JPH10245285A - Carbon composite material for reducing atmosphere furnace, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon composite material for a reducing atmosphere furnace capable of manifesting inhibiting effects against an excellent reducing gas reaction even in a high temperature reducing gas atmosphere over 1,000 deg.C and capable of largely elongating a product life, and further to provide a method for producing the carbon composite material. SOLUTION: This carbon composite material for a reducing atmosphere furnace has TaC coating membrane 3 of a crystalline structure comprising compactly accumulated fine particles formed on the surface of a graphite substrate 2 and further a thermal expansion coefficient as a characteristic value of the graphite substrate is regulated so as to be within the range of the thermal expansion coefficient of the tantalum carbide coating membrane ±2.0×10<-6> /K. The method for producing the carbon composition material for the reducing atmosphere furnace comprises the formation of the tantalum carbide coating membrane on the graphite substrate having the before thermal expansion value as the characteristic value by using metal tantalum as a target material and a reaction gas by an arc ion plating(AIP) type reactive evaporation method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon composite material having an excellent effect of suppressing a reaction with a reducing gas at a high temperature, and more particularly to a carbon composite material capable of reducing a carbon material even in a reducing gas atmosphere at a high temperature exceeding 1000.degree. TECHNICAL FIELD The present invention relates to a tantalum carbide-coated graphite-based material that can sufficiently exhibit a reaction suppression effect with a reactive gas.

[0002]

2. Description of the Related Art Conventionally, graphite-based materials exposed to reducing gas atmospheres such as nitrogen gas and ammonia gas at high temperatures are naturally deteriorated or reduced by the reaction with the reducing gas, and are required for the material. When the original function that has been performed can no longer be sufficiently performed, it is determined that the life has expired and replacement with a new member is performed.

[0003] For example, a heater made of a graphite-based material is arranged in a furnace, an ammonia gas is introduced into the furnace to form an ammonia atmosphere, and the furnace is heated to about 1200 ° C by the heater, and an ammonia atmosphere furnace is maintained. In the case of (1), a graphite-based material in which the surface of a graphite substrate is coated with silicon carbide is generally used as the heater. this is,
Since the graphite base itself reacts very easily with ammonia, the graphite heater wears out in a short time and starts to open holes, that is, breaks occur. As a means for alleviating the reaction with ammonia, the surface of a graphite substrate is coated with silicon carbide so that the life of the graphite substrate can be extended.

[0004]

However, the above-mentioned means of coating with silicon carbide is intended only to slow down the reaction between the heater and ammonia and to delay the consumption of the heater. The reaction between the film and ammonia gradually proceeds. The biggest reason is that the decomposition temperature of silicon carbide is about 1400
° C and high vapor pressure in the temperature range around the temperature. Then, when the silicon carbide film is gradually thinned by the reaction with the ammonia, and reaches the exposure of the graphite base, the graphite base and the ammonia react at a stretch, and as described above, the wear proceeds in a short time, and the hole progresses. Begin to open, that is, disconnection occurs, and the life of the heater is exhausted.

The present inventors have been researching carbon composite materials for reducing atmosphere furnaces for some time, and as a clue for developing a material superior to the above-mentioned silicon carbide-coated carbon composite material, a transition metal carbide has been used. Tantalum carbide (hereinafter “TaC”), which has the highest melting point and the highest chemical stability
To display. ). When forming a TaC film on a graphite substrate (heater), an experiment was first performed with reference to a physical vapor deposition method (so-called PVD method) and a CVD method by plasma spraying disclosed in Japanese Patent Application Laid-Open No. Hei 6-280117. Was done. After that, an experiment was performed by implementing a CVR (chemical vapor reaction) method.

However, since the melting point of TaC is as high as about 4000 ° C., it is extremely difficult to carry out the PVD method, and the TaC film obtained by the so-called CVR method becomes porous. It was judged that it was basically difficult to adopt it as a practical film forming method. Eventually, when the TaC-coated graphite substrate obtained by the CVD method was used in a high-temperature reducing gas atmosphere, cracks occurred in the TaC coating after only a few uses (about 30 hours), and the graphite substrate and the TaC coating were used. And peeling occurred.

The present invention has been made in view of the above circumstances, and has as its object to exhibit an excellent effect of suppressing a reducing gas reaction even in a high-temperature reducing gas atmosphere exceeding 1000 ° C. Another object of the present invention is to provide a carbon composite material for a reducing atmosphere furnace and a method for producing the same, which can greatly extend the product life.

[0008]

Means for Solving the Problems The present inventors attempted to elucidate the causes of cracks and separation easily occurring between a TaC coating obtained by a conventional method (CVD method) and a graphite base material at various angles. Has been considered since. As a result, the following facts were found. The crystal structure of the TaC coating on the graphite substrate has a fiber columnar shape (FIG. 5).
(See FIG. 5 (a)) or columnar (see FIG. 5 (b)).
Further, in any case, the structure has a weak adhesion to the graphite base material and the TaC film. The larger the difference between the thermal expansion coefficients of the graphite base material and the TaC coating is, the more the cracks and peeling tend to occur and progress.

[0009] As a result, the inventors of the present invention have proposed a device ((a)) from the viewpoint of the crystal structure that can realize a state in which fine particles are densely stacked as the crystal structure of the TaC film ((a)).
If a measure ((b)) is taken in view of the characteristics of the graphite base material such as keeping the difference in thermal expansion coefficient between the coating and the graphite base within a certain range, the progress of cracks in the TaC coating will be significantly slowed down, It is possible to obtain the knowledge that this should lead to a significant suppression of the occurrence of separation between the graphite base material and the TaC film, and after further studying based on this knowledge, the above-mentioned ideas (a) and (b) As a result, the present invention has been completed.

That is, one of the objects of the present invention that has achieved the above object is that a TaC film having a crystal structure in which fine particles are densely laminated is formed on the surface of a graphite substrate, and the characteristic value of the graphite substrate is obtained. Is the thermal expansion coefficient of the TaC coating ±
A carbon composite material for a reducing atmosphere furnace characterized by being in the range of 2.0 × 10 ⁻⁶ / K. In the second invention, the graphite substrate further has an average pore radius of 0.01 to 5 μm and a gas discharge pressure of 1000 ° C.
^-4 Pa / g or less, and the content of impurities is Al <
0.3 ppm, Fe <1.0 ppm, Mg <0.1 pp
m, Si <0.1 ppm, and has a characteristic value of a high-purity isotropic graphite base material having an ash content of 10 ppm or less.
In the third invention, the thickness of the TaC film is further reduced to 5 to 1.
It is a carbon composite material for a reducing atmosphere furnace, which has an additional component requirement of 00 μm.

A fourth invention is a use invention in which both of the above inventions are used as a carbon composite material for an ammonia atmosphere furnace, and a fifth invention is a heater for a film formation furnace using the carbon composite material for a reducing atmosphere furnace. It is a use invention used for. As the semiconductor thin film, Si, GaAs, GaInP, GaN, I
nGaN and the like can be exemplified. According to a sixth aspect of the present invention, an arc ion plating (AIP) type reactive deposition method (hereinafter, simply referred to as “AIP method”) is used on a surface of a graphite substrate using metal Ta as a target material and a reactive gas. A method for producing a carbon composite material for a reducing atmosphere furnace, which forms a TaC film, wherein the coefficient of thermal expansion as a characteristic value of the graphite base material is the coefficient of thermal expansion of the TaC film ± 2.0 × 1
A method for producing a carbon composite material for a reducing atmosphere furnace, wherein the carbon composite material is within a range of 0 ^-6 / K.

In a seventh aspect of the present invention, the graphite base material of the sixth aspect further has an average pore radius of 0.01 to 5 μm and a gas discharge pressure of 10 ^-4 P based on 1000 ° C.
a / g or less, and the content of impurities is Al <0.
3 ppm, Fe <1.0 ppm, Mg <0.1 ppm,
This is a production method having a characteristic value of a high-purity isotropic graphite base material with Si <0.1 ppm and an ash content of 10 ppm or less.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing a carbon composite material for a reducing atmosphere furnace according to the present invention.
Is a process diagram showing an example of the production method of the present invention, and FIG.
FIG. 2 is a principle explanatory diagram illustrating an AIP device for performing an IP process.

In FIG. 1A, a composite material 1 of the present invention is shown.
Has a structure in which a TaC coating 3 is formed on the surface of a graphite substrate 2. FIG. 1B is a schematic diagram in which a part of the TaC coating 3 is enlarged. The TaC coating 3 is a layer having a crystal structure in which TaC fine particles having a diameter of about 1 to 10 μm are uniformly and densely packed and stacked, and in this case, the bulk density is 1
It is desirable that the weight be 4.30 g / cm ³ or more.
The use of high-purity isotropic graphite substrate with low outgas
Low gas and impurities released from graphite base at high temperature,
In addition, the electrical resistivity and the coefficient of thermal expansion are less directional in each direction. In addition, in order to prevent formation of a porous TaC film, gas intrusion from the outside can be suppressed by setting the bulk density of the TaC film to 14.30 g / cm ³ or more. T having such a crystal structure and characteristics
In order to form the aC film 3, as will be described in detail later, A using metal tantalum and a reaction gas as a target material is used.
Implementation of the IP method is effective.

As the graphite base material 2, it is desirable to use a high-purity isotropic graphite base material having good affinity for the TaC coating 3, and the characteristic value of the graphite base material is set as follows.
It is desirable to adopt one that satisfies). The coefficient of thermal expansion is the coefficient of thermal expansion of the TaC coating ± 2.0 × 1
0 ⁻⁶ / K. This is to reduce thermal stress generated in the TaC film due to a difference in thermal expansion coefficient between the graphite base material and the TaC film.

The average pore radius is from 0.01 to 5 μm. Here, the “average pore radius” is a value of an average pore radius of a pore volume obtained from a mercury porosimeter, and is a value of a cumulative pore volume when a maximum pressure is 98 MPa and a contact angle between a sample and mercury is 141.3 °. It is a half value. When the average pore radius is less than 0.01 μm, the so-called anchor effect is not sufficiently exhibited, and the TaC coating is easily peeled. On the other hand, if it exceeds 5 μm, the amount of gas released from the graphite substrate at a high temperature increases.

The gas discharge pressure based on 1000 ° C. is 10 ^-4.
Pa / g or less. H ₂ ,
CH ₄ , C 0, C 0 ₂ , H ₂ 0, etc.
To minimize the amount of generated reacts with C easy C0, H ₂ 0, the following is desirable 10 ^-4 Pa / g.

When the content of impurities is Al <0.3 ppm,
Fe <1.0 ppm, Mg <0.1 ppm, Si <0.
At 1 ppm, the ash content is 10 ppm or less. If the amount of the impurities exceeds this range, the interface between the graphite base material and the TaC film tends to peel off due to a chemical reaction with TaC at a high temperature, so that this is prevented.

Therefore, even when the composite material 1 of the present invention is exposed to a high-temperature reducing gas, for example, an ammonia atmosphere, TaC
Since the coating 3 has a crystal structure in which fine particles are densely stacked, even if impurities (Fe, Al, etc.) in the graphite substrate 2
Is diffused and reaches the lower layer of the TaC coating 3, unlike the columnar or fiber columnar crystal structure, it is very difficult for the fine crystal structure to escape from the TaC coating 3. In addition, T
The time until pinholes and cracks occur in the aC coating can be extended very long.

In the case of the graphite substrate 2 according to the present invention,
Since the impurities themselves are extremely small from the beginning and have a unique pore structure, the amount of diffused gas is also very small. Accordingly, the TaC coating 3 coated on such a graphite substrate 2
Has good adhesion to the graphite substrate 2 and less gas is released from the graphite substrate 2 at high temperatures, so that the TaC coating 3 is less likely to deteriorate, and pinholes and cracks are less likely to occur. Further, the difference in thermal expansion coefficient between the TaC coating 3 and the graphite substrate 2 is relatively suppressed within ± 2.0 × 10 ⁻⁶ / K, and the graphite of the TaC coating 3 itself caused by the difference in thermal expansion coefficient is used. Peeling from the substrate 2 can be avoided. Therefore, unlike the conventional product, the phenomenon of peeling due to the promotion of pinholes and cracks does not occur, and this point also produces a further synergistic effect, and the adhesion between the TaC coating and the graphite substrate without the pinholes and cracks. The state is good.

After all, in the case of the composite material 1 of the present invention, the inherently desirable features of TaC are utilized as they are until pinholes and cracks occur. That is,
Effectively exhibit high heat resistance and chemical stability against high-temperature reducing gas (for example, ammonia gas is stable even at 1500 ° C., and hydrogen gas is stable even at 2000 ° C.) to extend the life of the composite material 1 It can be extended more than conventional products.

The TaC coating 3 has a thickness of 5 to 1
It is desirable that the thickness is set to be 00 μm, preferably 10 to 90 μm. 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.
This is because separation from the graphite substrate 2 easily occurs. T
By setting the thickness of the aC film 3 in such an optimum range, the effect of suppressing the reducing gas reaction can be sufficiently exhibited, but the cost required for forming the film more than necessary can be omitted, and the cost of the product can be increased. Can be prevented.

Next, an example of the manufacturing method of the present invention will be described with reference to FIGS. 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 led to an AIP process, and the graphite substrate 2 is
Is coated with TaC. The AIP process is usually performed by using an AIP apparatus as shown in FIG. 3 in a procedure (evacuation → heating → undercoating → coating → cooling) as shown in a dashed-dotted frame in FIG. That is, after one or a plurality of the cleaned graphite substrates 2 are placed 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 to 600 Torr. Heat to about ° C.

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

[0026]

【Example】

(Example 1) A cylindrical slit type shown in FIG.
m.times.t5 mm), wherein AIP treatment is performed on high-purity isotropic graphite (base material No.〜) having the characteristic values shown in Table 1 to obtain a graphite heater. A TaC film was formed on the surface. 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. Target material: Metal Ta Reaction gas: CH ₄ Heat treatment temperature: 400 to 600 ° C. Base pressure: 1 × 10 ⁻⁵ Torr Deposition pressure: 20 mTorr Deposition current: 200 A Deposition voltage: 43 V Bias voltage: −20 V 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 ammonia atmosphere furnace heaters as products obtained by the above-described AIP treatment, film formation experiments in a semiconductor thin film formation furnace in an ammonia atmosphere at 1200 ° C. were sequentially and repeatedly performed. . The life of the heater was defined as the time of disconnection. The results are shown in Table 1.

[0028]

[Table 1]

Comparative Example 1 Example 1 (Base No.)
CVD treatment is performed on each graphite heater having the same shape, dimensions and characteristics as above, and S
An iC coating was formed with a thickness of 20 μm. Using the obtained heater for an ammonia atmosphere furnace as a conventional product, a GaN film-forming experiment was repeatedly performed in a film-forming furnace for semiconductor thin films under the same conditions as in Example 1 at the time of disconnection. The heater life was determined. The results are shown in Table 1. As is clear from Table 1, in the case of the heater according to the present invention, 500 times were repeated in the case of the heater according to the present invention, whereas in the case of the conventional heater, all 50 times were used repeatedly (using 150 hours in total). Even after repeated use (even when used for a total of 1500 hours), no disconnection occurred.

FIG. 6 (a) shows the results of observing the respective TaC coatings of the example (base material No.) and the example (base material No.) after the heat treatment (film formation experiment) with a scanning electron microscope. 4) and (b) are SEM photographs. Also from this SEM photograph, when the characteristics of the graphite base material satisfy the requirements of the present invention (base material No.), no cracks are observed (FIG. 6 (a)), and when the requirements are not satisfied (base material No.). .)
Shows that cracks are progressing (Fig. 6
(B)).

Next, the same graphite substrate as in the example (substrate No.) was subjected to AIP treatment, and the surface of the graphite heater was variously changed in thickness from 5 to 100 μm as shown in Table 2. A TaC coating was formed. Using each of the heaters, a film forming experiment in a semiconductor thin film forming furnace in an ammonia atmosphere at 1200 ° C. was sequentially and repeatedly performed in the same manner as in Example 1. The life of the heater was defined as the time of disconnection. The results are also shown in Table 2.

[0032]

[Table 2]

(Comparative Example 1) A graphite heater having the same shape, dimensions, and characteristics as in Example 1 (base material No.) was subjected to CVD treatment, and a SiC film was formed on the heater surface.
It was formed with a thickness of 0 μm. Example 1 was obtained using the obtained heater for an ammonia atmosphere furnace as a conventional product.
A GaN film formation experiment was repeated in a semiconductor thin film formation furnace under the same conditions as in the case of (base material No.). The results are shown in Table 2. As is clear from Table 2, in the case of the conventional heater, 50 times of repeated use (15 times in total time)
In contrast, in the case of the heater according to the present invention, no disconnection occurred even when the heater according to the present invention was repeatedly used 500 times (even when used for a total of 1500 hours).

[0034]

According to the present invention, the following advantages (~)
Can be enjoyed. Since the composite material of the present invention has a structure in which the surface of the graphite base material is coated with a fine-grained dense and homogeneous laminated crystal structure on the surface of the graphite base material, the impurity (Fe) in the graphite base material under a high-temperature reducing atmosphere is used. , Al, etc.) diffuse and reach the TaC film, it is very difficult to escape from the TaC film, and the time until pinholes can be extended very long.

Further, in the case of the graphite substrate according to the present invention, since the impurities themselves are extremely small from the beginning and have a specific pore structure, the amount of gas diffused is also very small. Therefore, such a TaC film coated on a graphite substrate has good adhesion to the graphite substrate, and has a small amount of gas released from the graphite substrate at a high temperature. Is less likely to occur. Furthermore, T
The thermal expansion coefficient difference between the aC coating and the graphite substrate is relatively ± 2.
It is suppressed within 0 × 10 ⁻⁶ / K, and it is possible to prevent the TaC coating itself from peeling off from the graphite substrate due to the difference in thermal expansion coefficient. Therefore, the phenomenon of peeling due to the promotion of pinholes and cracks unlike the conventional product does not occur, and this point also produces a further synergistic effect. The state is good. After all, the above-mentioned improvement from the crystal structure side and the improvement of the graphite base material itself (selection of a preferable base material)
In combination with this, TaC effectively exhibits high heat resistance and chemical stability, which are inherently desirable features inherent in TaC, until pinholes and cracks are generated. it can.

Further, the thickness of the TaC film is set to 5 to 100 μm.
m, desirably from 10 to 90 μm, while sufficiently exhibiting the above effects,
Waste of the cost required for forming a film more than necessary can be avoided, and an increase in product cost can be prevented. When the composite material of the present invention is applied to a heater for a semiconductor thin film deposition furnace, the life of the heater is remarkably prolonged, so that the cost required for forming the semiconductor thin film can be reduced. The formation of the TaC film is economical because an AIP device which is a compact general-purpose device can be used.

[Brief description of 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 chart showing an example of the production method of the present invention.

FIG. 3 is a diagram illustrating the principle of an AIP device for performing an AIP process.

FIG. 4 is a schematic perspective view of a heater for a deposition furnace of a semiconductor thin film.

5A and 5B are schematic cross-sectional views of a principal part showing a crystal structure of a TaC film formed by a CVD method, wherein FIG. 5A is a diagram showing a fiber columnar structure, and FIG. 5B is a diagram showing a columnar crystal structure.

FIG. 6 is an SEM photograph of each TaC film of the example (base material No.) and the example (base material No.) after the heat treatment (GaN film formation experiment). Material No.), (b) shows the example (base material No.
)belongs to.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite material of this invention 2 Graphite base material 3 TaC coating 4 Cleaning 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 (7)

[Claims] 1. A tantalum carbide film having a crystal structure in which fine particles are densely stacked on a surface of a graphite substrate, and a thermal expansion coefficient as a characteristic value of the graphite substrate is a thermal expansion coefficient of the tantalum carbide film. A carbon composite material for a reducing atmosphere furnace, wherein the coefficient is within a range of ± 2.0 × 10 ⁻⁶ / K. 2. The method according to claim 1, wherein the graphite substrate further has a characteristic value
The average pore radius is 0.01 to 5 μm, the gas discharge pressure based on 1000 ° C. is 10 ⁻⁴ Pa / g or less, and the content of impurities is Al <0.3 ppm and Fe <1.0 pp.
2. The carbon composite material for a reducing atmosphere furnace according to claim 1, wherein the carbon composite material is a high-purity isotropic graphite substrate having m, Mg <0.1 ppm, Si <0.1 ppm, and an ash content of 10 ppm or less. 3. The film thickness of the tantalum carbide film is 5 to 1
The carbon composite material for a reducing atmosphere furnace according to claim 1 or 2, which has a thickness of 00 µm. 4. The carbon composite material for a reducing atmosphere furnace according to claim 1, wherein the reducing atmosphere furnace is an ammonia atmosphere furnace. 5. The carbon composite material for a reducing atmosphere furnace according to claim 1, wherein the carbon composite material is a heater for a film formation furnace. 6. An arc ion plating (AI) method using tantalum metal as a target material and a reaction gas.
P) A method for producing a carbon composite material for a reducing atmosphere furnace in which a tantalum carbide film is formed on the surface of a graphite substrate by a reactive vapor deposition method, wherein a thermal expansion coefficient as a characteristic value of the graphite substrate is Thermal expansion coefficient of the tantalum carbide coating ± 1.5 ×
A method for producing a carbon composite material for a reducing atmosphere furnace, which is within the range of 10 ^-6 / K. 7. The graphite substrate may further have a characteristic value
The average pore radius is 0.01 to 5 μm, the gas discharge pressure based on 1000 ° C. is 10 ⁻⁴ Pa / g or less, and the content of impurities is Al <0.3 ppm and Fe <1.0 pp.
The method for producing a carbon composite material for a reducing atmosphere furnace according to claim 6, which is a high-purity isotropic graphite substrate having m, Mg <0.1 ppm, Si <0.1 ppm, and an ash content of 10 ppm or less.