Graphite base with tantalum carbide coating and preparation method of graphite base

Abstract

The invention discloses a graphite base with a tantalum carbide coating and a preparation method of the graphite base. Belongs to the technical field of graphite bases. The preparation method comprises the following steps: ball-milling and mixing coating raw materials consisting of chloride, fluoride, a tantalum source and a sintering aid to obtain a raw material mixture; the pretreated graphite base and the raw material mixture are subjected to normal-pressure sintering for 2-10 h at the temperature of 1000-1300 DEG C; wherein the chlorides are selected from more than two of lithium chloride, sodium chloride, potassium chloride and calcium chloride; the fluoride is selected from sodium fluoride and / or potassium fluoride; the tantalum source is one or more of elemental tantalum, tantalum carbide and tantalum oxide; the sintering aid is selected from one or more of boron oxide, boron carbide and sodium borate. The preparation steps are simple, the temperature and pressure requirements are low, the raw material composition is simple, the binding force between the coating and the base in the obtained graphite base with the tantalum carbide coating is high, the coating purity is high, the crystallinity is high, and the performance is excellent.

Description

Technical Field

[0001] This invention relates to the technical field of graphite substrates, and particularly to graphite substrates with tantalum carbide coatings and their preparation methods. Background Technology

[0002] In existing technologies, when preparing third-generation wide-bandgap semiconductor materials such as silicon carbide (SiC) epitaxial growth, the substrates in crystal growth furnaces and / or epitaxial growth equipment, such as chemical vapor deposition furnaces, are mostly graphite substrates. The graphite substrate is the core component supporting the silicon carbide substrate (such as a SiC wafer), and its main functions include: efficiently transferring heat to the substrate through induction heating or resistance heating to ensure the stability of the epitaxial growth temperature; maintaining the substrate flatness under high temperature and gas flow impact, avoiding deformation or slippage; and preventing side reactions between the substrate material and the reactive gases or substrate. Meanwhile, to avoid problems such as high-temperature graphite volatilization, particulate contamination, and uneven surface temperature associated with pure graphite substrates, graphite substrates with added functional coatings are more commonly used, primarily those with added silicon carbide coatings.

[0003] The addition of silicon carbide coatings can improve the chemical stability, surface smoothness, and temperature uniformity of pure graphite substrates, but there are still many application problems. For example, silicon carbide coatings will inevitably crack during use; although the difference in the coefficient of thermal expansion between silicon carbide coatings and graphite substrates is small, coating peeling will still occur under extreme temperature changes due to the small difference in the coefficient of thermal expansion; and the chemical corrosion resistance of silicon carbide coatings is still not ideal when facing gases commonly used in semiconductor production, such as ammonia (NH3), hydrogen (H2), and silicon-containing vapors such as SiH4.

[0004] Tantalum carbide, as an alternative material that can improve upon the above-mentioned problems, exhibits unique advantages, such as: extremely high thermal stability at temperatures above 2000℃; its ability to withstand corrosion from harsh chemical environments such as NH3, H2, and SiH4, and its good chemical inertness. Furthermore, tantalum carbide coatings possess ultra-high purity, avoiding unnecessary impurities or contaminants. Based on these advantages, tantalum carbide coatings are suitable for the growth and preparation of various semiconductor materials, including silicon carbide, gallium nitride, and aluminum nitride.

[0005] However, the industrial production of tantalum carbide graphite substrates still faces many technical challenges. These include the complex raw materials, complicated steps, and high sintering temperatures required for the preparation of mainstream tantalum carbide coated graphite substrates, resulting in high production costs. In addition, the resulting products have insufficient bonding between the coating and the substrate, low crystallinity of the coating, and the presence of carbon impurities, leading to unsatisfactory performance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to propose a novel graphite substrate with tantalum carbide coating and its preparation method. The preparation method uses relatively simple raw materials and steps, has a low sintering temperature, and significantly reduces production costs. Furthermore, the resulting graphite substrate with tantalum carbide coating exhibits strong adhesion between the coating and the substrate, high coating purity, high crystallinity, and excellent performance.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a graphite substrate with a tantalum carbide coating, comprising:

[0009] (1) The graphite substrate is pretreated to obtain a pretreated graphite substrate with a smooth, clean, and dry surface; wherein the coefficient of thermal expansion of the graphite material in the graphite substrate is 6.0 × 10⁻⁶. -6 -6.4×10 -6 K -1 ;

[0010] (2) The coating raw materials are ball-milled and mixed to obtain a raw material mixture; the coating raw materials are composed of chloride, fluoride, tantalum source and sintering aid;

[0011] (3) The pretreated graphite substrate and the raw material mixture are heated to 1000-1300℃ at a heating rate of 5-10℃ / min and sintered at atmospheric pressure for 2-10h to obtain the graphite substrate with tantalum carbide coating.

[0012] Wherein, the chloride is selected from two or more of lithium chloride, sodium chloride, potassium chloride, and calcium chloride; the fluoride is selected from sodium fluoride and / or potassium fluoride; the tantalum source is one or more of elemental tantalum, tantalum carbide, and tantalum oxide; and the sintering aid is one or more of boron oxide, boron carbide, and sodium borate.

[0013] The mass ratio of the chloride, fluoride and tantalum source is 10-100:5-20:1-20, and the mass ratio of the tantalum source to the sintering aid is 10-100:1.

[0014] The preparation method of the present invention is simple in steps, has a low sintering temperature (1000-1300℃), and does not require further high-temperature treatment. It can be achieved by ordinary box furnace and / or tube furnace.

[0015] The above preparation method of the present invention uses coating raw materials that are few in variety, widely available, and low in cost. Through the synergistic effect between the raw materials, coating materials with high crystallinity and high bonding strength can be obtained at a lower sintering temperature.

[0016] The sintering aids used in the above preparation methods of the present invention can not only reduce the density of molten salt and promote the reaction, but also act as reducing agents to inhibit sample oxidation and enhance the bonding strength between the tantalum carbide coating and the graphite substrate.

[0017] In the above preparation method of the present invention, the coating uses a graphite substrate as a carbon source. That is, during sintering, the coating raw material directly reacts chemically with graphite carbon to form a tantalum carbide coating that is chemically bonded to the substrate surface, thereby significantly improving the bonding strength between the coating and the substrate.

[0018] According to some preferred embodiments of the present invention, the coating material is composed of sodium chloride, potassium chloride, potassium fluoride, tantalum oxide and boron carbide.

[0019] According to some preferred embodiments of the present invention, in the coating raw materials, the mass ratio of sodium chloride, lithium chloride, potassium fluoride and tantalum oxide is 20:30:8:1, and the mass ratio of tantalum oxide and boron carbide is 25-75:1.

[0020] More preferably, the mass ratio of tantalum oxide to boron carbide is 50:1.

[0021] The inventors unexpectedly discovered that this preferred embodiment has relatively better coating-base bonding strength.

[0022] According to some preferred embodiments of the present invention, the ball milling method has a ball milling speed of 200-800 r / min, a ball milling time of 2-10 h, and a ball-to-material ratio of 8:1.

[0023] According to some preferred embodiments of the present invention, the heating rate of the atmospheric pressure sintering is 10°C / min, and it is carried out in an inert gas atmosphere. After sintering, the furnace is cooled to room temperature.

[0024] According to some preferred embodiments of the present invention, the graphite material of the graphite substrate has a density of 1.75-1.88 g / cm³. 3 .

[0025] According to some preferred embodiments of the present invention, the temperature of the atmospheric pressure sintering is greater than or equal to 1000°C and less than 1300°C.

[0026] According to some preferred embodiments of the present invention, in the coating raw materials, the purity of the chloride is greater than 99.5%, the purity of the fluoride is greater than 99.5%, the purity of the tantalum source is greater than 99.5%, and the purity of the sintering aid is greater than 99.5%.

[0027] According to some preferred embodiments of the present invention, the preparation method further includes subjecting the product obtained by atmospheric pressure sintering to boiling water washing several times to obtain the graphite substrate with the tantalum carbide coating.

[0028] According to the above preferred embodiments, the preparation method of the present invention can obtain the finished tantalum carbide coated graphite substrate through a simple boiling water cleaning process. Compared with the subsequent high-temperature treatment usually required in the prior art, it greatly simplifies the preparation process, while improving production safety, reducing production costs, and saving preparation energy consumption.

[0029] The present invention further provides a graphite substrate with a tantalum carbide coating prepared according to the above preparation method.

[0030] In the graphite substrate of the tantalum carbide coating obtained by this invention, the tantalum carbide coating is tightly bonded to the graphite substrate, and the surface of the graphite substrate is completely and uniformly covered by the coating. The surface has high flatness and smoothness. The obtained coating is a single, highly crystalline tantalum carbide (TaC) phase without other impurities. The tantalum element in the coating is uniformly distributed, and the coating performance is excellent.

[0031] The present invention has the following beneficial effects:

[0032] The preparation method of the present invention is simple, has a short preparation cycle, uses readily available raw materials, requires little equipment investment, has low requirements for the reaction environment, and has low production costs.

[0033] The preparation method of the present invention has low sintering temperature and low pressure requirements, and the post-sintering treatment is simple, which can significantly reduce the energy consumption requirements in the preparation process and improve production safety.

[0034] The coating raw material in the preparation method of the present invention has a relatively simple composition, which can improve the purity of the obtained coating and avoid introducing new impurity elements into the graphite substrate, which would lead to a decrease in the performance of the graphite substrate or an increase in post-processing costs.

[0035] The coating obtained by this invention is a single, highly crystalline pure TaC phase, free of C phase and other impurities. The coating has a uniform tantalum distribution, which can significantly improve the physical properties and chemical stability of the coating, such as hardness and corrosion resistance.

[0036] The tantalum carbide coating obtained by this invention has strong adhesion between the coating and the base in the graphite substrate, and can be used stably for a long time in high temperature and highly corrosive environments. Attached Figure Description

[0037] Figure 1 The image shows a physical photograph of the graphite substrate with tantalum carbide coating obtained in Example 1 and its corresponding surface microstructure.

[0038] Figure 2 This is a distribution diagram of tantalum element in the tantalum carbide coating in the graphite substrate obtained in Example 1.

[0039] Figure 3 The image shows the X-ray diffraction characterization of the tantalum carbide coating in the graphite substrate obtained in Example 1.

[0040] Figure 4 Comparison of X-ray diffraction characterization of tantalum carbide coatings in graphite substrates obtained in Examples 1-3.

[0041] Figure 5 Comparative X-ray diffraction images of tantalum carbide coatings in graphite substrates obtained in Comparative Examples 1-4. Detailed Implementation

[0042] The technical solutions of the present invention will be further described below with reference to embodiments thereof. The embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0043] Example 1

[0044] The graphite substrate with tantalum carbide coating is prepared by the following steps:

[0045] (1) The surface of the graphite substrate is treated to make it smooth, and then cleaned sequentially with deionized water and anhydrous ethanol. The substrate is then dried at 80℃ for 10 hours to obtain a pretreated graphite substrate. The density of the graphite material used in the substrate is 1.86 g / cm³. 3 The coefficient of thermal expansion is 6.4 × 10⁻⁶. -6 K -1 ;

[0046] (2) The coating raw materials were mixed by ball milling at a speed of 400 r / min for 6 h and a ball-to-material ratio of 8:1 to obtain a raw material mixture. The coating raw materials were sodium chloride, potassium chloride, potassium fluoride, tantalum oxide and boron carbide. The mass ratio of sodium chloride, lithium chloride, potassium fluoride and tantalum oxide was 20:30:8:1 and the mass ratio of tantalum oxide and boron carbide was 50:1.

[0047] (3) The pretreated graphite substrate and the raw material mixture were placed in a corundum crucible and heated to 1200°C at a heating rate of 10°C / min. The mixture was sintered in an Ar atmosphere for 3 hours. After sintering, the mixture was cooled to room temperature in the furnace and washed 10 times with boiling water to obtain a graphite substrate with a tantalum carbide coating.

[0048] The morphology and coating characteristics of the obtained tantalum carbide coating on the graphite substrate are shown in the attached figure. Figure 1-3 As shown, where, Figure 1 The image shows a physical photograph of a graphite substrate with a tantalum carbide coating and the corresponding surface microstructure. Figure 2 The distribution of Ta element in the coating is shown. Figure 3The X-ray diffraction pattern of the coating is shown (with the X-ray diffraction patterns of B4C, Ta2C, and TaC crystals as references for comparison).

[0049] pass Figure 1 and Figure 2 As can be seen, the graphite substrate surface of the tantalum carbide coating obtained in this embodiment is completely and uniformly covered by the coating, with high surface flatness and smoothness, and the tantalum element in the coating is evenly distributed.

[0050] pass Figure 3 It can be seen that the tantalum carbide coating in the graphite substrate obtained in this embodiment has excellent crystallinity, and the coating contains only a single TaC phase without other impurities.

[0051] Example 2

[0052] The graphite substrate with tantalum carbide coating is prepared by the following steps:

[0053] (1) The surface of the graphite substrate is treated to make it smooth, and then cleaned sequentially with deionized water and anhydrous ethanol. The substrate is then dried at 80℃ for 10 hours to obtain a pretreated graphite substrate. The density of the graphite material used in the substrate is 1.86 g / cm³. 3 The coefficient of thermal expansion is 6.4 × 10⁻⁶. -6 K -1 ;

[0054] (2) The coating raw materials were mixed by ball milling at a speed of 400 r / min for 6 h and a ball-to-material ratio of 8:1 to obtain a raw material mixture. The coating raw materials were sodium chloride, potassium chloride, potassium fluoride, tantalum oxide and boron carbide. The mass ratio of sodium chloride, lithium chloride, potassium fluoride and tantalum oxide was 20:30:8:1 and the mass ratio of tantalum oxide and boron carbide was 25:1.

[0055] (3) The pretreated graphite substrate and the raw material mixture were placed in a corundum crucible and heated to 1200°C at a heating rate of 10°C / min. The mixture was sintered in an Ar atmosphere for 3 hours. After sintering, the mixture was cooled to room temperature in the furnace and washed 10 times with boiling water to obtain a graphite substrate with a tantalum carbide coating.

[0056] Example 3

[0057] The graphite substrate with tantalum carbide coating is prepared by the following steps:

[0058] (1) The surface of the graphite substrate is treated to make it smooth, and then cleaned sequentially with deionized water and anhydrous ethanol. The substrate is then dried at 80℃ for 10 hours to obtain a pretreated graphite substrate. The density of the graphite material used in the substrate is 1.86 g / cm³. 3 The coefficient of thermal expansion is 6.4 × 10⁻⁶.-6 K -1 ;

[0059] (2) The coating raw materials were mixed by ball milling at a speed of 400 r / min for 6 h and a ball-to-material ratio of 8:1 to obtain a raw material mixture. The coating raw materials were sodium chloride, potassium chloride, potassium fluoride, tantalum oxide and boron carbide. The mass ratio of sodium chloride, lithium chloride, potassium fluoride and tantalum oxide was 20:30:8:1 and the mass ratio of tantalum oxide and boron carbide was 75:1.

[0060] (3) The pretreated graphite substrate and the raw material mixture were placed in a corundum crucible and heated to 1200°C at a heating rate of 10°C / min. The mixture was sintered in an Ar atmosphere for 3 hours. After sintering, the mixture was cooled to room temperature in the furnace and washed 10 times with boiling water to obtain a graphite substrate with a tantalum carbide coating.

[0061] The bonding strength between the tantalum carbide coating and the graphite substrate obtained in Examples 1-3 was tested by the pull-out method, and the results are shown in Table 1.

[0062] Table 1. Coating bond strength test results for Examples 1-3

[0063] Example Example 1 Example 2 Example 3 Bond strength between coating and substrate (MPa) 11.218 10.705 9.122

[0064] It can be seen that the bonding strength between the tantalum carbide coating and the graphite substrate obtained in Examples 1-3 is relatively strong, with Example 1 showing the strongest bonding strength.

[0065] X-ray derivatization characterization was performed on the tantalum carbide coatings on the graphite substrates obtained in Examples 1-3, and the results are shown in the appendix. Figure 4 As shown.

[0066] pass Figure 4 As shown, Examples 1-3 all successfully prepared highly crystalline tantalum carbide coatings with a single TaC phase.

[0067] Comparative Example 1

[0068] The graphite substrate with tantalum carbide coating was prepared by the same steps as in Example 1, except that the heating rate in step (3) was 5 °C / min.

[0069] Comparative Example 2

[0070] The tantalum carbide-coated graphite substrate was prepared using the same steps as in Example 1, except that the graphite material used in the substrate had a density of 1.8 g / cm³. 3 The coefficient of thermal expansion is 4.5 × 10⁻⁶. -6 K -1 .

[0071] Comparative Example 3

[0072] The graphite substrate with tantalum carbide coating was prepared by the same steps as in Example 1, except that the sintering temperature in step (3) was 1300°C, i.e., the temperature was increased to 1300°C at a heating rate of 10°C / min.

[0073] Comparative Example 4

[0074] The graphite substrate with tantalum carbide coating was prepared using the same steps as in Example 1, except that the mass ratio of sodium chloride, lithium chloride, potassium fluoride, and tantalum oxide in the coating raw materials was 20:30:1:1, and the mass ratio of tantalum oxide and boron carbide was 50:1.

[0075] X-ray derivatization characterization was performed on the tantalum carbide coatings on the graphite substrates obtained in Comparative Examples 1-4, and the results are shown in the appendix. Figure 5 As shown.

[0076] From the appendix Figure 5 It can be seen that the crystallization quality of the coating materials obtained in Comparative Examples 1-4 is not as good as that in Example 1. The crystallization status and coating coverage are shown in Table 2 below:

[0077] Table 2 shows the XRD test results and coating coverage of Comparative Examples 1-4.

[0078]

[0079] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite substrate with a tantalum carbide coating, characterized in that, It includes: (1) The graphite substrate is pretreated to obtain a pretreated graphite substrate with a smooth, clean, and dry surface; wherein the coefficient of thermal expansion of the graphite material in the graphite substrate is 6.0 × 10⁻⁶. -6 -6.4×10 -6 K -1 ; (2) The coating raw materials are ball-milled and mixed to obtain a raw material mixture; the coating raw materials are composed of chloride, fluoride, tantalum source and sintering aid; (3) The pretreated graphite substrate and the raw material mixture are heated to 1000-1300℃ at a heating rate of 5-10℃ / min and sintered at atmospheric pressure for 2-10h to obtain the graphite substrate with tantalum carbide coating. Wherein, the chloride is selected from two or more of lithium chloride, sodium chloride, potassium chloride, and calcium chloride; the fluoride is selected from sodium fluoride and / or potassium fluoride; the tantalum source is one or more of elemental tantalum, tantalum carbide, and tantalum oxide; and the sintering aid is one or more of boron oxide, boron carbide, and sodium borate. The mass ratio of the chloride, fluoride and tantalum source is 10-100:5-20:1-20, and the mass ratio of the tantalum source to the sintering aid is 10-100:

1.

2. The preparation method according to claim 1, characterized in that, The coating material consists of sodium chloride, potassium chloride, potassium fluoride, tantalum oxide, and boron carbide.

3. The preparation method according to claim 2, characterized in that, In the coating raw materials, the mass ratio of sodium chloride, lithium chloride, potassium fluoride, and tantalum oxide is 20:30:8:1, and the mass ratio of tantalum oxide and boron carbide is 25-75:

1.

4. The preparation method according to claim 1, characterized in that, The ball milling method uses a ball milling speed of 200-800 r / min, a ball milling time of 2-10 h, and a ball-to-material ratio of 8:

1.

5. The preparation method according to claim 1, characterized in that, The atmospheric pressure sintering is carried out at a heating rate of 10℃ / min in an inert gas atmosphere, and the furnace is cooled to room temperature after sintering.

6. The preparation method according to claim 1, characterized in that, The graphite material in the graphite base has a density of 1.75-1.88 g / cm³. 3 .

7. The preparation method according to claim 1, characterized in that, The temperature of atmospheric pressure sintering is greater than or equal to 1000℃ and less than 1300℃.

8. The preparation method according to claim 1, characterized in that, In the coating raw materials, the purity of the chloride is greater than 99.5%, the purity of the fluoride is greater than 99.5%, the purity of the tantalum source is greater than 99.5%, and the purity of the sintering aid is greater than 99.5%.

9. The preparation method according to claim 1, characterized in that, It also includes, The product obtained by atmospheric pressure sintering is subjected to several boiling water washes to obtain the graphite base of the tantalum carbide coating.

10. A graphite substrate with a tantalum carbide coating prepared by the preparation method of any one of claims 1-9.

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