Mixing method for synthesizing silicon carbide powder

Abstract

The invention relates to a mixing method for silicon carbide powder synthesis, which comprises the following steps: putting carbon powder and silicon powder in a molar ratio of 1: 1.01 into a mixer for primary mixing, with the particle size of the carbon powder being 50 [mu] m and the particle size of the silicon powder being 3 mm; preparing a methyl cellulose aqueous solution with the temperature of 70 DEG C and the mass concentration of 2%, mixing the materials again, spraying the solution into the carbon powder and the silicon powder in the mixing process, and then carrying out a subsequent synthesis step. The method has the advantages that the method is reasonable in design, the particle size of the silicon carbide powder can be effectively increased, the situation that silicon is deposited at the bottom of a crucible due to the fact that the particle size difference of silicon powder and carbon powder is large can be avoided, the growth quality can be guaranteed, the crucible is prevented from being damaged, and stable powder discharging is guaranteed.

Description

Technical Field

[0001] The present invention relates to a mixing method, and more particularly to a mixing method for synthesizing silicon carbide powder materials. Background Art

[0002] As a third-generation semiconductor material, silicon carbide has advantages such as a wide bandgap, high thermal conductivity, high critical breakdown field strength, and high electron saturation drift rate, and has great application prospects in the field of semiconductor manufacturing.

[0003] Silicon carbide single crystals are generally grown by the PVT method. The specific growth method is as follows: Bond a silicon carbide seed crystal to the seed crystal stage at the top of a graphite crucible, place silicon carbide powder materials at the bottom of the crucible, and then place the graphite crucible in a crystal growth furnace for heating. As the temperature rises, the silicon carbide powder materials at the bottom of the crucible evaporate, and then crystallize at the top of the graphite crucible to grow silicon carbide crystals. During this process, the purity, particle size, and crystal form of the silicon carbide powder materials have a great influence on the growth of silicon carbide crystals.

[0004] The synthesis of silicon carbide powder materials mainly uses the self-propagating high-temperature synthesis method for growth. Specifically, high-purity carbon powder and silicon powder are fully mixed in a ratio of 1:1, and after mixing, they are placed in a high-purity graphite crucible, and then placed in a furnace, and then evacuated, and then high-purity argon gas is introduced as a protective atmosphere, and then heated. After the reaction is completed, the silicon carbide powder materials are taken out, and then crushed, screened, carbon-removed, screened, cleaned, and dried to obtain silicon carbide powder materials.

[0005] When using the prior art self-propagating high-temperature synthesis method to grow silicon carbide powder materials, there are restrictions on the particle size of the silicon powder. Small-particle-size silicon powder and carbon powder need to be used, and the obtained silicon carbide powder materials also have a small particle size. If larger-particle-size silicon powder is used for mixing, a large amount of silicon will be deposited at the bottom of the crucible due to the too large difference in particle size from the carbon powder, resulting in an imbalance in the silicon-carbon ratio in some areas, affecting the growth quality, and also causing cracking at the bottom of the crucible, damaging the crucible, and making it difficult to discharge the powder materials. Summary of the Invention

[0006] The present invention provides a mixing method for synthesizing silicon carbide powder materials, aiming to overcome the above-mentioned deficiencies of the prior art and realize mixing with large-particle-size silicon powder without affecting production to increase the particle size of the obtained silicon carbide powder materials.

[0007] The technical solution of the present invention: A mixing method for synthesizing silicon carbide powder materials includes the following steps:

[0008] 1) Put carbon powder and silicon powder with a molar ratio of 1:1.01 into a mixer for primary mixing, where the particle size of the carbon powder is 50 μm and the particle size of the silicon powder is 3 mm;

[0009] 2) Prepare an aqueous solution of methylcellulose with a temperature of 70 °C and a mass concentration of 2%, and mix again. During the mixing process, spray the solution onto the carbon powder and silicon powder;

[0010] 3) Load the mixed material into a graphite crucible, place the graphite crucible filled with the material into a synthesis furnace, and carry out the reaction. The heating temperature is 1800 °C, the pressure is maintained at 20 Torr, and the reaction time is 4 h;

[0011] 4) Subsequently, heat to 2200 °C, maintain the pressure at 50 Torr, and the reaction time is 6 h. Then, carry out the cooling treatment.

[0012] Preferably, the mixing time in step 1) is 2 h.

[0013] Preferably, the mixing time in step 2) is 2 h.

[0014] Preferably, after the graphite crucible is placed in the synthesis furnace in step 3), first perform evacuation treatment. After reaching the ultimate vacuum, perform leak detection, then heat and pump air. When heated to 600 °C, continue to maintain the pumping mode and react for 1 h to sinter and remove the methylcellulose. Subsequently, continue to heat to 1350 °C and maintain the pressure at 50 Torr for 2 h of reaction.

[0015] Preferably, after step 4) is completed and the cooling is finished, take out the graphite crucible, take out the silicon carbide powder from the graphite crucible, crush it with a crusher, and perform screening treatment with a screening machine after crushing is completed.

[0016] Preferably, after screening, place the screened silicon carbide powder in a tubular furnace, heat to 800 °C to remove carbon for 6 h, ultrasonically clean the silicon carbide powder after carbon removal for 1.5 h, and then perform drying to obtain the silicon carbide powder.

[0017] Advantages of the present invention: The method is reasonably designed, can effectively increase the particle size of the silicon carbide powder, and can avoid the situation where silicon is deposited at the bottom of the crucible due to the large difference in particle size between the silicon powder and the carbon powder, can ensure the growth quality, avoid damaging the crucible, and ensure stable powder discharge. Specific Embodiments

[0018] The present invention will be further described in detail below with reference to the embodiments and specific embodiments.

[0019] A mixing method for synthesizing silicon carbide powder is to add methylcellulose to increase the viscosity when mixing coarse-grained silicon powder and carbon powder.

[0020] The principle is that the solubility of methylcellulose in water is highly related to temperature, and it can be used as an adhesive. Methylcellulose can evenly mix carbon powder and silicon powder, bond the silicon powder and carbon powder together, avoid the situation of uneven local mixing, and thus avoid local silicon enrichment or carbon enrichment during the synthesis process. Moreover, due to the use of silicon powder with a coarse particle size, the particle size obtained after crushing is larger.

[0021] It can avoid the situation where a large amount of silicon is deposited at the bottom of the crucible due to a large difference in particle size between silicon powder and carbon powder, resulting in cracking at the bottom of the crucible and difficulty in discharging materials, as well as the situation where a large amount of silicon is at the bottom of the crucible, leading to an imbalance in the silicon-carbon ratio in some areas.

[0022] Specifically, it includes the following steps:

[0023] 1) Put carbon powder and silicon powder with a molar ratio of 1:1.01 into a mixer. The total mass can be 10 kg, where the particle size of the carbon powder is 50 μm and the particle size of the silicon powder is 3 mm, and conduct primary mixing.

[0024] 2) Subsequently, prepare 50 mL of an aqueous solution of methylcellulose with a temperature of 70 °C and a mass concentration of 2%, then conduct mixing again, and spray the solution onto the carbon powder and silicon powder during the mixing process.

[0025] 3) Load the mixed material into a graphite crucible, load the loaded graphite crucible into a synthesis furnace for reaction, heat to a temperature of 1800 °C, maintain a pressure of 20 Torr, and the reaction time is 4 h.

[0026] 4) Subsequently, heat to 2200 °C, maintain a pressure of 50 Torr, the reaction time is 6 h, and then conduct a cooling treatment.

[0027] Example

[0028] Weigh carbon powder with a particle size of 50 μm and silicon powder with a particle size of 3 mm, where the Si:C molar ratio is 1.01:1. Then put them into a mixer for mixing for 2 h, and prepare a 2% methylcellulose aqueous solution at 70 °C. Subsequently, spray the methylcellulose solution and mix for 2 h, and load the mixed silicon powder and carbon powder into a graphite crucible.

[0029] Load the graphite crucible into a silicon carbide powder synthesis furnace.

[0030] Subsequently, conduct evacuation treatment. After pumping to the ultimate vacuum, conduct leak detection, then heat and pump. When heating to 600 °C, continue to maintain the pumping mode and react for 1 h to sinter and remove methylcellulose. Then continue to heat to 1350 °C and maintain a pressure of 50 Torr for reaction for 2 h. Then continue to heat to 1800 °C and maintain a pressure of 20 Torr, with a reaction time of 4 h. Then heat to 2200 °C, maintain a pressure of 50 Torr, with a reaction time of 6 h, and then conduct a cooling treatment.

[0031] After the cooling is completed, take out the graphite crucible, take out the silicon carbide powder from the graphite crucible, crush it with a crusher, and perform screening treatment with a screening machine after the crushing is completed.

[0032] Place the screened silicon carbide powder in a tube furnace, heat it to 800 °C and remove carbon for 6 h.

[0033] Ultrasonically clean the silicon carbide powder after carbon removal for 1.5 h, and then dry it.

[0034] The screening data shows that the proportion of 8-20 mesh is 32%, and the proportion of 20-40 mesh is 51%.

[0035] Comparative example

[0036] The difference from the example is that the carbon powder and silicon powder are only mixed once, excluding the preparation of the aqueous methyl cellulose solution and the secondary mixing by spraying, and the sintering removal step of methyl cellulose. After the silicon carbide powder is taken out from the graphite crucible, it is crushed with a planetary ball mill.

[0037] The screening data shows that the proportion of 8-20 mesh is 24%, and the proportion of 20-40 mesh is 38%.

[0038] It can be seen that compared with the comparative example, the method of the example can effectively increase the particle size of the silicon carbide powder.

[0039] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the creative concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A mixing method for synthesizing silicon carbide powder materials, characterized in that The steps include: 1) Put carbon powder and silicon powder with a molar ratio of 1:1.01 into a mixer for primary mixing. The particle size of the carbon powder is 50 μm, and the particle size of the silicon powder is 3 mm. 2) Prepare an aqueous solution of methyl cellulose with a temperature of 70 °C and a mass concentration of 2%, and conduct mixing again. During the mixing process, spray the solution into the carbon powder and silicon powder. 3) Load the mixed material into a graphite crucible, and then load the graphite crucible filled with the material into a synthesis furnace for reaction. The heating temperature is 1800 °C, the pressure is maintained at 20 Torr, and the reaction time is 4 h. 4) Subsequently, heat to 2200 °C, maintain the pressure at 50 Torr, and the reaction time is 6 h. Then, perform a cooling treatment.

2. The mixing method for synthesizing silicon carbide powder materials according to claim 1, characterized in that, In the step 1), the mixing time is 2 h.

3. A mixing method for synthesizing silicon carbide powder materials as described in claim 1, characterized in that, In the step 2), the mixing time is 2 h.

4. The mixing method for synthesizing silicon carbide powder materials according to claim 1, characterized in that, After the graphite crucible is loaded into the synthesis furnace in the step 3), first perform a evacuation treatment. After pumping to the ultimate vacuum, conduct a leak detection. Then, heat and pump air. When heated to 600 °C, continue to maintain the pumping mode and react for 1 h to sinter and remove the methyl cellulose. Subsequently, continue to heat to 1350 °C and maintain the pressure at 50 Torr for reaction for 2 h.

5. The mixing method for synthesizing silicon carbide powder materials according to claim 1, characterized in that, After the step 4) is completed and the cooling is finished, take out the graphite crucible, take out the silicon carbide powder from the graphite crucible, crush it with a crusher, and perform a screening treatment with a screening machine after the crushing is completed.

6. The mixing method for synthesizing silicon carbide powder materials according to claim 5, wherein After the screening treatment, place the screened silicon carbide powder in a tube furnace, heat it to 800 °C to remove carbon for 6 h, ultrasonically clean the silicon carbide powder after carbon removal for 1.5 h, and then perform drying to obtain the silicon carbide powder.