A method for processing silicon carbide wafers and silicon carbide wafers

Abstract

This application discloses a method for processing silicon carbide wafers and the silicon carbide wafers themselves. The processing method includes surface pretreatment of a silicon carbide ingot to remove a graphite layer from a first surface; grinding a second surface to achieve a flatness ≤0.01 mm; and grinding the first surface to achieve a flatness ≤0.01 mm. By performing these steps sequentially, this application reduces silicon carbide loss while improving processing quality and surface accuracy, obtaining silicon carbide wafers with a surface roughness of 0.01 μm to 0.2 μm without the need for subsequent grinding and polishing processes. This processing method can adapt to irregular silicon carbide ingot geometry, balancing material utilization and processing safety.

Description

Technical Field

[0001] This application relates to the field of irregular crystal processing technology, and more specifically, to a method for processing silicon carbide wafers and silicon carbide wafers. Background Technology

[0002] Silicon carbide wafers, as a wide bandgap semiconductor material, are widely used in power devices, radio frequency devices, and high-temperature, high-voltage, and high-frequency electronic devices due to their excellent properties such as high thermal conductivity, high breakdown electric field, and high electron saturation drift velocity.

[0003] In existing technologies for preparing silicon carbide wafers, silicon carbide ingots are typically used as raw materials. The outer diameter of the ingot is first ground into a standard cylinder, and then sliced ​​to obtain silicon carbide wafers. However, due to inherent defects in the silicon carbide ingot preparation method, silicon carbide ingots often exhibit irregular shapes. For these irregular silicon carbide ingots, processing them into wafers using the aforementioned method results in the removal of a large amount of usable material, leading to material waste and reduced wafer yield. Furthermore, excessive grinding may introduce new microcracks, affecting the quality of subsequent wafers, resulting in low finished product yield and low processing efficiency.

[0004] In view of this, this application provides a method for processing silicon carbide wafers and a silicon carbide wafer. Summary of the Invention

[0005] In view of the above problems, this application provides a method for processing silicon carbide wafers and a silicon carbide wafer. The processing method of this application can be applied to the processing of irregular silicon carbide ingots, taking into account both material utilization and processing safety.

[0006] In a first aspect, this application provides a method for processing silicon carbide wafers, comprising the following steps:

[0007] Step 1, Preparation of silicon carbide ingots:

[0008] A graphite crucible with a slightly concave inner surface is used as a growth container. Silicon carbide raw material is placed in the graphite crucible, and silicon carbide ingots are prepared by physical vapor transport method.

[0009] The silicon carbide ingot has a first surface and a second surface opposite to the first surface; the first surface is the contact surface between the silicon carbide ingot and the graphite crucible during the physical vapor transport growth process, and the second surface is the growth surface of silicon carbide.

[0010] Step 2, Remove the graphite layer:

[0011] The silicon carbide ingot is subjected to surface pretreatment to remove the graphite layer on the first surface of the silicon carbide ingot.

[0012] Step 3, process the growth surface of silicon carbide:

[0013] The second surface of the silicon carbide ingot is used as the surface to be processed and clamped and fixed. The second surface is ground to make the flatness of the second surface ≤0.01mm.

[0014] Step 4: Machining the contact surface between the silicon carbide and the graphite crucible:

[0015] The silicon carbide ingot is flipped over, and the first surface of the silicon carbide ingot is used as the surface to be processed for clamping and fixing. The first surface is ground to make the flatness of the first surface ≤0.01mm.

[0016] It should be noted that during the preparation of silicon carbide ingots by physical vapor transport method, some carbon elements in the graphite crucible may react with the silicon carbide raw material at the bottom of the graphite crucible, resulting in the formation of a graphite layer on the first surface of the final silicon carbide ingot (i.e. the contact surface with the graphite crucible). Therefore, the prepared silicon carbide ingot cannot be directly processed into silicon carbide wafers and the graphite layer on its surface needs to be removed first.

[0017] Currently, silicon carbide wafers are primarily processed using silicon carbide ingots grown via physical vapor transport (PVT). However, due to factors such as temperature gradients, impurity distribution, and stress during silicon carbide single crystal growth, the resulting ingots often exhibit irregular shapes. These defects include uneven surfaces, tilted end faces, inconsistent diameters, cracks, or graphite layer inclusions, leading to irregular distribution of graphite and silicon carbide within the ingot. Existing technologies typically process silicon carbide ingots by extending the processing position 1-2 mm above and below the center of the cylindrical surface. This makes it difficult to precisely remove excess graphite and roughened growth surfaces, resulting in significant material loss, waste, and reduced wafer yield. Direct wire cutting of irregular ingots can easily lead to wire breakage, edge chipping, or even complete ingot scrap due to uneven stress, resulting in low yield and low processing efficiency. Furthermore, the resulting product has a deep sub-damage layer and poor surface finish, requiring multiple grinding and polishing processes, thus increasing processing costs and cycle time.

[0018] In view of this, this application takes the silicon carbide ingot obtained by physical vapor transport (PVT) growth as its starting point, and analyzes the characteristics of the silicon carbide ingot structure itself to provide a processing method that can adapt to its irregular morphology, so as to reduce the effective material removal rate while taking into account the processing quality, and improve the yield and processing efficiency of finished products.

[0019] This application selects a graphite crucible with a micro-concave inner surface as the growth vessel used in the preparation of silicon carbide single crystals by physical vapor transport method. This sets the growth interface of the silicon carbide ingot as a micro-concave surface (i.e., a downward-concave oblique / curved surface). This micro-concave growth interface is not only more conducive to obtaining high-quality silicon carbide crystals, but also makes the structure of the first surface of the prepared silicon carbide single crystal a micro-convex surface that is complementary to the micro-concave surface. Furthermore, by adjusting the structure of the micro-concave inner surface, the flatness of the first surface of the silicon carbide single crystal can be improved, which is more conducive to the removal of graphite layers that may exist on the second surface. Furthermore, this application addresses the structural characteristics of silicon carbide ingots obtained using the physical vapor transport method. Step 2 involves first removing the graphite layer from the silicon carbide ingot to make the silicon carbide ingot visible on its first surface. Then, using the first surface with the graphite layer removed as a positioning surface for clamping and fixing, the second surface is ground to remove the growth roughness, achieving a flatness ≤0.01mm. Next, using the second surface with the growth roughness removed as a positioning surface for clamping and fixing, the silicon carbide with micro-convex surfaces on the first surface is ground. By performing these steps sequentially, silicon carbide loss is reduced while improving processing quality and surface accuracy. Silicon carbide wafers with a surface roughness of 0.01μm~0.2μm can be obtained without subsequent grinding and polishing processes. This processing method can adapt to irregular silicon carbide ingot geometry, balancing material utilization and processing safety.

[0020] In some embodiments, in steps 3 and 4, a fixture is used for clamping and fixing, and molten liquid paraffin is used as a binder to form a wax film between the silicon carbide ingot and the fixture, so as to clamp and fix the silicon carbide ingot in the fixture.

[0021] In some embodiments, the tooling is a hollow tooling; the hollow tooling includes a tooling body, and the tooling body has through holes to form a hollow structure. Based on the above scheme, when the hollow tooling is used to clamp silicon carbide ingots, due to the hollow design, when the silicon carbide ingot is placed on the tooling body, the position of the first surface will be lowered as a whole due to gravity, thereby causing the contact point to also be lowered, thereby reducing the intermediate curvature between the first surface and the plane, and forming a closed flow channel between the silicon carbide surface and the fixture contact surface.

[0022] In some embodiments, the silicon carbide ingot is further secured to the tooling body by fasteners. Based on the above scheme, it is beneficial to improve the stability of the silicon carbide ingot during processing, thereby further improving processing efficiency and quality.

[0023] In some embodiments, the fixing component includes a fixing block and a fixing connector. Each fixing block has a first mounting hole, and the tooling body has a second mounting hole corresponding to the first mounting hole. By having several fixing connectors pass through the corresponding first and second mounting holes in sequence, the silicon carbide ingot is fixed and positioned on the tooling body to improve the stability of the silicon carbide ingot during the processing, thereby further improving processing efficiency and processing quality.

[0024] In some embodiments, the fasteners include, but are not limited to, bolts or screws.

[0025] In some embodiments, in step 3, the second surface of the silicon carbide ingot is placed in the tooling as the surface to be processed, so that the first surface of the silicon carbide ingot contacts the surface of the tooling and forms a flow channel; molten liquid paraffin enters the flow channel, and after solidification, a wax film is formed between the first surface of the silicon carbide ingot and the tooling to clamp and fix the silicon carbide ingot.

[0026] In some embodiments, in step 4, the first surface of the silicon carbide ingot is placed in the tooling as the surface to be processed, so that the second surface of the silicon carbide ingot comes into contact with the surface of the tooling; molten liquid paraffin forms a wax film between the second surface of the silicon carbide ingot and the tooling to clamp and fix the silicon carbide ingot.

[0027] In some embodiments, in step 1, after pretreatment, the planar curvature of the first surface of the silicon carbide ingot is ≤1mm.

[0028] In some embodiments, in step 1, a dry sandblasting machine is used to grind the first surface of the silicon carbide ingot to remove the graphite layer on the first surface.

[0029] In some embodiments, step 1, the surface pretreatment further includes edge treatment, and the edge treatment includes the following steps: grinding the edge of the silicon carbide ingot to remove the flash from the edge of the silicon carbide ingot.

[0030] In some embodiments, a belt abrasive is used to grind the edges of the silicon carbide ingot to remove burrs from the edges of the silicon carbide ingot.

[0031] In some embodiments, in step 2, the second surface is ground using a horizontal flat grinder.

[0032] In some embodiments, in step 3, a horizontal flat grinder is used to grind the first surface.

[0033] The second method is to provide a silicon carbide wafer obtained according to any of the above processing methods.

[0034] The beneficial effects of the technical solutions provided in some embodiments of this application include at least the following:

[0035] This application involves sequentially removing the graphite layer from a silicon carbide ingot to visualize the silicon carbide ingot on its first surface. Then, using the first surface with the graphite layer removed as a positioning surface for clamping and fixing, the second surface is ground to remove the growth roughness, achieving a flatness of ≤0.01mm. Next, using the second surface with the growth roughness removed as a positioning surface for clamping and fixing, the silicon carbide with micro-convex surfaces on the first surface is ground. By performing these steps sequentially, silicon carbide loss is reduced while improving processing quality and surface accuracy. Silicon carbide wafers with a surface roughness of 0.01μm~0.2μm can be obtained without subsequent grinding and polishing processes. This processing method can adapt to irregular silicon carbide ingot geometry, balancing material utilization and processing safety. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This refers to the planar tooling used in existing technologies.

[0038] Figure 2 The hollow tooling used in this application.

[0039] Figure 3 This is a schematic diagram of the structure after a silicon carbide ingot is clamped using a hollow tooling.

[0040] Figure 4 This is a schematic diagram of the product structure obtained after removing the graphite layer in this application.

[0041] Figure 5 This is a schematic diagram of the product structure obtained after removing the flash in this application.

[0042] Figure 6 This is a schematic diagram of the structure after the second surface of this application has been ground.

[0043] Figure 7 This is a schematic diagram of the structure after the first surface of this application has been ground.

[0044] Figures 1 to 3 Explanation of reference numerals in the attached figures:

[0045] 100-Tooling body; 101-Second mounting hole; 102-Through hole; 200-Fixing block; 300-Fixing connector; 400-Silicon carbide ingot. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0047] In the description of this application, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings, and are used only for ease of description and simplification of operation. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. In addition, the terms "first" and "second" are used only for descriptive distinction and have no special meaning.

[0048] The technical solutions in this application will now be described clearly and in detail with reference to the accompanying drawings.

[0049] This application explores and analyzes the reasons for material waste, low yield, and low processing efficiency in the existing process of processing irregular silicon carbide ingots into silicon carbide wafers. The findings suggest that this is related to the material and morphological characteristics of the silicon carbide ingot itself. Currently, silicon carbide wafers are mainly processed using silicon carbide ingots grown via physical vapor transport (PVT). However, due to factors such as temperature gradients, impurity distribution, and stress during silicon carbide single crystal growth, the resulting silicon carbide ingots often exhibit irregular shapes, such as uneven surfaces, tilted end faces, inconsistent diameters, cracks, or graphite layers. This results in irregular distribution of the graphite layer and silicon carbide within the ingot. Furthermore, in existing processes, the processing position typically extends 1mm to 2mm above and below the center of the cylindrical surface, making it impossible to accurately remove excess graphite and roughen the growth surface. This leads to significant material loss, material waste, and reduced wafer yield. Direct wire cutting of irregular crystal ingots can easily lead to wire breakage, edge chipping, or even scrapping of the entire ingot due to uneven stress, resulting in low yield and low processing efficiency. Furthermore, the processed product has a deep sub-damage layer and poor surface finish, requiring multiple grinding and polishing processes, which increases processing costs and time.

[0050] In view of this, this application takes the silicon carbide ingot obtained by physical vapor transport (PVT) growth as its starting point, and analyzes the characteristics of the silicon carbide ingot structure itself to provide a processing method that can adapt to its irregular morphology, so as to reduce the effective material removal rate while taking into account the processing quality, and improve the yield and processing efficiency of finished products.

[0051] Hollow tooling

[0052] This application takes into account that the tooling commonly used in the prior art is as follows: Figure 1 The planar tooling shown, if used as follows Figure 1 The tooling shown clamps the silicon carbide ingot 400 of this application, resulting in the contact point between the silicon carbide ingot 400 and the tooling plane being at the center of the surface of the silicon carbide ingot 400. At this time, there is a curvature height of 0.5 between the surface of the silicon carbide ingot 400 and the tooling plane.

[0053] To further reduce the surface area of ​​the silicon carbide ingot 400 relative to the tooling plane, this application employs the following method: Figure 2 The hollow fixture shown is used to clamp the silicon carbide ingot 400. (See reference...) Figure 2 As can be seen, the hollow tooling used in this application includes a tooling body 100, on which a through hole 102 is provided to form a hollow structure. Based on the above scheme, when the hollow tooling is used to clamp the silicon carbide ingot 400, due to the hollow design, after the silicon carbide ingot 400 is placed on the tooling body 100, the position of the first surface will be lowered as a whole due to gravity, thereby causing the contact point to also be lowered, thus reducing the intermediate curvature between the first surface and the plane, and forming a closed flow channel between the silicon carbide surface and the fixture contact surface.

[0054] In some embodiments, the silicon carbide ingot 400 is further secured to the tooling body 100 by fasteners. Based on the above solution, it is beneficial to improve the stability of the silicon carbide ingot 400 during processing, thereby further improving processing efficiency and quality.

[0055] In some embodiments, please refer to Figure 3 The fixing component includes several fixing blocks 200 and several fixing connectors 300. Each fixing block 200 has a first mounting hole, and the tooling body 100 has a second mounting hole 101 corresponding to the first mounting hole. By having several fixing connectors 300 pass through the corresponding first mounting hole and second mounting hole 101 in sequence, the silicon carbide ingot 400 is fixed and positioned on the tooling body 100, thereby improving the stability of the silicon carbide ingot 400 during the processing and further improving the processing efficiency and processing quality.

[0056] In some embodiments, the fixing connector 300 includes, but is not limited to, bolts or screws.

[0057] Processing methods for silicon carbide wafers

[0058] In this application, the method for processing silicon carbide wafers includes the following steps:

[0059] Step 1, Prepare silicon carbide ingot 400:

[0060] Using a graphite crucible with a slightly concave inner surface as a growth container, silicon carbide raw material is placed in the graphite crucible, and silicon carbide ingot 400 is prepared by physical vapor transport method.

[0061] The silicon carbide ingot 400 has a first surface and a second surface opposite to the first surface; the first surface is the contact surface between the silicon carbide ingot 400 and the graphite crucible during the physical vapor transport growth process, and the second surface is the growth surface of silicon carbide.

[0062] It should be noted that this application selects a graphite crucible with a micro-concave inner surface as the growth container when preparing silicon carbide single crystals by physical vapor transport method. This sets the growth interface of the silicon carbide ingot 400 as a micro-concave surface (i.e., a downwardly concave oblique / curved surface). This micro-concave growth interface is not only more conducive to obtaining high-quality silicon carbide crystals, but also makes the structure of the first surface of the prepared silicon carbide single crystal a micro-convex surface that is complementary to the micro-concave surface. Furthermore, by adjusting the structure of the micro-concave inner surface, the flatness of the first surface of the silicon carbide single crystal can be improved, which is more conducive to removing the graphite layer that may exist on the second surface.

[0063] In some embodiments, the micro-recessed depth of the graphite crucible is 200 μm to 500 μm. Based on the above scheme, it is beneficial to improve the flatness of the first surface of the silicon carbide ingot 400.

[0064] Step 2, Remove the graphite layer:

[0065] The silicon carbide ingot 400 is subjected to surface pretreatment to remove the graphite layer on the first surface of the silicon carbide ingot 400.

[0066] It should be noted that, considering that in the silicon carbide ingot 400 obtained by physical vapor transport method, the graphite layer is mainly distributed on the contact surface between the silicon carbide ingot 400 and the graphite crucible during the physical vapor transport growth process, that is, on the first surface of the silicon carbide ingot 400, this application first pre-treats the first surface of the silicon carbide ingot 400 to accurately remove the graphite layer on the first surface of the silicon carbide ingot 400. This can avoid the waste of a large amount of effective material due to grinding, thereby improving the wafer yield.

[0067] In some embodiments, this application does not limit the specific preprocessing method, as long as the graphite layer on the first surface of the silicon carbide ingot 400 can be removed so that the planar curvature of the first surface of the silicon carbide ingot 400 is ≤1mm.

[0068] In some preferred embodiments, a sandblasting machine is used to grind the first surface of the silicon carbide ingot 400 to remove the graphite layer on the first surface.

[0069] For example, in some embodiments, when this application uses a dry sandblasting machine to grind the first surface, the process parameters for the dry sandblasting machine are as follows: the abrasive is green silicon carbide abrasive grains, the mesh size of the green silicon carbide abrasive grains is 30# to 80#, the particle size is 0.2mm to 0.8mm, and the sandblasting pressure is 5kgf to 10kgf. Based on the above scheme, since the hardness of green silicon carbide is slightly lower than that of silicon carbide ingot 400, but higher than that of graphite, this application can achieve efficient removal of the graphite layer without damaging the silicon carbide ingot 400 when using green silicon carbide abrasive grains as the abrasive. Moreover, when this application uses green silicon carbide abrasive grains with the above-mentioned size limit and performs sandblasting under the above-mentioned sandblasting pressure, it is beneficial to improve the uniformity of the impact point of the abrasive on the graphite layer and the consistency of the shear force, further improving the efficient removal of the graphite layer. Understandably, since the macroscopic morphology of the graphite layer is a gray-black / black matte film, while the macroscopic morphology of the surface of the silicon carbide ingot 400 is a silver-gray matte metallic film, it can be directly observed with the naked eye that when the dry sandblasting machine grinds until there is no obvious gray-black / black matte film on the first surface, it is considered that the graphite layer has been completely removed.

[0070] This application takes into account that there may be flash or other defects at the edges of the silicon carbide ingot 400 obtained by physical vapor transport method. Therefore, in some embodiments of this application, the surface pretreatment also includes edge treatment after removing the graphite layer, so as to remove the flash from the edges of the silicon carbide ingot 400 by grinding the edges of the silicon carbide ingot 400, thereby improving the processing quality of the product.

[0071] It should be noted that this application does not limit the specific grinding method for edge treatment, as long as it can achieve the effect of this application. For example, in some embodiments, a belt abrasive can be used to grind the edges of the silicon carbide ingot 400 to remove burrs from the edges of the silicon carbide ingot 400. Based on the above solution, since the abrasive grains of the abrasive belt are flexibly arranged, the contact pressure with the silicon carbide ingot 400 during the grinding process is small, resulting in uniform grinding force. This effectively avoids grinding cracks, edge chipping, or lattice distortion in the silicon carbide ingot 400, thereby improving the processing quality of the product.

[0072] For example, in some embodiments, when the edge of the silicon carbide ingot 400 is ground using a belt abrasive machine, the abrasive grit size of the belt used in the belt abrasive machine is 80# to 320#, and the linear speed of the belt is 20m / s to 35m / s. Based on the above scheme, the flash on the edge of the silicon carbide ingot 400 can be removed more effectively, while improving the processing quality.

[0073] Step 3, process the second surface (the growth surface of silicon carbide):

[0074] The second surface of the silicon carbide ingot 400 is used as the surface to be processed and clamped and fixed. The second surface is ground to make the flatness of the second surface ≤0.01mm.

[0075] It is worth mentioning that, in the preparation process of the physical vapor transport method, the silicon carbide in contact with the graphite crucible is constrained by the structure of the inner surface of the graphite crucible, and will form a surface structure that matches the inner surface structure of the graphite crucible. However, the growth surface of the silicon carbide ingot 400 (i.e. the other side opposite to the contact surface of the graphite crucible) is not constrained by the graphite crucible, and its surface structure is more irregular (may have rough surface structures such as steps, hills, ravines, and polymorphic mixtures).

[0076] Therefore, this application first removes the graphite layer on the first surface through step 2, making the first surface of the silicon carbide ingot 400 a slightly convex surface. Since the slightly convex surface structure of the first surface of the silicon carbide ingot 400 is more regular than the irregular structure of the second surface, this application, based on the characteristic that the silicon carbide on the first surface of the silicon carbide ingot 400 exhibits a slightly convex surface after step 2, first uses the first surface as a positioning surface to clamp and fix the silicon carbide ingot 400 within the hollow tooling described above, thereby improving the stability during processing and providing processing quality. Furthermore, in order to verify that the first surface of the silicon carbide ingot 400 exhibits a slightly convex shape after step 1, this application takes a silicon carbide ingot 400 with multiple graphite crucibles having the above-mentioned slightly concave shape as an example, and uses a profilometer to test and analyze the first surface of the silicon carbide ingot 400 after step 1. The analysis results show that after step 1 of this application, the first surface of the silicon carbide ingot 400 all exhibits a uniformly convex, slightly convex slope, and the height difference between the product edge and the product center is about 0.5 mm.

[0077] Understandably, compared to directly grinding the first surface, the micro-protrusions on the first surface of the silicon carbide ingot 400 are uniformly distributed after step 2 of this application. This ensures a uniform distribution of contact points between the first surface and the hollow tooling surface, avoiding single-point contact or localized suspension caused by unevenness of the positioning surface. This facilitates effective control of the flatness and parallelism of the second surface during the processing of the silicon carbide ingot 400, thereby improving the processing efficiency of grinding the second surface to a flatness ≤0.01mm. Moreover, using the first surface as the positioning surface first results in a higher degree of contact between the positioning surface and the tooling plane, which helps to ensure more uniform stress on the silicon carbide ingot 400 during grinding. This avoids elastic or plastic deformation caused by excessive local stress on the silicon carbide ingot 400, which could lead to grinding cracks or edge chipping defects, further improving processing quality and product yield.

[0078] It should also be noted that this application does not limit the specific processing technology or the specific processing equipment used when grinding the second surface, as long as the effect of this application can be achieved.

[0079] To improve machining accuracy and surface quality, in some embodiments of this application, a horizontal surface grinder is preferably used to grind the second surface. The term "horizontal surface grinder" in this application, also known as a horizontal surface grinder, is a device that uses a horizontally arranged grinding wheel spindle to perform surface grinding on a workpiece. The grinding wheel in a horizontal surface grinder is typically a peripheral grinder. During the grinding process, the contact line between the cutting edge and the workpiece is short, the grinding force is concentrated and stable, and the machining accuracy is higher. It can achieve a flatness of the second surface ≤0.01mm without further processing. This improves machining efficiency and quality while reducing machining steps and shortening the machining cycle.

[0080] In some embodiments, step 3 uses molten liquid paraffin as a binder to form a wax film between the silicon carbide ingot 400 and the hollow tooling, so as to clamp and fix the silicon carbide ingot 400 in the hollow tooling.

[0081] Specifically, in some embodiments, the second surface of the silicon carbide ingot 400 is used as the surface to be processed and placed on one side of the tooling body 100 where the second mounting hole 101 is provided. Multiple fixing blocks 200 and multiple fixing connectors 300 are used to limit and fix the silicon carbide ingot 400 around its perimeter. That is, the first surface of the silicon carbide ingot 400 is used as the positioning surface so that the first surface of the silicon carbide ingot 400 contacts the surface of the tooling. The micro-convex surface on the first surface can form a nearly closed flow channel with the surface of the hollow tooling, which is conducive to the formation of a uniform wax film between the first surface of the silicon carbide ingot 400 and the surface of the hollow tooling after the molten paraffin liquid enters, so as to stably fix the silicon carbide ingot 400 in the hollow tooling and realize the clamping and fixing of the silicon carbide ingot 400.

[0082] Step 3, process the first surface (the contact surface between silicon carbide and the graphite crucible):

[0083] The silicon carbide ingot 400 is flipped over, and its first surface is used as the surface to be processed for clamping and fixing. The first surface is then ground to make its flatness ≤0.01mm.

[0084] Understandably, since there is still a wax film between the silicon carbide ingot 400 and the hollow tooling after step 2, it is not possible to flip it directly. Therefore, before step 3, the product obtained in step 2 needs to be heated to melt the wax film before flipping it.

[0085] In some embodiments, step 3 uses molten liquid paraffin as a binder to form a wax film between the silicon carbide ingot 400 and the hollow tooling, so as to clamp and fix the silicon carbide ingot 400 in the tooling.

[0086] Specifically, in some embodiments, the first surface of the silicon carbide ingot 400 is used as the surface to be processed and placed in a hollow tooling so that the second surface of the silicon carbide ingot 400 contacts the surface of the hollow tooling; molten liquid paraffin forms a wax film between the second surface of the silicon carbide ingot 400 and the hollow tooling to clamp and fix the silicon carbide ingot 400.

[0087] In some embodiments, in step 3, a horizontal flat grinder is used to grind the second surface; in step 4, a horizontal flat grinder is used to grind the first surface. Based on the above scheme, not only can the same processing effect as that for the second surface be achieved, but also the use of a horizontal flat grinder for grinding both the first and second surfaces helps to reduce the parallelism error between the upper and lower surfaces of the silicon carbide ingot 400, and it eliminates the need to replace other equipment, further improving the overall processing efficiency. Moreover, in the micro-convex surface structure of the first surface, the height difference between the edge and the center position is about 0.5 mm. This means that after removing the micro-convex surface, compared to the existing processing position which generally extends 1-2 mm above and below the center of the cylindrical surface, the loss of silicon carbide ingot 400 material can be effectively reduced, improving the material utilization rate of the formed silicon carbide wafer.

[0088] It should be noted that the grinding process for the second and first surfaces using a horizontal surface grinder is the same, both including rough grinding and fine grinding to improve the flatness and processing quality of the second or first surface through progressive processing. Since the grinding process is from top to bottom, the surface condition can be visually observed during grinding to detect the graphite layer and any remaining roughness. The specific amount of residue can then be confirmed using measuring tools, or the amount removed during grinding can be adjusted to ensure that silicon carbide is not removed along with the roughness, thereby increasing material utilization.

[0089] This application does not limit the specific processes for rough grinding and fine grinding; they can be selected according to actual conditions, as long as the intended function of this application is achieved. For example, in some embodiments, the grinding wheels used in both rough grinding and fine grinding are resin-bonded grinding wheels, and the grit size (mesh count) of the grinding wheels is between 100# and 300#. Based on the above scheme, it is beneficial to improve surface fineness and quality, and to ensure that the second or first surface is stably processed to a surface roughness Ra within the range of 0.01μm to 0.2μm. It is understood that the term "resin-bonded grinding wheel" in this application refers to a grinding tool that uses resin material as a binder to solidify diamond abrasive grains into a certain shape, hardness, and strength. It is a commonly used grinding wheel type for grinding hard and brittle semiconductor materials such as silicon carbide (SiC) and single-crystal silicon, and therefore will not be described in detail here.

[0090] In some embodiments, during grinding, the grinding wheel speed is 1000 r / min to 1800 r / min, and the rotary table speed is 50 r / min to 110 r / min, while maintaining a grinding wheel speed to rotary table speed ratio of 17:1; the rough grinding feed rate of the grinding wheel is 400 mm / min to 800 mm / min, and the removal amount per layer is 0.003 mm to 0.006 mm; the fine grinding feed rate is 300 mm / min to 500 mm / min, and the removal amount per layer is 0.002 mm to 0.004 mm; a cooling nozzle with a fixed angle is provided to continuously and precisely spray coolant at a flow rate of not less than 30 L / min onto the grinding contact area between the grinding wheel and the workpiece. Based on the above scheme, the surface accuracy is further improved, and the surface fineness and quality of silicon carbide after grinding are further guaranteed.

[0091] In some embodiments, before rough grinding and / or fine grinding, the resin-bonded grinding wheel is further dressed by using an auxiliary dressing tool to grind the resin-bonded grinding wheel, so that the resin-bonded grinding wheel can maintain its sharp grinding action. This application does not limit the specific dressing process, as long as it can achieve the above-mentioned effects. For example, in some embodiments, the grinding wheel used in this application is a green silicon carbide grinding wheel, and the grit size (mesh count) of the green silicon carbide grinding wheel is limited to between 80# and 240#. Based on the above scheme, while ensuring the green silicon carbide grinding wheel maintains its sharpness, the end face and radial face accuracy of the resin-bonded grinding wheel after rough grinding are further optimized, ensuring the fineness and quality of the second or first surface after silicon carbide grinding.

[0092] Secondly, this application provides a silicon carbide wafer obtained based on any of the above processing methods.

[0093] The following examples illustrate the implementation of this application in more detail.

[0094] Example 1

[0095] This embodiment provides a method for processing silicon carbide wafers, including the following steps:

[0096] Step 1, silicon carbide ingot 400 prepared by physical vapor transport method:

[0097] A graphite crucible with a micro-concave inner surface and a micro-concave depth of 300 μm was used as a growth container. SiC powder was used as a silicon carbide precursor and placed in the graphite crucible. A silicon carbide ingot 400 was prepared by physical vapor transport method.

[0098] Furthermore, the silicon carbide ingot 400 obtained in this embodiment has a first surface and a second surface opposite to the first surface. The first surface is the contact surface between the silicon carbide ingot 400 and the graphite crucible during the physical vapor transport growth process, and the second surface is the growth surface of silicon carbide.

[0099] Step 2, Remove the graphite layer:

[0100] The first surface of the silicon carbide ingot 400 was ground using a dry sandblasting machine. The grinding process parameters were as follows: 60# green silicon carbide abrasive grains were used; the sandblasting pressure was 8 kgf; and the grinding was continued until no obvious gray / black matte film layer was visible to the naked eye. This was considered as removal of the graphite layer from the first surface, and the obtained product was as follows: Figure 4 As shown.

[0101] Furthermore, in this embodiment, a profilometer was used to test and analyze the first surface after the graphite layer was removed. The analysis results showed that the first surface after the graphite layer was removed exhibited a slightly convex, uniformly inclined surface, and the height difference between the edge and the center of the first surface was approximately 0.5 mm. Subsequently, a belt abrasive was used to grind the edge of the silicon carbide ingot 400. The abrasive grit size of the belt used in the belt abrasive was 80# to 320#, and the linear speed was 25 m / s. It could be observed with the naked eye that the grinding was completed until there were no obvious flashes. The product obtained after processing was as follows: Figure 5 As shown.

[0102] Step 3, process the second surface:

[0103] 3.1 Clamping and fixing:

[0104] Adopting such Figure 2 The hollow fixture shown serves as a clamping jig. It includes a fixture body 100, four fixing blocks 200, and eight fixing connectors 300. Each fixing block 200 has a first mounting hole, and the fixture body 100 has a second mounting hole 101 corresponding to the first mounting hole. The fixture body 100 also has through holes 102. The second surface of the silicon carbide ingot 400 is placed on the side of the fixture body 100 with the second mounting hole 101, as the surface to be processed. The four fixing blocks 200 are placed around the silicon carbide ingot 400. Then, the eight fixing connectors 300 are sequentially passed through the corresponding first and second mounting holes 101 to fix the silicon carbide ingot 400 to the fixture body 100, resulting in the desired shape. Figure 3The diagram shows the structure. It should be noted that after the silicon carbide ingot 400 is fixed on the tooling body 100, the first surface of the silicon carbide ingot 400 contacts the surface of the tooling to form a nearly closed flow channel. Then, molten paraffin liquid is introduced into the flow channel and solidified to form a uniform wax film between the first surface of the silicon carbide ingot 400 and the surface of the tooling, thereby achieving the clamping and fixing of the silicon carbide ingot 400.

[0105] 3.2 Grinding process the second surface:

[0106] The second surface was ground using a horizontal surface grinder. A resin-bonded grinding wheel was used for rough grinding, and a green silicon carbide grinding wheel was used for finish grinding. The grinding wheel speed was 1700 rpm, and the rotary table speed was 100 rpm. The rough grinding feed rate was 500 mm / min, with a removal rate of 0.004 mm per layer. The finish grinding feed rate was 400 mm / min, with a removal rate of 0.002 mm per layer. A cooling nozzle with a fixed angle was used, and the coolant flow rate was 30 L / min to ensure the flatness of the second surface was ≤0.01 mm. The resulting product... Figure 6 As shown.

[0107] Step 4, process the first surface:

[0108] 4.1 Re-clamp and secure:

[0109] The product obtained in step 3.2 is heated to melt the wax film. The silicon carbide ingot 400 is then flipped over, with its first surface as the surface to be processed. It is placed in a hollow fixture so that the second surface of the silicon carbide ingot 400 contacts the surface of the fixture. Molten liquid paraffin forms a wax film between the second surface of the silicon carbide ingot 400 and the fixture, thereby re-clamping and fixing the silicon carbide ingot 400. For specific clamping and fixing operations, please refer to step 3.1 above; these details will not be repeated here.

[0110] 4.2 Grinding process the first surface:

[0111] The first surface is ground using a horizontal surface grinder to achieve a flatness of ≤0.01mm. For specific processing details, please refer to step 3.2 above; these will not be repeated here. The resulting product is as follows: Figure 7 As shown.

[0112] The silicon carbide wafer obtained in this embodiment has a smooth, crack-free surface, indicating that the processing method of this application is applicable to the processing of irregular silicon carbide ingots 400, balancing material utilization and processing safety, and achieving higher processing precision. Furthermore, the roughness of the two surfaces was tested separately, and the results show that the roughness Ra of the first surface is 0.113 μm, and the roughness of the second surface is 0.010 μm.

[0113] It should be noted that this application also conducted three parallel experiments according to the processing method of Example 1, and tested the material utilization rate and surface roughness of the silicon carbide wafers obtained in the three parallel experiments. The results show that the material utilization rate of the silicon carbide wafers obtained by the processing method of this application is in the range of 85% to 95%, and the surface roughness of the silicon carbide wafers is in the range of 0.01 μm to 0.2 μm. This indicates that the processing method of this application is applicable to the processing of irregular silicon carbide ingots, can balance material utilization and processing safety, and has higher processing precision. Without the need for subsequent grinding and polishing processes, it can achieve a surface roughness of 0.01 μm to 0.2 μm for silicon carbide wafers, while increasing the material utilization rate to 85% to 95%.

[0114] Wherein, the material utilization rate = mass of silicon carbide wafer / mass of silicon carbide ingot × 100%.

[0115] Comparative Example 1

[0116] The only difference between this comparative example and Example 1 is that the first surface is ground first, and then the second surface is ground.

[0117] It should be noted that in the actual processing of this comparative example, the stability of the processing process was poor due to the first surface being processed first, resulting in a high surface roughness (about 1 μm) of the final silicon carbide wafer, which could not meet the actual requirements.

[0118] Comparative Example 2

[0119] The only difference between this comparative example and Example 1 is that: [the method used is as follows] Figure 1 The planar tooling shown is used for clamping.

[0120] It should be noted that in the actual processing of this comparative example, since the contact point between the silicon carbide ingot and the tooling plane is at the center of the silicon carbide ingot surface, there is a curvature height of 0.5 between the silicon carbide ingot surface and the tooling plane, which leads to poor stability of the processing and obvious cracks on the surface of the final silicon carbide wafer.

[0121] It should also be noted that the processes or related parameters not specifically described in this application are all based on conventional operations in the field, such as the process of fixing silicon carbide ingots with paraffin wax, which should be known to those skilled in the art, and therefore will not be described in detail in this application.

[0122] Obviously, the above embodiments of this application are merely examples for clear illustration and are not intended to limit the implementation of this application. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection claimed by this application.

Claims

1. A method for processing silicon carbide wafers, characterized in that, Includes the following steps: Step 1: Using a graphite crucible with a micro-concave inner surface as a growth container, silicon carbide raw material is placed in the graphite crucible, and silicon carbide ingots are prepared by physical vapor transport method. The silicon carbide ingot has a first surface and a second surface opposite to the first surface; the first surface is the contact surface between the silicon carbide ingot and the graphite crucible during the physical vapor transport growth process, and the second surface is the growth surface of silicon carbide. Step 2: Perform surface pretreatment on the silicon carbide ingot to remove the graphite layer on the first surface of the silicon carbide ingot. Step 3: The second surface of the silicon carbide ingot is used as the surface to be processed and clamped and fixed. The second surface is ground to make the flatness of the second surface ≤0.01mm. Step 4: Flip the silicon carbide ingot over, clamp and fix it with the first surface of the silicon carbide ingot as the surface to be processed, and grind the first surface to make the flatness of the first surface ≤0.01mm.

2. The processing method according to claim 1, characterized in that, The depth of the concave surface is 200μm~500μm.

3. The processing method according to claim 1, characterized in that, In steps 3 and 4, tooling is used for clamping and fixing. Molten liquid paraffin is used as a binder to form a wax film between the silicon carbide ingot and the tooling, thereby clamping and fixing the silicon carbide ingot in the tooling.

4. The processing method according to claim 3, characterized in that, The tooling is a hollow tooling; The hollow tooling includes a tooling body (100), and a through hole (102) is provided on the tooling body (100).

5. The processing method according to claim 1, characterized in that, In step 2, after pretreatment, the planar curvature of the first surface of the silicon carbide ingot is ≤1mm.

6. The processing method according to claim 1, characterized in that, In step 2, a sandblasting machine is used to grind the first surface of the silicon carbide ingot to remove the graphite layer on the first surface.

7. The processing method according to claim 1, characterized in that, In step 2, the surface pretreatment further includes edge treatment, and the edge treatment includes the following steps: The edges of the silicon carbide ingot are ground to remove the flash.

8. The processing method according to claim 7, characterized in that, The edges of the silicon carbide ingot are ground using a belt abrasive machine to remove the burrs from the edges of the silicon carbide ingot.

9. The processing method according to claim 1, characterized in that, In step 3, a horizontal surface grinder is used to grind the second surface. In step 4, a horizontal surface grinder is used to grind the first surface.

10. A silicon carbide wafer obtained by any one of the processing methods according to claims 1 to 9.

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