Tantalum carbide coated carbon material

Abstract

To provide a carbon material coated with tantalum carbide having excellent corrosion resistance.SOLUTION: There is provided a carbon material coated with tantalum carbide which contains a carbon base material mainly composed of carbon and a tantalum carbide coating film for coating at least a part of the carbon base material, wherein the niobium content in the tantalum carbide coating film measured by glow discharge mass spectrometry is 15 mass ppm or more and the iron content in the tantalum carbide coating film measured by glow discharge mass spectrometry is 20 mass ppm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a tantalum carbide-coated carbon material in which a tantalum carbide film is coated on the surface of a carbon substrate.

Background Art

[0002] Carbides such as tantalum carbide and niobium carbide have a high melting point and are excellent in chemical stability, strength, toughness, and corrosion resistance. Therefore, by coating a carbon substrate with a carbide, properties such as the heat resistance, chemical stability, strength, toughness, and corrosion resistance of the carbon substrate can be improved. Carbide-coated carbon materials in which a carbide film is coated on the surface of a carbon substrate, particularly tantalum carbide-coated carbon materials, are used as members of single crystal manufacturing apparatuses for next-generation semiconductors such as SiC (silicon carbide), GaN (gallium nitride), and AlN (aluminum nitride).

[0003] A problem with next-generation semiconductors is that their manufacturing cost is higher than that of conventional Si semiconductors. As a method for further reducing this manufacturing cost, for example, manufacturing a single crystal of a next-generation semiconductor by the HTCVD (High Temperature Chemical Vapor Deposition) method can be mentioned. In this method, since the source gas is reacted at a high temperature, it is required to further enhance the corrosion resistance of the tantalum carbide-coated carbon material. For example, in the HTCVD method capable of manufacturing a single crystal of SiC at high speed, since gases such as H2, SiH4, C3H8, and HCl are used at a temperature of 2000 to 2500°C, excellent corrosion resistance is required for the tantalum carbide-coated carbon material as compared with the general SiC sublimation method (see Non-Patent Documents 1 and 2).

[0004] So far, attempts have been made to improve the corrosion resistance of tantalum carbide-coated carbon materials by various approaches. For example, Patent Document 1 improves the corrosion resistance of a tantalum carbide-coated carbon material by including iron at a concentration of 20 to 1000 mass ppm in a tantalum carbide film coating an isotropic graphite substrate. Further, Patent Document 2 improves the corrosion resistance by reducing the crystallinity of a tantalum carbide film coating a carbon substrate. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6888330 [Patent Document 2] Patent No. 3938361 [Non-patent literature]

[0006] [Non-Patent Document 1] "Current Status and Future Prospects of SiC Wafers," Shoichi Onda, DENSO TECHNICAL REVIEW Vol.22, pp41-50 (2017). [Non-Patent Document 2] "New Materials Power Semiconductor Project for Realizing a Low-Carbon Society," New Energy and Industrial Technology Development Organization (NEDO), Department of Electronics, Materials and Nanotechnology, pp. III-78-81 (2015 Document 5-1). [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, when tantalum carbide-coated carbon materials are used as components in next-generation semiconductor single-crystal manufacturing equipment, the environment for these materials during single-crystal manufacturing is extremely harsh. Therefore, after repeated single-crystal manufacturing, it is necessary to replace the components using tantalum carbide-coated carbon materials. From the perspective of next-generation semiconductor manufacturing costs, the less frequently components using tantalum carbide-coated carbon materials need to be replaced, the better. For this reason, further improvement in the corrosion resistance of tantalum carbide-coated carbon materials is desired.

[0008] Therefore, the present invention aims to provide a tantalum carbide-coated carbon material with excellent corrosion resistance. [Means for solving the problem]

[0009] The inventors diligently researched how to solve this problem and discovered that by lowering the iron concentration in the tantalum carbide coating and keeping the niobium content within a predetermined range, the corrosion resistance of tantalum carbide-coated carbon materials can be significantly improved compared to conventional tantalum carbide-coated carbon materials. Building upon this result, the inventors completed the present invention described below. The gist of the present invention is as follows. [1] A tantalum carbide coated carbon material comprising a carbon substrate mainly composed of carbon and a tantalum carbide coating film covering at least a portion of the carbon substrate, characterized in that the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 15 ppm by mass or more, and the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 20 ppm by mass or less. [2] The tantalum carbide coated carbon material according to [1] above, characterized in that the arithmetic mean roughness Ra of the surface of the tantalum carbide coated film is 0.1 μm or more and 10.0 μm or less. [3] The tantalum carbide coated carbon material according to [1] or [2] above, characterized in that the arithmetic mean roughness Ra of the carbon substrate surface is 0.1 μm or more and 9.5 μm or less. [4] The tantalum carbide coated carbon material according to any one of [1] to [3] above, characterized in that the number of tantalum atoms contained in the tantalum carbide coating film is 0.8 times or more and 1.2 times or less the number of carbon atoms contained in the tantalum carbide coating film. [5] The tantalum carbide coated carbon material according to any one of [1] to [4] above, characterized in that the thickness of the tantalum carbide coating film is 10 to 100 μm. [Effects of the Invention]

[0010] According to the present invention, a tantalum carbide-coated carbon material with excellent corrosion resistance can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an externally heated, reduced-pressure CVD apparatus. [Figure 2]It is a schematic diagram of a metal chloride generator. [Figure 3] It is a schematic diagram of an HTCVD apparatus. [Figure 4] It is a diagram showing the measurement results by glow discharge mass spectrometry of the tantalum carbide-coated carbon material in Example 4. [Figure 5] It is the result of XRD measurement of the tantalum carbide-coated carbon material of Example 4. [Figure 6] It is a diagram showing the relationship between the content of niobium in the tantalum carbide coating film measured by glow discharge mass spectrometry and the half-value width of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating film. [Figure 7] It is a diagram showing the relationship between the content of niobium in the tantalum carbide coating film measured by glow discharge mass spectrometry and the number of times of manufacturing of the SiC single crystal until the tantalum carbide-coated carbon material becomes unusable. [Embodiments for Carrying Out the Invention]

[0012] [Tantalum Carbide-Coated Carbon Material] The present invention is a tantalum carbide-coated carbon material including a carbon base material mainly composed of carbon and a tantalum carbide coating film covering at least a part of the carbon base material, wherein the content of niobium in the tantalum carbide coating film measured by glow discharge mass spectrometry is 15 mass ppm or more, and the content of iron in the tantalum carbide coating film measured by glow discharge mass spectrometry is 20 mass ppm or less. Thereby, the tantalum carbide-coated carbon material of the present invention has excellent corrosion resistance.

[0013] (Carbon Base Material) The carbon base material in the tantalum carbide-coated carbon material of the present invention is a base material mainly composed of carbon. The carbon base material may further contain chlorine. Examples of the material of the carbon base material include isotropic graphite, extruded graphite, pyrolytic graphite, carbon fiber reinforced carbon composite material (C / C composite), etc. The shape and characteristics of the carbon base material are not particularly limited, and those processed into any shape according to the use and the like can be used.

[0014] <Arithmetic surface roughness Ra> The arithmetic mean roughness Ra of the surface of the carbon substrate is preferably 0.1 μm or more and 9.5 μm or less. Since the surface roughness of the carbon substrate is reflected in the surface roughness of the tantalum carbide coating film, when the arithmetic mean roughness Ra of the surface of the carbon substrate is 0.1 μm or more and 9.5 μm or less, it becomes easy to make the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 0.1 μm or more and 10.0 μm or less. From such a viewpoint, the arithmetic mean roughness Ra of the surface of the carbon substrate is more preferably 1.0 μm or more and 8.0 μm or less, and still more preferably 2.0 μm or more and 6.0 μm or less. The arithmetic mean roughness Ra of the surface of the carbon substrate is a value measured based on JIS B 0633:2001 (ISO 4288:1996).

[0015] (Tantalum carbide coating film) The tantalum carbide coating film in the tantalum carbide-coated carbon material of the present invention contains niobium with tantalum carbide as the main component. Further, the tantalum carbide coating film does not contain iron, or when the tantalum carbide coating film contains iron, the content of iron in the tantalum carbide coating film is very small.

[0016] <Content of niobium> The niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 15 ppm by mass or more. If the niobium content in the tantalum carbide coating film is less than 15 ppm by mass, the effect of niobium on the corrosion resistance of the tantalum carbide coated carbon material may be insufficient. As a result, when tantalum carbide coated carbon material is used as a component in single crystal manufacturing equipment for next-generation semiconductors such as SiC (silicon carbide), GaN (gallium nitride), and AlN (aluminum nitride), the frequency of component replacement may not be sufficiently reduced, and the manufacturing cost of next-generation semiconductors may not be reduced. From this viewpoint, the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is preferably 20 ppm by mass or more, more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, even more preferably 200 ppm by mass or more, even more preferably 300 ppm by mass or more, and even more preferably 400 ppm by mass or more. Furthermore, while there is no particular upper limit to the range of niobium content in the tantalum carbide coating film measured by glow discharge mass spectrometry, the niobium content in the tantalum carbide coating film measured by glow discharge mass spectrometry is preferably 1000 ppm by mass or less. Moreover, from the viewpoint of further improving the corrosion resistance of the tantalum carbide coated carbon material, the niobium content in the tantalum carbide coating film measured by glow discharge mass spectrometry is more preferably 900 ppm by mass or less, even more preferably 800 ppm by mass or less, even more preferably 700 ppm by mass or less, even more preferably 600 ppm by mass or less, and even more preferably 500 ppm by mass or less.

[0017] Glow discharge mass spectrometry is a method in which a glow discharge is generated using a sample as the cathode in an argon atmosphere. This sputters the sample surface within the plasma, and the sputtered sample is ionized within the glow discharge. The generated ions are then analyzed using mass spectrometry. In this specification, the niobium content in the tantalum carbide coating is the average value of the niobium content relative to the tantalum carbide film in the range where the proportion of the tantalum carbide film in the sputtered depth direction is 20 to 80% by mass. In the range where the proportion of the sputtered tantalum carbide film is less than 20% by mass, the niobium content may be affected by impurities adhering to the surface of the tantalum carbide coating. On the other hand, in the range where the proportion of the sputtered tantalum carbide film is greater than 80% by mass, the niobium content may be affected by impurity elements derived from the carbon substrate. By measuring the niobium content in the tantalum carbide coating by glow discharge mass spectrometry in the range where the proportion of the sputtered tantalum carbide film is 20 to 80% by mass, the influence of impurities adhering to the surface of the tantalum carbide coating and impurity elements derived from the carbon substrate can be eliminated.

[0018] Specifically, glow discharge mass spectrometry was performed using VGS Scientific's VG9000, ElementGD, and Astrum, and Ar + Depth analysis is performed using sputtering. Here, when the number of sputtering cycles in the depth direction is plotted on the horizontal axis and the impurity concentration on the vertical axis, the point at which the elemental concentration of tantalum begins to decrease is Ar + The point at which the sputtering reaches the carbon substrate, i.e., the point at which the entire tantalum carbide film in the depth direction has been sputtered, is considered to be the point at which the sputtered tantalum carbide film is completely sputtered, and the proportion of sputtered tantalum carbide film at that point is defined as 100% by mass. The number of sputtering cycles within the range of 20-80% of the total number of sputtering cycles is considered to correspond to the range where the proportion of sputtered tantalum carbide film is 20-80% by mass, and the niobium content in the tantalum carbide coating film is defined by the niobium content measured by sputtering at that number of sputtering cycles. For example, if the elemental concentration of tantalum begins to decrease at the 60th sputtering cycle, it is assumed that 100% by mass of the tantalum carbide film has been sputtered at the 60th sputtering cycle. The average value of the niobium content in the tantalum carbide coating film measured at the 12th to 48th sputtering cycles, which correspond to the range where the proportion of sputtered tantalum carbide film is 20-80% by mass, is defined as the niobium content in the tantalum carbide coating film.

[0019] In glow discharge mass spectrometry analysis, the elements detected by a single sputtering pass represent the average value of all elements present from the surface immediately before sputtering to the depth excavated by that sputtering pass. Therefore, the analysis values ​​at the very surface immediately after the start of the analysis may include not only elements contained in the tantalum carbide film near the surface, but also elements originating from deposits on the surface. Similarly, when the sputtering depth reaches the carbon material of the substrate, impurity elements originating from the carbon substrate may also be detected. Therefore, to avoid the influence of surface deposits and carbon substrates, the evaluation of impurity concentrations in the tantalum carbide coating film is based on detected values ​​in the range of 20-80% by mass for the sputtered tantalum carbide film, as described above.

[0020] The reason why tantalum carbide-coated carbon materials exhibit excellent corrosion resistance when the tantalum carbide coating contains niobium within the aforementioned range is not entirely clear, but it can be inferred as follows. It is known that when the crystal orientation of tantalum carbide constituting a tantalum carbide coating is relatively aligned and a certain crystal plane develops, resulting in a crystalline structure, anisotropy occurs in the chemical and physical properties. For this reason, when tantalum carbide coated carbon materials are used for extended periods at high temperatures and in a reducing or reactive gas atmosphere, cracks and other damage may occur due to wear and tear, starting from specific chemically or physically weak areas of the tantalum carbide coating (see, for example, Patent Document 2). The tantalum carbide-coated carbon material of the present invention exhibits a more disordered crystalline state compared to conventional materials due to the presence of niobium in the tantalum carbide coating. As a result, the tantalum carbide coating has low overall crystallineity, approaching a so-called amorphous state. Consequently, anisotropy in chemical and physical properties is reduced, and chemically or physically weak areas are less likely to exist on the surface of the tantalum carbide coating. As a result, the surface of the tantalum carbide coating becomes less susceptible to wear even when in contact with reducing gases or reactive gases, and cracks and damage caused by wear are less likely to occur. Furthermore, the corrosion resistance of the tantalum carbide coating is improved, and consequently, the corrosion resistance of the tantalum carbide-coated carbon material is also expected to improve. The form of niobium present in the tantalum carbide coating is not limited. Niobium may be present in the tantalum carbide coating in the form of elemental niobium or a niobium compound, for example.

[0021] <Iron content> The iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 20 ppm by mass or less. If the iron content in the tantalum carbide coating film is greater than 20 ppm by mass, the corrosion resistance of the tantalum carbide coated carbon material may decrease. As a result, when tantalum carbide coated carbon material is used as a component in single-crystal manufacturing equipment for next-generation semiconductors, the frequency of component replacement may increase, potentially raising the manufacturing cost of next-generation semiconductors. From this perspective, the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is preferably 10 ppm by mass or less, more preferably 1 ppm by mass or less, even more preferably 0.1 ppm by mass or less, and even more preferably 0.01 ppm by mass or less. Furthermore, there is no particular lower limit to the range of niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, but for example, it is 0 ppm by mass. Note that the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, can be measured in the same manner as the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry.

[0022] The reason why the corrosion resistance of tantalum carbide-coated carbon materials deteriorates when the tantalum carbide coating contains iron beyond the aforementioned range is unclear, but it can be inferred as follows. If the iron content in the tantalum carbide coating is greater than 20 ppm by mass, it is presumed that under the high temperature and reducing or reactive gas atmosphere of an HTCVD environment, the tantalum carbide coating will react with HCl, gasify, and lose its density.

[0023] <Arithmetic mean roughness Ra> The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film is preferably 0.1 μm or more and 10.0 μm or less. When the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film is 0.1 μm or more and 10.0 μm or less, the adhesion to the substrate can be increased while maintaining the density of the tantalum carbide coating film. From this viewpoint, the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film is more preferably 1.0 μm or more and 8.5 μm or less, and even more preferably 2.0 μm or more and 6.5 μm or less. The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 11 is a value measured based on JIS B 0633:2001 (ISO 4288:1996).

[0024] The arithmetic mean roughness Ra of the tantalum carbide coating can be adjusted, for example, by adjusting the surface roughness of the carbon substrate. For example, if the thickness of the tantalum carbide coating is about 20 μm, the surface roughness of the carbon substrate will be the same as the surface roughness of the tantalum carbide coating. Alternatively, after forming the tantalum carbide coating on the carbon substrate, the arithmetic mean roughness Ra of the tantalum carbide coating can be adjusted by polishing the surface of the tantalum carbide coating using an abrasive or file.

[0025] <thickness> The thickness of the tantalum carbide coating is preferably 10 to 1000 μm. When the thickness of the tantalum carbide coating is 10 μm or more, the corrosion resistance of the tantalum carbide-coated carbon material can be further improved. When the thickness of the tantalum carbide coating is 1000 μm or less, the film formation time of the tantalum carbide coating can be shortened, and the production efficiency of the tantalum carbide-coated carbon material can be improved. From such a viewpoint, the thickness of the tantalum carbide coating is more preferably 20 to 500 μm, and even more preferably 30 to 200 μm.

[0026] <Multiple of the number of tantalum atoms to the number of carbon atoms> The number of tantalum atoms contained in the tantalum carbide coating is preferably 0.8 times or more and 1.2 times or less with respect to the number of carbon atoms. When the number of tantalum atoms contained in the tantalum carbide coating is 0.8 times or more and 1.2 times or less with respect to the number of carbon atoms, the corrosion resistance of the tantalum carbide-coated carbon material can be further improved. From such a viewpoint, the number of tantalum atoms contained in the tantalum carbide coating is more preferably 0.85 times or more and 1.15 times or less, and even more preferably 0.9 times or more and 1.1 times or less with respect to the number of carbon atoms. The number of tantalum atoms and the number of carbon atoms contained in the tantalum carbide coating can be estimated from the peak intensity of X-ray diffraction (XRD) measurement.

[0027] <XRD half-value width> The intensity of the X-ray diffraction line of the tantalum carbide coating is obtained by 2θ / θ measurement (out-of-plane) using an X-ray diffractometer (XRD). The peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating is observed around 2θ = 40°. The peak width at half maximum (FWHM) indicates the size of the crystallites constituting the tantalum carbide coating. This FWHM increases with decreasing crystallinity (approaching amorphous), crystallite refinement, and compositional variations. However, in the case of the tantalum carbide coating in the tantalum carbide-coated carbon material of the present invention, where the composition is stable, crystallinity is good, and the crystallites are of a certain size, the FWHM falls within a certain range. The FWHM is an optimal indicator for identifying the tantalum carbide coating in the tantalum carbide-coated carbon material of the present invention.

[0028] In X-ray diffraction, the full width at half maximum (FWHM) is the angle difference of 2θ at half the maximum value (fmax) of the peak (fmax / 2) when the diffraction peak due to the (hkl) plane of the X-ray diffraction spectrum is fitted with a pseudo-Voigt function. In this specification, the FWHM is determined by this method, including in the examples described later. The FWHM of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating film obtained in this way is preferably 0.6° or less, 0.5° or less, and even 0.4° or less. If the above FWHM is too large, the crystal grains are too small and the propagation of cracks etc. cannot be sufficiently blocked, or the low-crystallinity amorphous structure crystallizes under high-temperature conditions and undergoes structural changes, which is undesirable. The lower limit of the above FWHM is not particularly limited, but it is preferably 0.01° or even 0.1°. If the FWHM is too small, the crystal grains become too large and it becomes difficult to form a granular structure that is stacked without orientation. Furthermore, as the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, increases, the full width at half maximum (FWHM) of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating film increases.

[0029] (Method for manufacturing tantalum carbide coated carbon material) The following describes an example of a method for producing the tantalum carbide coated carbon material for heating according to the present invention. The tantalum carbide-coated carbon material of the present invention can be manufactured, for example, by forming a tantalum carbide layer on the surface of a carbon substrate. The tantalum carbide layer can be formed on the surface of the carbon substrate by methods such as chemical vapor deposition (CVD), sintering, or carbonization. Among these, the CVD method is preferred as a method for forming the tantalum carbide layer because it can form a uniform and dense film.

[0030] Furthermore, CVD methods include thermal CVD, photoCVD, and plasma CVD, and thermal CVD can be used, for example, to form the tantalum carbide layer. Thermal CVD has advantages such as a relatively simple apparatus configuration and no damage caused by plasma. Formation of a tantalum carbide coating film by thermal CVD can be carried out, for example, using an externally heated vacuum CVD apparatus 11 as shown in Figure 1. In the externally heated vacuum CVD apparatus 11, the carbon substrate 14 is supported by support means 15 in a reaction chamber 12 equipped with a heater 13, a raw material supply unit 16, an exhaust unit 17, etc.

[0031] An example of a method for producing the tantalum carbide-coated carbon material of the present invention will be described with reference to Figures 1 and 2. First, the carbon substrate 14 is placed in the reaction chamber 12 of the externally heated reduced-pressure CVD apparatus 11. The carbon substrate 14 is supported by a support means 15 having three support parts with pointed tips. The surface roughness Ra of the carbon substrate 14 is preferably 0.1 μm or more and 9.5 μm or less, as described above.

[0032] Next, the reaction chamber 12 is heated. For example, the reaction chamber 12 is heated under reduced pressure and at a temperature of 1000 to 2500°C.

[0033] Next, a tantalum carbide layer is formed on the surface of the carbon substrate 14. As raw material gases, a gas containing carbon atoms, such as methane (CH4), and a tantalum halogen gas, such as tantalum pentachloride (TaCl5), are supplied from the raw material supply unit 16 to the reaction chamber 12. The tantalum halogen gas can be generated, for example, by reacting tantalum metal with a halogen gas. For example, in the metal chloride generator 21 shown in Figure 2, tantalum metal and a small amount of niobium metal 25 are filled together in a container 24 and heated to 300°C to 1200°C by a heating device 23. At least one of chlorine gas and hydrogen chloride gas is then supplied to generate tantalum halogen gas and niobium halogen gas.

[0034] Next, the raw material gas supplied from the raw material supply unit 16 shown in Figure 1 is subjected to a thermal CVD reaction at a high temperature of 1000 to 2500°C under reduced pressure to form a niobium-containing tantalum carbide layer on the carbon substrate 14. [Examples]

[0035] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0036] The tantalum carbide-coated carbon materials of Examples 1-7 and Comparative Examples 1-2 were prepared as follows. (Example 1) First, a carbon substrate 14 was placed in the reaction chamber of the externally heated, reduced-pressure CVD apparatus 11 shown in Figure 1. A cylindrical member made of isotropic graphite was used as the carbon substrate 14. The carbon substrate 14 was supported by a support means 15 having three support parts with pointed ends. The surface roughness Ra of the carbon substrate 14 was 5.0 μm.

[0037] Next, the reaction chamber 12 was heated to a temperature of 1550°C. Then, a mixed gas of TaCl5 gas and NbCl5 gas, CH4 gas, and Ar gas were mixed, and the resulting mixed gas was supplied to the reaction chamber 12 to form a tantalum carbide layer on the surface of the carbon substrate 14, thereby producing the tantalum carbide coated carbon material of Example 1. The film formation time for the tantalum carbide layer was 3 hours. The flow rates of CH4 gas and carrier gas (Ar gas) were controlled by a mass flow controller to 1.0 SLM and 1.0 SLM, respectively.

[0038] A mixed gas of TaCl5 and NbCl5 was prepared as follows. A quartz container 24 containing 1000g of Ta metal and 0.10g of Nb metal was placed in the metal chloride generator 21 shown in Figure 2. Next, the Ta metal and Nb metal were heated to 850°C by a heating device 23, and a mixed gas of HCl gas and Cl2 gas was supplied to the metal chloride generator 21 to react with the Ta metal and Nb metal with the mixed gas of HCl gas and Cl2 gas (HCl gas:Cl2 gas = 1:1 (molar ratio)) to produce a mixed gas of TaCl5 and NbCl5. The mixed gas of TaCl5 and NbCl5 was controlled to 0.25 SLM and supplied into the reaction chamber 12. Ta metal and Nb metal with a purity of 99.999% were used. The thickness of the tantalum carbide layer was 40 μm.

[0039] (Example 2) The tantalum carbide-coated carbon material of Example 2 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 0.50g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0040] (Example 3) The tantalum carbide-coated carbon material of Example 3 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 1.00g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0041] (Example 4) The tantalum carbide-coated carbon material of Example 4 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 2.00g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0042] (Example 5) The tantalum carbide-coated carbon material of Example 5 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 3.00g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0043] (Example 6) The tantalum carbide-coated carbon material of Example 6 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 4.00g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0044] (Example 7) The tantalum carbide-coated carbon material of Example 7 was prepared in the same manner as in Example 1, except that 1000g of Ta metal and 5.00g of Nb metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and NbCl5 gas.

[0045] (Comparative Example 1) A tantalum carbide-coated carbon material for Comparative Example 1 was prepared in the same manner as in Example 1, except that 1000 g of Ta metal and 5.00 g of Fe metal were placed in a quartz container 24 to generate a mixed gas of TaCl5 gas and FeCl3 gas instead of a mixed gas of TaCl5 gas and NbCl5 gas.

[0046] (Comparative Example 2) The tantalum carbide-coated carbon material of Comparative Example 2 was prepared in the same manner as in Example 1, except that 1000g of Ta metal was placed in a quartz container 24 to generate TaCl5 gas instead of a mixed gas of TaCl5 gas and NbCl5 gas.

[0047] The tantalum carbide-coated carbon materials prepared as described above in Examples 1-7 and Comparative Examples 1-2 were evaluated as follows.

[0048] (Surface roughness Ra of tantalum carbide coating) The surface roughness Ra of the tantalum carbide coating was measured according to JIS B 0633:2001 (ISO 4288:1996).

[0049] (Surface roughness Ra of carbon substrate) The surface roughness Ra of the carbon substrate was measured according to JIS B 0633:2001 (ISO 4288:1996).

[0050] (Multiple of the number of tantalum atoms to the number of carbon atoms in a tantalum carbide coating) The number of tantalum atoms and carbon atoms contained in the tantalum carbide coating film was determined based on the peak intensity measured by X-ray diffraction (XRD).

[0051] (Niobium content in tantalum carbide coating measured by glow discharge mass spectrometry) The niobium content in the tantalum carbide coating was measured by glow discharge mass spectrometry in accordance with the method described in the above specification.

[0052] (Iron content in tantalum carbide coating measured by glow discharge mass spectrometry) The iron content in the tantalum carbide coating was measured by glow discharge mass spectrometry in accordance with the method described in the above specification.

[0053] (Full width at half maximum of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating film) The full width at half maximum (FWHM) of the peaks corresponding to the (200) plane of the tantalum carbide crystals in the tantalum carbide coating film was measured according to the method described in the above specification.

[0054] (Evaluation of durability in HTCVD) Figure 3 shows a schematic diagram of the HTCVD apparatus 30. First, a SiC single crystal 32 is grown on a seed crystal 33 that is in close contact with the support surface of the base 35. Specifically, the raw material gas is thermally decomposed in the gas decomposition chamber of the HTCVD apparatus 30 and supplied to the seed crystal 33. SiH4 gas, C3H8 gas, and HCl gas were used as the raw material gas, and H2 gas was used as the carrier gas. The C / Si ratio was set to approximately 1.0, and the growth pressure was set to 53 kPa. The surface temperature of the seed crystal 33 was 2200 to 2400 °C, the reaction time was 6 hours, and the temperature of the crucible 31 in the gas decomposition chamber was 2300 to 2500 °C. The tantalum carbide-coated carbon materials of Examples 1 to 7 and Comparative Examples 1 to 2 were used as the crucible 31 in the gas decomposition chamber. The production of SiC single crystals was repeated multiple times, and the number of SiC single crystal production cycles until the tantalum carbide-coated carbon material could no longer be used due to peeling of the tantalum carbide film was measured.

[0055] (Concentration of niobium in SiC single crystals fabricated by HTCVD) The niobium concentration in SiC single crystals was calculated using secondary ion mass spectrometry (SIMS).

[0056] (Iron concentration in SiC single crystals fabricated by HTCVD method) The iron concentration in SiC single crystals was calculated using secondary ion mass spectrometry (SIMS).

[0057] The evaluation results are shown in Table 1. Figure 4 shows an example of the distribution of thallium, carbon, niobium, and iron content from the surface to the depth direction of the tantalum carbide coating film, as measured by glow discharge mass spectrometry, for the tantalum carbide coating film of Example 4. Furthermore, Figure 5 shows an example of the XRD measurement results for the tantalum carbide coating carbon material of Example 4. Figure 6 shows the relationship between the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, and the full width at half maximum of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating film. Figure 7 shows the relationship between the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, and the number of SiC single crystal manufacturing cycles until the tantalum carbide coating carbon material becomes unusable.

[0058] [Table 1]

[0059] From the evaluation results of the tantalum carbide-coated carbon materials in Examples 1-7 and Comparative Examples 1-2 shown in Table 1, and from Figure 7, it was found that when the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 15 ppm by mass or more, and the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 20 ppm by mass or less, the number of SiC single crystals that can be manufactured before the tantalum carbide-coated carbon material becomes unusable increases. From this, it was found that the corrosion resistance of the tantalum carbide-coated carbon material is improved when the niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 15 ppm by mass or more, and the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 20 ppm by mass or less.

[0060] Figure 6 shows that the niobium content in the tantalum carbide coating can be estimated by measuring the full width at half maximum (FWHM) of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating, based on the relationship between the niobium content in the tantalum carbide coating and the FWHM of the peak corresponding to the (200) plane of the tantalum carbide crystal in the tantalum carbide coating. [Explanation of symbols]

[0061] 11. External Heating Type Reduced Pressure CVD Apparatus 12 Reaction Chambers 13 Heater 14 Carbon substrate 15 Support means 16 Raw material supply department 17 Exhaust section 21 Metal Chloride Generator 23 Heating device 24. Container (quartz container) 25. Tantalum metal and small amounts of niobium metal 23 Heater 24 Carbon-based substrate 25 Support means 30 HTCVD equipment 31 Crucible 32 SiC single crystal 33 Seed Crystal 35 Pedestal

Claims

1. A tantalum carbide coated carbon material comprising a carbon substrate mainly composed of carbon and a tantalum carbide coating film covering at least a portion of the carbon substrate, The niobium content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 100 ppm by mass or more and 900 ppm by mass or less. A tantalum carbide-coated carbon material characterized in that the iron content in the tantalum carbide coating film, as measured by glow discharge mass spectrometry, is 20 ppm by mass or less.

2. The tantalum carbide coated carbon material according to claim 1, characterized in that the arithmetic mean roughness Ra of the surface of the tantalum carbide coated film is 0.1 μm or more and 10.0 μm or less.

3. The tantalum carbide coated carbon material according to claim 1 or 2, characterized in that the arithmetic mean roughness Ra of the carbon substrate surface is 0.1 μm or more and 9.5 μm or less.

4. The tantalum carbide coated carbon material according to claim 1 or 2, characterized in that the number of tantalum atoms contained in the tantalum carbide coating film is 0.8 times or more and 1.2 times or less the number of carbon atoms contained in the tantalum carbide coating film.

5. The tantalum carbide coated carbon material according to claim 1 or 2, characterized in that the thickness of the tantalum carbide coating film is 10 to 100 μm.

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