JPH0648899A - Production of silicon carbide single crystal - Google Patents

Abstract

PURPOSE:To simplify the process from the single crystal growth to the epitaxial layer growth and to obtain an inexpensive high-quality epitaxially grown silicon carbide crystal. CONSTITUTION:A gas (a) sublimated from a silicon carbide raw powder 4 is grown on a seed crystal 2 as a single crystal (b). When the single crystal (b) is grown, the ratio of the sublimation atmosphere pressure P in a reaction furnace 5 to the sublimation temp. T is kept at 0.03-0.05 Torr/ deg.C, and an epitaxial layer (c) is grown on the single crystal (b). A doping gas is introduced into the reaction chamber 5 from a gas feed pipe 8 or 9 in epitaxy to impart n-or p-type characteristic to the epitaxial layer (c). Consequently, since the epitaxial layer (c) is grown on the surface of the flawless single crystal (b), a high-quality epitaxially grown crystal is obtained. Besides, as an expensive gaseous semiconductor, etc., are not used, the production cost is drastically reduced.

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 an inexpensive and high quality silicon carbide single crystal.

[0002]

2. Description of the Related Art Silicon carbide devices, which are expected as semiconductor materials, are manufactured by a single crystal growth process, a slicing process,
It is manufactured through a polishing process, an epitaxial film growth process, and a function building process. Silicon carbide single crystals have been conventionally produced by a sublimation method. In the sublimation method, for example, a seed crystal is attached to a lid of a graphite crucible containing a raw material powder of silicon carbide so as to face the raw material powder. 2000-24
When heated to 00 ° C., the raw material powder in the graphite crucible sublimes. The sublimated silicon carbide grows on the seed crystal in the same crystal orientation and is grown as a single crystal.

The CVD method is generally adopted as a means for growing an epitaxial film on a single crystal. For example, a reactive gas such as silane or propane is used to vapor-deposit an epitaxial layer on a substrate crystal such as Si or SiC. LPE in which the Si melt having the adjusted components is housed in a graphite crucible and the SiC substrate is immersed in the Si melt.
In some cases, a molecular beam of Si, C, a dopant, or the like is generated in a high vacuum, and an MBE method in which a heated substrate crystal is irradiated is used to grow an epitaxial film.

[0004]

The substrate crystal used in the epitaxial film growth step is prepared through steps such as slicing and polishing after the crystal growth. Substrate crystals are slices,
When processing such as polishing is performed, defects such as scratches are likely to be introduced on the surface. Defects in the substrate crystal cause crystal defects such as dislocations in the epitaxial layer grown thereon. As a result, the obtained epitaxial wafer is inferior in the control of the single crystal in the epitaxial layer, resulting in a defective product.
When performing the epitaxial growth by the CVD method or the MBE method, an expensive semiconductor gas is required. Therefore, the manufacturing cost becomes high. On the other hand, when the LPE method is adopted, the film thickness of the epitaxial layer cannot be controlled with high precision, and it becomes difficult to set the processing conditions and the like when the subsequent function is built. The present invention has been devised in order to solve such a problem, and makes it possible to continuously grow a single crystal and an epitaxial layer in one reactor, and to correlate the growth temperature and the atmospheric pressure. The purpose of this is to grow a low-cost and high-quality silicon carbide epitaxial layer on the substrate crystal by controlling the temperature.

[0005]

In order to achieve the object, the method for producing a silicon carbide single crystal according to the present invention has a pressure-controlled inert gas atmosphere in which a crucible containing a silicon carbide raw material powder is placed facing a seed crystal. The vapor is sublimated from the silicon carbide raw material powder by heating with a temperature gradient and is grown as a single crystal on the seed crystal, and the ratio P / T between the sublimation atmosphere pressure P and the sublimation temperature T is 0. An epitaxial layer is grown on the single crystal under the condition of maintaining 0.03 to 0.05 Torr / ° C.

[0006]

[Operation] In the present invention, the first-layer single crystal is grown on the seed crystal by the sublimation method, and the second-layer epitaxial layer is grown using this single crystal as a substrate. According to this method, it is not necessary to use an expensive semiconductor gas such as the CVD method and the MBE method, and the difficulty of controlling the film thickness found in the LPE method is solved. Moreover, since defects such as flaws are not introduced into the single crystal surface of the first layer, a high quality silicon carbide epitaxial layer can be grown.

The present invention will be described in detail below with reference to the drawings. In the present invention, for example, an apparatus having the equipment configuration shown in FIG. 1 is used. Seed crystal 2 on top of crucible 1
And the crucible 1 is placed on the crucible base 3. The silicon carbide raw material powder 4 housed in the crucible 1 is opposed to the seed crystal 2. Alternatively, the silicon carbide raw material powder 4 may be arranged on the upper part of the crucible 1 and the seed crystal may be arranged on the bottom part of the crucible 1. The crucible 1 is set at the center of a cylindrical heater 6 arranged in the reaction furnace 5. Although the drawing shows the heater 6 in one zone, it is divided into a plurality of blocks in the vertical direction so that a predetermined temperature distribution is formed in the reaction furnace 5, and the amount of electricity supplied to each block is controlled. A heater can also be used.

The reaction furnace 5 includes a gas supply pipe 7 for introducing argon as an atmosphere gas, a gas supply pipe 8 for introducing a nitrogen gas for providing an n-type characteristic, and Al (C) for providing a p-type characteristic.
A gas supply pipe 9 for introducing H ₃ ) ₃ gas is provided in the upper part, and an exhaust pipe 10 is provided in the lower part. Flow rate adjusting valves 7a to 10a are incorporated in the gas supply pipes 7 to 9 and the exhaust pipe 10, respectively, and the atmospheric pressure in the reaction furnace 5 is controlled by adjusting the openings of the flow rate adjusting valves 7a to 10a. . The silicon carbide raw material powder 4 is heated by the heater 6 to a high temperature of 2000 to 2400 ° C. Sublimation gas a generated from silicon carbide raw material powder 4 by heating at high temperature grows on seed crystal 2 maintained at a relatively low temperature to become silicon carbide single crystal b. Until the silicon carbide single crystal b grows to a predetermined thickness,
Continue the crystal growth process.

When the silicon carbide single crystal b has grown to a predetermined thickness, the growth conditions in the reaction furnace 5 are switched to grow the second epitaxial layer c on the silicon carbide single crystal b. That is, the pressure in the reaction furnace 5 is adjusted so that the ratio P / T between the sublimation atmosphere pressure P and the sublimation temperature T is 0.03 to 0.05 Torr / ° C. When maintaining the ratio P / T in this range, a high-quality epitaxial layer c grows on the surface of a sound silicon carbide single crystal b. Nitrogen gas is introduced from the gas supply pipe 8 to grow the epitaxial layer c having the n-type characteristic, and Al (C 2) is supplied from the gas supply pipe 9 to grow the epitaxial layer c having the p-type characteristic.
H ₃ ) ₃ gas is introduced.

Generally speaking, the smaller the ratio P / T, the greater the amount of sublimation of the silicon carbide raw material powder 4. However, if it is less than 0.03 Torr / ° C., it becomes difficult to control the film thickness of the epitaxial layer c with high accuracy, and it is easy to generate a polycrystal. On the contrary, when the ratio P / T exceeds 0.05 Torr / ° C., the sublimation amount of the silicon carbide raw material powder 4 decreases, so that the surface layer of the single crystal b, which is the first layer, is resublimated and the surface of the single crystal b is Unevenness is formed. As a result, not only it becomes difficult to control the film thickness of the second epitaxial layer c, but also defects such as dislocations are easily introduced into the epitaxial layer c due to the unevenness.

[0011]

Example Silicon carbide having an average particle diameter of 200 μm and a purity of 99.99% was placed as a raw material powder 4 in the crucible 1 and faced the seed crystal 2. The crucible 1 was set in the center of the heater 6 in the reaction furnace 5. Prior to the growth of the single crystal, an argon gas was fed into the reaction furnace 5 from the gas supply pipe 7 to create an argon atmosphere in the reaction furnace 5. Then, the atmospheric pressure in the reaction furnace 5 was reduced to 10 ^-2 Torr. The inside of the reaction furnace 5 was cleaned by repeating this argon gas introduction and exhaust 5 times.

After cleaning, argon gas was introduced into the reaction furnace 5 at a flow rate of 1 liter / minute. Then, the heater temperature was maintained at 2200 ° C., and the first layer of silicon carbide single crystal b
Has grown up. When crystal growth was continued for 1 hour under these conditions, the thickness of the silicon carbide single crystal b reached 1 mm. Next, the ratio P / of the sublimation atmosphere pressure P and the sublimation temperature T
Flow rate 0.01 while maintaining T at 0.04 Torr / ° C.
Nitrogen gas was introduced into the reaction furnace 5 at a rate of 1 / min. When the reaction was continued for 1 hour under these conditions, the thickness was 500 μm.
Epitaxial layer c was grown on the silicon carbide single crystal b.

The obtained epitaxial layer c exhibited an n-type characteristic because nitrogen gas was used as a doping gas, and was formed on the silicon carbide single crystal b with a uniform thickness. It is speculated that this is because the silicon carbide single crystal b does not have defects such as surface defects and has good surface flatness.

[0014]

As described above, in the present invention, single crystal growth and epitaxial layer growth are continuously performed in one reactor. Therefore, not only the process is simplified, but an epitaxial crystal having excellent quality characteristics can be obtained. Moreover, since it is not necessary to use expensive semiconductor gas, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a single crystal production apparatus for carrying out the present invention.

[Explanation of symbols]

1 crucible 2 seed crystal 3 crucible stand 5 reactor 6 heater 7-9
Gas supply pipe 10 Exhaust pipe 7a to 10a Flow rate control valve a Sublimation gas b Silicon carbide single crystal c Epitaxial layer

Claims (1)

[Claims] 1. A crucible containing a silicon carbide raw material powder facing a seed crystal is placed in a pressure-controlled inert gas atmosphere, and vapors sublimated from the silicon carbide raw material powder by heating with a temperature gradient are heated. A single crystal is grown on the seed crystal, and the ratio P between the sublimation atmosphere pressure P and the sublimation temperature T is P.
A method for producing a silicon carbide single crystal, wherein an epitaxial layer is grown on the single crystal under the condition that / T is maintained at 0.03 to 0.05 Torr / ° C.