Process for producing silicon carbide single crystal and...

Details Process for producing silicon carbide single crystal and... Process for producing silicon carbide single crystal and...

2000-04-28

2002-06-18

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S205000, C117S099000, C117S108000, C117S935000, C117S951000, C118S715000

Reexamination Certificate

active

06406539

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for producing a silicon carbide single crystal and a production apparatus therefor, in which a silicon material is reacted with a carbon material to yield a silicon carbide single crystal, and more specifically, to a process for producing a silicon carbide single crystal and a production apparatus therefor, in which a melted or vaporized silicon material is introduced into a carbon material in order to generate a silicon carbide gas, which is then caused to reach a silicon carbide seed crystal substrate to thereby grow a silicon carbide single crystal.
BACKGROUND OF THE INVENTION
Since silicon carbide is a substance having a hardness close to that of diamond and considerably high thermal and chemical stability, and serves as a semiconductor material having a wide energy band gap (about 3 eV), silicon carbide has conventionally been used as a polishing material, a refractory material, a heat generating material, or the like, and is expected to be used as a material for elements having high environmental resistance that are usable at elevated temperature, radiation resistance elements, power elements for electrical power control, and short-wavelength light-emitting elements.
A sublimation method is generally used in order to produce a silicon carbide single crystal (see, for example, Japanese Kohyo (PCT) Patent Publication No. 3-501118).
FIG. 8
is a sectional view showing a conventional apparatus for producing a silicon carbide single crystal, in which a sublimation method is employed. In
FIG. 8
, reference numeral
1
denotes a hollow crucible which is made of graphite and is composed of a crucible body
2
having a closed-bottomed cylindrical shape, and a lid plate
3
removably disposed on the upper end of the crucible body
2
. A silicon carbide material
4
in the form of a powder is stored at the bottom of the crucible body
2
, and a silicon carbide seed crystal substrate
5
is attached to the lower surface of the lid plate
3
. Heating and heat-retaining heaters
6
and
7
are disposed outside the crucible
1
, and temperature control is performed such that the temperature of the silicon carbide seed crystal substrate
5
is lower than that of the silicon carbide material
4
.
When a silicon carbide single crystal is produced by use of the above-described apparatus, a predetermined amount of the powdery silicon carbide material
4
is placed at the bottom of the crucible body
2
, and the silicon carbide seed crystal substrate
5
is attached to the lower surface of the lid plate
3
, which is then fixed to the crucible body
2
. Subsequently, the interior of the crucible
1
is filled with an inert gas such as Ar to create an inert gas atmosphere, and the silicon carbide material
4
and the silicon carbide seed crystal substrate
5
are heated to respective desired temperatures by use of heaters
6
and
7
.
The powdery silicon carbide material
4
decomposes and sublimes due to heat and rises in the form of silicon carbide gas. The silicon carbide gas reaches the silicon carbide seed crystal substrate
5
maintained within a growth temperature region, so that a silicon carbide single crystal
8
is grown epitaxially.
A method in which a silicon carbide single crystal is grown through utilization of reaction between vaporized silicon and solid carbon is also used.
FIG. 9
is a sectional view showing a conventional apparatus for producing a silicon carbide single crystal through utilization of reaction between silicon and carbon. In
FIG. 9
, reference numeral
11
denotes a silicon material stored at the bottom of a crucible body
2
; and reference numeral
12
denotes a carbon material which is disposed in the crucible body
2
to be located above the silicon material
11
and which reacts with vaporized silicon gas.
The carbon material
12
is composed of a carbon plate
13
having a large number of through holes
13
a
, and a powdery/granular carbon material
14
charged on the carbon plate
13
.
When a silicon carbide single crystal is produced by use of the above-described apparatus, a predetermined amount of the silicon carbide material
11
in the form of granules or powder is placed at the bottom of the crucible body
2
, and a silicon carbide seed crystal substrate
5
is attached to the lower surface of a lid plate
3
, which is then fixed to the crucible body
2
. Subsequently, the interior of the crucible
1
is depressurized. The silicon material
11
is heated by heater
7
such that the silicon material
11
is melted and vaporized, and the silicon carbide seed crystal substrate
5
is heated by heater
6
such that the silicon carbide seed crystal substrate
5
is maintained at a temperature suitable for growth of a silicon carbide single crystal.
Upon being heated, the silicon material
11
is melted and vaporized, so that the silicon material
11
rises in the form of silicon gas and passes through the through holes
13
a
of the carbon plate
13
and the powdery/granular carbon material
14
. While passing through the carbon material
12
, the silicon gas reacts with the carbon material
12
to generate a silicon carbide gas. The silicon carbide gas reaches the silicon carbide seed crystal substrate
5
maintained within a growth temperature region, so that a silicon carbide single crystal
8
is grown epitaxially.
However, these conventional methods have a drawback in that silicon gas or molten silicon reacts with graphite, which is the material of the crucible, thereby damaging the crucible. In the worst case, a hole is formed in the crucible, with the result that silicon gas and silicon melt accommodated within the crucible may leak outside, leading to a situation in which the production must be stopped. In this case, the damaged crucible is replaced with a new crucible so that a single crystal can again be grown. However, the expense of purchase of the new crucible for replacement and time loss caused by the operation of heating the new crucible to a temperature required for crystal growth lead to various problems, such as an increase in production cost and a decrease in productivity.
Especially, in the conventional sublimation method, when powdery silicon carbide material
4
is heated, not only SiC, but also Si, Si
2
C, and SiC
2
are generated in the form of decomposition/sublimation gases. Since the amount of the silicon component in the sublimation gas as a whole becomes equimolar or greater with respect to the amount of the carbon component, the composition of the powdery silicon carbide material
4
changes gradually during the course of the sublimation process such that the carbon content becomes in excess. Therefore, when the powdery silicon carbide material
4
sublimes, the partial pressures of the above-described decomposition/sublimation gases change with time, so that crystal defects tend to be generated to a greater extent in a silicon carbide single crystal, with the result that the crystallinity of the silicon carbide single crystal obtained decreases.
Meanwhile, in the conventional single crystal growth method utilizing the reaction between silicon and carbon, the proportions of the respective components of a reaction gas, such as SiC, Si, Si
2
C, and SiC
2
, are difficult to accurately control because of difficulty in controlling, to a predetermined amount, the quantity of silicon gas supplied to the carbon material. As a result, generation of crystal defects occurs easily during crystal growth, resulting in decreased crystallinity of the silicon carbide single crystal obtained.
The reason why the amount of silicon gas supplied to the carbon material is difficult to control is as follows. The amount of silicon gas supplied is controlled through control of the amount of silicon material vaporized by the temperature of silicon material. However, since the amount of the silicon material changes with time and the temperature inside the crucible changes, the amount of silicon gas supplied is difficult to control to a constant level.
In order to grow a single crys

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