JPH06128094A - Production of silicon carbide single crystal - Google Patents

Abstract

PURPOSE:To produce a high-quality silicon carbide single crystal free from contamination of an Si particle or a carbon particle according to the sublimation method. CONSTITUTION:Powdery silicon carbide raw material 2 in a crucible 1 is heated by using a heater 5 so as to be sublimated. A carbon component gas such as propane is introduced into a crystal growth zone at the initial stage of sublimation and a silicon component gas such as silane is introduced at the latter stage. Thereby, variation in the sublimated gas composition generated from the powdery silicon carbide raw material 2 with passage of time can be canceled. The sublimated gas is allowed to grow as a silicon carbide single crystal 6 on a seed crystal set to a lower cover 3. Since the crystal grows from the sublimated gas having a composition controlled to a constant value, the obtained silicon carbide single crystal 6 is free from contamination of an Si particle or a carbon particle. Accordingly, a stoichiometrically pure and high-quality product can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a long silicon carbide single crystal of stable quality by a sublimation method.

[0002]

2. Description of the Related Art Since a silicon carbide single crystal is a semiconductor material having a wide energy bandgap and being thermally and chemically stable, it has attracted attention as a material replacing conventional silicon-based semiconductor materials. ing. At present, silicon carbide single crystals are produced by a sublimation method using silicon carbide powder as a raw material. In the sublimation method, as shown in FIG. 1, a raw material powder 2 of silicon carbide is put in an upper portion of a graphite crucible 1 and a lower lid 3 having a seed crystal is placed in a lower portion thereof. Alternatively, a seed crystal may be attached to the upper lid of the crucible 1 and the raw material powder 2 may be placed below. Usually 1
About 20 to 30 g of raw material powder 2 is used per batch.

When arranging the raw material powder 2 on the upper part of the crucible 1, the inside of the crucible 1 is partitioned by a porous graphite plate 4, and the raw material powder 2 is charged on the graphite plate 4. Then, the heater 5 surrounding the crucible 1 heats the raw material powder 2 with a temperature gradient such that the seed crystal side is lower than the raw material powder 2 side. As the heater 5, a resistance heating method, a high frequency induction heating method, or the like is adopted.

The raw material powder 2 is sublimated by being heated by the heater 5 to a high temperature near 2400 ° C., and Si, Si ₂
It becomes a sublimation gas such as C, SiC ₂ , or SiC. The sublimation gas flows down inside the crucible 1 having a temperature gradient, and falls on the seed crystal attached to the lower lid 3. Since the sublimation gas is maintained at a temperature near 200 ° C. near the seed crystal, the sublimation gas is about 0.5 as the silicon carbide single crystal 6.
Grow on seed crystals at a growth rate of ~ 2 mm / hr.

[0005]

The raw material powder 2 is sublimated,
In the process of growing as a single crystal, the composition of the sublimation gas tends to change. One of the major fluctuation factors is due to the nonuniformity of the sublimation reaction. The sublimation reaction of silicon carbide does not generate a sublimation gas component in an amount proportional to the amount of the raw material powder 2 contained in the crucible 1, but Si becomes excessive vapor at the initial stage of sublimation, and then C becomes excessive. It becomes steam.

Naturally, such fluctuations in the components of the sublimation gas adversely affect the growth process of the single crystal. For example, precipitation of Si particles, incorporation of C, and the like occur on the crystal plane, which causes crystal defects, dislocations, and the like to be introduced into the obtained silicon carbide single crystal. Therefore, in order to grow a stoichiometrically pure and high-quality single crystal, it is necessary that vapor having a constant composition always pours onto the crystal growth surface.

The present invention has been devised in order to meet such a requirement, and sends the silicon component gas and / or the carbon component gas to the crystal growth region separately from the sublimation gas from the silicon carbide raw material powder. Aims to grow a high-quality silicon carbide single crystal under stable conditions.

[0008]

In order to achieve the object, the method for producing a silicon carbide single crystal according to the present invention, in order to achieve the object, when a silicon carbide single crystal is grown on a seed crystal by sublimation reaction, a sublimation reaction It is characterized in that a silicon component gas and / or a carbon component gas, which offsets the time-dependent component fluctuations of the sublimation gas, are introduced into the growth reaction zone. As the silicon component gas, silane SiH ₄ , Si ₂ H ₆ , tetramethylsilane Si (CH ₃ ) ₄ , tetraethylsilane Si
(C ₂ H ₅ ) ₄ Tetranormal Propylsilane Si (n-
C ₃ H _{7) 4,} tetrabutyl silane Si (C ₄ H _{9) 4} and the like are used. As the carbon component gas, methane CH ₄ , ethane C ₂ H ₆ , propane C ₃ H ₈ , acetylene C ₂ H ₂
Hydrocarbon-based gas such as is used. The silicon component gas and the carbon component gas are introduced into the growth reaction region using an inert gas such as argon as a carrier.

The basic structure of equipment for carrying out the sublimation method is as follows:
As shown in FIG. 2, the crucible 1 and the heater 5 are set in a chamber 7 provided with a heat insulating lining, and the chamber 7 is maintained under an appropriate reduced pressure by evacuation and introduction of an inert gas. In the present invention, a gas supply pipe 8 communicating from the outside of the chamber 7 to the inside of the crucible 1 is provided, and the silicon component gas and / or the carbon component gas is fed into the crucible 1 via the gas supply pipe 8. The gas supply pipe 8 is preferably made of a high temperature resistant material such as graphite or tungsten because it is exposed to a high temperature atmosphere of more than 2000 ° C. in the chamber 7.

In FIG. 2, the gas supply pipe 8 is opened in the crucible 1 above the silicon carbide raw material powder 2. But,
The present invention is not limited to this, and for example, when the silicon carbide raw material powder 2 is arranged below the crucible 1, the gas supply pipe 8 is opened below the crucible 1.

When the seal between the gas supply pipe 8 and the upper lid 9 of the crucible 2 poses a problem, the gas supply pipe 8 and the upper lid 9 can be integrally formed. Gas supply pipe 8 is chamber 7
When the portion passing through is insulated with a water cooling flange or the like, the gas supply pipe 8 outside the chamber 7 may be a stainless steel pipe, a quartz pipe or the like which is usually used as a semiconductor industrial pipe.

When the crucible 2 reaches a predetermined temperature by heating by the heater 5, the silicon carbide raw material powder 2 starts to sublime,
Sublimation gas is generated. The sublimation gas flows down in the crucible 2 and is poured onto the seed crystal attached to the lower lid 3 to form a single crystal 6
To grow as. As the sublimation progresses, a carbon component gas is introduced into the crucible 1 together with the carrier gas. As the sublimation continues, carbon starts to remain excessively in the raw material powder 2. When this state is reached, the supply of the carbon component gas is stopped and the supply of the silicon component gas is started. Then, after a lapse of a predetermined time, the heating is stopped and the crystal growth is completed.

Flow rates of carbon component gas and silicon component gas,
The introduction time and the like can be controlled based on the data accumulated in the past regarding the silicon carbide raw material powder to be used. The carbon component gas and the silicon component gas may be introduced simultaneously or at different flow rate ratios depending on the conditions such as the sublimation temperature and the sublimation rate of the raw material powder 2. For example, when using a raw material powder containing a large amount of unreacted carbon, an appropriate amount of carbon component gas is introduced at the same time as the introduction of the silicon component gas.

[0014]

[Operation] When the silicon carbide single crystal 6 is grown while replenishing the carbon component gas and the silicon component gas in accordance with the progress of the sublimation reaction, the time-dependent component variation of the sublimation gas generated from the raw material powder 2 is offset, Crystal growth from a sublimated gas that has been stabilized becomes possible. Therefore, the obtained silicon carbide single crystal 6 is a high-purity, high-quality product without inclusion of Si particles, carbon particles, or the like that cause crystal defects and the like.

[0015]

Example A seed crystal was placed on the pedestal of the lower lid 3 of the graphite crucible 1, and a porous graphite plate 4 was attached to the upper part of the crucible 1 to contain the silicon carbide raw material powder 2. Here, a device was used in which a graphite gas supply pipe 8 attached to a flange penetrating the chamber 7 was exposed to the inside of the crucible 1 via an upper lid 9. The gas supply pipe 8 was connected to the gas supply system outside the chamber 7 via a stainless steel pipe.

The chamber 7 was evacuated and a reduced pressure inert atmosphere was created by introducing an inert gas, and then the heater 7 was energized to start heating. When the temperature inside the crucible 1 reached 2200 ° C., sublimation gas began to be generated from the raw material powder 2. Therefore, propane as a carbon component gas was introduced into the crucible 1 together with the carrier gas at a flow rate of 15 ml / min. At this time, the flow rate of the carrier gas was adjusted so that the inside of the chamber 1 was maintained in a predetermined reduced pressure atmosphere.

After 3 hours from the start of sublimation, silane as a silicon component gas was added to propane at a flow rate of 15 ml / min and introduced into the crucible 1. After the simultaneous introduction of propane and silane was continued for 1 hour, the supply of propane was stopped and the sublimation reaction was continued for 3 hours while introducing only silane gas at the same flow rate. Throughout the entire process, the inside of the chamber 7 was maintained at a constant reduced pressure atmosphere by controlling the flow rate of the carrier gas.

After the sublimation process was completed, the heater 5 was turned off to complete the crystal growth. The obtained silicon carbide single crystal 6 is
It had a diameter of 20 mm and a height of 5 mm. This silicon carbide single crystal 6 was sequentially sliced in the height direction, and test pieces produced in the early, middle, and late stages of crystal growth were cut out. When the surface and the inside of each test piece were observed with a microscope, Si generated in the single crystal obtained by the conventional sublimation method was observed.
No inclusion of particles or carbon particles in the crystal was observed in any of the test pieces. Further, it was a stoichiometrically pure and high quality single crystal.

[0019]

As described above, according to the present invention, the silicon component gas and / or the carbon component gas is sent to the crystal growth region in accordance with the progress of sublimation of the silicon carbide raw material powder, and the sublimation gas is time-series. It offsets the fluctuation of the component.
As a result, the stabilized sublimation vapor falls on the crystal growth surface, and a silicon carbide single crystal grows. Therefore, a high-quality silicon carbide single crystal can be obtained without Si particles and carbon particles taken into the crystal as in the conventional case.

[Brief description of drawings]

FIG. 1 Conventional single crystal production apparatus using silicon carbide raw material powder

FIG. 2 is a single crystal manufacturing apparatus incorporating a gas supply pipe for feeding a silicon component gas and a carbon component gas into a crystal growth region according to the present invention.

[Explanation of symbols]

1 Graphite crucible 2 Silicon carbide raw material powder 3
Lower lid of crucible 4 Porous graphite plate 5 Heater 6
Silicon carbide single crystal 7 Chamber 8 Gas supply pipe 9
Top lid

Claims (3)

[Claims] 1. A silicon component gas and / or carbon that offsets a time-dependent component variation of a sublimation gas with the progress of a sublimation reaction when a silicon carbide raw material is sublimated to grow a silicon carbide single crystal on a seed crystal. A method for producing a silicon carbide single crystal, which comprises introducing a component gas into a growth reaction zone. 2. The method according to claim 1, wherein the silicon component gas is one kind or two or more kinds of silane, tetramethylsilane, tetraethylsilane, tetranormalpropylsilane and tetrabutylsilane. 3. The method according to claim 1, wherein the carbon component gas is a hydrocarbon-based gas such as methane, ethane, propane and acetylene.