JP4641536B2 - Carbon composite material for reducing atmosphere furnace and method for producing the same - Google Patents

Description

  The present invention relates to a carbon composite material excellent in the effect of suppressing reaction with a reducing gas at a high temperature and a method for producing the same, and more specifically, even in a high-temperature reducing gas atmosphere exceeding 1000 ° C., the carbon material and the reducing gas The present invention relates to a tantalum carbide-coated graphite material capable of sufficiently exhibiting the reaction suppressing effect of and a method for producing the same.

  Conventionally, graphite materials exposed to a reducing gas atmosphere such as nitrogen gas and ammonia gas at high temperatures are naturally altered or lost by the reaction with the reducing gas. When the function cannot be sufficiently performed, it is replaced with a new member because the lifetime is exhausted.

  For example, in the case of an ammonia atmosphere furnace in which a heater made of graphite material is arranged in the furnace, ammonia gas is introduced into the furnace to form an ammonia atmosphere, and the furnace is heated and held at about 1200 ° C. by the heater. For example, as the heater, a graphite material in which silicon carbide is coated on the surface of a graphite substrate is generally used. This is because the graphite base material itself is very easy to react with ammonia, so in a graphite heater, consumption proceeds in a short time and holes begin to open, that is, disconnection occurs. As a means for relaxing the reaction with ammonia, the surface of the graphite base material is coated with silicon carbide so that the life as a heater can be extended as much as possible.

  However, the above-mentioned means of coating silicon carbide is intended only to slow down the reaction between the heater and ammonia and delay the consumption of the heater, and the reaction between the silicon carbide coating on the graphite substrate and ammonia gradually There is no change in progress. The biggest reason is that the decomposition temperature of silicon carbide is about 1400 ° C., and the vapor pressure in the temperature range in the vicinity thereof is high. Then, when the silicon carbide coating is gradually thinned by the reaction with ammonia and the graphite base material is exposed, the graphite base material and ammonia react at once, and as described above, the consumption proceeds in a short time and the holes Begins to open, that is, breakage occurs, and the life as a heater is exhausted.

  The present inventors have been researching carbon composite materials for reducing atmosphere furnaces for a long time, and as the clue for developing materials superior to the above silicon carbide-coated carbon composite materials, transition metal carbides have the highest melting point. Attention has been focused on tantalum carbide (hereinafter referred to as “TaC”), which has high chemical stability. When a TaC film is formed on a graphite substrate (heater), an experiment is first conducted with reference to a physical vapor deposition method (so-called PVD method) and a CVD method by plasma spraying disclosed in JP-A-6-280117. Went. Thereafter, an experiment was also conducted by performing a CVR (Chemical Vapor Phase Reaction) method.

  However, since the melting point of TaC is about 4000 ° C., the PVD method is extremely difficult to perform, and the TaC film obtained by the so-called CVR method becomes porous. It was judged that it was basically difficult to adopt the film formation method. Eventually, when the TaC-coated graphite base material obtained by the CVD method was used in a high-temperature reducing gas atmosphere, cracks occurred in the TaC film when used only a few times (about 30 hours). Peeling occurred between.

  The present invention has been made in view of the above circumstances, and its purpose is to exhibit an excellent reducing gas reaction suppression effect even in a high temperature reducing gas atmosphere exceeding 1000 ° C. The object of the present invention is to provide a carbon composite material for a reducing atmosphere furnace capable of greatly extending the life and a method for producing the same.

  The inventors of the present invention have studied especially from the crystal structure surface in order to elucidate the cause of cracks and peeling that easily occur between the TaC film obtained by the conventional method (CVD method) and the graphite substrate. As a result, the crystal structure of the TaC coating on the graphite substrate is fiber columnar (see FIG. 5A) or columnar (see FIG. 5B), and in either case, the graphite substrate and the TaC coating. It was found that it has a weak structure with respect to adhesion. It has also been found that the greater the difference between the thermal expansion coefficients of the graphite substrate and the TaC coating, the more prominent the occurrence and progress of cracks and delamination.

As a result, the present inventors found that the heat for improvement in the crystal sets ruled surface that allows realizing a state in which fine particles are densely stacked as crystal structure of the TaC film and ((b)), and the TaC film and the graphite substrate If a measure ((b)) from the characteristic side of the graphite base material such as keeping the difference in expansion coefficient within a certain range is applied, the progress of cracks in the TaC coating is remarkably delayed. We were able to obtain the knowledge that it should lead to a significant suppression of the occurrence of peeling, and after further investigation based on this knowledge, we reached the optimal specific means as the devices (b) and (b) above. The present invention has been completed.

In other words, the carbon composite material for a reducing atmosphere furnace of the present invention that has achieved the above object is obtained by carbonizing the tantalum fine particles together with the reactive gas particles containing carbon on the surface of the graphite substrate. A tantalum carbide film having a crystalline structure formed by densely laminating tantalum fine particles is formed, and the thermal expansion coefficient as a characteristic value of the graphite base material is a thermal expansion coefficient ± 2.0 × 10 ^{−6 of the} tantalum carbide film. Ri Ah in the range of / K, further having any of the following features (a) (B) (C ).
(A) The graphite substrate is an isotropic graphite substrate having an average pore radius of 0.01 to 5 μm.
(B) The graphite base material is an isotropic graphite base material whose gas discharge pressure on the basis of 1000 ° C. is 10 ⁻⁴ Pa / g or less.
(C) The graphite substrate contains impurities of Al <0.3 ppm, Fe <1.0 ppm, Mg <0.1 ppm, Si <0.1 ppm, and an ash content of 10 ppm or less. in the invention, the thickness of the T aC film may be 5~100μ m.

In the present invention, the reducing atmosphere furnace may be an ammonia atmosphere furnace, the carbon composite material may be heaters for deposition furnace. Examples of the semiconductor thin film include Si, GaAs, GaInP, GaN, and InGaN. Further , according to another aspect of the present invention, the reactive gas containing metal tantalum and carbon as a target material is used, and the reactive ion deposition method is performed by an arc ion plating (AIP) reactive deposition method in an atmosphere of 400 to 600 ° C. A step of forming a tantalum carbide film having a crystalline structure formed by densely laminating fine particles of tantalum carbide on the surface by adhering fine particles of metal tantalum together with particles of the reaction gas to the surface of the graphite substrate. cage, thermal expansion coefficient as the characteristic value of the graphite substrate, wherein Ri Ah within the thermal expansion coefficient of ± 2.0 × ^{10 -6} / K in the TaC film, further the (a) (B) (C method of making any of a reducing atmosphere furnace carbon composite material that have a characteristic of) the Ru is provided.

According to the present invention, the following benefits ((1) to (4)) can be enjoyed.
(1) Since the composite material of the present invention has a structure in which a TaC film having a fine, dense and homogeneous laminated crystal structure is coated on the surface of the graphite substrate, the composite material in the graphite substrate in a high temperature reducing atmosphere. Even if impurities (Fe, Al, etc.) diffuse and reach the TaC film, it is very difficult to escape from the TaC film, and the time until a pinhole is generated can be extended very long.

In addition, according to the present invention, by having any one of the characteristics (A), (B), and (C), the effect of suppressing the peeling of the TaC film (effect by A and C) and the graphite base material at high temperature The effect of suppressing pinholes and cracks (A, B) by reducing the amount of gas released from the gas can be obtained. Therefore, the Ru good kuna adhesion between the TaC film and the graphite substrate. Further, the difference in thermal expansion coefficient between the TaC film and the graphite base material is relatively suppressed to within ± 2.0 × 10 ⁻⁶ / K, and the TaC film itself is caused by the difference in thermal expansion coefficient from the graphite base material of the TaC film itself. The peeling of can be avoided. Therefore, the phenomenon of peeling due to the promotion of pinholes and cracks does not occur as in the conventional product, so this point also produces a further synergistic effect, there is no pinholes and cracks, and the TaC coating and the graphite substrate are in close contact with each other. It is in a good state. Eventually, the improvement from the crystal structure surface and the improvement of the graphite base material itself (selection of a preferred base material) combined with high heat resistance and chemical properties, which are inherently preferred features of TaC, until pinholes and cracks occur. Stability is effectively exhibited, and the life of the product made of the composite material can be extended more than the conventional product.

(2) Moreover, by forming the thickness of the TaC film to be 5 to 100 μm, preferably 10 to 90 μm, the film can be formed more than necessary while the effect of the above (1) is sufficiently exhibited. It is possible to eliminate unnecessary cost and prevent an increase in product cost.
(3) When the composite material of the present invention is applied to a heater for a semiconductor thin film deposition furnace, the cost required for film formation of the semiconductor thin film can be reduced by significantly extending the life of the heater.
(4) Since the AIP apparatus which is also a compact general-purpose apparatus can be used for forming the TaC film, it is economical.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a carbon composite material for a reducing atmosphere furnace according to the present invention, FIG. 2 is a process diagram showing an example of the production method of the present invention, and FIG. 3 is for carrying out an AIP process. It is a principle explanatory view showing an AIP device.

In FIG. 1A, the composite material 1 of the present invention has a structure in which a TaC film 3 is formed on the surface of a graphite substrate 2. FIG. 1B is an enlarged schematic view of a part of the TaC film 3. The TaC film 3 is a layer composed of a crystal structure in which TaC fine particles having a diameter of about 1 to 10 μm are packed uniformly and densely, and in that case, a bulk density of 14.30 g / cm ³ or more is desirable. . The reason why the high-purity isotropic graphite base material with little outgas is used is that there are few gases and impurities released from the graphite base material at high temperature, and there is little directivity in each direction in electrical resistivity and thermal expansion coefficient. In addition, in order to prevent formation of a porous TaC film, gas penetration from the outside can be suppressed by setting the bulk density of the TaC film to 14.30 g / cm ³ or more. In order to form the TaC film 3 having such a crystal structure and characteristics, it is effective to perform the AIP method using metal tantalum as a target material and a reactive gas as will be described in detail later.

As the graphite substrate 2, it is desirable to use a high purity isotropic graphite substrate having good affinity with the TaC coating 3, and the characteristic values of the graphite substrate are the following conditions ((1) to ( It is desirable to adopt one that satisfies 4)).
(1) The thermal expansion coefficient is the thermal expansion coefficient ± 2.0 × 10 ⁻⁶ / K of the TaC film. The difference in the thermal expansion coefficient between the graphite substrate and the TaC film is to reduce the thermal stress generated in the TaC target membrane.

(2) The average pore radius is 0.01 to 5 μm. Here, the “average pore radius” is the value of the average pore radius of the pore volume obtained from the mercury porosimeter, and is the cumulative pore volume when the maximum pressure is 98 MPa and the contact angle between the sample and mercury is 141.3 °. It is a half value. This is because when the average pore radius is less than 0.01 μm, the so-called anchor effect is not sufficiently exhibited and the TaC film is easily peeled off. On the other hand, if the thickness exceeds 5 μm, the amount of gas released from the graphite base material at high temperatures increases.

(3) The gas discharge pressure based on 1000 ° C. is 10 ⁻⁴ Pa / g or less. Examples of the released gas include H ₂ , CH ₄ , CO, CO ₂ , and H ₂ O. In order to reduce the amount of CO and H ₂ O that easily react with TaC as much as possible, 10 ^{− 4} Pa / g or less is desirable.

(4) The impurity content is Al <0.3 ppm, Fe <1.0 ppm, Mg <0.1 ppm, Si <0.1 ppm, and the ash content is 10 ppm or less. When the amount of impurities exceeds this range, the surface of the graphite substrate and TaC the film is easily peeled off by the chemical reaction with TaC in a high temperature, in order to prevent this.

  Therefore, even if the composite material 1 of the present invention is exposed to a high-temperature reducing gas, for example, in an ammonia atmosphere, the TaC film 3 has a crystal structure in which fine particles are densely laminated. Even if (Fe, Al, etc.) diffuses and reaches the lower layer of the TaC film 3, it is very difficult to pull out the fine grain crystal structure from the TaC film 3 unlike the columnar or fiber columnar crystal structure. In addition, the time until pinholes and cracks are generated in the TaC film at a high temperature can be extended very long.

Moreover, in the case of the graphite base material 2 according to the present invention, since the impurities themselves are extremely small from the beginning and have a specific pore structure, there is very little gas to diffuse. Therefore, the TaC coating 3 coated on the graphite substrate 2 has good adhesion to the graphite substrate 2 and less gas is released from the graphite substrate 2 at a high temperature. And pinholes and cracks are less likely to occur. Furthermore, the difference in thermal expansion coefficient between the TaC film 3 and the graphite substrate 2 is relatively suppressed within ± 2.0 × 10 ⁻⁶ / K, and the graphite of the TaC film 3 itself due to the difference in thermal expansion coefficient. Peeling from the substrate 2 can be avoided. Therefore, the phenomenon of peeling due to the promotion of pinholes and cracks does not occur as in the conventional product, so this point also produces a further synergistic effect, and there is no pinholes and cracks, and the adhesion between the TaC coating and the graphite substrate It is in a good state.

  After all, in the case of the composite material 1 of the present invention, the preferable characteristics inherent in TaC are utilized as they are until pinholes and cracks are generated. That is, the composite material 1 effectively exhibits chemical stability against high heat resistance and high temperature reducing gas (for example, a property stable at 1500 ° C. for ammonia gas and stable at 2000 ° C. for hydrogen gas). The service life can be extended more than the conventional product.

  Further, the TaC film 3 is desirably formed to have a thickness of 5 to 100 μm, preferably 10 to 90 μm. This is because, in order to form the TaC coating 3 on the surface of the graphite substrate 2 without any support, at least 5 μm is required, but when it exceeds 100 μm, the TaC coating 3 and the graphite substrate 2 are liable to be peeled off. . By setting the thickness of the TaC coating 3 in the optimal range in this manner, while reducing the reactive gas reaction sufficiently, the unnecessary cost for forming the coating is eliminated and the product cost is increased. Can be prevented.

Next, an example of the manufacturing method of this invention is demonstrated, referring FIG.2 and FIG.3. First, the graphite substrate 2 is introduced into the cleaning unit 4 and the surface is cleaned with an organic solvent. The cleaned graphite substrate 2 is guided to the AIP process, and the surface of the graphite substrate 2 is coated with TaC in the process. The AIP process is usually carried out by using an AIP apparatus as shown in FIG. 3 according to the procedure (evacuation → heating → base treatment → coating → cooling) as shown in a one-dot chain line in FIG. That is, after placing one or more cleaned graphite substrates 2 on the rotary table 6 in the chamber 5, the inside of the chamber 5 is evacuated to about ^10-5 Torr, and then the inside of the chamber 5 is 400-600. Heat to about ℃.

Next, Ar gas is introduced into the chamber 5 from the supply port 7, and dry etching by Ar sputtering is performed while a bias power supply 8 of −600 V is loaded. This is a so-called ground treatment. Thereafter, the coating operation is started, and the arc power supply 11 and the bias power supply 8 for energizing the target material (metal Ta) 10 are set to a predetermined current and voltage, respectively, and a reaction gas such as CH ₄ gas is supplied from the supply port 7 to a predetermined The Ta fine particles jumping out from the target material 10 are attached to the surface of the graphite substrate 2 as TaC fine particles together with the reaction gas particles. By holding this coating operation for a predetermined time, a TaC film having a crystal structure in which TaC fine particles are densely and uniformly laminated on the surface of the graphite substrate 2 can be freely formed in a required thickness within a range of 5 to 100 μm. .

  When the coating operation is completed, the inside of the chamber 5 is cooled to a predetermined temperature, and then the TaC-coated graphite material as a product is taken out from the chamber 5.

Example 1
Example 1 (base No. 1 to No. 1) of a high purity isotropic graphite having a characteristic value shown in Table 1, which is a graphite heater having a cylindrical slit type (φ100 mm × t5 mm) shape shown in FIG. 4) and Reference Example 1 (Substrate Nos. 1 and 2) were subjected to AIP treatment to form a TaC film on the surface of the graphite heater. The composition ratio (Ta / C) of the TaC film was set to 1, and the film thickness was changed by adjusting the deposition time. The AIP conditions are as follows.
(1) Target material: Metal Ta
(2) Reaction gas: CH ₄
(3) Heat treatment temperature: 400-600 ° C
(4) Base pressure: 1 × 10 ⁻⁵ Torr
(5) Deposition pressure: 20 mTorr
(6) Vapor deposition current: 200A
(7) Vapor deposition voltage: 43V
(8) Bias voltage: -20V
(9) Deposition time: 25 minutes (5 μm) to 500 minutes (100 μm)
The bulk density of the obtained TaC coating was 14.30 g / cm ³ or more.

  Using each of the heaters for an ammonia atmosphere furnace as a product obtained by the AIP treatment, film formation experiments in a semiconductor thin film film formation furnace under an ammonia atmosphere at 1200 ° C. were sequentially and repeatedly performed. The time when the wire was disconnected was regarded as the life of the heater. The results are also shown in Table 1.

(Comparative Example 1)
Each of the graphite heaters having the same shape and characteristics as those of Example 1 (Base Nos. 1 to 4) and Reference Example 1 (Base Nos. 1 and 2) is subjected to a CVD treatment to obtain a heater surface. A SiC film was formed to a thickness of 20 μm. Using the ammonia atmosphere furnace heater as the conventional product thus obtained, the GaN film formation experiment was repeated in the semiconductor thin film film formation furnace under the same conditions as in Example 1, and when the wire was disconnected. The life of the heater was assumed. The results are also shown in Table 1. As is clear from Table 1, all of the conventional heaters were disconnected 50 times (with a total time of 150 hours), whereas the heater according to the present invention was 500 times. Even after repeated use (1500 hours in total), disconnection did not occur.

  In addition, the result observed with the scanning electron microscope about each TaC film of the Example (base material No. 1) and (base material No. 2) after heat processing (film-forming experiment) is shown in FIG. It is a SEM photograph shown in b). Also from this SEM photograph, in the case where the characteristics of the graphite base material satisfy the requirements of the present invention (base material No. 1), the occurrence of cracks was not recognized (FIG. 6 (a)), and the reference example deviating from the requirements (Substrate No. 2) shows that the cracks are progressing (FIG. 6B).

  Next, an AIP treatment was performed on the same graphite base material as in the example (base material No. 1), and the TaC coating was formed on the surface of the graphite heater by varying the film thickness from 5 to 100 μm as shown in Table 2. Formed. Using each heater, film forming experiments in a semiconductor thin film forming furnace under an ammonia atmosphere at 1200 ° C. were sequentially performed in the same manner as in Example 1. The time when the wire was disconnected was regarded as the life of the heater. The results are also shown in Table 2.

(Comparative Example 2)
A CVD process was performed on the graphite heater having the same shape and characteristics as those of Example 1 (base No. 1), and an SiC film having a thickness of 100 μm was formed on the surface of the heater. Using the ammonia atmosphere furnace heater as the conventional product thus obtained, the GaN film formation experiment was repeated in the semiconductor thin film film formation furnace under the same conditions as in Example 1 (Substrate No. 1). The heater life was determined at the time when the wire was disconnected. The results are also shown in Table 2. As is clear from Table 2, the conventional heater was disconnected 50 times (using 150 hours in total), whereas the heaters according to the present invention were all 500 times. Even after repeated use (1500 hours in total), disconnection did not occur.

  The present invention can be changed in design without departing from the scope of the claims, and is not limited to the above-described embodiments and examples.

It is a cross-sectional schematic diagram which shows the carbon composite material for reducing atmosphere furnaces concerning this invention. It is process drawing which shows an example of the manufacturing method of this invention. It is principle explanatory drawing which shows the AIP apparatus for implementing AIP processing. It is a schematic perspective view of the heater for film-forming furnaces of a semiconductor thin film. It is a principal part cross-section figure which shows the crystal structure of the TaC film formed by CVD method, (a) is a figure where a crystal structure is a fiber column shape, (b) is a figure which shows a column shape. It is a SEM photograph about each TaC film of Example 1 (base material No. 1) and reference example 1 (base material No. 1) after heat processing (GaN film-forming experiment), and (a) is Example 1 ( Base No. 1) and (b) are those of Reference Example 1 (Base No. 1).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 This invention composite material 2 Graphite base material 3 TaC film 4 Washing part 5 Chamber 6 Rotary table 7 Supply port 8 Bias power supply 9 Exhaust port 10 Target material (metal Ta)
11 Arc power supply 12 Anode

Claims (6)

By attaching the tantalum fine particles together with the reactive gas particles containing carbon to the surface of the graphite substrate, a tantalum carbide film having a crystalline structure formed by densely laminating tantalum carbide fine particles on the surface is formed, and As a characteristic value of the graphite base material, a thermal expansion coefficient is in a range of ± 2.0 × 10 ⁻⁶ / K of the tantalum carbide coating, and the graphite base material has an average pore size of 0.01 to 5 μm. A carbon composite material for a reducing atmosphere furnace, characterized by being an isotropic graphite substrate having a radius. By attaching the tantalum fine particles together with the reactive gas particles containing carbon to the surface of the graphite substrate, a tantalum carbide film having a crystalline structure formed by densely laminating tantalum carbide fine particles on the surface is formed, and As a characteristic value of the graphite base material, a thermal expansion coefficient is in a range of ± 2.0 × 10 ⁻⁶ / K of the tantalum carbide coating, and the graphite base material has a gas discharge pressure on the basis of 1000 ° C. A carbon composite material for a reducing atmosphere furnace, which is an isotropic graphite base material of 10 ⁻⁴ Pa / g or less. By attaching the tantalum fine particles together with the reactive gas particles containing carbon to the surface of the graphite substrate, a tantalum carbide film having a crystalline structure formed by densely laminating tantalum carbide fine particles on the surface is formed, and As a characteristic value of the graphite base material, a thermal expansion coefficient is in a range of ± 2.0 × 10 ⁻⁶ / K of the tantalum carbide coating, and the graphite base material has Al <0.3 ppm, Fe < A carbon composite for a reducing atmosphere furnace characterized by being an isotropic graphite base material containing impurities of 1.0 ppm, Mg <0.1 ppm, Si <0.1 ppm and an ash content of 10 ppm or less material. Using a reactive gas containing metallic tantalum and carbon as a target material, the fine particles of metallic tantalum together with the reactive gas particles by an arc ion plating (AIP) reactive deposition method in an atmosphere of 400 to 600 ° C. A step of forming a tantalum carbide film formed by densely laminating tantalum carbide fine particles on the surface of the graphite substrate, and having a coefficient of thermal expansion as a characteristic value of the graphite substrate. The thermal expansion coefficient of the tantalum carbide coating is within a range of ± 1.5 × 10 ⁻⁶ / K, and the graphite base material is an isotropic graphite base material having an average pore radius of 0.01 to 5 μm. A method for producing a carbon composite material for a reducing atmosphere furnace characterized by: Using a reactive gas containing metallic tantalum and carbon as a target material, the fine particles of metallic tantalum together with the reactive gas particles by an arc ion plating (AIP) reactive deposition method in an atmosphere of 400 to 600 ° C. A step of forming a tantalum carbide film formed by densely laminating tantalum carbide fine particles on the surface of the graphite substrate, and having a coefficient of thermal expansion as a characteristic value of the graphite substrate. the tantalum carbide coating is in the range of thermal expansion coefficient ± 1.5 × ^{10 -6} / K, the graphite base material is isotropic gas discharge pressure of 1000 ° C. criteria below ¹⁰ -4 Pa / g A method for producing a carbon composite material for a reducing atmosphere furnace, which is a graphite substrate. Using a reactive gas containing metallic tantalum and carbon as a target material, the fine particles of metallic tantalum together with the reactive gas particles by an arc ion plating (AIP) reactive deposition method in an atmosphere of 400 to 600 ° C. A step of forming a tantalum carbide film formed by densely laminating tantalum carbide fine particles on the surface of the graphite substrate, and having a coefficient of thermal expansion as a characteristic value of the graphite substrate. The thermal expansion coefficient of the tantalum carbide coating is within a range of ± 1.5 × 10 ⁻⁶ / K, and the graphite base material is Al <0.3 ppm, Fe <1.0 ppm, Mg <0.1 ppm, Si <The manufacturing method of the carbon composite material for reducing atmosphere furnaces characterized by being an isotropic graphite base material which contains impurities of the amount of 0.1 ppm and ash content of 10 ppm or less.