Method for processing silicon carbide ingot and method for processing silicon carbide substrate

Abstract

The invention relates to a processing method of a silicon carbide crystal ingot and a processing method of a silicon carbide substrate, and the processing method of the silicon carbide crystal ingot comprises the following steps: providing a chemical modifier comprising monovalent solid alkali and a solid oxysalt type oxidant, heating to prepare a molten mixed solution, immersing a to-be-treated surface of the silicon carbide crystal ingot into the molten mixed solution, and then plane mechanical grinding is carried out, and the to-be-treated face of the silicon carbide crystal ingot is machined into a plane. In the machining method, the used molten mixed solution can enable the surface of the silicon carbide crystal ingot to become porous and loose, the hardness of the silicon carbide crystal ingot becomes soft, the mechanical stress in the mechanical grinding process is reduced, meanwhile, a new surface exposed in the mechanical grinding process can continue to react with the molten mixed solution, and the process is repeated, so that the mechanical stress of the silicon carbide crystal ingot is reduced. And finally, a relatively flat silicon carbide crystal ingot with a smooth and crack-free surface and relatively low stress can be obtained, so that the processing efficiency is extremely high, the yield of subsequent slicing can be effectively improved, and the preparation of a high-quality silicon carbide substrate is realized.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for processing a silicon carbide ingot and a method for processing a silicon carbide substrate. Background Art

[0002] Surface grinding and circular grinding of silicon carbide ingots are important foundations for the preparation of silicon carbide substrates and devices. However, the silicon carbide ingots currently grown by physical vapor transport (PVT) often present a convex morphology, which becomes more obvious as the diameter increases. The convex stress of this type of silicon carbide ingot is relatively large, and it is very easy for the ingot to crack due to stress concentration during the grinding process; in addition, the edge of the silicon carbide ingot often presents a relatively sharp morphology due to the expansion of the diameter. During the growth process, it is inevitable that microcracks of a certain depth will be generated on the edge and extend radially inward. Therefore, during the grinding process, under the action of stress, the microcracks are prone to expand, which in turn causes the silicon carbide ingot to crack. Therefore, the cracking problem of silicon carbide ingots during the grinding process seriously limits the production of high-quality silicon carbide substrates and devices. Summary of the invention

[0003] Based on this, it is necessary to provide a processing method for a silicon carbide ingot and a processing method for a silicon carbide substrate to address the above problems. The processing method for the silicon carbide ingot can effectively reduce processing stress, reduce the risk of cracking of the silicon carbide ingot, and has extremely high processing efficiency.

[0004] A method for processing a silicon carbide ingot comprises the following steps: Providing a chemical modifier, the chemical modifier comprising a monovalent solid base and a solid oxygen-containing acid salt type oxidant; heating the chemical modifier to form a molten mixed liquid; The surface to be processed of the silicon carbide crystal ingot is immersed in the molten mixed liquid, and then plane mechanical grinding is performed to process the surface to be processed of the silicon carbide crystal ingot into a plane.

[0005] In one embodiment, the monovalent solid base is at least one of KOH or NaOH.

[0006] In one embodiment, the solid oxygen-containing acid salt type oxidant is KMnO 4 or KIO 4 At least one of .

[0007] In one embodiment, the molar ratio of the monovalent solid base to the solid oxygen-containing acid salt type oxidant is 2:1-4:1.

[0008] In one embodiment, the surface to be processed of the silicon carbide ingot is immersed in the molten mixed solution and maintained for 10 min-60 min, and then plane mechanical grinding is performed.

[0009] In one embodiment, in the step of immersing the surface to be treated of the silicon carbide ingot into the molten mixed solution, the temperature of the molten mixed solution is maintained at 400°C-800°C.

[0010] In one embodiment, the plane mechanical grinding uses a grinding wheel, and the grinding wheel reciprocates on the surface to be processed of the silicon carbide ingot.

[0011] In one embodiment, the plane mechanical grinding uses a grinding wheel with a mesh size of 200-1000, and the non-grinding surface of the grinding wheel is coated with polytetrafluoroethylene.

[0012] In one embodiment, the diameter of the silicon carbide ingot is 2 inches to 12 inches.

[0013] The present invention also provides a method for processing a silicon carbide substrate, including the method for processing the silicon carbide ingot mentioned above.

[0014] In the processing method of the present invention, the surface to be processed of the silicon carbide ingot is first immersed in a molten mixed liquid of a specific composition to react with the molten mixed liquid, so that the surface to be processed of the silicon carbide ingot becomes porous and loose and the hardness becomes soft, thereby reducing the mechanical stress in the subsequent mechanical grinding process and avoiding the risk of cracking; at the same time, in the process of mechanical grinding, a new surface will be exposed, and the new surface will continue to react with the molten mixed liquid to reduce the mechanical stress in the mechanical grinding process. After such a cycle, a relatively flat silicon carbide ingot with a smooth surface, no cracks and low stress can be obtained in the end. Not only is the processing efficiency extremely high, but the yield of subsequent slicing can also be effectively improved, thereby realizing the preparation of high-quality silicon carbide substrates and the manufacture of devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It is a schematic diagram of the process of the method for processing silicon carbide ingot of the present invention; Figure 2 It is a schematic diagram of the process of plane and circumference processing of silicon carbide ingots of the present invention; Figure 3This is a photo of the silicon carbide ingot after processing in Example 1 of the present invention; Figure 4 This is a photo of the silicon carbide ingot after processing according to Example 2 of the present invention.

[0017] In the figure: 1. Silicon carbide ingot; 2. container; 3. carrier; 4. molten mixed liquid; 5. grinding wheel. DETAILED DESCRIPTION

[0018] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific implementation methods or embodiments, and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the combinations include any two related listed items, any more related listed items, or all related listed items.

[0020] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0021] like Figure 1 As shown, the method for processing silicon carbide ingot provided by the present invention comprises the following steps: S1, providing a chemical modifier, wherein the chemical modifier comprises a monovalent solid base and a solid oxygen-containing acid salt type oxidant; S2, heating the chemical modifier to form a molten mixed liquid; S3, immersing the surface to be processed of the silicon carbide crystal ingot into the molten mixed liquid, and then performing plane mechanical grinding to process the surface to be processed of the silicon carbide crystal ingot into a flat surface.

[0022] Silicon carbide crystals have high hardness, high brittleness, good wear resistance, and extremely stable chemical properties, which makes precision processing of silicon carbide ingots very difficult. In the processing method of silicon carbide ingots provided by the present invention, a chemical modifier is first prepared using a monovalent solid base and a solid oxygen-containing acid salt type oxidant, and heated to form a molten mixed liquid, and then the surface to be processed of the silicon carbide ingot is immersed in the molten mixed liquid of this specific component. The surface to be processed of the silicon carbide ingot will react with the molten mixed liquid. During the reaction, thanks to the synergistic effect of the base and the oxygen-containing acid salt type oxidant in the molten mixed liquid, the surface to be processed of the silicon carbide ingot becomes porous and loose and the hardness becomes soft, thereby reducing the mechanical stress in the subsequent mechanical grinding process and avoiding the risk of cracking.

[0023] At the same time, during the mechanical grinding process, the surface to be processed of the silicon carbide ingot will expose a new surface, and the new surface will continue to react with the molten mixture to reduce the mechanical stress during the mechanical grinding process. This cycle will eventually result in a relatively flat silicon carbide ingot with a smooth surface, no cracks, and low stress. This not only has extremely high processing efficiency, but can also effectively improve the yield of subsequent slicing, thereby realizing the preparation of high-quality silicon carbide substrates and the manufacture of devices.

[0024] In order to enable the alkali and oxygen-containing acid salt type oxidant in the molten mixed liquid to play a better synergistic role, so that the treated surface of the silicon carbide ingot becomes more porous and loose, and the hardness becomes softer, in step S1, the molar amount of the monovalent solid base in the chemical modifier is greater than the molar amount of the solid oxygen-containing acid salt type oxidant. Preferably, the molar ratio of the monovalent solid base to the solid oxygen-containing acid salt type oxidant is 2:1-4:1, including but not limited to 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, or a range composed of any two of these values, and the present invention is not limited to this.

[0025] The specific selection of the monovalent solid base and the solid oxygen-containing acid salt type oxidant may not be limited. Preferably, the monovalent solid base is selected from at least one of KOH and NaOH, and the solid oxygen-containing acid salt type oxidant is KMnO 4 or KIO 4 At least one of, for example, the chemical modifier includes KOH and KMnO 4 Alternatively, chemical modifiers include KOH and KIO 4 Alternatively, chemical modifiers include NaOH and KMnO 4 Alternatively, chemical modifiers include NaOH and KIO 4 Alternatively, chemical modifiers include KOH, NaOH, and KMnO 4 Alternatively, chemical modifiers include KOH, NaOH and KIO 4 Alternatively, chemical modifiers include KOH, KMnO 4 and KIO4 Alternatively, chemical modifiers include NaOH, KMnO 4 and KIO 4 Alternatively, chemical modifiers include KOH, NaOH, KMnO 4 and KIO 4 .

[0026] In step S2, in the step of heating the chemical modifier to form a molten mixed solution, the heating temperature is preferably 400°C-800°C, including but not limited to 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, or a range consisting of any two of these values, and the present invention is not limited to this. In actual operation, the mixed and prepared chemical modifier is first placed in a container such as a crucible that can hold the molten mixed solution, wherein the crucible and other containers are preferably containers made of materials such as nickel, platinum, gold, etc., which are not only resistant to high temperatures, but also have stable chemical properties and will not react with the molten mixed solution of the present invention.

[0027] Thus, in step S3, in the step of immersing the surface to be processed of the silicon carbide ingot into the molten mixed liquid, the temperature of the molten mixed liquid is maintained at 400°C-800°C, and preferably the temperature is kept constant. Similarly, during the mechanical surface grinding process, the temperature is preferably kept constant, which is beneficial to the stability and uniformity of the reaction.

[0028] Optionally, the surface to be treated of the silicon carbide ingot is immersed in the molten mixed liquid, first held for a certain time, and then subjected to plane mechanical grinding. Preferably, the holding time is 10min-60min, including but not limited to 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min, or a range consisting of any two of these values. The present invention is not limited to this, and the surface to be treated of the silicon carbide ingot can be fully chemically reacted in the molten mixed liquid first, so that the surface to be treated of the silicon carbide ingot has a porous structure and the hardness becomes lower, which is beneficial to reduce the stress in mechanical grinding and avoid cracking of the silicon carbide ingot during processing.

[0029] It should be noted that during the mechanical surface grinding, the molten mixed liquid can still contact and react with the surface in the grinding process, making the surface porous and loose and the hardness softened. Optionally, when the present invention performs plane mechanical grinding, it is preferred to use a grinding wheel. Further, it is preferred that the grinding wheel reciprocates on the surface to be treated of the silicon carbide ingot, so that the new surface exposed by the grinding process can be fully contacted and reacted with the molten mixed liquid again, re-forming a porous and loose structure, while reducing the hardness, which is conducive to improving the processing effect and processing efficiency.

[0030] Preferably, the plane mechanical grinding uses a grinding wheel with a mesh size of 200-1000, including but not limited to 200 mesh, 400 mesh, 600 mesh, 800 mesh or 1000 mesh, or a range consisting of any two of these values, and the present invention is not limited thereto. By adjusting the mesh size of the grinding wheel, a relatively flat, smooth surface and crack-free silicon carbide ingot can be obtained. Further, it is preferred that the non-grinding surface of the grinding wheel is coated with polytetrafluoroethylene, because polytetrafluoroethylene and the diamond on the grinding surface do not react with the molten mixed solution of the present invention, thereby avoiding the grinding wheel from reacting with the molten mixed solution and affecting the processing effect.

[0031] In the processing method of the present invention, the processed silicon carbide ingots include the currently mainstream n-type ingots, p-type ingots and semi-insulating ingots with diameters of 2 inches to 12 inches. However, it should be noted that the processing method of the present invention is applicable to all silicon carbide ingots and is not limited by the type and size of the silicon carbide ingots.

[0032] For example, refer to Figure 2 As shown, for the silicon carbide ingot 1 with a convex plane and sharp edges currently grown by physical vapor transport (PVT), the processing process usually includes planar processing and circular processing. It can be understood that there is no special requirement for the order of planar processing and circular processing. Circular processing can be performed first and then planar processing, or planar processing can be performed first and then circular processing.

[0033] Specifically, in the actual processing process, a chemical modifier composed of a monovalent solid base and a solid oxygen-containing acid salt type oxidant is first placed in a container 2 such as a crucible, heated to form a molten mixed solution 4, and then a carrier 3 such as nickel, platinum, gold, etc. that is resistant to high temperatures and does not react with the molten mixed solution 4 of the present invention is used to support the silicon carbide ingot 1. The convex surface of the silicon carbide ingot 1 is first immersed in the molten mixed solution 4 as the surface to be treated, and maintained for 10 minutes to 60 minutes, so that the surface to be treated reacts with the molten mixed solution 4 to become porous and loose and the hardness becomes soft, and then the grinding wheel 5 is started for mechanical surface grinding. During grinding, the grinding wheel 5 reciprocates on the surface to be treated of the silicon carbide ingot 1 until a relatively flat surface is obtained.

[0034] Then, the silicon carbide ingot 1 after surface grinding is subjected to circumferential processing, and the carrier 3 is used to carry the silicon carbide ingot 1, and the edge of the silicon carbide ingot 1 with a sharp morphology is used as a new surface to be processed, and it is first immersed in the molten mixed liquid 4 and kept for 10min-60min, so that the surface to be processed reacts with the molten mixed liquid 4 to become porous and loose and the hardness becomes soft, and then the grinding wheel 5 is started for mechanical surface grinding. During grinding, the grinding wheel 5 reciprocates on the surface to be processed of the silicon carbide ingot 1 until a relatively flat circumferential surface is obtained, and finally a relatively flat, smooth surface without cracks and low stress silicon carbide ingot is obtained. Preferably, during the processing, the container 2 such as the crucible can be sealed to reduce the volatilization of the molten mixed liquid 4.

[0035] Therefore, based on the processing method of the present invention, a relatively flat silicon carbide ingot with a smooth surface without cracks and low stress can be obtained, and the processing efficiency is extremely high.

[0036] The present invention also provides a method for processing a silicon carbide substrate, including the above-mentioned method for processing a silicon carbide ingot. Since the method for processing a silicon carbide ingot of the present invention can obtain a relatively flat silicon carbide ingot with a smooth surface, no cracks, and low stress, the yield of subsequent slicing can be effectively improved, thereby realizing the preparation of high-quality silicon carbide substrates.

[0037] Hereinafter, the processing method of the silicon carbide ingot and the processing method of the silicon carbide substrate will be further described through the following specific embodiments.

[0038] Example 1 First, solid sodium hydroxide (NaOH) and potassium permanganate (KMnO 4 ) are mixed into a crucible and heated to 500°C to prepare a molten mixed solution.

[0039] The convex surface of a 6-inch diameter silicon carbide ingot was immersed in the molten mixed liquid. After 30 minutes, the surface was mechanically ground using an 800-mesh grinding wheel. During grinding, the grinding wheel reciprocated on the surface to be processed until a relatively flat surface was obtained.

[0040] The sharp edge of the silicon carbide ingot after plane grinding is used as the new surface to be processed, and it is immersed in the molten mixed liquid to make the irregular edge of the silicon carbide ingot contact the molten mixed liquid. After 25 minutes, a 800-mesh grinding wheel is used for circular mechanical grinding. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat circular surface is obtained, completing the entire processing process. The results are as follows Figure 3 As shown, the silicon carbide ingot did not crack and no new cracks were introduced.

[0041] Example 2 First, solid sodium hydroxide (NaOH) and potassium periodate (KIO 4 ) are mixed into a crucible and heated to 600°C to prepare a molten mixed solution.

[0042] The convex surface of an 8-inch diameter silicon carbide ingot is immersed in the molten mixed liquid. After 20 minutes, the surface is mechanically ground using a 600-mesh grinding wheel. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat surface is obtained.

[0043] The sharp edge of the silicon carbide ingot after plane grinding is used as the new surface to be processed, and is immersed in the molten mixed liquid to make the irregular edge of the silicon carbide ingot contact the molten mixed liquid. After 10 minutes, a 600-mesh grinding wheel is used for circular mechanical grinding. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat circular surface is obtained, completing the entire processing process. The results are as follows Figure 4 As shown, the silicon carbide ingot did not crack and no new cracks were introduced.

[0044] Example 3 First, solid potassium hydroxide (KOH) and potassium periodate (KIO 4 ) are mixed into a crucible and heated to 550°C to prepare a molten mixed solution.

[0045] The convex surface of a 12-inch diameter silicon carbide ingot was immersed in the molten mixed liquid. After 40 minutes, the surface was mechanically ground using an 800-mesh grinding wheel. During grinding, the grinding wheel reciprocated on the surface to be processed until a relatively flat surface was obtained.

[0046] The sharp edge of the silicon carbide ingot after surface grinding is used as a new surface to be processed and immersed in the molten mixed liquid so that the irregular edge of the silicon carbide ingot contacts the molten mixed liquid. After 20 minutes, circular mechanical grinding is performed using an 800-mesh grinding wheel. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat circular surface is obtained, completing the entire processing process. During the entire processing process, the silicon carbide ingot does not crack and no new cracks are introduced.

[0047] Example 4 First, solid sodium hydroxide (NaOH) and potassium permanganate (KMnO 4 ) are mixed into a crucible and heated to 800°C to prepare a molten mixed solution.

[0048] The convex surface of a 12-inch-thick silicon carbide ingot was immersed in the molten mixed liquid. After 15 minutes, the surface was mechanically ground using a 400-mesh grinding wheel. During grinding, the grinding wheel reciprocated on the surface to be processed until a relatively flat surface was obtained.

[0049] The sharp edge of the silicon carbide ingot after surface grinding is used as a new surface to be processed and immersed in the molten mixed liquid so that the irregular edge of the silicon carbide ingot contacts the molten mixed liquid. After 10 minutes, circular mechanical grinding is performed using a 400-mesh grinding wheel. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat circular surface is obtained, completing the entire processing process. During the entire processing process, the silicon carbide ingot does not crack and no new cracks are introduced.

[0050] Example 5 First, solid sodium hydroxide (NaOH) and potassium permanganate (KMnO 4 ) are mixed into a crucible and heated to 400°C to prepare a molten mixed solution.

[0051] The convex surface of a 12-inch diameter silicon carbide ingot is immersed in the molten mixed liquid. After 60 minutes, the surface is mechanically ground using a 1000-mesh grinding wheel. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat surface is obtained.

[0052] The sharp edge of the silicon carbide ingot after surface grinding is used as a new surface to be processed and immersed in a molten mixed liquid so that the irregular edge of the silicon carbide ingot contacts the molten mixed liquid. After 40 minutes, a 1000-mesh grinding wheel is used for circular mechanical grinding. During grinding, the grinding wheel reciprocates on the surface to be processed until a relatively flat circular surface is obtained, completing the entire processing process. During the entire processing process, the silicon carbide ingot does not crack and no new cracks are introduced.

[0053] It can be seen from the above-mentioned Examples 1-5 that the processing method of the present invention can effectively reduce the mechanical stress in the mechanical grinding process and avoid the risk of cracking of the silicon carbide ingot, and the processing efficiency is extremely high. It is possible to obtain a relatively flat silicon carbide ingot with a smooth surface, no cracks, and low stress, effectively improve the yield of subsequent slicing, and realize the preparation of high-quality silicon carbide substrates and the manufacture of devices.

[0054] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for processing a silicon carbide ingot, characterized in that: The following steps are involved: Providing a chemical modifier, the chemical modifier comprising a monovalent solid base and a solid oxygen-containing acid salt type oxidant; heating the chemical modifier to form a molten mixed liquid; The surface to be processed of the silicon carbide crystal ingot is immersed in the molten mixed liquid, and then plane mechanical grinding is performed to process the surface to be processed of the silicon carbide crystal ingot into a plane.

2. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The monovalent solid base is at least one of KOH and NaOH.

3. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The solid oxygen-containing acid salt type oxidant is at least one of KMnO4 or KIO4.

4. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The molar ratio of the monovalent solid base to the solid oxygen-containing acid salt type oxidant is 2:1-4:

1.

5. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The surface to be processed of the silicon carbide ingot is immersed in the molten mixed solution and maintained for 10 minutes to 60 minutes, and then plane mechanical grinding is performed.

6. The method for processing a silicon carbide ingot according to claim 1, characterized in that: In the step of immersing the surface to be treated of the silicon carbide ingot into the molten mixed solution, the temperature of the molten mixed solution is maintained at 400°C-800°C.

7. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The plane mechanical grinding adopts a grinding wheel, and the grinding wheel reciprocates on the surface to be processed of the silicon carbide ingot.

8. The method for processing a silicon carbide ingot according to claim 7, characterized in that: The plane mechanical grinding adopts a grinding wheel with mesh sizes of 200 to 1000, and the non-grinding surface of the grinding wheel is coated with polytetrafluoroethylene.

9. The method for processing a silicon carbide ingot according to claim 1, characterized in that: The silicon carbide ingot has a diameter of 2 inches to 12 inches.

10. A method for processing a silicon carbide substrate, characterized in that: A method for processing a silicon carbide ingot comprising the steps of:

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