JPH0229629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a pyrolytic boron nitride (hereinafter referred to as p-BN) molded body produced by a CVD method.

The p-BN molded body is disclosed in, for example, US Pat. No. 3,152,006.
As is known from the above publication, boron nitride is usually synthesized by the CVD method using BCl ₃ and NH ₃ as reaction gases, and therefore boron nitride ( Unlike BN), it is synthesized directly from the gas phase without using a sintering aid, so it has the characteristics of high density and high purity.

For example, as a material utilizing the features of such a p-BN molded product, -V
It has been proposed to use it as a crucible for pulling single crystals of group compound semiconductors (Japanese Patent Application Laid-Open No. 1989-1999).
(See Publication No. 109912 and Japanese Patent Application Laid-open No. 145169/1983, etc.).

That is, when pulling -V group compound semiconductor single crystals, SiO ₂ crucibles have traditionally been used, but in the case of SiO ₂ crucibles, there is a risk that Si will dissolve into the single crystal as an impurity.
An attempt was made to use a p-BN crucible instead of the SiO ₂ crucible.

In order to put the above-mentioned p-BN molded product into practical use, the inventors of the present application attempted to create a crucible made of p-BN alone as an example, and found that in the process of removing the p-BN molded product from the base, there were problems that should be improved. I found out that there is a point.

That is, in order to obtain a crucible of p-BN alone, the present inventors deposited p-BN to a thickness of about 1 mm by CVD on a graphite substrate formed into a desired shape, and removed the graphite substrate after the vapor deposition. I tried that. However, since the vapor deposition temperature is as high as 1600°C to 2000°C, the adhesion force at the interface between the graphite substrate and p-BN becomes strong, and when the p-BN crucible is removed from the graphite substrate, the p-BN
It was discovered that the crucible was damaged. For this reason, we have adopted a method to remove _p-
A BN molded crucible was obtained.

However, in the method of oxidizing and removing the graphite substrate, the oxidation rate of graphite is slow, for example, 15φ×20
An industrially important drawback is that it takes a long time of 10 hours to remove the graphite substrate. In addition, although this method requires the use of expensive high-density graphite, there is also the problem that the graphite substrate can only be used once. This is a major drawback in manufacturing large p-BN crucibles of 100φ or more.

An object of the present invention is to improve the drawbacks of the above-mentioned techniques and to provide a method by which a p-BN molded body can be easily released from a graphite substrate without damaging the graphite substrate.

In order to achieve the above object, the present invention provides a powder layer for peeling on the surface of a substrate made of graphite, and forms a molded body by depositing pyrolytic boron nitride on the powder layer by CVD method. This method is characterized in that the molded body is released from the graphite substrate using the powder layer as a peeling part.

In the present invention, it is necessary that the powder layer is not sintered at a temperature of 1600 to 2000°C and not mixed into p-BN as an impurity. For this reason, it is desirable to mold from boron nitride powder or graphite powder. In the present invention, the powder layer can be easily formed by, for example, dissolving boron nitride powder in a solvent such as alcohol, uniformly coating it on the graphite surface, and then heating to remove the solvent. Further, in the present invention, for the purpose of protecting the surface of the graphite substrate, it is also effective to first deposit a p-BN film on the graphite substrate and then apply a BN powder layer or a graphite powder layer.

According to the present invention having the above configuration, for example, as shown in FIG.
A peeling powder layer 2 made of BN powder is applied to a thickness of about 10 to 30 μm, and then heated in a CVD furnace at a predetermined temperature for about 10 minutes with H ₂
Heat treatment is performed in an atmosphere of gas or the like, and then a p-BN molded body 3 is deposited to a thickness of about 1 mm by CVD. 1600 because BN powder is difficult to sinter.
It does not sinter at ~2000℃, so regardless of the size of the graphite substrate, the produced p-BN compact 3
The graphite base 1 can be easily separated from the BN powder layer 2. Moreover, according to the present invention, damage to the graphite substrate is extremely small, so that it can be used repeatedly. In addition, in the present invention, the thermal stress caused by the difference in thermal expansion coefficient between p-BN and graphite during quenching can be absorbed at the powder layer 2, so no residual stress remains in the p-BN, making it resistant to thermal shock. Excellent p-
It is possible to produce BN molded bodies.

The present invention will be described in detail below with reference to Examples.

Example 1 Commercially available
BN powder was applied uniformly and heated at 1800℃ for 10 minutes in a CVD furnace.
Heat treatment in _H2 stream for min followed by CVD
p-BN was deposited to a thickness of 1 mm using the method.

The CVD conditions were: BCl ₃ flow rate: 200 SCCM, NH ₃ flow rate: 1000 SCCM, H ₂ flow rate: 1000 SCCM, reaction temperature: 1800°C, and reaction pressure: 10 Torr.

After cooling, the sample was taken out of the furnace and an attempt was made to release the graphite substrate from the mold. Since the graphite substrate could be released from the mold in about 10 minutes with almost no damage, this graphite substrate was used repeatedly and five samples were made. In addition, the obtained sample was heated to 600℃.
When we conducted a thermal shock test by dropping the product into water, no cracking occurred until an average of 15 times. still,
For comparison, when a p-BN crucible of the same shape was formed by a method of oxidizing and removing graphite without providing a powder layer, the time required for demolding was approximately 600 minutes, and the resulting sample was When a thermal shock resistance test was conducted in the same manner, cracking occurred after 7 tests.

Example 2 A p-BN crucible was manufactured under the same conditions as in Example 1, except that graphite powder was uniformly applied to a graphite substrate having the same shape as in Example 1. The time spent for demolding was approximately 10 It was also confirmed that five or more samples could be prepared without damaging the graphite substrate. Furthermore, when the obtained sample was subjected to a thermal shock resistance test under the same conditions as in Example 1, no cracking occurred up to an average of 16 times.

Example 3 A graphite substrate of the same shape as Example 1 was first subjected to CVD.
p-BN was deposited to a thickness of 30 μm using the method. CVD conditions are
BCl ₃ flow rate: 100SCCM, NH ₃ flow rate: 500SCCM,
H ₂ flow rate: 500 SCCM, reaction temperature: 1600°C, reaction pressure: 10 Torr. On top of the deposited p-BN
Apply BN powder uniformly and heat it in a CVD furnace at 1950℃ for 10 minutes.
Heat treatment in _H2 stream for min followed by CVD
p-BN was deposited to a thickness of 1.5 mm using the method. The CVD conditions at this time were: BCl ₃ flow rate: 200 SCCM, NH ₃ flow rate: 1000 SCCM, H ₂ flow rate: 1000 SCCM, reaction temperature: 1950° C., and reaction pressure: 10 Torr.

After cooling, the sample was taken out of the furnace and released from the graphite substrate, and it took approximately 10 minutes to release the sample without damaging the substrate. The released substrate was used repeatedly to prepare 5 samples under the above conditions, and the resulting samples were subjected to a thermal shock resistance test in the same manner as in Example 1. No cracking occurred after an average of 21 cycles.

, Example 4 After coating graphite powder on a graphite substrate on which p-BN was deposited to a thickness of 30 μm in the same manner as in Example 3, p-BN was deposited to a thickness of 1.5 mm under the same conditions as in Example 3.

After cooling, the sample was taken out of the furnace and an attempt was made to release the graphite substrate from the mold, which was completed in about 10 minutes without damaging the substrate. The graphite substrate that could be released from the mold without damage was used repeatedly to prepare five samples. When the released sample was subjected to a thermal shock test by dropping it into water at 600°C, no cracking occurred until an average of 19 times.

As detailed above, the present invention is not only excellent as a method for releasing p-BN from a graphite substrate, but also
It is possible to produce a p-BN crucible with excellent thermal shock resistance, and it is extremely effective industrially. In the above example, only the method of obtaining a p-BN crucible as a p-BN molded body was described, but this is because the crucible was suitable for confirming the effects of the present invention and for putting it into practical use. However, p-BN according to the present invention
The molded body is not necessarily limited to a crucible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the method for manufacturing a pyrolytic boron nitride crucible according to the present invention. 1: Graphite base, 2: Peeling powder layer made of BN powder, 3: p-BN.

Claims (1)

[Scope of Claims] 1. A powder layer for peeling is provided on the surface of a base made of graphite, and pyrolytic boron nitride is deposited on the powder layer by CVD to form a compact, and then the powder layer is attached to a peeling part. 1. A method for producing a pyrolytic boron nitride molded body, comprising: releasing the molded body from a graphite substrate. 2. In the method described in claim 1,
A method for producing a pyrolytic boron nitride molded body, characterized in that a thin layer of pyrolytic boron nitride is deposited on the substrate in advance by a CVD method, and then the peeling powder layer is provided. 3. A method for producing a pyrolytic boron nitride compact according to claim 1 or 2, wherein the powder layer is made of boron nitride powder. 4. A method for producing a pyrolytic boron nitride compact according to claim 1 or 2, wherein the powder layer is made of graphite powder. 5. A method for producing a pyrolytic boron nitride molded body according to any one of claims 1 to 4, wherein the molded body is a single crystal crucible.