JPH05208897A - Production of silicon carbide single crystal substrate - Google Patents

Abstract

PURPOSE:To produce a silicon carbide single crystal having high purity, uniform crystal orientation and excellent quality while preventing the contamination of the growing part of the single crystal by the diffusion of impurities from a seed crystal. CONSTITUTION:An SiC film 12 formed on an Si base 11 by epitaxial growth is used as a seed crystal for growing a silicon carbide single crystal. The substrate 10 for growth is placed in a crystal-growing furnace in a state holding a graphite base 20 on the substrate. A fused reaction part 13 is formed by the reaction of the Si base 11 with the graphite base 20 in the course of raising the temperature to the sublimation temperature range of the silicon carbide raw material and exclusively the SiC film 12 acting as a seed crystal is left after the reaction.

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 single crystal growth substrate used when producing a silicon carbide single crystal useful as a functional material for semiconductor devices and the like.

[0002]

2. Description of the Related Art A silicon carbide single crystal has been conventionally produced by a sublimation method and is expected to be used in various fields as a highly functional material such as a semiconductor device. In the sublimation method, the silicon carbide powder raw material is heated to a high temperature of 2000 to 2500 ° C. to be sublimated. Therefore, the crucible, the heater and the like necessary for crystal growth are made of graphite.

For example, there is a method in which a seed crystal is attached to a lid of a graphite crucible containing a silicon carbide powder raw material so as to face the raw material powder, and the raw material powder in the graphite crucible is sublimated by heating at 2000 to 2500 ° C. Sublimated silicon carbide condenses and grows in the crystallographic orientation of the seed crystal to become a single crystal. At this time, in order to prevent impurities from mixing into the grown single crystal, a graphite crucible is placed in a vacuum chamber where the pressure is adjusted in the range from reduced pressure to normal pressure, and a high-purity inert gas is placed in the vacuum chamber. The inside of the device is cleaned by introducing.

In addition, a porous hollow graphite cylinder is placed inside a graphite crucible having a seed crystal attached to the bottom thereof, and a silicon carbide powder raw material is filled between the inner wall surface of the graphite crucible and the hollow cylinder to heat it at a high temperature. The method of sublimating the silicon carbide powder raw material is also adopted. The sublimed silicon carbide passes through the hollow cylinder and is condensed and grown on the seed crystal at the bottom of the crucible.

[0005]

Impurities that affect lattice defects and characteristic changes are likely to be mixed in the silicon carbide single crystal that has grown. The mixed impurities include those derived from the raw material powder, those derived from the graphite crucible, and those derived from the seed crystal. Among them, those derived from seed crystals have the greatest influence.

The seed crystal has been conventionally produced by reducing SiO ₂ with C, and usually contains several percent or more of impurities. When growing a silicon carbide single crystal from such a seed crystal, impurities of the seed crystal are mixed into the crystal growth portion by thermal diffusion or the like. The mixed impurities give a lattice defect to the silicon carbide single crystal and also have an adverse effect on the characteristics when used as a semiconductor device or the like.

The present invention has been devised to solve such a problem. By using a SiC deposited film obtained by epitaxial growth as a seed crystal, the crystal growth portion is caused by impurities that thermally diffuse from the seed crystal. The purpose of the present invention is to prevent the contamination of carbon and to produce a high-purity, high-quality silicon carbide single crystal.

[0008]

In order to achieve the object, the method for producing a substrate for growing a silicon carbide single crystal of the present invention has an SiC film formed on the surface of a Si plate by epitaxial growth so that the Si base side is a graphite substrate. The Si substrate is placed on the graphite base so as to be in contact with the graphite base, and the Si base is fused and integrated with the graphite base during the temperature rising process of the silicon carbide raw material to reach the sublimation temperature range, and the SiC film is used as a seed crystal. Characterized by leaving.

[0009]

[Operation] The epitaxial growth method is a method suitable for growing a crystalline film on the substrate surface, and a highly pure functional film is formed. In the present invention, a seed crystal of SiC is formed on the substrate by utilizing this epitaxial growth method.
The seed crystal thus formed is of high purity in which the crystal orientation is controlled and does not serve as an impurity supply source for the silicon carbide single crystal grown thereon.

Moreover, the SiC seed crystal formed by the epitaxial growth method can have the same shape as the Si plate. Therefore, when a SiC seed crystal is formed over a large area of a large-diameter Si plate, a single-crystal growth substrate suitable for growing a large-diameter silicon carbide single crystal can be obtained.

A high-purity Si plate is used as the substrate on which the seed crystal is formed. The purity of the Si plate is preferably 99.9999% or more in order to eliminate the influence of impurities. Such high-purity Si plate is commercially available, for example, for manufacturing semiconductor devices.

S is formed on the high-purity Si plate by the CVD method or the like.
iC is epitaxially grown to form a SiC layer.
For example, using a silane-based gas such as high-purity propane or methane as a raw material, cubic or hexagonal SiC crystals grow in accordance with the crystal plane of the Si plate. For the epitaxial growth itself, a general method known in the related art can be adopted.

As shown in FIG. 1, a substrate 10 having a seed crystal formed therein is formed into a high-purity graphite substrate 20 having a smooth surface.
Place on top. At this time, the Si base 11 is brought into contact with the graphite base 20 so that the SiC film 12 deposited on the Si base 11 by epitaxial growth serves as a seed crystal. Then, it is placed inside the crystal growth furnace 30.

In the crystal growth furnace 30, a pipe 31 for introducing Ar gas is opened in order to maintain the inside of the furnace in an inert atmosphere. Further, a vacuum is drawn through an exhaust pipe 32 connected to a vacuum device (not shown), and a predetermined degree of vacuum is maintained. Further, a cylindrical heater 3 for heating and sublimating the raw material powder
3 is arranged in the furnace.

The substrate 10 in which the seed crystal is formed is arranged at the center of the bottom of the crystal growth furnace 30 surrounded by the cylindrical heater 33 together with the graphite substrate 20. And the substrate 1
The crucible 40 is placed on the upper part of 0. The crucible part 40 is
It has a porous bottom wall 41 and contains a powdery or granular silicon carbide raw material 42 therein.

Inside the crystal growth furnace 30, the SiC film 12 is formed.
Ar gas is caused to flow downward from above so that clean Ar gas always reaches the surface of the single crystal growing on the top surface. As a result, the surfaces of the seed crystal and the single crystal in the growing process are always kept clean.

The temperature at which the silicon carbide raw material 42 sublimes and the crystals grow is 2200 to 2500 ° C. Since the melting point of Si is 1413 ° C., the Si base 11 of the substrate 10
Starts to melt in the process of reaching the crystal growth temperature range. In this process, the crystal growth furnace 3 is provided so that a temperature difference of T ₁ <T ₂ <T ₃ is applied around the substrate 10 as shown in FIG.
The temperature gradient inside 0 is set. This temperature difference is obtained by moving the crucible moving / rotating shaft 34 up and down to move the portion of the graphite base 20 to the central portion of the heater 33. Therefore, the melting of the Si base 11 is started from the contact portion with the graphite base 20, and proceeds toward the SiC film 12.

Simultaneously with the start of melting, Si reacts with the graphite base 20 in contact with the lower part, and diffuses and permeates into the graphite base 20. As a result, the fusion reaction part 13 is formed at the interface between the Si base 11 and the graphite base 20. When the Si base 11 is completely melted, the fusion reaction part 1
The SiC film 12 remains on the upper surface of the metal film 3. Then, the crucible 40 and the graphite substrate 20 are moved downward by operating the crucible moving / rotating shaft 34 to remove the remaining SiC film 12 from the silicon carbide raw material 42.
It is used as a seed crystal for crystal growth of SiC sublimated from.

The fusion reaction part 13 in which the Si base 11 is fused with the graphite substrate 20 is basically SiC and holds the SiC film 12 which becomes a seed crystal in the fusion reaction process. Further, the fusion reaction part 13 prevents the impurities from being mixed into the SiC film 12 from the graphite base 20.

When the temperature inside the crystal growth furnace 30 reaches the crystal growth temperature range 2200 to 2500 ° C., the sublimation of the silicon carbide raw material 42 starts. When sublimated SiC comes into contact with the seed crystal portion, silicon carbide single crystal 14 grows using SiC film 12 as a seed crystal, as shown in FIG. SiC film 1
Since No. 2 was produced by epitaxial growth, its crystal orientations are aligned. Therefore, the SiC film 12
The silicon carbide single crystal 14 formed on the above also has an excellent crystal structure and crystal orientation. Further, since the SiC film 12 as the seed crystal is of high purity, contamination of impurities is prevented, and a high-purity silicon carbide single crystal 14 having stable crystal orientation, lattice constant, etc. can be obtained.

[0021]

EXAMPLE A Si plate having a diameter of 4 inches (purity 99.9999)
%), A SiC film 12 having a thickness of 20 μm was formed by epitaxial growth. At this time, C using monosilane gas and propane gas as hydrogen as carrier gas
The SiC film 12 was epitaxially grown by VD. First, a Si plate having a (100) crystal plane is placed in a CVD reaction tube, heated to a temperature of 1500 ° C., and then monosilane gas and propane gas are introduced at a flow rate of 3 liters / minute using hydrogen as a carrier gas. The vapor deposition reaction was continued for 10 hours.

The substrate 10 on which the SiC film 12 is formed is
The i base 11 was placed on the graphite base 20 so that the i base 11 was in contact with the graphite base 20. Then, the crucible 40 containing the silicon carbide raw material 42 was placed above the substrate 10 and set in the crystal growth furnace 30. Ar at a flow rate of 500 ml / min in the crystal growth furnace 30 while maintaining the atmospheric pressure at 10 Torr.
Gas was supplied. The temperature around the crucible 40 is 230
It is heated to 0 ° C. to sublimate silicon carbide, and the temperature is set to 22.
Crystal growth was performed using the SiC film 12 maintained at 00 ° C. as a seed crystal.

The obtained silicon carbide single crystal 14 had the same diameter as the original Si plate 11. In addition, there was no contamination by impurities, and the product was of high purity and high quality with an excellent crystal structure, crystal orientation and the like.

[0024]

As described above, according to the present invention, a defect-free high-purity silicon carbide single crystal can be obtained by using a SiC film whose crystal orientation is controlled by epitaxial growth as a seed crystal. Further, since the shape and size of the seed crystal can be freely adjusted depending on the Si plate used, epitaxial growth conditions, etc., a large-diameter silicon carbide single crystal can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a diagram for specifically explaining the present invention.

FIG. 2 is a diagram showing a process in which a Si base having a seed crystal formed therein reacts with a graphite substrate.

[Explanation of symbols]

10 substrate 11 Si base 1
2 SiC film 13 Fusion reaction part 14 Silicon carbide single crystal 2
0 Graphite substrate 30 Crystal growth furnace 34 Crucible moving / rotating shaft 4
0 Crucible 42 Raw material for silicon carbide

Claims (1)

[Claims] 1. A SiC film is formed on a surface of a Si plate by epitaxial growth, and the Si substrate is placed on the graphite base so that the Si base side contacts the graphite base.
In the process of raising the temperature of the silicon carbide raw material to reach the sublimation temperature range, the Si
A method for manufacturing a substrate for growing a silicon carbide single crystal, characterized in that a base is fused and integrated with the graphite base, and the SiC film is left as a seed crystal.