JPS62176981A - Boron nitride-coated crucible - Google Patents

Abstract

PURPOSE:To obtain the titled high-strength and inexpensive crucible having excellent adhesion between the substrate and respective layers and capable of preventing the oozing out of impurities by forming a surface layer consisting of thermally decomposed BN on the surface of the crucible substrate consisting of graphite through two specified intermediate layers. CONSTITUTION:The first intermediate layer for sealing a carbon component consisting of Si, B, or their carbides is provided on the surface of the crucible substrate consisting of graphite. The second intermediate layer for relieving the thermal expansion difference consisting of random oriented BN is furnished on the first intermediate layer. The outermost layer of thermally decomposed BN (hereinafter referred to as PBN) is finally formed by the conventional vapor growth method. Since the first and the second intermediate layers and the PBN film are continuously formed, the adhesion between the respective layers is excellent, the oozing out of impurities is prevented, and the release of the films by a heating-cooling cycle can be eliminated. Since the crucible has high strength, the wall thickness can be reduced, and a lightweight and large-sized crucible can be formed. The production cost can be reduced, since the thickness of the PBN layer can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crucible coated with boron nitride, and particularly to improvements in crucibles 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 they also have some reactions, so when producing high-purity semiconductor single crystals, there are problems such as the crucible material getting 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 the conventionally used crucibles made of quartz, graphite, silicon carbide, and precious metals, recently crucibles such as boron nitride (BN), especially pyrolytic boron nitride (PBN), have been used to make graphite, A crucible coated on a substrate or a crucible constructed 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 excellent chemical stability, oxidation resistance, and lubricity at high temperatures, and is also highly pure. It is optimal 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 is a problem that some carbon inevitably leaches into the PIIN film as an impurity, and that there is almost no carbon between the graphite and PBN films. There is no adhesive property, and the coefficient of thermal expansion of the PBN film in the direction parallel to the film layer is a negative expansion of 2 x 10-'/'C, so the coefficient of thermal expansion is significantly different between the graphite substrate and the PBN film. A problem has arisen in that peeling occurs quickly when subjected to heating-cooling cycles.

On the other hand, when the entire crucible is made of 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.

[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, a first layer made of Si, B, or a carbide thereof for sealing a carbon component on the surface of a crucible-shaped molded body made of graphite, and a randomly oriented nitrided layer for alleviating the difference in thermal expansion. The above object is achieved by providing a PBN layer via a second layer of boron.

The present invention will be explained in detail below.

According to the present invention, graphite, which is low cost and has excellent workability, is selected as the base material of the crucible, and when providing the PBN film as the outermost layer, Si, B, or at least one of these carbides is used as the first intermediate layer. A layer consisting of This layer is formed by a known vapor phase growth method. In the production of St or B, according to the vapor phase growth method, St or B is in an active state and reacts with carbon, which is a base component, to form SiC or B, which is a carbide of these.
C is generated. When this reaction occurs, the base component is sealed by the first layer, so that the base component can be prevented from leaching out of the system.

A second intermediate layer of randomly oriented boron nitride is then provided on the first intermediate layer.

The PBN film, which is the outermost layer of the crucible of the present invention, has a
Approximately 2 Xl0-6/” C1C approximately 30 in the axial direction
XIO-6/ has a thermal expansion coefficient of C, but when PBN is normally produced by vapor phase growth, it is approximately aligned along the C axis. Therefore, the thermal expansion in the direction parallel to the film plane of graphite and PBN films. There is a difference of more than twice in the coefficients.

In the present invention, this difference can be alleviated to some extent by forming the first N, but this is insufficient from the viewpoint of film adhesion.

According to the research conducted by the present inventors, it has been found that the randomness of the orientation of the film is a factor that determines the coefficient of thermal expansion of the film itself, especially when the film has anisotropy such as PBN.

That is, although the PBN film itself is composed of polycrystals, if the orientation of each crystal is inconsistent, the coefficient of thermal expansion is determined by the C-axis orientation and the ratio of the C-axis orientation. In other words, by controlling the randomness, the thermal expansion coefficient of the BN film can be adjusted to approximately 2 to 30xlO-6/"c.
It was found that it is possible to control within the range of .

Therefore, in the present invention, a second intermediate layer made of boron nitride, which is controlled to exhibit an intermediate value of thermal expansion coefficient by random orientation, is provided between the graphite substrate on which the first intermediate layer is formed and the PBN film. It is important to provide By forming this second intermediate layer, the difference in thermal expansion from the base to the PBN film is alleviated, so that the adhesion between each layer is improved and the strength of the crucible itself is also improved.

In the present invention, the thickness of each layer of the crucible is 0.05 mm for the first intermediate layer.
1 to 20 μm, the second intermediate layer is 1 to 100 μm,
From the viewpoint of film strength and cost, it is desirable to provide the PBN film with a thickness in the range of 10 to 1000 μm.

As mentioned above, the vapor phase growth method is used to manufacture the crucible in the present invention.

Initially, when forming the first intermediate layer, a crucible-shaped molded body made of graphite was placed in a reaction tank, and
Heat to a temperature of °C. Then, in the reaction tank, S I
A mixed gas consisting of a Si-containing gas such as II a + SiCl 4 + or a B-containing gas such as BCI:11BtH6 and hydrogen is introduced. At this time, when, for example, B and C are introduced in a 1:1 ratio on the graphite substrate surface, the reaction of 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 (134c) is formed at the interface of the base body.
) A film is formed, and as time passes, boron becomes excessive due to reaction (1), and a continuous layer of boron is formed.

Further, if a Si-containing gas and a B-containing gas are introduced simultaneously, the first intermediate layer becomes a mixed layer consisting of Si, B, or a carbide thereof.

Next, a randomly oriented BN film is provided as the second intermediate layer, but this random orientation is mainly due to the reaction gases used during film formation, namely boron-containing gases such as BCh, IhH, etc., nitrogen-containing gases such as Nlh, and hydrogen gas. Determined by mixing ratio and substrate temperature. In the present invention, the thermal expansion coefficient of this intermediate layer is set to an intermediate value between the upper and lower layers, specifically, 3 to 8×1.
Since it is necessary to set the reaction gas to 0-#'/°C, the reaction gas mixture ratio Nlh/BC1+ may be controlled within the range of 1 to 50, and the substrate temperature may be controlled within the range of 800 to 1200°C.

Therefore, when a Si-containing gas is used to form the first intermediate layer, a nitrogen-containing gas is introduced at the same time as the gas is switched, but when a B-containing gas is used, only the nitrogen-containing gas needs to be introduced, which is economical. and from the first to the second
Since the formation of the intermediate layer can be performed continuously, the adhesion between the layers is further improved.

Then, the PB that is finally formed through these intermediate layers
The N film has a substrate temperature of 1000 to 2000 in the same reaction tank.
℃ and NHi/BCh ratio from 0.5 to 10.
It is generated by

As described above, during manufacturing of the crucible of the present invention, each layer can be formed continuously in the same reaction tank, and the adhesion between each layer is improved, and the mechanical strength of the crucible is also improved. The invention is illustrated by the following example.

Example 1 A crucible-shaped molded body made of graphite was placed and heated to 1500°C.
Heated to a pressure of 5 Torr and BClz, 10 cc/mi
A mixed gas was introduced at a flow rate of 1Iz150cc/min to perform a boriding reaction for 1 hour to form a 3μm intermediate layer of B and C, and then the substrate was heated to 800°C and Nl+3
, BCl3.11□ at 20cc/min each,
10cc/m1n (Nllz/[1C1z=2) 15
The reaction was carried out for 2 hours at a pressure of 0 cc/min and a randomly oriented B with a thermal expansion coefficient of 4 x 10-'/'C.
A N film was formed by LoIJm.

Thereafter, a reaction was carried out for 5 hours under the same conditions except that the substrate temperature was raised to 1500° C. to form a PBN film of 150 μm.

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 (
PBN I
No peeling or cranking occurred in 11, and no impurities were mixed into the GaAs melt from the crucible, making it possible to produce a high-purity semiconductor GaAs single crystal of good quality.

Example 2 A graphite crucible shaped body was placed in a reaction tank and heated to 1200°C, and the pressure was 3 Torr, 5iH43cc/min.
A mixed gas was introduced at a flow rate of 280 CC/min to carry out a silicification reaction for 1 hour to form a first intermediate layer of SiC with a thickness of 1 μm.

Then NtlslOOcc instead of 5illa gas
/min, BCl310cc/m1n(N)1:+/
BC1*=lO) flow rate, substrate temperature 1200℃, pressure 3
The reaction was carried out at Torr, and randomly oriented BN with a thermal expansion coefficient of 3.7 xlO-'/'c was used as the second intermediate layer.
15 μl of II was formed.

After that, the substrate temperature was lowered to 1500°C and N113. B.C.
l3゜ and 112 at 20cc/min, 10cc/
The reaction was carried out at 3 Torr and 200 cc/min for 5 hours to form a PBN film with a thickness of 150 μm.

The obtained boron nitride-coated crucible was heated 10 times as a crucible for producing GaAs single crystals in the same manner as in Example 1.
Although cooling was repeated, there was no peeling or cranking of the PBN film, and a high-purity GaAs single crystal could be obtained.

Comparative Example A graphite crucible-shaped molded body was set at 1500°C, and the NI
I+10cc/lll1n,, BCl310cc/
m1n (Nll:+/BCI:+=1), Hz150c
The reaction gas was introduced at a flow rate of c/min, and the pressure was
The reaction was carried out for 5 hours under the following conditions to form a PBN film with a thickness of 115μ.

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.

(Effects of the Invention) As described above, the boron nitride-coated crucible of the present invention has
A reaction tank is formed on the graphite substrate as a first intermediate layer between Si, B, or these and carbon as a substrate component, and a second intermediate layer is formed on the graphite substrate.
By providing a pyrolytic boron nitride (PBN) film on top of which a randomly oriented BN film is provided as an intermediate layer to alleviate the thermal expansion difference between the base and the PBN film, the base component is sealed by the first intermediate layer. At the same time, adhesion is improved, and peeling due to differences in thermal expansion can be prevented. Furthermore, since the first and second intermediate layers and the PBN film are formed as continuous layers during their manufacture, they have excellent adhesion between each layer, which prevents impurities from leaching out as a crucible, and allows the film to be formed by heating and cooling cycles. Peeling can also be eliminated. Furthermore, since the crucible of the present invention has high strength, even if the wall thickness of the crucible is thinned, it can be made lightweight and large.
Since there is no need to increase the thickness of the IN layer, there is an excellent advantage that manufacturing costs can be reduced.

The crucible of the present invention can be applied to a crucible for manufacturing a semiconductor single crystal, a crucible for metal deposition, a boat, etc.

Claims (2)

[Claims] (1) A first layer made of at least one selected from Si, B, or carbides thereof as an intermediate layer on the surface of a crucible-shaped molded body made of graphite, a second layer made of randomly oriented boron nitride, and a thermal decomposition layer. A boron nitride-coated crucible comprising a third layer made of boron nitride. (2) The boron nitride-coated crucible according to claim 1, wherein the first to third layers are continuous layers.