished. However, when the gallium nitride substrate has not been ground and polished at all, due to the presence of its own dislocations, the gallium nitride substrate will be concave upward, that is, the curvature of the gallium nitride substrate is less than 0. Currently, when grinding the gallium nitride substrate, due to the relatively single grinding scheme, the gallium nitride substrate will have serious warpage after grinding, which will further cause the gallium nitride substrate to be prone to chipping, resulting in a low grinding and polishing yield.

[0004] Therefore, how to improve the grinding and polishing yield of gallium nitride is an urgent problem to be solved. Summary of the Invention

[0005] Based on this, it is necessary to provide a method for reducing the warpage of a gallium nitride substrate to effectively improve the grinding and polishing yield of gallium nitride.

[0006] An embodiment of the present application provides a method for reducing the warpage of a gallium nitride substrate, including the following steps:

[0007] Provide a gallium nitride substrate, where the gallium nitride substrate includes an opposite gallium surface and nitrogen surface;

[0008] Use a first grinding wheel to perform a first gallium surface grinding on the gallium surface of the gallium nitride substrate;

[0009] Use a second grinding wheel to perform a first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, where the maximum particle size of the abrasive in the second grinding wheel is less than the minimum particle size of the abrasive in the first grinding wheel;

[0010] Use a third grinding wheel to perform a second nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, where the maximum particle size of the abrasive in the third grinding wheel is less than the minimum particle size of the abrasive in the second grinding wheel;

[0011] Use a fourth grinding wheel to perform a second gallium surface grinding on the gallium surface of the gallium nitride substrate, where the maximum particle size of the abrasive in the fourth grinding wheel is less than the minimum particle size of the abrasive in the third grinding wheel;

[0012] Perform chemical mechanical polishing on the gallium nitride substrate obtained in the previous step to obtain a gallium nitride substrate with a preset thickness.

[0013] Optionally, during the first gallium - face grinding process, the difference between the thickness removal amount of the gallium nitride substrate and the difference between the initial thickness of the gallium nitride substrate minus the preset thickness is greater than or equal to 0 and less than or equal to 30 μm; the difference between the thickness of the gallium nitride substrate obtained after the first nitrogen - face grinding and the preset thickness is 60 μm to 150 μm.

[0014] Optionally, the abrasive particle sizes in the second grinding wheel are normally distributed; the abrasive particle sizes in the third grinding wheel are normally distributed; during the second nitrogen - face grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the second grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the second grinding wheel; during the second gallium - face grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the third grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the third grinding wheel.

[0015] Optionally, during the chemical mechanical polishing process, the thickness removed by polishing the gallium nitride substrate is less than or equal to 2 μm.

[0016] Optionally, after using a fourth grinding wheel to perform a second gallium - face grinding on the gallium - face of the gallium nitride substrate and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, it further includes:

[0017] Using a fifth grinding wheel to perform a third nitrogen - face grinding on the nitrogen - face of the gallium nitride substrate, and the maximum particle size of the abrasive in the fifth grinding wheel is less than the minimum particle size of the abrasive in the fourth grinding wheel;

[0018] Using a sixth grinding wheel to perform a third gallium - face grinding on the gallium - face of the gallium nitride substrate, and the maximum particle size of the abrasive in the sixth grinding wheel is less than the minimum particle size of the abrasive in the fifth grinding wheel.

[0019] Optionally, the abrasive particle sizes in the fourth grinding wheel are normally distributed, and the abrasive particle sizes in the fifth grinding wheel are normally distributed; during the third nitrogen - face grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the fourth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the fourth grinding wheel; during the third gallium - face grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the fifth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the fifth grinding wheel.

[0020] Optionally, after using a sixth grinding wheel to perform a third gallium - face grinding on the gallium - face of the gallium nitride substrate and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, it further includes:

[0021] Perform another nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate using another grinding wheel, where the maximum particle size of the grinding wheel in this step is smaller than the minimum particle size of the grinding wheel used for gallium surface grinding of the gallium nitride substrate in the previous step;

[0022] Perform another gallium surface grinding on the gallium surface of the gallium nitride substrate using another grinding wheel, where the minimum particle size of the grinding wheel in this step is smaller than the minimum particle size of the grinding wheel used for nitrogen surface grinding of the gallium nitride substrate in the previous step.

[0023] Optionally, after performing another gallium surface grinding on the gallium surface of the gallium nitride substrate using another grinding wheel and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, it further includes:

[0024] Repeat the above steps at least once.

[0025] Optionally, the abrasive particle sizes in each grinding wheel are all normally distributed; during each grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step.

[0026] Optionally, the average particle size of the abrasive in the grinding wheel used in the last grinding process is not greater than 15 μm.

[0027] During the grinding process of the gallium nitride substrate, a damaged layer will be formed on the gallium nitride surface without a damaged layer, thereby forming stress, causing the gallium nitride substrate to bend in the opposite direction. The larger the particle size of the grinding wheel used, the greater the damage caused. In the above method for reducing the warping of the gallium nitride substrate, first perform the first gallium surface grinding on the gallium surface of the gallium nitride substrate using the first grinding wheel, and then perform the first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate using the second grinding wheel. When grinding the gallium nitride substrate, the damage to the gallium surface will cause the gallium nitride substrate to bend towards the nitrogen surface, and the damage to the nitrogen surface will cause the gallium nitride substrate to bend towards the gallium surface; since the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel, the damage caused during the first gallium surface grinding is greater than the damage caused during the first nitrogen surface grinding. Therefore, the gallium nitride substrate bends more towards the nitrogen surface than towards the gallium surface. Due to the property of the gallium nitride itself to be concave towards the gallium surface, the warping caused by stress and the characteristics of the gallium nitride substrate itself can make the surface of the gallium nitride substrate tend to be flat.

[0028] Meanwhile, after the first N-face grinding, the N-face of the gallium nitride substrate is also subjected to a second N-face grinding using a third grinding wheel. The maximum particle size of the abrasive in the third grinding wheel is smaller than the minimum particle size of the abrasive in the second grinding wheel. This step is equivalent to reducing the damaged layer on the N-face of the existing larger damaged layer, which will reduce the degree of bending of the substrate towards the Ga-face. The step of performing a second Ga-face grinding on the Ga-face of the gallium nitride substrate using a fourth grinding wheel, where the maximum particle size of the abrasive in the fourth grinding wheel is smaller than the minimum particle size of the abrasive in the third grinding wheel. This step is equivalent to reducing the damaged layer on the Ga-face of the existing larger damaged layer, which will reduce the degree of bending of the substrate towards the N-face. Thus, the warpage of the gallium nitride substrate can be adjusted, making the surface of the gallium nitride substrate more flat, and further improving the grinding and polishing yield of the gallium nitride substrate. Since the first Ga-face grinding and the first N-face grinding both generate damaged layers, while the subsequent Ga-face grinding and N-face grinding are both to reduce the damage. After the first N-face grinding of the gallium nitride substrate using the second grinding wheel, immediately followed by the second N-face grinding of the gallium nitride substrate using the third grinding wheel, and then the second Ga-face grinding of the gallium nitride substrate, it is more conducive to the gradual flattening of the gallium nitride substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 is a flowchart of the method for reducing the warpage of a gallium nitride substrate provided by the present application;

[0031] Figure 2 is a schematic cross-sectional structure diagram of the structure obtained after step S10 in the method for reducing the warpage of a gallium nitride substrate provided by the present application;

[0032] Figure 3 is a schematic cross-sectional structure diagram of the structure obtained after step S20 in the method for reducing the warpage of a gallium nitride substrate provided by the present application;

[0033] Figure 4 is a schematic cross-sectional structure diagram of the structure obtained after step S30 in the method for reducing the warpage of a gallium nitride substrate provided by the present application.

[0034] Figure 5 is a schematic cross-sectional structure diagram of the structure obtained after step S40 in the method for reducing the warpage of a gallium nitride substrate provided by the present application.

[0035] Figure 6Schematic cross-sectional structure diagram of the structure obtained in step S50 of the method for reducing the warpage of a gallium nitride substrate provided in this application.

[0036] Figure 7 Schematic cross-sectional structure diagram of the structure obtained in step S60 of the method for reducing the warpage of a gallium nitride substrate provided in this application.

[0037] Description of reference numerals:

[0038] 10 - Gallium nitride substrate without grinding and polishing; 11 - Gallium nitride substrate after the first gallium surface grinding; 12 - Gallium nitride substrate after the first nitrogen surface grinding; 13 - Gallium nitride substrate after the second nitrogen surface grinding; 14 - Gallium nitride substrate after the second gallium surface grinding; 15 - Gallium nitride substrate after chemical mechanical polishing. Detailed implementation manners

[0039] To facilitate the understanding of the present disclosure, the present disclosure will be described more comprehensively below with reference to the relevant accompanying drawings. Embodiments of the present disclosure are shown in the accompanying drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present disclosure is thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this disclosure belongs. The terms used in the description of this disclosure herein are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure.

[0041] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of the present disclosure. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0042] It can be understood that the terms "first", "second", "third", "fourth", etc. used in this application can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, the first control device can be called the second control device, and similarly, the second control device can be called the first control device. Both the first control device and the second control device are control devices, but they are not the same control device.

[0043] It can be understood that for the "connection" in the following embodiments, if there is a transfer of electrical signals or data between the connected circuits, modules, units, etc., it should be understood as "electrical connection", "communication connection", etc.

[0044] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising", "including" or "having", etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the related listed items.

[0045] Gallium nitride semiconductor materials have unique excellent properties such as a large bandgap width, a high electron saturation drift velocity, a small dielectric constant, a strong radiation resistance, and high chemical stability. Therefore, gallium nitride has broad application prospects in the fields of optoelectronic devices and microelectronic devices.

[0046] Before gallium nitride is applied to optoelectronic devices, it needs to be ground and polished. However, when the gallium nitride substrate has not been ground and polished at all, due to the existence of its own dislocations, the gallium nitride substrate will be concave upward, that is, the curvature of the gallium nitride substrate is less than 0. Currently, when grinding the gallium nitride substrate, due to the relatively single grinding scheme, the gallium nitride substrate will have serious warping after grinding, which will further cause the gallium nitride substrate to be prone to chipping, resulting in a low grinding and polishing yield.

[0047] In view of the above deficiencies of the prior art, the purpose of this application is to provide a method for reducing the warping of a gallium nitride substrate, aiming to effectively improve the grinding and polishing yield of gallium nitride.

[0048] Please refer to Figure 1 , this application embodiment provides a method for reducing the warping of a gallium nitride substrate, including the following steps:

[0049] S10: Provide a gallium nitride substrate, where the gallium surface of the gallium nitride substrate is the gallium surface and the nitrogen surface of the gallium nitride substrate is the nitrogen surface;

[0050] S20: Use a first grinding wheel to perform a first gallium surface grinding on the gallium surface of the gallium nitride substrate;

[0051] S30: Use a second grinding wheel to perform a first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, and the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel;

[0052] S40: Use a third grinding wheel to perform a second nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, where the maximum particle size of the abrasive in the third grinding wheel is smaller than the minimum particle size of the abrasive in the second grinding wheel;

[0053] S50: Use a fourth grinding wheel to perform a second gallium surface grinding on the gallium surface of the gallium nitride substrate, where the maximum particle size of the abrasive in the fourth grinding wheel is smaller than the minimum particle size of the abrasive in the third grinding wheel;

[0054] S60: Perform chemical mechanical polishing on the gallium nitride substrate obtained in the previous step to obtain a gallium nitride substrate with a preset thickness.

[0055] During the grinding process of the gallium nitride substrate, a damaged layer will be formed on the gallium nitride surface without a damaged layer, and then stress will be formed, causing the gallium nitride substrate to bend towards the opposite surface. The larger the particle size of the grinding wheel used, the greater the damage caused. In the above method for reducing the warping of the gallium nitride substrate, first use a first grinding wheel to perform a first gallium surface grinding on the gallium surface of the gallium nitride substrate, and then use a second grinding wheel to perform a first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate. When grinding the gallium nitride substrate, the damage to the gallium surface will cause the gallium nitride substrate to bend towards the nitrogen surface, and the damage to the nitrogen surface will cause the gallium nitride substrate to bend towards the gallium surface; since the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel, the damage caused during the first gallium surface grinding is greater than the damage caused during the first nitrogen surface grinding. Therefore, the gallium nitride substrate bends towards the nitrogen surface more than towards the gallium surface. Due to the property of the gallium nitride itself to be concave towards the gallium surface, the warping caused by stress and the characteristics of the gallium nitride substrate itself can make the surface of the gallium nitride substrate tend to be flat.

[0056] Meanwhile, after the first nitrogen-side grinding, the gallium nitride substrate is further subjected to a second nitrogen-side grinding of the nitrogen side of the gallium nitride substrate using a third grinding wheel. Moreover, the maximum particle size of the abrasive in the third grinding wheel is smaller than the minimum particle size of the abrasive in the second grinding wheel. This step is equivalent to reducing the damaged layer on the nitrogen side of the existing larger damaged layer, which will reduce the degree of bending of the substrate towards the Ga side. In the step of performing a second gallium-side grinding on the gallium side of the gallium nitride substrate using a fourth grinding wheel, the maximum particle size of the abrasive in the fourth grinding wheel is smaller than the minimum particle size of the abrasive in the third grinding wheel. This step is equivalent to reducing the damaged layer on the gallium side of the existing larger damaged layer, which will reduce the degree of bending of the substrate towards the N side. Thus, the warpage of the gallium nitride substrate can be adjusted, making the surface of the gallium nitride substrate more flat, and further improving the grinding and polishing yield of the gallium nitride substrate. Since the first gallium-side grinding and the first nitrogen-side grinding both generate damaged layers, while the subsequent gallium-side grinding and nitrogen-side grinding are both to reduce the damage. After performing the first nitrogen-side grinding on the nitrogen side of the gallium nitride substrate using the second grinding wheel, immediately perform the second nitrogen-side grinding on the nitrogen side of the gallium nitride substrate using the third grinding wheel, and then perform the second gallium-side grinding on the gallium side of the gallium nitride substrate, which is more conducive to the gradual flattening of the gallium nitride substrate.

[0057] In step S10, please refer to Figure 1 step S10 in Figure 2 and provide a gallium nitride substrate, which includes an opposite gallium side and nitrogen side.

[0058] It should be noted that the gallium nitride substrate provided in this step is a gallium nitride substrate 10 that has not been ground and polished. When the gallium nitride growth is completed and no grinding and polishing has been performed, due to the presence of its own dislocations, the gallium side of the unground and unpolished gallium nitride substrate 10 will be concave, that is, the curvature of the unground and unpolished gallium nitride substrate 10 will be less than 0, that is, the unground and unpolished gallium nitride substrate 10 protrudes towards the nitrogen side. At this time, the curvature of the unground and unpolished gallium nitride substrate 10 is denoted as Bow1, and Bow1 is negative at this time (the concave curvature of the gallium side is negative, and the convex curvature of the gallium side is positive).

[0059] In some examples, the unground and unpolished gallium nitride substrate 10 may include but is not limited to a single-crystal gallium nitride substrate or a polycrystalline gallium nitride substrate epitaxially grown by an epitaxial process.

[0060] Specifically, the front side of the unground and unpolished gallium nitride substrate 10 may be the gallium side, and the back side of the unground and unpolished gallium nitride substrate 10 may be the nitrogen side.

[0061] In step S20, please refer to Figure 1 step S20 in Figure 3 and use a first grinding wheel (not shown) to perform a first gallium-side grinding on the gallium side of the gallium nitride substrate.

[0062] In this step, the first grinding wheel is used to perform the first gallium surface grinding on the gallium surface of the unground and unpolished gallium nitride substrate 10, that is, the first grinding wheel is used to perform the first gallium surface grinding on the gallium surface of the unground and unpolished gallium nitride substrate 10. After step S20, the gallium nitride substrate 11 after the first gallium surface grinding is obtained.

[0063] In some examples, the mesh number of the abrasive of the first grinding wheel can be less than or equal to 400 mesh, for example, 400 mesh, 350 mesh, 300 mesh, 250 mesh, 200 mesh, 150 mesh or 100 mesh, etc.

[0064] It should be noted that during the first gallium surface grinding process, the thickness of the removed gallium nitride substrate can be set according to actual needs, that is, during the first gallium surface grinding process, the thickness removal amount of the gallium nitride substrate can be set according to actual needs; generally, the closer the gallium nitride substrate is to the gallium surface, the better the crystal quality. The first gallium surface grinding only needs to make the gallium surface of the gallium nitride substrate flat, but the thickness of the removed gallium nitride substrate should not be too much, but the thickness removal amount of the gallium nitride substrate should be at least higher than the thickness non-uniformity (that is, the thickness removal amount of the gallium nitride substrate should be at least higher than the difference between the initial thickness of the gallium nitride substrate and the preset thickness).

[0065] In some examples, during the first gallium surface grinding process, the difference between the thickness removal amount of the gallium nitride substrate and the difference between the initial thickness of the gallium nitride substrate and the preset thickness is greater than or equal to, and less than or equal to 30 μm; that is, taking the thickness removal amount of the gallium nitride substrate as A and the difference between the initial thickness of the gallium nitride substrate and the preset thickness as B, 0 ≤ A - B ≤ 30 μm.

[0066] It should be noted that during the first gallium surface grinding of the gallium nitride substrate, damage will be introduced to the gallium surface of the gallium nitride substrate, so that the concavity of the gallium nitride substrate 11 after the first gallium surface grinding is reduced compared with the unground and unpolished gallium nitride substrate 10, as Figure 2 shown. At this time, the curvature of the gallium nitride substrate 11 after the first gallium surface grinding is denoted as Bow2, and Bow2 is also negative. Of course, in other examples, after this step, the shape of the gallium nitride substrate 11 after the first gallium surface grinding may also become convex upward, that is, convex toward the gallium surface of the gallium nitride substrate 11 after the first gallium surface grinding. The flatness of the gallium nitride substrate 11 after the first gallium surface grinding is better than that of the unground and unpolished gallium nitride substrate 10.

[0067] In step S30, please refer to Figure 1 the S30 step in Figure 4, the nitrogen surface of the gallium nitride substrate is subjected to the first nitrogen surface grinding using a second grinding wheel (not shown), and the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel.

[0068] In this step, the gallium nitride substrate 11 after the first gallium surface grinding obtained in step S20 is subjected to the first nitrogen surface grinding, and the gallium nitride substrate 12 after the first nitrogen surface grinding is obtained after step S30.

[0069] It should be noted that in step S30, the thickness of the substrate 11 after the first gallium surface grinding removed can be set according to actual needs; in step S30, the substrate 11 after the first gallium surface grinding can be ground off more. On the one hand, the crystal quality of the gallium nitride substrate on the nitrogen surface is not good, and on the other hand, it is to improve the grinding and polishing efficiency to achieve the purpose of thinning the gallium nitride substrate.

[0070] In some examples, the difference between the thickness of the gallium nitride substrate 12 obtained after the first nitrogen surface grinding and the preset thickness can be 60 μm to 150 μm. For example, it can be 60 μm, 80 μm, 100 μm, 120 μm or 150 μm, etc.

[0071] In step S30, since the maximum particle size of the abrasive in the second grinding wheel is smaller than the minimum particle size of the abrasive in the first grinding wheel, the damage caused to the nitrogen surface of the gallium nitride substrate in step S30 using the second grinding wheel is less than the damage caused to the gallium surface of the gallium nitride substrate in step S20; taking the gallium nitride substrate 11 after the first gallium surface grinding as an example, since the damage is generated on the nitrogen surface of the gallium nitride substrate at this time, the concave of the gallium nitride substrate 12 after the first nitrogen surface grinding will be slightly increased compared with the concave of the gallium nitride substrate 11 after the first gallium surface grinding; the curvature of the gallium nitride substrate 12 after the first nitrogen surface grinding is denoted as Bow3, and Bow3 is also a negative value. Under the combined action of the two grindings, the flatness of the gallium nitride substrate 12 after the first nitrogen surface grinding is better than that of the gallium nitride substrate 11 after the first gallium surface grinding.

[0072] In step S40, please refer to Figure 1 step S40 in Figure 5 , and the nitrogen surface of the gallium nitride substrate is subjected to the second nitrogen surface grinding using a third grinding wheel (not shown), and the maximum particle size of the abrasive in the third grinding wheel is smaller than the minimum particle size of the abrasive in the second grinding wheel.

[0073] In this step, the gallium nitride substrate 12 after the first nitrogen surface grinding obtained in step 320 is subjected to the second nitrogen surface grinding, and the gallium nitride substrate 13 after the second nitrogen surface grinding is obtained after step S40.

[0074] It should be noted that during the second nitrogen surface grinding process, the removal amount of the gallium nitride substrate can be set according to actual needs.

[0075] In one example, the abrasive particle size in the second grinding wheel follows a normal distribution; the abrasive particle size in the third grinding wheel follows a normal distribution; during the second nitrogen surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the second grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the second grinding wheel.

[0076] In step S40, since the maximum particle size of the abrasive in the third grinding wheel used is smaller than the minimum particle size of the abrasive in the second grinding wheel used in step S30, the damage formed during grinding in step S30 can be reduced, and the degree of bending towards the Ga surface can be decreased. Taking the concave of the gallium nitride substrate as an example, the concave of the gallium nitride substrate 13 after the second nitrogen surface grinding obtained after step S40 is smaller than the concave of the gallium nitride substrate 12 after the first nitrogen surface grinding. At this time, the curvature of the gallium nitride substrate 13 after the second nitrogen surface grinding is denoted as Bow4, and Bow4 is still negative. Under the combined action of the three grindings, the flatness of the gallium nitride substrate 13 after the second nitrogen surface grinding is better than that of the gallium nitride substrate 12 after the first nitrogen surface grinding.

[0077] In step S50, please refer to Figure 1 step S50 in Figure 6 and, a second Ga surface grinding is performed on the Ga surface of the gallium nitride substrate using a fourth grinding wheel (not shown), and the maximum particle size of the abrasive in the fourth grinding wheel is smaller than the minimum particle size of the abrasive in the third grinding wheel.

[0078] In this step, a second Ga surface grinding is performed on the gallium nitride substrate 13 after the second nitrogen surface grinding obtained in step 40, and the gallium nitride substrate 14 after the second Ga surface grinding is obtained after step S50.

[0079] It should be noted that during the second Ga surface grinding process, the removal amount of the gallium nitride substrate can be set according to actual needs.

[0080] In one example, during the second Ga surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the third grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the third grinding wheel.

[0081] In step S50, since the maximum particle size of the abrasive in the fourth grinding wheel used in step S50 is smaller than the minimum particle size of the abrasive in the third grinding wheel in step S40, and even smaller than the minimum particle size of the abrasive in the first grinding wheel used in step S20, it can reduce the damage formed when the first grinding wheel grinds the Ga surface in step S20. Taking the concave of the gallium nitride substrate as an example, the concave of the gallium nitride substrate 14 after the second Ga surface grinding obtained in step S50 is slightly larger than the concave of the gallium nitride substrate 13 after the second N surface grinding. At this time, the curvature of the gallium nitride substrate 14 after the second Ga surface grinding is denoted as Bow5, and Bow5 is still negative. Under the combined action of the four grindings, the flatness of the gallium nitride substrate 14 after the second Ga surface grinding is better than that of the gallium nitride substrate 13 after the second N surface grinding.

[0082] In step S60, please refer to Figure 1 step S60 in Figure 7 and perform chemical mechanical polishing on the gallium nitride substrate obtained in the previous step to obtain a gallium nitride substrate with a preset thickness.

[0083] In an optional example, if chemical mechanical polishing is performed immediately after step S50, then in step S60, chemical mechanical polishing is performed on the gallium nitride substrate obtained in step S50. After step S60, a chemically mechanically polished gallium nitride substrate 15 is obtained.

[0084] Specifically, in step S60, single-sided chemical mechanical polishing can be performed only on the Ga surface of the gallium nitride substrate, or single-sided chemical mechanical polishing can be performed only on the N surface of the gallium nitride substrate, or double-sided chemical mechanical polishing can be performed on both the Ga surface and the N surface of the gallium nitride substrate.

[0085] In an example, the thickness of the gallium nitride substrate removed in step S60 can be set according to actual needs; in this embodiment, in step S60, the thickness of the gallium nitride substrate polished and removed can be less than or equal to 2 μm; specifically, in step S60, the thickness of the gallium nitride substrate polished and removed can be 2 μm, 1.5 μm, 1 μm, etc.

[0086] In an optional example, after step S50 and before step S60, the following steps can also be included:

[0087] S51: Use a fifth grinding wheel (not shown) to perform a third N surface grinding on the N surface of the gallium nitride substrate, and the maximum particle size of the abrasive in the fifth grinding wheel is smaller than the minimum particle size of the abrasive in the fourth grinding wheel;

[0088] S52: Use a sixth grinding wheel (not shown) to perform a third Ga surface grinding on the Ga surface of the gallium nitride substrate, and the maximum particle size of the abrasive in the sixth grinding wheel is smaller than the minimum particle size of the abrasive in the fifth grinding wheel.

[0089] In one example, in step S51, a fifth grinding wheel is used to perform a third nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate 14 after the second gallium surface grinding obtained in step S50. In step S52, a sixth grinding wheel is used to perform a third gallium surface grinding on the gallium surface of the gallium nitride substrate after the third nitrogen surface grinding obtained in step S51.

[0090] In one example, the abrasive particle sizes in the fourth grinding wheel are normally distributed, and the abrasive particle sizes in the fifth grinding wheel are normally distributed; during the third nitrogen surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the fourth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the fourth grinding wheel; during the third gallium surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the fifth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the fifth grinding wheel.

[0091] In an alternative example, after using the sixth grinding wheel to perform a third gallium surface grinding on the gallium surface of the gallium nitride substrate and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, that is, between step S52 and step S60, it further includes:

[0092] S53: Use another grinding wheel to perform another nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate. In this step, the maximum particle size of the grinding wheel is smaller than the minimum particle size of the grinding wheel used to perform gallium surface grinding on the gallium surface of the gallium nitride substrate in the previous step;

[0093] S54: Use another grinding wheel to perform another gallium surface grinding on the gallium surface of the gallium nitride substrate. In this step, the maximum particle size of the grinding wheel is smaller than the minimum particle size of the grinding wheel used to perform nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate in the previous step.

[0094] In another alternative example, after using another grinding wheel to perform another gallium surface grinding on the gallium surface of the gallium nitride substrate and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, it further includes:

[0095] Repeat the above steps at least once.

[0096] It should be noted that the specific number of times of repeating the above steps can be set according to actual needs and is not specifically limited here.

[0097] In one example, the abrasive particle sizes in each grinding wheel are all normally distributed; during each grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step.

[0098] In one example, the average particle size of the abrasive in the grinding wheel used in the last grinding process can be set according to actual needs. In this embodiment, the average particle size of the abrasive in the grinding wheel used in the last grinding process is not greater than 15 μm. Specifically, the average particle size of the abrasive in the grinding wheel used in the last grinding process can be 15 μm, 10 μm, 5 μm, 1 μm, etc.

[0099] It should be noted that when steps S50 and S60 include steps S51, S52 and other subsequent steps, step S60 is to perform chemical mechanical polishing on the gallium nitride substrate obtained after the last grinding.

[0100] It should be noted that during the grinding process of the gallium nitride substrate, after each grinding of the gallium surface or the nitrogen surface of the gallium nitride substrate, the flatness of the gallium nitride substrate will be improved better.

[0101] In the description of this specification, the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0102] The above embodiments only represent several implementation manners of the present disclosure. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent application. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several modifications and improvements can still be made, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A method for reducing the warpage of a gallium nitride substrate, characterized in that, It includes the following steps: Provide a gallium nitride substrate, the gallium nitride substrate including an opposite gallium surface and nitrogen surface; Use a first grinding wheel to perform a first gallium surface grinding on the gallium surface of the gallium nitride substrate; Use a second grinding wheel to perform a first nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, the maximum particle size of the abrasive in the second grinding wheel being smaller than the minimum particle size of the abrasive in the first grinding wheel; Use a third grinding wheel to perform a second nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, the maximum particle size of the abrasive in the third grinding wheel being smaller than the minimum particle size of the abrasive in the second grinding wheel; Use a fourth grinding wheel to perform a second gallium surface grinding on the gallium surface of the gallium nitride substrate, the maximum particle size of the abrasive in the fourth grinding wheel being smaller than the minimum particle size of the abrasive in the third grinding wheel; Perform chemical mechanical polishing on the gallium nitride substrate obtained in the previous step to obtain a gallium nitride substrate with a preset thickness.

2. The method for reducing the warpage of a gallium nitride substrate according to claim 1, characterized in that, During the first gallium surface grinding process, the thickness removal amount of the gallium nitride substrate is greater than or equal to 0 and less than or equal to 30 μm from the difference between the initial thickness of the gallium nitride substrate and the preset thickness; the difference between the thickness of the gallium nitride substrate obtained after the first nitrogen surface grinding and the preset thickness is 60 μm to 150 μm.

3. The method for reducing the warpage of a gallium nitride substrate according to claim 1, characterized in that, The abrasive particle size in the second grinding wheel is normally distributed; the abrasive particle size in the third grinding wheel is normally distributed; during the second nitrogen surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the second grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the second grinding wheel; During the second gallium surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the third grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the third grinding wheel.

4. The method for reducing the warpage of a gallium nitride substrate according to claim 1, characterized in that, During the chemical mechanical polishing process, the thickness polished and removed from the gallium nitride substrate is less than or equal to 2 μm.

5. The method for reducing the warpage of a gallium nitride substrate according to any one of claims 1 to 4, characterized in that, After using a fourth grinding wheel to perform a second gallium surface grinding on the gallium surface of the gallium nitride substrate and before performing chemical mechanical polishing on the gallium nitride substrate obtained in the previous step, it further includes: Use a fifth grinding wheel to perform a third nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, the maximum particle size of the abrasive in the fifth grinding wheel being smaller than the minimum particle size of the abrasive in the fourth grinding wheel; Use a sixth grinding wheel to perform a third gallium surface grinding on the gallium surface of the gallium nitride substrate, the maximum particle size of the abrasive in the sixth grinding wheel being smaller than the minimum particle size of the abrasive in the fifth grinding wheel.

6. The method for reducing the warpage of a gallium nitride substrate according to claim 5, characterized in that, The abrasive particle size in the fourth grinding wheel is normally distributed, the abrasive particle size in the fifth grinding wheel is normally distributed; during the third nitrogen surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the fourth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the fourth grinding wheel; During the third gallium surface grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle size in the fifth grinding wheel and less than 5 times the median value of the normal distribution of the abrasive particle size in the fifth grinding wheel.

7. The method for reducing the warpage of a gallium nitride substrate according to claim 6, characterized in that, After the third gallium surface grinding of the gallium nitride substrate using the sixth grinding wheel and before the chemical mechanical polishing of the gallium nitride substrate obtained in the previous step, the following steps are further included: Using another grinding wheel to perform another nitrogen surface grinding on the nitrogen surface of the gallium nitride substrate, where the maximum particle size of the grinding wheel in this step is smaller than the minimum particle size of the grinding wheel for gallium surface grinding of the gallium nitride substrate in the previous step; Using yet another grinding wheel to perform another gallium surface grinding on the gallium surface of the gallium nitride substrate, where the maximum particle size of the grinding wheel in this step is smaller than the minimum particle size of the grinding wheel for nitrogen surface grinding of the gallium nitride substrate in the previous step.

8. The method for reducing the warpage of a gallium nitride substrate according to claim 7, characterized in that, After using yet another grinding wheel to perform another gallium surface grinding on the gallium surface of the gallium nitride substrate and before the chemical mechanical polishing of the gallium nitride substrate obtained in the previous step, the following steps are further included: Repeating the above steps at least once.

9. The method for reducing the warpage of a gallium nitride substrate according to claim 8, characterized in that, The abrasive particle sizes in each grinding wheel are all normally distributed; during each grinding process, the removal amount of the gallium nitride substrate is greater than the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step and less than 5 times the median value of the normal distribution of the abrasive particle sizes in the grinding wheel in the previous step.

10. The method for reducing the warpage of a gallium nitride substrate according to claim 8, characterized in that, The average particle size of the abrasive in the grinding wheel used in the last grinding process is not greater than 15 μm.

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