JPS62153189A - Boron nitride coated crucible and production thereof - Google Patents

Abstract

PURPOSE:To improve adhesivity of boron nitride film to substrate while preventing admixture of impurities, by applying pyrolytic boron nitride through a middle layer containing boron carbide and/or boron to the surface of substrate of molded crucible consisting of graphite. CONSTITUTION:A substrate of molded crucible consisting of graphite is set in a reaction tank, heated to 800-2,000 deg.C and a mixed gas of a boron-containing gas (e.g., BCl3, B2H5, etc.) and hydrogen is introduced into a reaction tank. Consequently, a middle layer containing boron carbide and/or boron is formed on the surface of the substrate. Then, a nitrogen-containing gas (e.g., NH3) is introduced and a pyrolytic boron nitride film is formed on the middle layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crucible coated with boron nitride, and more particularly to an improvement in a crucible used for high-purity semiconductor single crystals or vapor deposition.

[Prior art]

In recent years, in the semiconductor industry, in order to manufacture high-quality semiconductor products, high-purity single crystal semiconductor materials such as silicon, germanium, and gallium arsenide (GaAs) have been developed that do not contain impurities. It's coming.

Usually, single crystals are produced by the pulling method,
In order to bring the semiconductor material into a molten state at this time, crucibles made of various ceramics, noble metal materials, etc. are used.

These crucibles themselves contain various sintering agents and are subject to some reactions, so when producing high-purity semiconductor single crystals, there are problems such as crucible materials being mixed into the single crystal as impurities. is occurring. In addition, in the recent large semiconductor wafer manufacturing industry, large-capacity crucibles are required, so the amount of crucible material used has increased, and the strength of the crucible material must also be increased in order to safely accommodate large-capacity contents. Must be.

Further, contamination of impurities from the crucible into the vapor deposition crucible or boat was unavoidable.

Therefore, instead of crucibles made of quartz, graphite, silicon carbide, or precious metals, which have been used in the past, recently crucibles have been made using boron nitride (BN), especially pyrolytic boron nitride (PBN), through a gas phase reaction to produce graphite, A crucible coated on a base body, or a crucible made entirely of a boron nitride sintered body have been proposed. This pyrolytic boron nitride has excellent electrical insulation, thermal conductivity, and thermal shock resistance, as well as chemical stability at high temperatures, oxidation resistance, and lubricity, and is highly pure. It is the most suitable for crucibles.

[Problem that the invention seeks to solve]

However, when trying to use the above crucible for single crystal production or vapor deposition, there are problems with some carbon inevitably leaching into the PBN film as an impurity, and also because there is no bond between the graphite and the PBN film. The adhesion between the graphite substrate and the PBN film is very weak because there is no thermal expansion, and the thermal expansion coefficient of the PBN film in the direction parallel to the film layer is ~2 × 1 O-67-c, which is a negative expansion. Due to the large difference in rate, a problem arises in that delamination occurs quickly when subjected to heating-cooling cycles.

On the other hand, when the entire crucible is made of a boron nitride sintered body, the structure requires a certain thickness or more, and when manufactured by means such as vapor phase growth, it takes a long time and costs are high. was there.

[Purpose of the invention]

Therefore, the present invention was completed in order to solve the problem of ridges, and its purpose is to improve the strength of the crucible by improving the adhesion between the substrate and the boron nitride film while preventing the contamination of impurities. An object of the present invention is to provide a boron nitride coated crucible which is improved and also has a lower cost.

[Means for solving problems]

According to the present invention, the above object can be achieved by coating the surface of a crucible-shaped molded substrate made of graphite with pyrolytic boron nitride via an intermediate layer containing boron carbide and/or boron.

Further, a crucible-shaped molded base made of graphite is placed in a reaction tank, and a mixed gas of boron-containing gas and hydrogen is introduced into the hindlimb reaction tank heated to 800 to 2000°C to coat the surface of the base with boron carbide and Alternatively, the boron nitride-coated crucible described above can be obtained by forming an intermediate layer containing boron, and then further introducing a nitrogen-containing gas to form a pyrolytic boron nitride film on the intermediate layer.

The present invention will be explained in detail below.

According to the present invention, it is important to provide an intermediate layer made of boron carbide and/or boron between the graphite substrate and the PBN film, which is low in cost and has excellent processability. Boron carbide and boron themselves have a coefficient of thermal expansion similar to that of graphite;
It has the function of alleviating distortion caused by the difference in thermal expansion between the film and the PBN film. In particular, if this intermediate layer is formed using a known vapor phase growth method, the intermediate layer can be formed as a reaction gas with the substrate, as described later, and all processes up to the formation of the PBN film can be performed continuously in a single reaction tank. The resulting film is also formed as a continuous layer without boundaries. Therefore, the adhesion between each layer can be significantly improved.

The thickness of the intermediate layer provided in the present invention is 0.1 to 5
0 μm is preferable, while PBN film has a thickness of 10 to 1000 μm.
It is provided within a range of m.

Specifically, the manufacturing method thereof will be explained by placing a crucible-shaped molded body made of graphite in a reaction tank and heating it to a temperature of 800 to 2000°C. Then, first, BCl3, B,
A mixed gas consisting of a boron-containing gas such as H, and hydrogen is introduced. At this time, when BCl, for example, is introduced on the surface of the graphite substrate, a reaction according to the following formula (1) % formula % (1) proceeds and boron is produced. Furthermore, the reaction of the following formula (2)% formula (2) with carbon, which is a base component, proceeds, and boron carbide (84C) is formed at the interface of the base body.
After the film is formed, as time passes, boron becomes excessive due to reaction (1), and a boron film is formed as an intermediate layer.

Next, when a nitrogen-containing gas such as NH is introduced into the reaction tank, a PBN film is formed on the intermediate layer. At this time, the middle class and PB
Since the N film is produced almost continuously in the same reaction tank, the intermediate layer and the PBN film form a continuous layer with almost no boundaries.

That is, according to the present manufacturing method, an intermediate layer made of a product resulting from a reaction with a base component is provided on the base, and a PBN film that is a continuous layer with the intermediate layer is provided, so that the PBN film is a component of the base. Carbon is sealed by the intermediate layer and can be prevented from entering the PBN layer, thereby preventing impurities from entering the crucible.

Incidentally, in order to increase the thickness of boron carbide in the intermediate layer, it is sufficient to further introduce a hydrocarbon or the like into the reaction gas.

Example 1 A crucible-shaped molded body made of graphite was placed and heated to 1500°C under a pressure of 5 Torr and BCl at 10 cc/mi.
A mixed gas was introduced at a flow rate of 150 cc/win, Hz, and a boriding reaction was performed for 1 hour to form an intermediate layer of B and C with a thickness of 10 μm. Furthermore, under the same conditions, N1(
3 gases were introduced at a flow rate of 10 cc/min, and after 3 hours 60
A .mu.m PBN film was formed.

The obtained sample was used as a crucible for producing semiconductor GaAs single crystals by the pulling method, and as a result, it was used 10 times (
To produce a high-purity semiconductor GaAs single crystal of good quality without peeling or cranking in the PBN film even after applying one heating-cooling cycle, and without any impurities being mixed into the GaAs melt from the crucible. was completed.

Example 2 After applying a boron carbide film of 1μ steel for 6 minutes under the same conditions as Example 1, Nlh was introduced at 100cc/n+in, PBN was grown for 15 minutes in a nitrogen excess state, and NH3 was added at 10c/n+in.
The PBN film was further grown for 5 hours with the growth rate reduced to c/min, and a PBN film with a thickness of 120 μm was finally formed.

When A1 was vapor-deposited using the obtained sample as a crucible for vapor deposition, a highly pure vapor-deposited film of AI was obtained without any contamination of impurities from the crucible.

Comparative Example A graphite crucible-shaped molded body was set at 1500°C, and NH
zlOcc/lll1n SBC1zlocc/m1n
(NH*/BCj! != 1), Hz150cc/
A reaction gas was introduced at a flow rate of min., and the reaction was carried out for 5 hours at a pressure of ITorr to form a PBN film with a thickness of 115 μm.

When the fractured surface of the obtained sample was observed, it was found that there were parts where the PBN film had peeled off from the base, and the adhesion was poor.

〔Effect of the invention〕

As described above, the boron nitride-coated crucible of the present invention continuously decomposes B on a graphite substrate through a film of boron carbide or boron by the reaction of carbon and boron in the substrate.
By providing the N film (PBN film), it is possible to prevent peeling due to the difference in thermal expansion between the PBN film and the substrate, improve the adhesion between the PBN film and the substrate, and seal the substrate components to prevent impurities from the substrate. leaching can be prevented.

Therefore, the PBN film does not peel off due to heating and cooling cycles. Furthermore, since the crucible of the present invention has high strength, it is possible to make the crucible strong enough, lightweight, and large even if the wall thickness of the crucible is thinned.In addition to using inexpensive graphite, the thickness of the PBN layer Since there is no need to increase the size of , there is an excellent advantage that manufacturing costs can be reduced.

Note that the crucible of the present invention is a crucible for producing semiconductor single crystals,
It can be applied to crucibles or boats for metal deposition.

Claims (2)

[Claims] (1) A boron nitride-coated crucible characterized in that the surface of a crucible-shaped molded substrate made of graphite is coated with pyrolytic boron nitride via a boron carbide film and/or a boron film. (2) After placing a crucible-shaped molded base made of graphite in a reaction tank and heating it to 800 to 2000°C, a mixed gas of boron-containing gas and hydrogen is introduced into the reaction tank to coat the surface of the base. A method for manufacturing a boron nitride-coated crucible, comprising forming an intermediate layer containing boron carbide and/or boron, and then further introducing a nitrogen-containing gas to form a pyrolytic boron nitride film on the intermediate layer.