A method for preparing tantalum carbide coating

Abstract

The present invention belongs to the field of semiconductor crystal growth technology, and specifically relates to a method for preparing a tantalum carbide coating. In the present invention, the addition of tantalum increases the bonding performance between the coating and the substrate, and the addition of tantalum oxide enhances the diffusivity of the tantalum carbide during sintering, which is beneficial for achieving sintering densification and reducing the sintering temperature. At the same time, combining the CVD process with the sintering method is beneficial for obtaining a high-purity, low-surface-roughness tantalum carbide coating. In addition, due to the poor diffusivity of tantalum carbide, a small amount of pores that are not covered by tantalum carbide are inevitably present during the sintering process. Therefore, the CVD process is used to cover the pores remaining during the sintering of tantalum carbide, effectively improving the corrosion resistance of the carbon substrate.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor crystal growth, and in particular relates to a method for preparing a tantalum carbide coating. Background Art

[0002] With the rapid development of the semiconductor industry in recent years, traditional silicon single crystals have been limited by material properties. Crystalline materials such as silicon carbide and aluminum nitride have broader application prospects in high-frequency, high-voltage, high-temperature power, and radio frequency semiconductor fields. Currently, the growth of silicon carbide and aluminum nitride single crystals is mainly achieved through physical vapor transport (PVT).

[0003] Because the PVT process must be performed at high temperatures of 1500-2400°C, graphite is currently the most commonly used crucible material in PVT processes. However, in the physical vapor transport process for growing silicon carbide or aluminum nitride single crystals, the strong corrosiveness of Si- or N-containing atmospheres on the graphite substrate can easily cause carbon powder inside the graphite crucible to fall off and enter the growing crystal with the airflow, or the atmosphere to heterogeneously nucleate on the inner wall of the graphite crucible, forming irreversible crystal defects. Therefore, to promote high-quality growth of silicon carbide or aluminum nitride single crystals, a tantalum carbide coating is required on the inner surface of the graphite crucible, either in contact with the crystal growth area or on the surface of the guide groove.

[0004] Tantalum carbide coatings are usually prepared using the CVD process. However, due to the long coating time of the CVD process, the raw materials used in the coating are expensive, and the coating is significantly corrosive to heating and insulation materials in high-temperature furnaces, the coating cost is high and the resulting coating has poor bonding with the carbon substrate, which cannot effectively prevent corrosion of the carbon substrate. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a tantalum carbide coating. The method provided by the present invention has low cost, and the obtained tantalum carbide coating has good bonding with the carbon substrate, which can effectively prevent corrosion of the carbon substrate.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a tantalum carbide coating, comprising the following steps:

[0008] Mixing a solid mixture, a binder and a solvent to obtain a slurry; the solid mixture includes tantalum oxide, tantalum and tantalum carbide;

[0009] coating the slurry on the surface of the carbon substrate, and sequentially curing and sintering to obtain a sintered coating;

[0010] Tantalum carbide is deposited on the surface of the sintered coating by chemical vapor deposition to obtain the tantalum carbide coating.

[0011] Preferably, the particle sizes of the tantalum oxide, tantalum and tantalum carbide are independently 0.1 to 5 μm.

[0012] Preferably, the mass concentration of the solid mixture in the slurry is 50-80%;

[0013] The mass percentage of the tantalum carbide in the solid mixture is 50 to 99%;

[0014] The mass percentage of the tantalum in the solid mixture is 0.1 to 20%;

[0015] The mass percentage of the tantalum oxide in the solid mixture is 0.1-20%.

[0016] Preferably, the binder comprises one or more of thermosetting phenolic resin, epoxy resin, polyvinyl alcohol and polyvinyl butyral;

[0017] The mass percentage of the binder in the slurry is 0.5-10%.

[0018] Preferably, the thickness of the wet coating obtained by the coating is 10 to 100 μm.

[0019] Preferably, the curing temperature is 100-300° C., and the holding time is 0.5-5 h.

[0020] Preferably, the sintering temperature is 1000-2200° C., the holding time is 0.5-5 h, and the pressure is less than 90 kPa.

[0021] Preferably, the temperature of the chemical vapor deposition is 1000-2200° C., the holding time is 1-10 h, and the pressure is 0.1-90 kPa.

[0022] Preferably, the chemical vapor deposition is carried out in a mixed atmosphere comprising tantalum chloride, argon, hydrocarbon gas and hydrogen;

[0023] The molar ratio of tantalum chloride to hydrogen is 1:5-30;

[0024] The chemical vapor deposition comprises sequentially performing a first chemical vapor deposition and a second chemical vapor deposition;

[0025] In the first chemical vapor deposition, the molar ratio of the tantalum chloride to the carbon atoms in the hydrocarbon gas is 1:1 to 1.5, excluding 1:1; and the time of the first chemical vapor deposition is 0.1 to 5 hours;

[0026] In the second chemical vapor deposition, the molar ratio of the tantalum chloride to the carbon atoms in the hydrocarbon gas is 1:1; and the time of the second chemical vapor deposition is 0.1 to 5 hours.

[0027] Preferably, the thickness of the tantalum carbide obtained by chemical vapor deposition is 1 to 10 μm.

[0028] The present invention provides a method for preparing a tantalum carbide coating, comprising the following steps: mixing a solid mixture, a binder, and a solvent to obtain a slurry; the solid mixture comprising tantalum oxide, tantalum, and tantalum carbide; applying the slurry to the surface of a carbon substrate, curing and sintering the mixture in sequence to obtain a sintered coating; and chemically vapor depositing tantalum carbide on the surface of the sintered coating to obtain the tantalum carbide coating. In the present invention, the addition of tantalum improves the bonding between the coating and the substrate, and the addition of tantalum oxide enhances the diffusivity of the tantalum carbide during sintering, facilitating densification and reducing the sintering temperature. Combining a chemical vapor deposition (CVD) process with the sintering method facilitates obtaining a high-purity, low-surface-roughness tantalum carbide coating. Furthermore, due to the poor diffusivity of tantalum carbide, a small amount of pores that are not covered by the tantalum carbide are inevitably present during the sintering process. Therefore, the CVD process masks the pores remaining during the sintering of the tantalum carbide, effectively improving the corrosion resistance of the carbon substrate. The preparation method provided by the present invention is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention provides a schematic flow chart of the preparation method.

[0030] Figure 2 OM image of the tantalum carbide coating obtained in Example 1 of the present invention;

[0031] Figure 3 This is a macroscopic image of the tantalum carbide coating prepared by traditional technology after high temperature treatment;

[0032] Figure 4 This is the OM image of the tantalum carbide coating prepared by traditional technology. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a tantalum carbide coating, comprising the following steps:

[0034] Mixing a solid mixture, a binder and a solvent to obtain a slurry; the solid mixture includes tantalum oxide, tantalum and tantalum carbide;

[0035] coating the slurry on the surface of the carbon substrate, and sequentially curing and sintering to obtain a sintered coating;

[0036] Tantalum carbide is deposited on the surface of the sintered coating by chemical vapor deposition to obtain the tantalum carbide coating.

[0037] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0038] The present invention mixes a solid mixture, a binder and a solvent to obtain a slurry; the solid mixture comprises tantalum oxide, tantalum and tantalum carbide.

[0039] In the present invention, the particle sizes of the tantalum oxide, tantalum and tantalum carbide are independently preferably 0.1 to 5 μm, more preferably 0.1 to 3.0 μm, and even more preferably 0.1 to 2 μm.

[0040] In the present invention, the mass percentage of the tantalum carbide in the solid mixture is preferably 50-99%, more preferably 60-90%, and more preferably 70-80%. In the present invention, the mass percentage of the tantalum in the solid mixture is preferably 0.1-20%, more preferably 0.1-12%, and more preferably 0.1-10%. In the present invention, the mass percentage of the tantalum oxide in the solid mixture is preferably 0.1-20%, more preferably 0.1-15%, and more preferably 0.1-10%.

[0041] In the present invention, the mass concentration of the solid mixture in the slurry is preferably 50 to 80%, more preferably 60 to 80%.

[0042] In the present invention, the binder preferably includes one or more of thermosetting phenolic resin, epoxy resin, polyvinyl alcohol and polyvinyl butyral ester; the mass percentage of the binder in the slurry is preferably 0.5-10%, more preferably 1-8%, and more preferably 2-5%.

[0043] In the present invention, the solvent preferably includes one or more of ethanol, xylene, toluene, acetone and deionized water.

[0044] After obtaining the slurry, the present invention applies the slurry on the surface of the carbon substrate, and sequentially performs solidification and sintering to obtain a sintered coating.

[0045] The present invention has no particular limitation on the coating method, and any method well known to those skilled in the art may be used.

[0046] In the present invention, the thickness of the wet coating obtained by the coating is preferably 10 to 100 μm, more preferably 20 to 80 μm, and even more preferably 50 to 60 μm.

[0047] Before curing, the present invention further preferably includes drying the wet coating. The present invention has no particular limitation on the drying process, and any method known to those skilled in the art can be used.

[0048] In the present invention, the curing temperature is preferably 100-300° C., and the holding time is preferably 0.5-5 h. In the present invention, the curing is preferably carried out in a drying oven.

[0049] In the present invention, the sintering temperature is preferably 1000-2000°C, more preferably 1200-1800°C, and even more preferably 1500-1600°C; the holding time is preferably 0.5-5 hours, more preferably 1.0-4.0 hours, and even more preferably 2.0-3.0 hours; and the pressure is preferably less than 90 kPa. In the present invention, the sintering is preferably performed in an argon atmosphere. In the present invention, the sintering is preferably performed in a vacuum heating furnace.

[0050] After obtaining the sintered coating, the present invention performs chemical vapor deposition on the surface of the sintered coating to obtain the tantalum carbide coating.

[0051] In the present invention, the temperature of the chemical vapor deposition is preferably 1000-2200°C, more preferably 1200-1800°C, and more preferably 1500-1600°C; the holding time is preferably 1-10h, more preferably 1-8h, and more preferably 1-6h; and the pressure is preferably 0.1-90kPa.

[0052] In the present invention, the chemical vapor deposition is preferably carried out in a mixed atmosphere, and the mixed atmosphere preferably includes tantalum chloride, argon, hydrocarbon gas and hydrogen. In the present invention, the hydrocarbon gas preferably includes methane or propylene.

[0053] In the present invention, the molar ratio of tantalum chloride to hydrogen is preferably 1:5 to 30. In the present invention, the chemical vapor deposition preferably includes a first chemical vapor deposition and a second chemical vapor deposition in sequence; in the first chemical vapor deposition, the molar ratio of tantalum chloride to carbon atoms in the hydrocarbon gas is preferably 1:1 to 1.5, excluding 1:1, further preferably 1:1.2 to 1.4, and more preferably 1:1.3; the time of the first chemical vapor deposition is preferably 0.1 to 5 hours; in the second chemical vapor deposition, the molar ratio of tantalum chloride to carbon atoms in the hydrocarbon gas is preferably 1:1; the time of the second chemical vapor deposition is preferably 0.1 to 5 hours. The present invention does not specifically limit the amount of argon used, and any amount familiar to those skilled in the art can be used.

[0054] The present invention has no special limitation on the chemical vapor deposition process, and any process known to those skilled in the art may be used.

[0055] After the chemical vapor deposition, the present invention preferably further comprises cooling the obtained coating to room temperature in a furnace.

[0056] In the present invention, the thickness of the tantalum carbide obtained by chemical vapor deposition is preferably 1 to 10 μm, more preferably 2 to 8 μm, and even more preferably 5 to 6 μm.

[0057] The schematic flow diagram of the preparation method provided by the present invention is as follows Figure 1 shown.

[0058] In order to further illustrate the present invention, a method for preparing a tantalum carbide coating provided by the present invention is described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] 20 g of tantalum oxide, 20 g of tantalum, 160 g of tantalum carbide, 20 g of thermosetting phenolic resin, 22 g of polyvinyl butyral (PVB), and 50 mL of ethanol were mixed by mechanical stirring and ultrasonic stirring to form a tantalum carbide slurry, wherein the tantalum oxide particle size was 0.5 μm, the tantalum particle size was 0.5 μm, and the tantalum carbide particle size was 2 μm;

[0061] The slurry was applied to the carbon substrate by doctor blade coating, and the resulting wet coating thickness was 50 μm;

[0062] The wet coating was dried in an oven and then placed in a drying oven to cure the binder at a temperature of 200°C for 3 hours. The coating was then sintered at a temperature of 2000°C under an argon atmosphere and a pressure of 50 kPa to obtain a sintered coating.

[0063] A mixed atmosphere of tantalum chloride, argon, methane and hydrogen was introduced into a high-temperature furnace, and chemical vapor deposition was performed on the surface of the sintered coating. The deposition temperature was 2000°C and the pressure was 50 kPa. The initial molar ratio of tantalum chloride, methane and hydrogen was 1:1.5:10, and the deposition was performed for 2 hours. The amount of methane introduced was then adjusted to make the molar ratio of methane to tantalum chloride 1:1, and the deposition was performed for 1 hour. After the deposition was completed, the furnace was cooled to room temperature to obtain a tantalum carbide coating with a thickness of 50 μm, wherein the thickness of the vapor-deposited tantalum carbide was 5 μm, and its surface morphology SEM image is shown as follows Figure 2 shown.

[0064] Example 2

[0065] 5 g of tantalum oxide, 5 g of tantalum, 100 g of tantalum carbide, 3 g of thermosetting phenolic resin, 1 g of polyvinyl butyral (PVB), 4 mL of toluene, and 10 mL of ethanol were mixed by mechanical stirring and ultrasonic stirring to form a tantalum carbide slurry, wherein the tantalum oxide particle size was 0.5 μm, the tantalum particle size was 0.5 μm, and the tantalum carbide particle size was 1 μm;

[0066] The slurry was applied to the carbon substrate by spraying, and the resulting wet coating thickness was 50 μm;

[0067] The wet coating was dried in an oven and then placed in a drying oven to cure the binder at a temperature of 200°C for 1 hour. The coating was then sintered at a temperature of 2000°C under an argon atmosphere and a pressure of 10 kPa to obtain a sintered coating.

[0068] A mixed atmosphere of tantalum chloride, argon, propylene and hydrogen is introduced into a high-temperature furnace, and chemical vapor deposition is performed on the surface of the sintered coating. The deposition temperature is 2000°C and the pressure is 10kPa. The initial molar ratio of tantalum chloride, propylene and hydrogen is 2:1:30, and the deposition is carried out for 2 hours. Then, the amount of propylene introduced is adjusted to make the molar ratio of propylene to tantalum chloride 1:3, and the deposition is carried out for 1 hour. After the deposition is completed, the furnace is cooled to room temperature to obtain a tantalum carbide coating with a thickness of 50 μm, wherein the thickness of the vapor-deposited tantalum carbide is 5 μm.

[0069] Example 3

[0070] The tantalum carbide coating was prepared in the same manner as in Example 2, except that the added amount of tantalum oxide and tantalum was 1 g, and the deposition temperature was 2200°C.

[0071] Example 4

[0072] The tantalum carbide coating was prepared in the same manner as in Example 1, except that the deposition pressure was 10 KPa and the thickness of the obtained tantalum carbide coating was 47 μm.

[0073] Example 5

[0074] A tantalum carbide coating was prepared in the same manner as in Example 2, except that the thermosetting phenolic resin in the binder was replaced by epoxy resin.

[0075] Comparative Example 1

[0076] The carbon substrate is directly placed in a high-temperature furnace for chemical vapor deposition, wherein the temperature is 2000°C, the pressure is 0.5 atm, the molar ratio of tantalum chloride, methane and hydrogen in the mixed atmosphere of tantalum chloride, argon, methane and hydrogen is 1:1:10, the deposition time is 25 hours, and a 50 μm thick tantalum carbide coating is obtained after the deposition is completed.

[0077] Comparative Example 2

[0078] 1 g of tantalum oxide, 1 g of tantalum, 100 g of tantalum carbide, 3 g of thermosetting phenolic resin, 1 g of polyvinyl butyral (PVB), 4 mL of toluene, and 10 mL of ethanol were mixed by mechanical stirring and ultrasonic stirring to form a tantalum carbide slurry, wherein the tantalum oxide particle size was 0.5 μm, the tantalum particle size was 0.5 μm, and the tantalum carbide particle size was 1 μm;

[0079] The slurry was applied to the carbon substrate by doctor blade coating, and the resulting wet coating thickness was 50 μm;

[0080] After drying the wet coating in an oven, the coating was placed in a drying oven to cure the binder at a temperature of 200°C for 1 hour. The coating was then sintered at a temperature of 2000°C under an argon protective atmosphere and a pressure of 10 kPa to obtain a sintered coating.

[0081] Comparative Example 3

[0082] A tantalum carbide coating was prepared in the same manner as in Example 1, except that no tantalum powder was added.

[0083] Comparative Example 4

[0084] A tantalum carbide coating was prepared in the same manner as in Example 1, except that no tantalum oxide powder was added.

[0085] Performance Testing

[0086] For carbon-based tantalum carbide coatings used in crystal growth, there are two main performance requirements: the bonding strength of the tantalum carbide coating and the density of the tantalum carbide coating. The present invention proposes two simple methods for testing the reliability of tantalum carbide coatings.

[0087] During crystal growth, the tantalum carbide coating is prone to fall off due to the mismatch in thermal expansion coefficient with the carbon-based material. Local peeling of the coating will form wrinkles, such as Figure 3 Therefore, the prepared coating was placed in a high-temperature furnace and heated at 2200℃ for 1 hour, then cooled and its surface morphology was observed. If there was no shedding or wrinkling of the surface coating, the bonding strength was considered qualified.

[0088] The main drawbacks of tantalum carbide coatings prepared by sintering are low coating density and many pores, such as Figure 4 Therefore, the surface of different areas of the sample of the prepared coating was observed by SEM or OM, and 10 samples were randomly sampled. The area ratio occupied by the holes was calculated by general image processing software to obtain the porosity.

[0089] The test results are shown in Table 1.

[0090] Table 1 Properties of tantalum carbide coatings obtained in Examples 1 to 5 and Comparative Examples 1 to 4

[0091] Bonding strength Porosity Example 1 qualified 2.2％ Example 2 qualified 2.5％ Example 3 qualified 1.8％ Example 4 qualified 2.6％ Example 5 qualified 2.3％ Comparative Example 1 Unqualified 3.5％ Comparative Example 2 qualified 18％ Comparative Example 3 Unqualified 4％ Comparative Example 4 qualified 8％

[0092] It can be seen from Table 1 that the tantalum carbide coating prepared by combining the sintering method with the CVD method has a significant improvement on the bonding strength and porosity of the tantalum carbide coating.

[0093] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a tantalum carbide coating, characterized in that: The steps are: A solid mixture, a binder and an organic solvent are mixed to obtain a slurry; the solid mixture consists of tantalum oxide, tantalum and tantalum carbide; the mass concentration of the solid mixture in the slurry is 50-80%; the mass percentage of tantalum carbide in the solid mixture is 50-99%; the mass percentage of tantalum in the solid mixture is 0.1-20%; and the mass percentage of tantalum oxide in the solid mixture is 0.1-20%. coating the slurry on the surface of the carbon substrate, and sequentially curing and sintering to obtain a sintered coating; Chemical vapor deposition of tantalum carbide on the surface of the sintered coating to obtain the tantalum carbide coating; The chemical vapor deposition temperature is 1000-2200° C., the holding time is 1-10 hours, and the pressure is 0.1-90 kPa; The chemical vapor deposition is carried out in a mixed atmosphere consisting of tantalum chloride, argon, hydrocarbon gas and hydrogen; The molar ratio of tantalum chloride to hydrogen is 1:5-30; The chemical vapor deposition is a first chemical vapor deposition and a second chemical vapor deposition performed in sequence; In the first chemical vapor deposition, the molar ratio of the tantalum chloride to the carbon atoms in the hydrocarbon gas is 1:1 to 1.5, excluding 1:1; and the time of the first chemical vapor deposition is 0.1 to 5 hours; In the second chemical vapor deposition, the molar ratio of the tantalum chloride to the carbon atoms in the hydrocarbon gas is 1:1; and the time of the second chemical vapor deposition is 0.1 to 5 hours.

2. The preparation method according to claim 1, characterized in that The particle sizes of the tantalum oxide, tantalum and tantalum carbide are independently 0.1 to 5 μm.

3. The preparation method according to claim 1, characterized in that The binder includes one or more of thermosetting phenolic resin, epoxy resin, polyvinyl alcohol and polyvinyl butyral; The mass percentage of the binder in the slurry is 0.5-10%.

4. The preparation method according to claim 1, characterized in that The thickness of the wet coating obtained by the coating is 10 to 100 μm.

5. The preparation method according to claim 1, characterized in that The curing temperature is 100-300° C., and the heat preservation time is 0.5-5 hours.

6. The preparation method according to claim 1, characterized in that The sintering temperature is 1000-2200° C., the holding time is 0.5-5 hours, and the pressure is less than 90 kPa.

7. The preparation method according to claim 1, characterized in that The thickness of the tantalum carbide obtained by chemical vapor deposition is 1 to 10 μm.

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