A method for removing graphite from silicon carbide

Abstract

The present application relates to the technical field of silicon carbide impurity removal, and specifically discloses a method for removing graphite from silicon carbide, comprising the following steps: S1, placing silicon carbide with a graphite substrate in a heating container; S2, introducing oxygen into the heating container and evacuating; S3, adjusting the temperature of the heating container in a step-by-step heating and heat preservation manner, with a heating range of 0-1200°C, a heating rate of 5-20°C / min, and a heat preservation time of each stage of T, 0h<T≤2h. The method for removing graphite from silicon carbide of the present application has the advantages of high graphite removal rate, low degree of silicon carbide oxidation, low residual stress, and is suitable for large-scale production.

Description

Technical Field

[0001] The present application relates to the technical field of silicon carbide impurity removal, and more specifically, to a method for removing graphite on silicon carbide. Background Art

[0002] Silicon carbide is a man-made material, a non-metallic carbide composed of carbon and silicon elements covalently bonded. The two elements in silicon carbide belong to the IVA group in the periodic table and have the highest electron affinity. In its crystal structure, each silicon atom is surrounded by four adjacent carbon atoms, which are the four vertices of a tetrahedron. The carbon atoms and silicon atoms are bonded by sp3 bonds, thus forming silicon carbide with a strong covalent bond and a diamond crystal structure. Therefore, silicon carbide is the only stable compound of C and Si. Silicon carbide has excellent high-temperature oxidation resistance and chemical stability, as well as high hardness, high strength, high wear resistance, and corrosion resistance. It has gradually been applied to many technical fields such as aerospace, machinery, metallurgy, energy, environmental protection, chemical industry, medicine, electronics, and military industry. Among them, the application of making semiconductor equipment has received widespread attention and is slowly developing. However, as a special functional material, silicon carbide has a large application in semiconductors and electronics, and has relatively strict requirements on purity.

[0003] At present, chemical vapor deposition technology is an effective method to obtain dense, uniform, and high-purity silicon carbide. Because graphite hardly reacts with silicon carbide at the interface, the two have good chemical compatibility, and the difference in thermal expansion coefficient is small, it is easy to obtain a good gradient transition at the interface of silicon carbide and graphite. Therefore, graphite is a good substrate for obtaining silicon carbide. After silicon carbide is formed on the graphite substrate, in order to obtain a separate silicon carbide product, the graphite and silicon carbide products need to be separated.

[0004] At present, the common graphite exfoliation methods are divided into heating oxidation method and chemical oxidation method. The heating oxidation method refers to the process of calcining silicon carbide at high temperature to make the free carbon and graphite in the silicon carbide powder react with oxygen in the air and separate from the silicon carbide in the form of carbon dioxide or carbon monoxide, thereby achieving the purpose of carbon removal. However, if the heating temperature is too high, it is easy to cause part of the silicon carbide to be oxidized, forming a silicon dioxide oxide layer on the surface, which wraps the graphite inside and prevents the internal graphite from further oxidation, which is not conducive to the complete removal of graphite and is costly.

[0005] The chemical oxidation method uses a mixed acid composed of one or more of nitric acid, sulfuric acid and perchloric acid, or adds potassium permanganate and potassium dichromate as inorganic oxidants to the acid to volatilize the carbon impurities in silicon carbide in the form of gas, thereby removing graphite and free carbon. Although the chemical oxidation method can also oxidize the graphite in silicon carbide into gas and volatilize it, the strong oxidizing acid added by the oxidation process is highly corrosive to the human body and its environment, and the by-products that may be produced by the chemical oxidation process are adsorbed on the surface of silicon carbide, so it is not conducive to large-scale industrial production.

[0006] With respect to the above-mentioned related technologies, the inventors found that in actual applications, the heating oxidation method and the chemical oxidation method are prone to cause oxidation of silicon carbide, and silicon carbide is prone to residual stress, while the chemical oxidation method is prone to cause corrosion to the human body and machines. Summary of the invention

[0007] In order to reduce the oxidation phenomenon of silicon carbide during high temperature calcination and reduce the residual stress of silicon carbide, the present application provides a method for removing graphite on silicon carbide.

[0008] In a first aspect, the present application provides a method for removing graphite on silicon carbide, using the following technical solution:

[0009] A method for removing graphite on silicon carbide comprises the following steps:

[0010] S1. placing silicon carbide with a graphite substrate in a heating container;

[0011] S2, introducing oxygen into the heating container and evacuating the container;

[0012] S3. Adjust the temperature of the heating container in a step-by-step heating and insulation method. The heating range is 0-1200°C, the heating rate is 5-20°C / min, and the insulation time of each stage is T, 0h<T≤2h.

[0013] By adopting the above technical scheme, the graphite on silicon carbide is subjected to step-by-step temperature-raising and heat-insulating annealing and calcination under low pressure and oxygen-assisted vacuum conditions, so that the graphite is removed by gradually increasing the temperature, the residual stress of silicon carbide is reduced, the high-temperature oxidation of silicon carbide is avoided, and the quality of silicon carbide is improved.

[0014] Optionally, in step S2, the flow rate of oxygen when it is introduced is 20-200 ml / min.

[0015] By adopting the above technical solution, at this oxygen flow rate, the graphite in silicon carbide can slowly generate carbon dioxide or carbon monoxide and release it, thereby improving the purity of silicon carbide.

[0016] Optionally, in step S2, the flow rate of oxygen when it is introduced is 20-80 ml / min.

[0017] By adopting the above technical solution, the flow rate of oxygen is optimized, so that the graphite removal rate on silicon carbide is high and the removal is complete.

[0018] Optionally, in step S2, the vacuum degree is 20-300Pa.

[0019] By adopting the above technical solution, graphite on silicon carbide can be removed under low pressure environment, with high removal rate and low residual stress.

[0020] Optionally, in step S2, the vacuum degree is 200-300Pa.

[0021] By adopting the above technical solution, the vacuum degree of graphite oxidation is further optimized, so that the graphite oxidation is completely removed.

[0022] Optionally, in step S3, the step heating and insulation method is: heating to 800°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 900°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 1000°C at a rate of 5-10°C / min, keeping warm for 1-2h, then heating to 1100°C at a rate of 5-10min, keeping warm for 1-2h, and then cooling naturally.

[0023] By adopting the above technical solution, under the conditions of heating and insulation, the graphite on the silicon carbide can be completely removed, and the silicon carbide is not easily oxidized and has small residual stress.

[0024] Optionally, in step S3, the step heating and insulation method is: heating to 450-560°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 650-700°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 800°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 900°C at a rate of 5-10°C / min, keeping warm for 1-2h, heating to 1000°C at a rate of 5-10°C / min, keeping warm for 1-2h, and then heating to 1100°C at a rate of 5-10min, keeping warm for 1-2h, and then cooling naturally.

[0025] By adopting the above technical solution, the number of calcined step layers of graphite on silicon carbide is increased, the removal rate of graphite on silicon carbide is increased, and the residual stress of silicon carbide is reduced.

[0026] Optionally, the heating container is a box-type atmosphere furnace or a tube furnace.

[0027] In summary, this application has the following beneficial effects:

[0028] 1. Since the present application adopts a step-by-step heating and insulation method to remove graphite from silicon carbide, the graphite removal rate is high and the removal is complete. The silicon carbide after the graphite is removed meets the requirements of semiconductor electronics and other aspects for silicon carbide, and under the cooperation of low-pressure oxygen, it can prevent silicon carbide from being oxidized and affecting the removal efficiency of graphite.

[0029] 2. In the present application, it is preferred to use a step-by-step heating and insulation method under low pressure and oxygen-assisted conditions to remove graphite from silicon carbide produced by chemical vapor deposition. The degree of oxidation of silicon carbide is small, the graphite is completely removed, and the residual stress of silicon carbide is small, which is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Optical image of silicon carbide after oxidation and removal of graphite using the method in Example 1;

[0031] Figure 2 The following are scanning electron microscope micrographs of the original silicon carbide product containing graphite and the silicon carbide after removing the graphite using the methods in Example 1, Example 2, Example 3 and Example 4. DETAILED DESCRIPTION

[0032] Example

[0033] Embodiment 1: A method for removing graphite from silicon carbide, comprising the following steps:

[0034] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0035] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated by a vacuum pump. The flow rate of oxygen is 80 ml / min, and the vacuum degree in the tubular furnace is 200 Pa;

[0036] S3. Adjust the temperature of the tubular furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally.

[0037] like Figure 1 and Figure 2 As shown, under low pressure conditions, the oxygen-assisted step-by-step heating and insulation method is used to remove silicon carbide from graphite, with a low degree of surface oxidation and low residual stress.

[0038] Embodiment 2: A method for removing graphite from silicon carbide, comprising the following steps:

[0039] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0040] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated by a vacuum pump. The flow rate of oxygen is 80 ml / min, and the vacuum degree in the tubular furnace is 300 Pa;

[0041] S3. Adjust the temperature of the tube furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after insulation, heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after the insulation ends, heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after the insulation ends, heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally. The scanning electron microscope micrograph of silicon carbide with graphite removed is shown in the following figure. Figure 2 shown.

[0042] Embodiment 3: A method for removing graphite on silicon carbide, comprising the following steps:

[0043] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0044] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated using a vacuum pump. The flow rate of oxygen is 200 ml / min, and the vacuum degree in the tubular furnace is 300 Pa;

[0045] S3. Adjust the temperature of the tube furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after insulation, heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after the insulation ends, heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, continue to heat it after the insulation ends, heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally. The scanning electron microscope micrograph of silicon carbide with graphite removed is shown in the following figure. Figure 2 As shown in Figure 3.

[0046] Embodiment 4: A method for removing graphite on silicon carbide, comprising the following steps:

[0047] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0048] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated by a vacuum pump. The flow rate of oxygen is 80 ml / min, and the vacuum degree in the tubular furnace is 200 Pa;

[0049] S3. Adjust the temperature of the tube furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 2 hours, and then continue to heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, and then continue to heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, and then continue to heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally. The scanning electron microscope micrograph of silicon carbide with graphite removed is shown in the figure. Figure 2 As shown in Figure 4.

[0050] Embodiment 5: A method for removing graphite on silicon carbide, comprising the following steps:

[0051] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0052] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated by a vacuum pump. The flow rate of oxygen is 20 ml / min, and the vacuum degree in the tubular furnace is 200 Pa;

[0053] S3. Adjust the temperature of the tubular furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally.

[0054] Embodiment 6: A method for removing graphite on silicon carbide, comprising the following steps:

[0055] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0056] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated using a vacuum pump. The flow rate of oxygen is 80 ml / min, and the vacuum degree in the tubular furnace is 20 Pa;

[0057] S3. Adjust the temperature of the tubular furnace in a step-by-step heating and insulation method. First, heat it to 800°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 900°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1000°C at a rate of 10°C / min, keep it for 1 hour, continue heating it after insulation, heat it to 1100°C at a rate of 10°C / min, keep it for 1 hour, and then cool it naturally.

[0058] Embodiment 7: A method for removing graphite on silicon carbide, comprising the following steps:

[0059] S1, placing 10 g of silicon carbide with a graphite substrate in a heating container, wherein the silicon carbide with a graphite substrate is prepared by chemical vapor deposition, and the heating container is a tubular furnace;

[0060] S2. Oxygen is introduced into the tubular furnace, and the tubular furnace is evacuated by a vacuum pump. The flow rate of oxygen is 80 ml / min, and the vacuum degree in the tubular furnace is 200 Pa;

[0061] S3. Adjust the temperature of the tubular furnace in a step-by-step heating and insulation method. First, heat it to 450°C at a rate of 5°C / min and keep it for 2h. Then heat it to 650°C at a rate of 5°C / min and keep it for 2h. Then heat it to 800°C at a rate of 10°C / min and keep it for 2h. Then continue heating it to 900°C at a rate of 10°C / min and keep it for 1h. After the insulation, continue heating it to 1000°C at a rate of 10°C / min and keep it for 1h. After the insulation, continue heating it to 1100°C at a rate of 10°C / min and keep it for 1h.

[0062] Comparative Example

[0063] Comparative Example 1: A method for removing graphite on silicon carbide, which differs from Example 1 in that, in step S2, the tubular furnace is evacuated to a pressure of 1 MPa.

[0064] Comparative Example 2: A method for removing graphite on silicon carbide, which differs from Example 1 in that in step S2, the pressure in the tubular furnace is set to normal pressure.

[0065] Comparative Example 3: A method for removing graphite on silicon carbide, which differs from Example 1 in that oxygen is not introduced in step S2.

[0066] Comparative Example 4: A method for removing graphite on silicon carbide, which differs from Example 1 in that in step S2, the oxygen flow rate is 10 ml / min.

[0067] Comparative Example 5: A method for removing graphite on silicon carbide, which differs from Example 1 in that in step S2, the oxygen flow rate is 300 ml / min.

[0068] Comparative Example 6: A method for removing silicon carbide graphite, which differs from Example 1 in that in step S3, the heating rate is 20°C / min.

[0069] Comparative Example 7: A method for removing silicon carbide graphite, which differs from Example 1 in that in step S3, the heating rate is 2°C / min.

[0070] Comparative Example 8: A method for removing silicon carbide graphite, which differs from Example 1 in that in step S3, the insulation time for each stage is 4 hours.

[0071] Comparative Example 9: A method for removing graphite on silicon carbide, which differs from Example 1 in that, in step S3, high-temperature calcination is adopted, the calcination temperature is 900° C., and the calcination time is 3 hours.

[0072] Comparative Example 10: A method for removing graphite on silicon carbide, which differs from Example 1 in that, in step S3, high-temperature calcination is adopted, the calcination temperature is 450° C., and the calcination time is 2 h.

[0073] Performance testing

[0074] The graphite on the silicon carbide was removed by the methods in the examples and comparative examples, and the obtained silicon carbide was subjected to the following tests. The test results are recorded in Table 1.

[0075] 1. Removal of graphite from the surface of silicon carbide: Take the same mass of silicon carbide from which graphite is removed by the methods in the embodiment and the comparative example, and observe whether the graphite on the surface is completely removed.

[0076] 2. The degree of oxidation of silicon carbide surface: detected by PHI4300X photoelectron spectrometer (XPS).

[0077] 3. Residual stress of silicon carbide: detected using XRD.

[0078] Table 1

[0079]

[0080]

[0081] It can be seen from the data in Table 1 that the method in Example 1 is used to remove graphite on silicon carbide, the graphite is completely removed, and the degree of oxidation on the surface of silicon carbide is low, and it is not easy to be oxidized into silicon dioxide. In addition, the residual stress is small, and it is not easy to cause deformation or cracks.

[0082] The difference between Example 2 and Example 1 is that the vacuum degree in the tube furnace is increased to 300 Pa. Table 1 shows that after the graphite on the surface of silicon carbide is removed in Example 2, the residual stress on the surface of silicon carbide is further reduced.

[0083] The difference between Example 3 and Example 1 is that the rate of introducing oxygen into the tubular furnace is increased to 200 ml / min. Although the surface oxidation degree of silicon carbide treated by the method in Example 3 is greater than that in Example 1, the surface residual stress is reduced.

[0084] In Example 4, after the temperature was raised to 800° C. and then kept at that temperature for 2 h, the degree of oxidation on the surface of silicon carbide was greater than that in Example 1, but the residual stress was significantly reduced.

[0085] Compared with Example 1, Example 5 reduces the flow rate of oxygen. Although the degree of oxidation on the surface of silicon carbide increases, the graphite on the surface is completely removed and the residual stress is small.

[0086] Compared with Example 1, Example 6 reduces the vacuum degree in the tube furnace. In Example 6, some graphite remains on the silicon carbide, but the degree of oxidation on the silicon carbide surface is small, and the residual stress is the same as that in Example 1, indicating that the vacuum degree is within the scope of the present application and can effectively improve the residual stress of silicon carbide and avoid oxidation of the silicon carbide surface.

[0087] Compared with Example 1, Example 7 increases the step gradient. The silicon carbide is first kept at 450°C for 2 hours and then heated to 650°C and kept there. Then, the test results are the same as those in Example 1, indicating that increasing the temperature gradient has little effect on the removal of graphite on silicon carbide, the degree of oxidation on the surface of silicon carbide, and the residual stress.

[0088] Compared with Example 1, in Comparative Example 1, the vacuum degree in the tube furnace is increased to 1 MPa, and the high-pressure environment increases the oxidation degree of silicon carbide.

[0089] In Comparative Example 2, the vacuum degree in the tube furnace is normal pressure, and the oxidation degree of the silicon carbide surface increases, indicating that low pressure can reduce the oxidation degree of the silicon carbide surface.

[0090] The difference between Comparative Example 3 and Example 1 is that without the introduction of oxygen, the removal of graphite on the silicon carbide surface is incomplete, which indicates that the introduction of oxygen can facilitate the removal of graphite on silicon carbide and increase the graphite removal effect.

[0091] In Comparative Examples 4 and 5, the oxygen flow rates were lowered and increased, respectively. Table 1 shows that in Comparative Example 4 where the oxygen flow rate was too low, although the degree of surface oxidation of silicon carbide was reduced, surface graphite was not completely removed and some remained, while in Comparative Example 5, the degree of oxidation of silicon carbide was increased.

[0092] In Comparative Example 6, the heating rate of each stage during calcination is 20°C / min. As the heating rate increases, the residual stress on the silicon carbide surface increases. In Comparative Example 7, the heating rate of each stage is reduced to 2°C / min, and some graphite remains on the silicon carbide surface, indicating that the heating rate is too slow, which will affect the removal of graphite.

[0093] In Comparative Example 8, the insulation time for each stage is 4 hours. The extended insulation time has little effect on the residual stress, oxidation degree and graphite removal effect of silicon carbide.

[0094] Comparative Example 9 uses a single temperature for calcination and insulation, and the degree of oxidation on the silicon carbide surface is greater than that in Example 1; Comparative Example 10 uses high-temperature calcination, the calcination temperature is 450°C, and the insulation time is 4h, the residual stress on the silicon carbide surface increases, indicating that the calcination temperature is low, which is not conducive to the release of residual stress.

[0095] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for removing graphite from silicon carbide, characterized in that: The following steps are involved: S1. placing silicon carbide with a graphite substrate in a heating container; S2. Oxygen is introduced into the heating container and vacuumized. The flow rate of oxygen is 20-200 ml / min and the vacuum degree is 200-300 Pa. S3. Adjust the temperature of the heating container in a step-by-step heating and insulation method. The insulation time of each stage is T, 0h<T≤2h. The step-by-step heating and insulation method is: heating to 800℃ at a rate of 5-10℃ / min, insulation for 1-2h, heating to 900℃ at a rate of 5-10℃ / min, insulation for 1-2h, heating to 1000℃ at a rate of 5-10℃ / min, insulation for 1-2h, heating to 1100℃ at a rate of 5-10min, insulation for 1-2h, and then cooling naturally; or heating to 800℃ at a rate of 5-10℃ / min, insulation for 1-2h, heating to 900℃ at a rate of 5-10℃ / min, insulation for 1-2h, heating to 1000℃ at a rate of 5-10min, insulation for 1-2h, and then cooling naturally; or heating to 1100℃ at a rate of 5-10min, insulation for 1-2h, and then cooling naturally. Increase the temperature to 450-560℃ at a rate of 0℃ / min, keep warm for 1-2h, increase the temperature to 650-700℃ at a rate of 5-10℃ / min, keep warm for 1-2h, increase the temperature to 800℃ at a rate of 5-10℃ / min, keep warm for 1-2h, increase the temperature to 900℃ at a rate of 5-10℃ / min, keep warm for 1-2h, increase the temperature to 1000℃ at a rate of 5-10℃ / min, keep warm for 1-2h, increase the temperature to 1100℃ at a rate of 5-10min, keep warm for 1-2h, and then cool down naturally.

2. The method for removing graphite from silicon carbide according to claim 1, characterized in that: In step S2, the flow rate of oxygen when introduced is 20-80 ml / min.

3. The method for removing graphite from silicon carbide according to claim 1, characterized in that: The heating container is a box-type atmosphere furnace or a tube furnace.

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