JP7544671B2 - Tantalum carbide coated carbon material - Google Patents

Description

The present invention relates to a tantalum carbide-coated carbon material in which the surface of a carbon substrate is coated with a tantalum carbide coating film.

Tantalum carbide has the highest melting point (approximately 3900°C) among transition metal carbides, and is also excellent in chemical stability, strength, toughness, and corrosion resistance. Therefore, tantalum carbide-coated carbon materials, in which a tantalum carbide film is coated on the surface of a carbon substrate, have a longer life than pure carbon materials, and are used in semiconductor single crystal manufacturing equipment for growing crystals of SiC (silicon carbide), GaN (gallium nitride), and the like in environments of 2000°C or higher.
Non-Patent Document 1 describes a method for forming a tantalum carbide film on a carbon substrate by reacting a carbon (C) source such as propane, a tantalum (Ta) source such as tantalum pentachloride, and argon (Ar) and hydrogen as carrier gases in a low-pressure chemical vapor deposition (LPCVD) apparatus.

Daejong Kim, et al., Journal of the Korean Ceramic Society, Vol. 53, No. 6, pp. 597-603, 2016.

However, although the carbon substrate coated with a tantalum carbide film has excellent durability in a high-temperature environment, the tantalum carbide film on the surface has a low emissivity, and when used as a heating member in a high-temperature environment of a manufacturing device, the efficiency of energy conversion from electric power to heat is low. Note that emissivity is a physical property value that indicates the ease with which a material emits heat, and is defined in JIS Z8117:2002 as "the ratio of the radiant emittance of a radiator to the radiant emittance of a black body at the same temperature as the radiator."
SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a tantalum carbide-coated carbon material having high emissivity.

As a result of intensive research, the inventors have found that the emissivity of a tantalum carbide coating film can be increased by forming the tantalum carbide coating film into a predetermined multi-layer structure, and have completed the present invention.
[1] A tantalum carbide-coated carbon material comprising a carbon substrate and a tantalum carbide coating film coating at least a portion of the carbon substrate, wherein the tantalum carbide coating film comprises a first tantalum carbide layer comprising first tantalum carbide crystals, and a second tantalum carbide layer comprising second tantalum carbide crystals having a tantalum carbide composition different from that of the first tantalum carbide crystals.
[2] The tantalum carbide-coated carbon material according to the above [1], wherein the apex position of a peak in an X-ray diffraction pattern of the first tantalum carbide crystal is different from the apex position of a peak in an X-ray diffraction pattern of the second tantalum carbide crystal.
[3] The tantalum carbide-coated carbon material according to the above [1] or [2], wherein the first tantalum carbide crystal is a Ta ₂ C crystal, and the second tantalum carbide crystal is a TaC crystal.
[4] The tantalum carbide-coated carbon material according to the above [3], wherein the second tantalum carbide layer is present on the carbon substrate side relative to the first tantalum carbide layer.
[5] The tantalum carbide-coated carbon material according to the above [4], wherein the outermost layer of the tantalum carbide coating film is the first tantalum carbide layer.
[6] The tantalum carbide-coated carbon material according to any one of the above [3] to [5], wherein the Ta ₂ C crystal is hexagonal Ta ₂ C (α-Ta ₂ C), the first tantalum carbide layer further contains cubic Ta (α-Ta), and in an X-ray diffraction pattern of the _first tantalum carbide layer, the peak intensity ratio ( _ITa2C (110)/ _ITa (002)) of the peak corresponding to the (110) plane of hexagonal Ta 2 C (α-Ta 2 C) to the peak corresponding to the (002) plane of cubic Ta (α- _Ta ) is 0.5 or more.
[7] The tantalum carbide-coated carbon material according to any one of the above [1] to [6], characterized in that the tantalum carbide coating film has a surface having an arithmetic mean roughness Ra of 1 to 30 μm.
[8] The tantalum carbide-coated carbon material according to any one of the above [1] to [7], wherein the emissivity of the surface of the tantalum carbide coating film, measured under conditions of a measurement temperature of 25° C. and a measurement wavelength of 2 to 22 μm, is 0.30 or more.
[9] The tantalum carbide-coated carbon material according to any one of the above [1] to [8], wherein the thermal expansion coefficient of the carbon substrate is 4.0 to 7.0×10 ⁻⁶ /° C.
[10] The tantalum carbide-coated carbon material according to any one of the above [1] to [9], wherein the tantalum carbide coating film has a thickness of 3 to 100 μm.
[11] The tantalum carbide-coated carbon material according to any one of [1] to [10] above, characterized in that the concentration of components other than Ta and C in the tantalum carbide coating film is 1500 mass ppm or less.

The present invention provides a tantalum carbide-coated carbon material with high emissivity.

FIG. 1 is a schematic cross-sectional view illustrating a tantalum carbide-coated carbon material according to an embodiment of the present invention. FIG. 1 is a schematic diagram of an example of an externally heated reduced pressure CVD apparatus used for producing a tantalum carbide-coated carbon material according to an embodiment of the present invention. 1 is an electron microscope photograph of a cross section of the tantalum carbide-coated carbon material of Example 1. 1 shows the results of an XRD measurement of the tantalum carbide-coated carbon material of Example 1. FIG. 1 is a schematic diagram of an apparatus for measuring the rate of temperature rise by induction heating. FIG. 1 is a schematic diagram of an induction heating corrosion resistance test device.

[Tantalum carbide coated carbon material]
Hereinafter, the tantalum carbide-coated carbon material of the present invention will be described using the tantalum carbide-coated carbon material according to this embodiment as an example.

Hereinafter, the tantalum carbide-coated carbon material of this embodiment will be described with reference to FIG.
The tantalum carbide-coated carbon material according to this embodiment includes a carbon substrate 13 and a tantalum carbide coating film 10 that coats at least a portion of the carbon substrate 13 .

The carbon substrate 13 is a substrate whose main component is carbon. Examples of materials for the carbon substrate 13 include isotropic graphite, extruded graphite, pyrolytic graphite, and carbon fiber reinforced carbon composite material (C/C composite). There are no particular limitations on the shape or characteristics of the carbon substrate 13, and it can be processed into any shape depending on the application.

The tantalum carbide coating film 10 includes a first tantalum carbide layer 11 including a first tantalum carbide crystal, and a second tantalum carbide layer 12 including a second tantalum carbide crystal having a different tantalum carbide composition from the first tantalum carbide crystal. By combining tantalum carbide layers including tantalum crystals having different tantalum carbide compositions, the tantalum carbide coating film can include a tantalum carbide layer including tantalum carbide crystals having a high emissivity, so that the emissivity of the tantalum carbide coating film can be increased. In addition, by combining tantalum carbide layers including tantalum crystals having different tantalum carbide compositions, the durability of the tantalum carbide coating film can also be improved. In addition, examples of the tantalum carbide crystal include TaC _x crystals, which are solid solutions of carbon interstitial compounds in tantalum, hexagonal Ta ₂ C crystals, and cubic TaC crystals.

As long as the first tantalum carbide layer 11 contains the first tantalum carbide crystal, it may contain other tantalum carbide crystals having a different tantalum carbide composition from the first tantalum carbide crystal. In this case, it is necessary that the peak intensity of the main peak in the X-ray diffraction pattern of the first tantalum carbide crystal is higher than the peak intensity of the main peak in the X-ray diffraction pattern of the other tantalum carbide crystal. That is, among the tantalum carbide crystals contained in the first tantalum carbide layer 11, the tantalum carbide crystal having the highest peak intensity of the main peak in the X-ray diffraction pattern of the first tantalum carbide layer 11 is the first tantalum carbide crystal.
Similarly, the second tantalum carbide layer 12 may contain other tantalum carbide crystals having a different tantalum carbide composition from the second tantalum carbide crystals, so long as it contains the second tantalum carbide crystals. In this case, it is necessary that the peak intensity of the main peak in the X-ray diffraction pattern of the second tantalum carbide crystals is higher than the peak intensity of the main peak in the X-ray diffraction pattern of the other tantalum carbide crystals. That is, among the tantalum carbide crystals contained in the second tantalum carbide layer 12, the tantalum carbide crystal having the highest peak intensity of the main peak in the X-ray diffraction pattern of the second tantalum carbide layer 11 is the second tantalum carbide crystal.

In addition, the tantalum carbide coating film may further include other tantalum carbide layers, so long as it includes a first tantalum carbide layer including a first tantalum carbide crystal and a second tantalum carbide layer including a second tantalum carbide crystal having a different tantalum carbide composition from the first tantalum carbide crystal. For example, the tantalum carbide coating film may include a first tantalum carbide layer including a first tantalum carbide crystal, a second tantalum carbide layer including a second tantalum carbide crystal, a third tantalum carbide layer including the first tantalum carbide crystal, and a fourth tantalum carbide layer including the second tantalum carbide crystal.

It is preferable that the apex position of the peak in the X-ray diffraction pattern of the first tantalum carbide crystal is different from the apex position of the peak in the X-ray diffraction pattern of the second tantalum carbide crystal.By combining layers containing tantalum crystals with different apex positions of the peak in the X-ray diffraction pattern, the tantalum carbide coating film can include a tantalum carbide layer containing tantalum carbide crystals with a higher emissivity, so that the emissivity of the tantalum carbide coating film can be further increased.In addition, by combining layers containing tantalum crystals with different apex positions of the peak in the X-ray diffraction pattern, the occurrence of microcracks in the tantalum carbide coating film can be further suppressed, so that the durability of the tantalum carbide coating film 10 can be further improved.
The apex position of the peak in the X-ray diffraction pattern of each tantalum carbide layer is obtained by performing 2θ/θ measurement (out-of-plane) using an X-ray diffraction (XRD) device on powder of each tantalum carbide layer obtained by scraping off each tantalum carbide layer from the tantalum carbide-coated carbon material.

It is preferable that the first tantalum carbide crystal is a Ta ₂ C crystal, and the second tantalum carbide crystal is a TaC crystal. The first tantalum carbide layer 11 containing Ta ₂ C crystal has a high emissivity, so the emissivity of the tantalum carbide coating film can be made higher than that of a conventional tantalum carbide coating film made only of TaC crystal. As a result, the heat absorption rate of the tantalum carbide-coated carbon material is high. In addition, the first tantalum carbide layer 11 containing Ta ₂ C crystal is less likely to cause microcracks than the tantalum carbide layer containing TaC crystal. This makes the durability of the tantalum carbide-coated carbon material even better than that of a conventional tantalum carbide coating film made only of TaC crystal. From the viewpoint of increasing the emissivity of the tantalum carbide coating film 10, it is preferable that the second tantalum carbide layer 12 containing TaC crystals is present on the carbon substrate 13 side relative to the first tantalum carbide layer 11 containing _Ta2C crystals, and it is more preferable that the most superficial layer of the tantalum carbide coating film is the first tantalum carbide layer 11 containing _Ta2C crystals.

In addition, even when the tantalum carbide coating film is composed only of the first tantalum carbide layer containing Ta ₂ C crystals, the emissivity of the tantalum carbide coating film can be increased. However, the deposition speed of Ta ₂ C crystals is about half that of TaC, so when the tantalum carbide coating film is composed only of the first tantalum carbide layer containing Ta ₂ C crystals, the deposition time is long and the deposition cost is high. In the tantalum carbide-coated carbon material according to this embodiment, the tantalum carbide coating film contains the second tantalum carbide layer 12 containing TaC crystals, so the deposition time of the tantalum carbide coating film is short, and as a result, the emissivity of the tantalum carbide coating film can be increased while suppressing the deposition cost of the tantalum carbide coating film. In addition, the generation of microcracks in the tantalum carbide coating film can be suppressed while suppressing the deposition cost of the tantalum carbide coating film, and as a result, the durability of the tantalum carbide-coated carbon material can be improved. In addition, the second tantalum carbide layer 12 is preferably composed mainly of TaC, and may be composed only of TaC crystal, or may contain components other than TaC crystal.In addition, even if the second tantalum carbide layer 12 is composed only of TaC crystal, the second tantalum carbide layer 12 may contain crystals and impurities other than TaC crystal that are unavoidable when forming TaC crystal.

The first tantalum carbide layer 11 is preferably composed mainly of Ta ₂ C, and may be composed only of Ta ₂ C crystals, or may contain components other than Ta ₂ C crystals. Even if the first tantalum carbide layer 11 is composed only of Ta ₂ C crystals, it may contain crystals and impurities other than Ta ₂ C crystals that are unavoidable when forming Ta ₂ C crystals. However, from the viewpoint of the emissivity of the first tantalum carbide layer 11 and the viewpoint of suppressing the occurrence of microcracks in the tantalum carbide coating film, the higher the content of Ta ₂ C crystals in the first tantalum carbide layer, the better. In addition, when the tantalum carbide-coated carbon material is used in a compound semiconductor growth device, the tantalum carbide-coated carbon material may be exposed to ammonia gas at high temperatures. If the tantalum content in the tantalum carbide coating film is high, the tantalum in the tantalum carbide coating film reacts with ammonia gas to form tantalum nitride on the surface of the tantalum carbide coating film. Since tantalum nitride has excellent ammonia resistance, the ammonia resistance of the tantalum carbide coating film is improved. From this viewpoint, in order to increase the tantalum content in the first tantalum carbide layer 11, the higher the _Ta2C crystal content in the first tantalum carbide layer, the better.

From the viewpoint of the emissivity of the first tantalum carbide layer 11, when the first tantalum carbide layer 11 contains hexagonal Ta ₂ C (α-Ta ₂ C) and cubic Ta (α-Ta), it is preferable that in an X-ray diffraction pattern of the first tantalum carbide layer 11, the peak intensity ratio (I Ta2C (110)/I Ta (002) of the peak corresponding to the (110) plane of hexagonal Ta _{2 C} (α-Ta ₂ C) to the peak corresponding to the (002) plane of cubic Ta (α- _Ta ) is 0.5 or more.
In epitaxial wafer manufacturing equipment, metal chloride is often used as a raw material, and hydrogen chloride is generated as a by-product. When the tantalum carbide-coated carbon material of this embodiment is used in an epitaxial wafer manufacturing equipment, if the peak intensity ratio (I _Ta2C (110)/I _Ta (002)) is 0.5 or more, it is possible to suppress the reaction of hydrogen chloride generated as a by-product with cubic Ta (α-Ta) in the first tantalum carbide layer 11. From this viewpoint, it is more preferable that the peak intensity ratio (I _Ta2C (110)/I _Ta (002)) is 0.9 or more.

The X-ray diffraction pattern of the first tantalum carbide layer 11 is obtained by performing 2θ/θ measurement (out-of-plane) using an X-ray diffraction (XRD) device on a powder of the first tantalum carbide layer 11 obtained by scraping off the first tantalum carbide layer from the tantalum carbide-coated carbon material.
According to Reference 1, the XRD crystal data of hexagonal Ta ₂ C (α-Ta ₂ C) is as shown below.
(010): 2θ = 33.293°, I [%]: 21.2
(002): 2θ = 36.343°, I [%]: 23.8
(011): 2θ = 38.071°, I [%]: 100.0
(012): 2θ = 50.107°, I [%]: 16.3
(110): 2θ = 59.494°, I [%]: 18.0
(013): 2θ = 66.533°, I [%]: 17.9
(020): 2θ = 69.909°, I [%]: 2.3
(112): 2θ = 71.753°, I [%]: 18.0
(021): 2θ = 72.849°, I [%]: 13.4
(004): 2θ = 77.177°, I [%]: 2.6
Reference 1: Windisch, S.;Brukl, CE;Rudy, E., Zeitschrift fuer Metallkunde, 54, 345 - 353, (1963)
According to Reference 2, the XRD crystal data of cubic Ta (α-Ta) is as shown below.
(011): 2θ = 38.539, I [%]: 100.0
(002): 2θ = 55.642, I [%]: 16.5
(112): 2θ = 69.723, I [%]: 31.9
(022): 2θ = 82.603, I [%]: 9.7
Reference 2: Ohtani, M.; Hirata, K.; Waseda, Y., High Temperatures-High Pressures, 7, 221 - 226, (1975)

The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 is preferably 1 to 30 μm. If the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 is 1 to 30 μm, the emissivity of the tantalum carbide coating film 10 can be further increased. From this perspective, the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 is more preferably 3 to 10 μm. The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 is a value measured based on JIS B 0633:2001 (ISO 4288:1996).

The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 can be adjusted, for example, by adjusting the surface roughness of the carbon substrate 13. For example, when the thickness of the tantalum carbide coating film 10 is about 20 μm, the surface roughness of the carbon substrate 13 becomes the surface roughness of the tantalum carbide coating film 10 as it is. In addition, after the tantalum carbide coating film 10 is formed on the carbon substrate 13, the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film 10 may be adjusted by polishing the surface of the tantalum carbide coating film 10 using an abrasive, file, or the like.

The thickness of the tantalum carbide coating film 10 is preferably 3 to 100 μm. If the tantalum carbide coating film 10 is 3 μm or more, the effect of impurities diffusing from the carbon substrate 13 on the emissivity of the tantalum carbide coating film 10 can be suppressed. If the tantalum carbide coating film is 100 μm or less, the deposition time of the tantalum carbide coating film can be shortened, and the production efficiency of the tantalum carbide-coated carbon material of this embodiment can be improved. From this perspective, the thickness of the tantalum carbide coating film 10 is more preferably 20 to 50 μm.

From the standpoint of the emissivity of the tantalum carbide coating film 10 and the standpoint of film formation costs, the thickness of the first tantalum carbide layer 11 containing _Ta2C crystals is preferably 2 to 50%, and more preferably 10.0% to 33.3%, of the thickness of the tantalum carbide coating film 10. Also, the thickness of the second tantalum carbide layer 12 containing TaC crystals is preferably 50 to 98%, and more preferably 66.7% to 90.0%, of the thickness of the tantalum carbide coating film 10.

The concentration of other components excluding Ta and C in the tantalum carbide coating film 10 is preferably 1500 mass ppm or less. When the tantalum carbide-coated carbon material of this embodiment is used in an epitaxial wafer manufacturing apparatus, if the concentration of other components excluding Ta and C in the tantalum carbide coating film 10 is 1500 mass ppm or less, impurities can be further suppressed from being mixed into the wafer manufactured by the epitaxial wafer manufacturing apparatus. From this perspective, the concentration of other components excluding Ta and C in the tantalum carbide coating film 10 is more preferably 100 mass ppm or less. The lower the concentration of other components excluding Ta and C in the tantalum carbide coating film 10, the more preferable it is. The concentration of other components excluding Ta and C can be analyzed by glow discharge mass spectrometry (GDMS).

From the same viewpoint as above, the concentration of other components, excluding Ta and C, in the first tantalum carbide layer 11 is preferably 1500 mass ppm or less, more preferably 100 mass ppm or less. From the same viewpoint as above, the concentration of other components, excluding Ta and C, in the second tantalum carbide layer 12 is also preferably 1500 mass ppm or less, more preferably 100 mass ppm or less.

The emissivity of the surface of the tantalum carbide coating film 10 measured under conditions of a measurement temperature of 25°C and a measurement wavelength of 2 to 22 μm is preferably 0.30 or more. If the emissivity of the surface of the tantalum carbide coating film 10 is 0.30 or more, the heat absorption rate of the tantalum carbide-coated carbon material of this embodiment can be further increased. In addition, the upper limit of the range of the emissivity of the surface of the tantalum carbide coating film 10 measured under conditions of a measurement temperature of 25°C and a measurement wavelength of 2 to 22 μm is not particularly limited, but is usually 0.70 or less. The emissivity of the surface of the tantalum carbide coating film 10 can be measured by the method described in the Examples below.

From a similar perspective, the emissivity of the surface of the first tantalum carbide layer 11 measured under conditions of a measurement temperature of 25°C and a measurement wavelength of 2 to 22 μm is preferably 0.30 or more. In addition, the upper limit of the range of the emissivity of the surface of the first tantalum carbide layer 11 measured under conditions of a measurement temperature of 25°C and a measurement wavelength of 2 to 22 μm is not particularly limited, but is usually 0.70 or less.

The thermal expansion coefficient of the carbon substrate 13 is preferably 4.0 to 7.0×10 ^-6 /°C. When the thermal expansion coefficient of the carbon substrate 13 is 4.0 to 7.0×10 ^-6 /°C, the occurrence of microcracks on the surface of the tantalum carbide-coated carbon material can be further suppressed. From this viewpoint, the thermal expansion coefficient of the carbon substrate 13 is more preferably 5.8×10 ^-6 to 6.5×10 ^-6 /°C. The thermal expansion coefficient of the tantalum carbide coating film is approximately 6.3×10 ^-6 /°C.

The tantalum carbide-coated carbon material of this embodiment has a high emissivity, so it can be suitably used in silicon carbide epitaxial wafer growth devices and gallium nitride epitaxial wafer manufacturing and growth devices.

[Method of manufacturing tantalum carbide-coated carbon material]
The method for producing the tantalum carbide-coated carbon material of the present invention will now be described.
The method for producing a tantalum carbide-coated carbon material according to this embodiment includes the steps of forming a first tantalum carbide layer containing Ta ₂ C crystals and forming a second tantalum carbide layer containing TaC crystals.

(1) Step of forming a first tantalum carbide layer containing Ta ₂ C crystals The step of forming a first tantalum carbide layer containing Ta ₂ C crystals includes supplying a source gas containing a hydrocarbon gas, a tantalum halide gas, and a hydrogen gas into a CVD (chemical vapor deposition) reaction chamber, and reacting the source gas by a CVD method to form a first tantalum carbide layer containing Ta ₂ C crystals. At this time, the molar ratio of tantalum atoms contained in the tantalum halide gas and hydrogen atoms contained in the hydrogen gas in the source gas satisfies the following formula:
Tantalum atom (Ta):hydrogen atom (H)=1:x (x≧16)
If the value of x in the above formula is less than 16, the chlorine in the tantalum halide gas is not sufficiently removed, and the decomposition property of the tantalum halide gas may be deteriorated. As a result, TaC is generated instead of Ta ₂ C. If the value of x in the above formula is 16 or more, in the step of forming the first tantalum carbide layer containing Ta ₂ C crystals, cubic Ta (α-Ta) may be generated in addition to Ta ₂ C.
Here, the molar ratio of tantalum atoms contained in the tantalum halide gas in the raw material gas and hydrogen atoms contained in the hydrogen gas can be calculated from the volumetric flow rates of the tantalum halide gas and the hydrogen gas in the standard state. For example, when tantalum pentachloride is used as the tantalum halide gas, 1 mole of the tantalum halide gas contains 1 mole of tantalum atoms. On the other hand, 1 mole of hydrogen gas contains 2 moles of hydrogen atoms. Since the volume ratio of the gases in the standard state is equivalent to the molar ratio of each gas, when tantalum pentachloride is supplied at 1 SLM (Standard Liter/Minutes) and hydrogen is supplied at 8 SLM, the molar ratio of tantalum atoms contained in the tantalum halide gas in the raw material gas and hydrogen atoms contained in the hydrogen gas is as follows:
Tantalum atom (Ta):hydrogen atom (H)=1:16
In this case, the standard condition refers to 20° C. and 1 atmospheric pressure, and "SLM" is a volumetric flow unit obtained by converting the volume of gas to 20° C. and 1 atmospheric pressure.

As described above, the first tantalum carbide layer is formed by CVD. Examples of CVD methods include thermal CVD, photo-CVD, and plasma CVD. Among these CVD methods, thermal CVD is preferred because the device configuration is relatively simple and there is no damage caused by plasma.

The film formation temperature in the step of forming the first tantalum carbide layer containing Ta ₂ C crystals is preferably 850 to 2500°C. When the film formation temperature is 850°C or higher, the crystal growth of tantalum carbide is promoted, and the tantalum carbide coating film tends to become dense. When the film formation temperature is 2500°C or lower, the influence of the difference in thermal expansion coefficient between the carbon substrate and tantalum carbide can be reduced. From this viewpoint, the film formation temperature is more preferably 1000 to 1500°C. Furthermore, in the tantalum carbide coating film formation step, the pressure in the CVD reaction chamber is preferably 1 to 100 Pa.

(2) Step of forming a second tantalum carbide layer containing TaC crystals A second tantalum carbide layer containing TaC crystals can be formed in the same manner as in the step of forming a first tantalum carbide layer containing _Ta2C crystals, except that the flow rates of the hydrocarbon gas and the tantalum halide gas supplied into the CVD reaction chamber are adjusted so that the molar ratio of tantalum to carbon in the raw material gas supplied into the CVD reaction chamber is approximately 1:1.

The arithmetic mean roughness Ra of the surface of the carbon substrate is preferably 1 to 30 μm. As described above, the surface roughness of the carbon substrate is directly the surface roughness of the tantalum carbide coating film, so if the arithmetic mean roughness Ra of the surface of the carbon substrate is 1 to 30 μm, it becomes easy to set the arithmetic mean roughness Ra of the surface of the tantalum carbide coating film to 1 to 30 μm. The arithmetic mean roughness Ra of the surface of the tantalum carbide coating film is more preferably 3 to 10 μm, so the arithmetic mean roughness Ra of the surface of the carbon substrate is also more preferably 3 to 10 μm.

The method for producing the tantalum carbide-coated carbon material according to this embodiment can be carried out, for example, by using an externally heated reduced pressure CVD apparatus 21 as shown in FIG.
In the external heating type reduced pressure CVD apparatus 21, the carbon substrate 24 is supported by a support means 25 in a reaction chamber 22 equipped with a heater 23, an exhaust unit 27, a raw material supply unit 28, etc. Then, as raw material gases, hydrocarbon gas, hydrogen (H ₂ ) gas, and halogenated tantalum gas are supplied from the raw material supply unit 28. The halogenated tantalum gas can be generated, for example, by a method of heating and vaporizing tantalum halide, or a method of reacting tantalum metal with a halogen gas. Next, the raw material gas supplied from the raw material supply unit 28 is subjected to a thermal CVD reaction at a heating temperature of preferably 850 to 2500° C., more preferably 1000° C. to 1500° C., and at a high temperature and reduced pressure of preferably 1 to 100 Pa, to form a tantalum carbide coating film on the carbon substrate 24.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these.

The tantalum carbide-coated carbon materials of Examples 1 to 4, the tantalum carbide-coated carbon material of Comparative Example 1, and the carbon material of Reference Example 1 were prepared as follows.

Example 1
First, a carbon substrate 24 was placed in a reaction chamber 22 of an external heat type reduced pressure CVD apparatus 21 shown in Fig. 2. A sector-shaped member (central angle 120°, radius 225 mm, thickness 12 mm, thermal expansion coefficient 6.0 x ^10-6 /°C) made of isotropic graphite (product name "MC-4423", manufactured by Mechanical Carbon Kogyo Co., Ltd.) was used as the carbon substrate 24. The carbon substrate 24 was supported by a support means 25 having three supporting parts with pointed tips. The carbon substrate 24 was subjected to a blasting treatment to adjust the arithmetic mean roughness Ra of the surface of the carbon substrate 24 to 5.0 µm.

Next, the carbon substrate 24 was heated to a temperature of 1100°C. Methane ( _CH4 ) gas, hydrogen ( _H2 ) gas, tantalum pentachloride ( _TaCl5 ) gas and argon (Ar) gas were supplied from the raw material supply unit 28 to the reaction chamber 22 to the heated carbon substrate 24, and a TaC layer with a thickness of 20.4 μm was formed on the surface of the carbon substrate 24. The flow rates of methane gas, hydrogen gas, tantalum pentachloride gas and argon gas were controlled by a mass flow controller to be 1 SLM (Standard Liter/Minutes), 1 SLM, 1 SLM and 1 SLM, respectively. The raw material gas supply time was 5 hours.

Next, while maintaining the temperature of the carbon substrate 24 at 1100°C, methane ( _CH4 ) gas, hydrogen ( _H2 ) gas, tantalum pentachloride ( _TaCl5 ) gas and argon (Ar) gas were supplied from the raw material supplying part 28 to the reaction chamber 22 of the carbon substrate 24 on which the TaC layer was formed, and a _Ta2C layer with a thickness of 5.1 μm was formed on the TaC layer of the carbon substrate 24, thereby producing the tantalum carbide-coated carbon material of Example 1. The flow rates of the methane gas, hydrogen gas, tantalum pentachloride gas and argon gas were controlled by the mass flow controller to be 1 SLM, 8 SLM, 1 SLM and 1 SLM, respectively. The raw material gas supply time was 5 hours. FIG. 3 shows an SEM image of the cross section of the tantalum carbide-coated carbon material of Example 1.

Example 2
The raw material gas supply time when forming the _Ta2C layer was changed from 5 hours to 10 hours. Otherwise, the same method as in Example 1 was used to prepare a tantalum carbide-coated carbon material of Example 2 in which the thickness of the TaC layer was 21.1 μm and the thickness of the _Ta2C layer was 10.2 μm.

Example 3
First, a tantalum carbide-coated carbon material was prepared in the same manner as in Example 1, except that the raw material gas supply time when forming the TaC layer was changed from 5 hours to 2.5 hours, and the TaC layer had a thickness of 10.2 μm and the Ta ₂ C layer had a thickness of 5.2 μm.

Next, in the same manner as in Example 1, except that the raw material gas supply time when forming the TaC layer was changed from 5 hours to 2.5 hours, a TaC layer with a thickness of 10.3 μm was formed on the Ta ₂ C layer of the above tantalum carbide-coated carbon material, and a Ta ₂ C layer with a thickness of 5.5 μm was further formed on the TaC layer, thereby producing the tantalum carbide-coated carbon material of Example 3.

Example 4
First, a TaC layer having a thickness of 26.0 μm was formed on the surface of the carbon substrate 24 in the same manner as in Example 1, except that the raw material gas supply time when forming the TaC layer was changed from 5 hours to 7 hours.

Next, a Ta ₂ C layer containing Ta crystals and having a thickness of 4.9 μm was formed on the TaC layer in the same manner as in Example 1, except that the flow rate of hydrogen gas was changed from 8 SLM to 16 SLM, thereby producing a tantalum carbide-coated carbon material of Example 4.

(Comparative Example 1)
A tantalum carbide-coated carbon material of Comparative Example 1 having a TaC layer with a thickness of 21.0 μm was produced in the same manner as in Example 1, except that the Ta ₂ C layer was not formed.

(Reference Example 1)
The carbon substrate used in producing the tantalum carbide-coated carbon material of Example 1 was used as the carbon material of Reference Example 1.

The tantalum carbide-coated carbon materials of Examples 1 to 4, the tantalum carbide-coated carbon material of Comparative Example 1, and the carbon material of Reference Example 1 prepared as described above were evaluated as follows.

(1) Calculation of peak intensity ratio: I _Ta2C (110)/I _Ta (002) Using an XRD device (trade name "EMPYREAN", manufactured by Malvern Panalytical Co.), 2θ/θ measurement (out-of-plane) of a powder sample of a Ta ₂ C layer was performed. The powder sample of the Ta ₂ C layer to be measured was prepared by scraping off the Ta ₂ C layer from a tantalum carbide-coated carbon material.
The results of XRD measurement of a powder sample of the Ta ₂ C layer in the tantalum carbide-coated carbon material of Example 1 are shown in Figure 4. The peak intensity ratio I Ta2C (110)/I Ta (002) between the peak corresponding to the (110) plane of hexagonal Ta _{2 C} (α-Ta ₂ C) and the peak corresponding to the (002) plane of cubic Ta (α- _Ta ) was calculated. The results are shown in Table 1.

(2) Emissivity measurement method at room temperature First, a flat carbon substrate with a diameter of 40 mm or more was coated with various films to prepare a measurement sample. Then, using an emissivity meter (product name "TSS-5X", manufactured by Japan Sensor Co., Ltd.), the emissivity was measured at a measurement temperature of room temperature (25°C) and a measurement wavelength of 2 to 22 μm. The results are shown in Table 1.

(3) Measurement of temperature rise time by induction heating First, the tantalum carbide-coated carbon materials of Examples 1 to 4, the tantalum carbide-coated carbon material of Comparative Example 1, and the carbon material of Reference Example 1 were each placed as a susceptor 44 in a quartz tube 42 of an induction heating device shown in FIG. 5, and a SiC wafer 45 was placed on the susceptor 44. Thereafter, the pressure inside the quartz tube 42 was reduced, and induction heating was started under the following conditions. The surface temperature at the center of the SiC wafer 45 was measured with a radiation thermometer 40 (product name "FLHX-TNE-0090-200-B-003-00-5", manufactured by Japan Sensor Co., Ltd.), and the time until the temperature reached 1500°C was measured. The measurement results are shown in Table 1.
[Measurement conditions]
Heating method: induction heating Power output: 2kW
Frequency: 50kHz
Argon flow rate: 2 SLM
Emissivity setting: 1.0
Measurement wavelength: 1.95-2.6μm
Measurement temperature: 1500℃
SiC wafer: 3 inches Susceptor size: 100 mm x 100 mm x 10 mm

(5) Calculation of weight loss rate by _NH3 corrosion test First, the tantalum carbide-coated carbon materials of Examples 1 to 4, the tantalum carbide-coated carbon material of Comparative Example 1, and the carbon material of Reference Example 1 were placed as susceptors 44 in the quartz tube 42 of the induction heating device shown in Fig. 6. Then, the pressure in the quartz tube 42 was reduced, and the temperature in the quartz tube 42 was raised by induction heating until the surface temperature of the susceptor 44 reached 1500°C. After the surface temperature of the susceptor 44 stabilized at 1500°C, _NH3 gas was supplied into the quartz tube 42 from the gas supply port 46 at a flow rate of 1.0 SLM. Then, the susceptor 44 with a surface temperature of 1500°C and the _NH3 gas were reacted for 6 hours, and the weight loss rate (%) after the _NH3 corrosion test for each sample was calculated from the following formula.
Weight loss rate (%) after _NH3 corrosion test = (weight of carbon material before test (g) - weight of carbon material after test (g)) ÷ weight of carbon material before test (g)
[Test conditions]
Sample surface temperature: 1500°C
_NH3 : 1.0SLM
Pressure: -20 kPa (gauge pressure)
Duration: 6 hours

By comparing the emissivity at room temperature of the tantalum carbide coated carbon materials of Examples 1 to 4 with that of Comparative Example 1, it was found that the emissivity of the tantalum carbide coating film can be increased by including a first tantalum carbide layer (Ta ₂ C layer) containing _{a first tantalum carbide crystal (Ta 2 C} crystal) and a second tantalum carbide layer (TaC layer) containing a second tantalum carbide crystal (TaC crystal) having a different tantalum carbide composition from the first tantalum carbide crystal (Ta 2 C crystal). As a result, it was found that the heating time for the SiC wafer to reach 1500°C by induction heating was shortened. It was also found that the corrosion resistance against NH ₃ gas was good.
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REFERENCE SIGNS LIST 10 Tantalum carbide coating film 11 First tantalum carbide layer 12 Second tantalum carbide layer 13 Carbon substrate 21 External heat type reduced pressure CVD apparatus 22 Reaction chamber 23 Heater 24 Carbon substrate 25 Support means 26 Turntable 27 Exhaust section 28 Raw material supply section 40 Radiation thermometer 41 RF coil 42 Quartz tube 43 Insulation material 44 Susceptor 45 SiC wafer 46 Gas supply port

Claims (10)

A tantalum carbide-coated carbon material comprising a carbon substrate and a tantalum carbide coating film coating at least a portion of the carbon substrate,
the tantalum carbide coating film includes a first tantalum carbide layer including first tantalum carbide crystals, and a second tantalum carbide layer including second tantalum carbide crystals having a tantalum carbide composition different from that of the first tantalum carbide crystals;
The tantalum carbide coated carbon material , wherein the first tantalum carbide crystal comprises a _Ta2C crystal and the second tantalum carbide crystal is a TaC crystal . The tantalum carbide-coated carbon material according to claim 1, wherein the apex position of a peak in the X-ray diffraction pattern of the first tantalum carbide crystal is different from the apex position of a peak in the X-ray diffraction pattern of the second tantalum carbide crystal. 3. The tantalum carbide coated carbon material according to claim 1, wherein the second tantalum carbide layer is present on the carbon substrate side relative to the first tantalum carbide layer. 4. The tantalum carbide coated carbon material according to claim 3 , wherein the outermost layer of the tantalum carbide coating film is the first tantalum carbide layer. The Ta ₂ C crystal is hexagonal Ta ₂ C (α-Ta ₂ C),
the first tantalum carbide layer further comprises cubic Ta (α-Ta);
5. The tantalum carbide-coated carbon material according to claim 1 , wherein in an X-ray diffraction pattern of the first tantalum carbide layer, a peak intensity ratio ( _ITa2C (110)/ _ITa (002)) of a peak corresponding to a (110) plane of hexagonal _Ta2C (α-Ta2C) to a peak corresponding to a (002) plane of cubic _Ta (α - Ta) is 0.5 or more. 6. The tantalum carbide coated carbon material according to claim 1, wherein the tantalum carbide coating film has a surface having an arithmetic mean roughness Ra of 1 to 30 μm. 7. The tantalum carbide-coated carbon material according to claim 1, wherein the emissivity of the surface of the tantalum carbide coating film is 0.30 or more, measured under conditions of a measurement temperature of 25° C. and a measurement wavelength of 2 to 22 μm. 8. The tantalum carbide coated carbon material according to claim 1, wherein the thermal expansion coefficient of the carbon substrate is 4.0 to 7.0×10 ⁻⁶ /° C. 9. The tantalum carbide-coated carbon material according to claim 1, wherein the tantalum carbide coating film has a thickness of 3 to 100 μm. 10. The tantalum carbide-coated carbon material according to claim 1, wherein the concentration of components other than Ta and C in the tantalum carbide coating film is 1500 ppm by mass or less.