JPH0798708B2 - Method for producing pyrolytic boron nitride coated article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a pyrolytic boron nitride based on graphite (hereinafter referred to as P
-BN), particularly to a method for producing a P-BN-coated article in which a graphite base material and a P-BN coating layer are firmly adhered to each other.

[Prior Art] P-BN is a material that is widely used as high-purity boron nitride in crucibles for manufacturing semiconductors and special alloys.
For example, in the liquid-sealed Czochralski method, which is one of the methods for growing a compound semiconductor single crystal such as GaAs, a self-standing P-
BN crucibles are widely used, and it has been attempted to apply P-BN coating to the surface of various graphite members in order to prevent the inclusion of graphite impurities in the single crystals from various graphite members used in single crystal growth furnaces. There is.

Freestanding P-BN and P-BN coated articles are disclosed, for example, in U.S. Pat. No. 3,152,006.
So-called chemical vapor thermal decomposition that uses boron halides such as boron trichloride and ammonia as gaseous raw materials and deposits boron nitride on the surface of a suitable substrate such as graphite under the conditions of temperature of 1,450 to 2,300 ° C and pressure of less than 50 Torr. By removing the base material from the boron nitride deposited on the surface of the base material, which is produced by the method, a self-standing P-BN article is obtained, and when the base material is left as it is, a P-BN coated article is obtained.

[Problems to be solved by the invention]

However, when the P-BN-coated article obtained according to the conventional technique is used as various jigs in a compound semiconductor single crystal growth furnace, it is used under conditions where heating and cooling are repeated, and therefore, only a few If the heat is not enough, the first heating
In the cooling cycle, cracks may enter the P-BN coating layer,
-The BN coating layer may peel off from the base material and become unusable, and its reliability is extremely low. Japanese Unexamined Patent Publication (Kokai) No. 61-236672 discloses a P-BN coated article, but it does not show the optimum conditions for producing the article having the above-mentioned performance.

As a result of intensive studies aimed at solving the above-mentioned drawbacks, the present inventors have found that the P-BN coating layer does not easily peel off or fall off even if it is repeatedly heated and cooled because of its excellent adhesion to a graphite base material. The inventors have found that it is necessary to set the bulk density and surface roughness Rmax of the graphite base material and the thickness of the P-BN coating layer within a specific range in order to obtain a P-BN coated article, and have arrived at the present invention. Is.

[Means for solving problems]

That is, the present invention, in coating the boron nitride on the surface of the graphite substrate by the chemical vapor pyrolysis method using boron halide gas and ammonia gas as raw materials, as the graphite substrate, bulk density 1.70 ~ 1.95 g / Surface roughness Rmax of 10 μm at cm ³
A method for producing a pyrolytic boron nitride-coated article, characterized in that the above-mentioned material is used and the thickness of the pyrolytic boron nitride-coated layer is 10 to 300 μm.

Hereinafter, the present invention will be described in more detail.

The graphite base material used in the present invention has a bulk density of 1.70 to 1.95 g /
The surface roughness Rmax in cm ³ must be 10 μm or more.
If the bulk density is a graphite base material other than this, the adhesive force of the P-BN coating layer to the graphite base material is less than 2.0 MPa, and a P-BN coated article excellent in the adhesive force aimed at by the present invention is produced. I can't. Further, even if a graphite base material having a surface roughness Rmax of less than 10 μm is used, the adhesion of the P-BN coating layer to the graphite base material cannot be 2.0 MPa or more, and spontaneous peeling may occur. . When the substrate surface roughness Rmax is 10 μm or more, the adhesive strength tends to increase as Rmax increases.
It is considered that the cause of the difference in the adhesive force of the P-BN coating layer depending on the value of the substrate surface roughness Rmax is due to the difference in the anchor effect on the surface of the graphite substrate.

The thickness of the P-BN coating layer is 10 to 30 μm, preferably 50 to 150
It must be in the μm range. If the thickness is less than 10 μm, the thickness of the P-BN coating layer is thin, and the graphite of the base material easily diffuses out of the P-BN coating film to the outside, reducing the cycle resistance of heating / cooling. To do. If the thickness exceeds 300 μm, the residual stress in the P-BN coating layer increases and P-BN
Natural peeling of the coating layer is likely to occur.

As a condition for carrying out the chemical vapor pyrolysis method, the pressure is usually 50
It is preferable that the temperature is not higher than Torr and the deposition temperature is in the range of 1,800 to 1,930 ° C. If the deposition temperature is less than 1,800 ° C, the crystallinity of the P-BN coating layer formed will be low, and the strength of the coating layer itself will be reduced, such being undesirable. Also, the deposition temperature is 1,
If it exceeds 930 ° C, B ₄ C will start to form at the interface between the graphite base material and the P-BN coating layer, causing a problem in the uniformity of adhesion. The most preferred temperature is 1800 to 1850 ° C. Further, in order to control the crystallinity of the P-BN coating layer and increase the strength of the coating layer itself, it is preferable to set the deposition temperature of the P-BN coating layer to 300 μm / hr or less, preferably 150 μm / hr. Chemical vapor phase pyrolysis is carried out under preferable conditions, that is, a pressure of 0.5 to 5 Torr, a deposition temperature of 1,800 to 1,850 ° C., and a deposition temperature of 150 μm / hr or less,
Further, by setting the thickness of the P-BN coating layer to 50 to 150 μm, the strength of the P-BN coating layer is further increased, and the adhesive force can be obtained firmly and stably.

The P-BN coated article produced by the method of the present invention has an adhesion of the P-BN coating layer to the graphite base material of 2.0 MPa or more, that is, 10.0 MPa.
Since it is as strong as a or more and the strength of the P-BN coating layer is also high,
Even if heating and cooling are repeated, the P-BN coating layer will crack.
It has the characteristics that it does not peel off or fall off, and the adhesion strength of the P-BN coating layer to the graphite base material is not significantly reduced.

〔Example〕

Example 1. A graphite cylindrical reaction tube having an inner diameter of 15 cm and a length of 45 cm was provided in a resistance heating type vacuum heating furnace, and two P- tubes were provided on one side of the reaction tube.
The BN gas introduction pipe was connected coaxially. Bulk density 1.90 with surface roughness Rmax of 0.7 cm × 4 cm × 15 cm changed in the reaction tube
A graphite substrate of g / cm ³ was placed, the furnace was evacuated to 10 ^-2 Torr, and then heated to the precipitation temperature. Boron trichloride and ammonia diluted with nitrogen gas were introduced into the reaction chamber under a pressure of 2.5 Torr, and P-BN was deposited on the graphite substrate to a thickness of 100 μm to prepare a sample of P-BN-coated article. A part of the sample thus obtained is used for measuring the adhesive strength, and the rest is heated to a temperature of 1,800 ° C in a nitrogen atmosphere, and then cooled to room temperature. Repeat the test, and carefully observe the surface condition of the sample each time. At the same time, the adhesion strength was measured after 100 times.
Table 1 shows the experimental results. In the comparative example, the adhesion strength was weak and the cycle resistance of heating / cooling was very weak, and in Experiment No. 9, peeling occurred during cooling after film deposition.

Example 2 Example 1 except that graphite substrates having different bulk densities with a surface roughness Rmax of 20 μm were placed in the same reaction tube as in Example 1.
A P-BN-coated article was manufactured in the same manner as above and the same measurement was performed. The results are shown in Table 2.

In the comparative example, the adhesion strength was weak, the cycle resistance to heating and cooling was very weak, and in Experiment No. 18, cracking occurred immediately after precipitation.

Example 3 The same procedure as in Example 1 was carried out except that a graphite substrate with a surface roughness Rmax of 20 μm and a bulk density of 1.90 g / cm ³ was placed in the same reaction tube, and the deposition rate was 150 μm / hr, and the film thickness was changed. A P-BN coated article was manufactured in the same manner as in Example 1 and the same measurement was performed. The results are shown in Table 3. In the comparative example in which the film thickness exceeds 300 μm, the adhesion strength is lowered and peeling occurs due to cooling after film deposition.

[Effect of the invention] As is clear from the examples, the P-BN coated article produced according to the present invention has a high strength of the P-BN coating layer and an adhesion strength to the graphite substrate of 2.0 MPa or more. Strong, repetitive heating
Cracking may occur in the P-BN coating layer due to cooling, and P
-The BN coating layer does not peel off. Moreover, even if the heating and cooling are repeated, the adhesion strength of the P-BN coating layer to the graphite base material is hardly reduced, so that the P-BN coating layer can be stably used under a thermal cycle for a long period of time. In particular, it can be repeatedly used for a long period of time in various jigs in a compound semiconductor single crystal growing furnace.

Claims (1)

[Claims] 1. When coating a graphite substrate surface with boron nitride by a chemical vapor pyrolysis method using boron halide gas and ammonia gas as raw materials, the graphite substrate has a bulk density of 1.70 to 1.95 g / cm 3. ³ with a surface roughness Rmax of 10 μm or more, and the thickness of the pyrolytic boron nitride coating layer is 10 to 30
A method for producing a pyrolytic boron nitride-coated article, which has a thickness of 0 μm.