JPH0431309A - Production of thermally decomposed boron nitride formed article - Google Patents

Abstract

PURPOSE:To reduce anchor effect between a substrate and the aimed P-BN film and prevent layer release of the P-BN formed article by using a material obtained by forming a P-BN layer on a substrate by chemical vapor phase reaction as a base and forming a P-BN film thereon. CONSTITUTION:A mixed gas of a boron halide and ammonia is subjected to chemical vapor phase reaction in <=20Torr at 1500-2400 deg.C and the resultant P-BN is formed into a P-BN film as a base. A P-BN film is prepared on the base by a CVD method of a boron halide with ammonia. The P-BN film is released from the base to provide the thermally decomposed boron (P-BN) nitride formed article. Thereby high-purity P-BN formed article having high mechanical strength is obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing pyrolytic boron nitride, and in particular, to a crucible for pulling up compound semiconductors, a method for producing pyrolytic boron nitride, and a method for producing pyrolytic boron nitride. The present invention relates to a method for producing a pyrolytic nitrided aluminium molded body, which is useful as a crucible for metal evaporation for wire epitaxy, a jig for crystal growth, a heat sink, an electrical insulation component, and the like.

(Prior art) Pyrolytic boron nitride (hereinafter abbreviated as P-BN) is a highly pure and inert boron nitride, so it can be used in crucibles for pulling up compound semiconductors, crucibles for metal evaporation for molecular beam epitaxy, and crystallization. It is used in a wide range of areas, including growing jigs.

Several methods are known for producing this P-BN, but among them, boron halide and ammonia gas are mixed at a temperature of 1,450 to 2,300°C and a pressure of less than 50 torr. A method of precipitating P-BN using a chemical vapor phase reaction method (hereinafter abbreviated as CVD method) (U.S. Patent No. 3,15
2,000) is widely used, and this is P-
This method uses a base body with a unique shape that has a different coefficient of thermal expansion from BN, deposits P-BN on this base body, and then separates the base body and P-BNg to obtain a P-BN molded body with a unique shape. There is.

(Problem to be solved by the present invention) However, in this method, there is a so-called anchor effect between the base and the P-BN film, so a part of the base to be separated adheres to a part of the P-BN molded body. or the P-BN molded body may peel off, so after separating the P-BN layer from the substrate, the portion of the substrate adhering to the P-8N film must be removed by machining or oxidation treatment. As a result, there is a problem that the P-BN layer is damaged or its mechanical strength is deteriorated.

Therefore, for this purpose, the pressure in the reaction layer into which boron halide and ammonia gas are introduced is set to less than 5 torr, and the reaction is carried out by the CVD method at a temperature of 1.000 to 1,400°C. A method has been proposed in which amorphous boron nitride or low crystalline boron nitride with a thickness of 10 μm or more is deposited on a substrate and used as a substrate (Japanese Patent Application Laid-Open No.
249406), but it is said that because the amorphous boron nitride obtained in this way has low strength, it is not effective for large molds or molds with complex structures. There are drawbacks.

(Means for Solving the Problems) The present invention relates to a method for producing P-BN that solves the above-mentioned disadvantages, and this invention involves forming a P-BN layer on a substrate using a CVD method from boron halide and ammonia gas. After forming the P-BN layer, the P-BN layer is peeled from the substrate.
In the method for producing a molded article, boron halide and ammonia gas are heated on a substrate at a pressure of 20 Torr or less at a pressure of 1,500 Torr or less.
This method is characterized in that a P-BN layer having a thickness of 10 to 200 μm is formed on the substrate by a chemical vapor phase reaction at a temperature of ~2,400° C. and is used as the substrate.

That is, the present inventors have conducted various studies on methods of reducing the anchoring effect between the substrate surface and the P-BNtL film to obtain a P-BN molded body with good peelability from the substrate, high purity, and high quality. If a conventionally known substrate on which a P-BN layer is formed by a known method is used as the substrate on which this P-BN molded body is formed, then this substrate has a P-BN layer formed in advance. Therefore, the substrate and the target P-BN
The anchor effect between the layers is significantly reduced, and when the P-BN layer is separated from the substrate, a part of the substrate does not stick to the P-BN molded body, causing delamination of the P-BN molded body. In addition to discovering that the P-BN layer formed on this substrate has high strength, it has been confirmed that it can provide sufficient effects even for large molds and molds with complex structures. The present invention has been completed.

This will be explained in more detail below.

(Function) The present invention is based on CVD of boron halide and ammonia gas.
This invention relates to an improvement in a method for producing a P-BN molded body by a method.

The method for producing a P-BN molded body according to the present invention is carried out by a known method of reacting boron halide and ammonia gas by CVD method. A BN layer is formed thereon.

The boron halide used here may be boron trichloride (BeIL) or boron trifluoride (BF3), which are normally used in this type of method, and ammonia gas may also be of conventionally known types. do it.

In addition, since the substrate used here needs to be able to withstand high temperatures, it is usually made of graphite, titanium boride, etc., and its shape depends on the purpose of use. It may have any size and shape.

However, it is necessary that the substrate used in the present invention be previously coated with a P-BN layer.

The P-BN layer may be coated in accordance with a known method by placing the substrate in a reactor using a CVD method using boron halide and ammonia gas. This CV
The reaction conditions for Method D are to carry out the reaction at high temperature in a reactor with a reaction pressure of 20 Torr or less, but as shown in Figure 1, if the reaction temperature is 1,000°C or less, the P- BN becomes unstable and 1,5
At high temperatures above 00℃, it becomes dense and stable,
As shown in Figure 2, this tensile strength also increases as Wakkanai becomes hotter, but below 1,500℃, the generated P-BN becomes unstable and the tensile strength decreases as shown in Figure 2. Although it is weak, the P- generated when heated above 2,400℃
1,500~ to avoid deterioration of P-BN such as an increase in impurities due to carbon contamination in BN and discoloration of P-ON.
The temperature should be 2,400°C, more preferably 1,600 to 2,400°C.

In addition, if the mixing ratio of boron halide and ammonia gas introduced into this reaction system is less than 1, P-B
When B (boron) alone is mixed into the N layer, impurities may be mixed into the P-BN, and black coloration may occur due to warping. In addition to consuming more
1 to 15, since the film formation rate will be low and the yield will be low.
The amount may be within a molar range, but the preferred range is 2 to 10 moles.

Therefore, in the production of the P-BN molded body according to the present invention, a mixed gas of 1 mole of boron halide and 2 to 10 moles of ammonia gas is heated at a pressure of 20 Torr or less and a temperature of 1,500 to 2.4 Torr.
P-B produced by chemical vapor phase reaction at 00℃
N is formed as a P-BN film on the substrate, and P-B is formed on the surface.
A base on which a N film is formed is prepared, and then boron halide and ammonia gas are deposited on this base by CVD using a known method.
The thickness of the P-BN film, which is made by making P-BN[ by the method and peeling this P-BNg from the substrate, or is pre-formed on this substrate, is too thin if it is less than 10 μm, and if it is less than 200 μm. If it is thicker, the laminated P-88 layer will be easily peeled off partially from the substrate, so the thickness should be 10 to 200 μm.
It may be within the range of . If this is done, the substrate will be P-B in advance.
Since it has NM, P-B provided on this substrate
The anchoring effect between the N film and the substrate is significantly reduced, so that when the P-BN film is peeled off from the substrate, part of the substrate will not adhere to the P-BN molded body, and the P-BN film will not be attached to the P-BN molded body. Since the BN molded body is prevented from delaminating, it is advantageous that the desired P-BN molded body can be obtained with high purity and high mechanical strength.

(Example) Next, examples of the present invention and comparative examples will be given.

Example A cylindrical graphite substrate with a diameter of 150 mm and a length of 200 mm was placed in an electric furnace. A vacuum pump was connected to the furnace to reduce the pressure inside the furnace to 1 Torr, and then boron trichloride IA/ A mixed gas of 1012 min and ammonia gas was supplied, and the reaction was carried out at 2.050°C for 2 hours. After the reaction was completed, the substrate was cooled to room temperature and then taken out.
The graphite surface of this substrate is coated with a P-BN film with a thickness of 100 mm.
It was covered with μm.

Next, this P-BN″r: coated substrate was placed in the same electric furnace as above, and after the pressure was reduced to 1 torr, a mixed gas of 1427 minutes of boron trichloride and 2 fl/minute of ammonia gas was added thereto. After the reaction was completed, nitrogen gas was introduced to cool the substrate, and the substrate was taken out after the temperature reached room temperature. This P-BNl
When i was peeled off from the substrate, the substrate with the P-BN coating obtained above and the P-BN crucible formed thereon could be easily peeled off, and the obtained P-BN crucible was peeled off near its surface. As shown in Figure 3, there was no carbon adhesion on the inner wall surface, and the P-BN surface had disappeared from the surface, and there was no black matter adhering to it. Since no treatment was necessary and no sand vapor treatment was necessary, there was no fear of abrasive material being mixed into the inner wall surface, and therefore a P-BN crucible with an inner wall of high quality quality could be obtained.

Comparative Example Instead of using the P-BN-coated substrate used in the above examples, a cylindrical graphite substrate not coated with P-BN was used, and this was placed in the furnace in the same manner as in Example 1. After reducing the pressure to 1 Torr at
A mixed gas of 1 fl/min and 2 fl/min of ammonia gas was supplied and reacted for 24 hours to form a P-BN film on the substrate at 1.2 fl/min.
Formed to a thickness of 0 μm and taken out from the cooling back tilt, P-BN
When the film was peeled off and a P-BN crucible was made, the inner wall of this crucible became P-BN from the surface as shown in Figure 4, but this had black carbon on the surface. Kimono is often seen, and 800 yen is required to remove this carbon.
As a post-treatment, oxidation treatment was required in which 8 hours of heat treatment was performed in a heating furnace (air atmosphere) at ℃, and polishing with sandpaper was also required, resulting in contamination of the walls with abrasives. In terms of quality, there was a disadvantage in that the product contained many impurities.

(Effects of the Invention) The present invention relates to a method for producing a P-BN molded article with high purity and good releasability from a substrate. In a method for producing a P-BN molded body, in which a P-BN layer is formed on the substrate and then the P-BN layer is peeled from the substrate, boron halide and ammonia gas are heated on the substrate at a pressure of 20 torr or less, , 500 to 2. This is characterized in that a P-BN layer with a thickness of 10 to 200 μm is formed on the substrate by a chemical vapor phase reaction at a temperature of 500 to 2.400°C. According to P
- Since it is coated with a BN layer, this results in a significantly reduced anchoring effect between the substrate and the P-BN layer formed thereon, and therefore the P-BN layer is removed from this substrate.
When separating the N layer, a part of the substrate will not stick to the P-BN molded body, and the P-BN molded body will not peel off, so the desired P-BN molded body can be obtained with high purity. Moreover, it has the advantage of being able to have high mechanical strength.

[Brief explanation of the drawing]

Figure 1 shows CVD of boron halide and ammonia gas.
Figure 2 is a diagram showing the relationship between reaction temperature and reaction pressure and physical properties of P-BN obtained by this method. Figure 3 is a diagram showing the relationship between reaction temperature and tensile strength of this P-BN. -BN
FIG. 4 is a photomicrograph showing the structure of crystals on the inner surface of the molded article. FIG. 4 is a photomicrograph showing the structure of the crystals on the inner surface of the P-BN molded article obtained in a comparative example. 231゛Ward 1 □Nibo I fake ('C) Figure 1] Maro (0C) Figure 2

Claims (1)

[Claims] 1. Pyrolytic boron nitride forming, in which a pyrolytic boron nitride layer is formed on a substrate using a chemical vapor phase reaction method from boron halide and ammonia gas, and then the pyrolytic boron nitride film is peeled from the substrate. In the method for producing a film, boron halide and ammonia gas are subjected to a chemical vapor phase reaction on the substrate at a pressure of 20 torr or less and a temperature of 1,500 to 2,400°C to form a film with a thickness of 10 to 200 μm on the substrate. 1. A method for producing a pyrolytic boron nitride molded article, characterized in that a material on which a pyrolytic boron nitride layer is formed is used as a substrate.