JPH1160391A - Production of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method of a silicon carbide single crystal by which a high-quality α-type bulk silicon carbide single crystal can be accurately obtd. SOLUTION: A sapphire substrate 8 is prepared, and an α-type silicon carbide single crystal layer 5 is grown on the surface of the sapphire substrate 8 at a temp. higher than the melting point of silicon and lower than the melting point of sapphire. The obtd. α-type silicon carbide single crystal layer 5 is used as a seed crystal to form a silicon carbide single crystal 7. By growing the crystal at a temp. higher than the melting point of silicon and lower than the melting point of sapphire on the sapphire substrate 8, the α-type silicon carbide single crystal layer 5 can be obtd. when using the α-type silicon carbide single crystal layer 5 as a seed crystal to form a silicon carbide single crystal 7, a high quality α-type (6H) silicon carbide single crystal 7 can be accurately produced without inducing such a crystal defect caused by a solid phase transfer in the case that a cubic (3C) silicon carbide single crystal is subjected to solid phase transfer into a 6H silicon carbide single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a bulk silicon carbide single crystal.

[0002]

2. Description of the Related Art In recent years, a silicon carbide single crystal substrate has been developed as a semiconductor substrate of a high-voltage high-power semiconductor device such as a high-voltage transistor or a high-voltage diode. An α-type silicon carbide single crystal is used for this silicon carbide single crystal substrate. As a method for producing this α-type silicon carbide single crystal, as shown in JP-A-9-77595, a cubic (3C) silicon carbide single crystal layer serving as a seed crystal is grown on a silicon wafer, A method of growing a bulk α-type (6H) silicon carbide single crystal on this seed crystal by a sublimation recrystallization method has been proposed.

[0003] That is, when sublimation growth is performed using a 3C silicon carbide single crystal as a seed crystal, 6H
The solid-state transition to a silicon carbide single crystal is used to grow a bulk α-type silicon carbide single crystal (Journal of Crystal Growth 99 (1990) 27
8-283 [Journal of Crystal G
row 99 (1990) 278-283]).

[0004]

However, during the solid phase transition from the 3C silicon carbide single crystal to the 6H silicon carbide single crystal during the sublimation growth period, crystal defects are induced in the 3C silicon carbide single crystal and the 6H silicon carbide single crystal. It turned out to be. That is, since the growth and the transition occur simultaneously, a crystal defect occurs in the seed crystal during the solid phase transition, and the defect of the seed crystal is inherited in the sublimated crystal.
For this reason, it is difficult to obtain a high-quality α-type bulk silicon carbide single crystal.

The present invention has been made in view of the above problems, and has as its object to provide a method for producing a silicon carbide single crystal capable of accurately obtaining a high-quality α-type bulk silicon carbide single crystal.

[0006]

In order to achieve the above object, the following technical means are employed. According to the first aspect of the present invention, a sapphire substrate (8) is prepared, and an α-type silicon carbide single crystal layer ( 5) is grown, and a silicon carbide single crystal (7) is formed using the α-type silicon carbide single crystal layer (5) as a seed crystal.

As described above, if the crystal is grown on the sapphire substrate (8) at a high temperature of not less than the melting point of silicon and less than the melting point of sapphire, the α-type silicon carbide single crystal layer (5)
Is obtained. Then, when silicon carbide single crystal (7) is formed using such α-type silicon carbide single crystal layer (5) as a seed crystal, solidification is changed from cubic (3C) silicon carbide single crystal to 6H silicon carbide single crystal. Unlike in the case of phase transition, crystal defects due to solid phase transition are not induced.
H) The silicon carbide single crystal (7) can be formed accurately.

By using a sapphire substrate (8) having a smaller lattice constant difference from the silicon carbide single crystal layer than the silicon substrate, cracking of the silicon carbide single crystal layer (5) is prevented. That is, when a silicon carbide single crystal layer grown on a silicon substrate is used, a crack may occur in the silicon carbide single crystal layer. However, the use of the sapphire substrate (8) can prevent the crack.

According to the second aspect of the present invention, the silicon single crystal (10) grown on the surface of the sapphire substrate (8) is carbonized to form a cubic silicon carbide single crystal layer (11). An α-type silicon carbide single crystal layer (5) is grown on the cubic silicon carbide single crystal layer (11) at a temperature equal to or higher than the melting point of silicon and lower than the melting point of sapphire. ) As a seed crystal to form a silicon carbide single crystal (7).

In this way, the cubic silicon carbide single crystal layer (11) is formed once on the sapphire substrate (8),
The same effect as in claim 1 can be obtained by using the α-type silicon carbide single crystal layer (5) formed on the cubic silicon carbide single crystal layer (11) as a seed crystal. The silicon carbide single crystal (7) in claims 1 and 2 can be specifically formed by supplying a raw material gas for the silicon carbide single crystal (7).

According to the third aspect of the present invention, the thickness of the silicon single crystal (10) during carbonization is
0) is characterized in that it has a thickness to be carbonized. Thus, the thickness of the silicon single crystal (10) is
By making the thickness of the silicon single crystal (10) such that all of the silicon single crystal (10) can be carbonized at the time of carbonization, the silicon single crystal (10) does not exist after carbonization, so that the cubic silicon carbide single crystal layer (11) The α-type silicon carbide single crystal layer (12) can be grown at a high temperature equal to or higher than the melting point of silicon. Therefore, a high-quality α-type silicon carbide single crystal layer (12) can be formed, and the high-quality α-type silicon carbide single crystal layer (7) is used as a seed crystal.
Can be manufactured.

According to a fourth aspect of the present invention, the surface of the sapphire substrate (8) is constituted by a (0001) plane. Since the silicon carbide single crystal layer (5) formed based on the sapphire substrate (8) and the silicon carbide single crystal (7) finally formed are both crystals having a (0001) crystal plane, sapphire If the surface of the substrate (8) has the same atomic arrangement as these, a silicon carbide single crystal (7) having less defects can be manufactured.

In the third step, the silicon carbide raw material powder (2) is heated and sublimated in an inert gas atmosphere in a graphite crucible (1), and the silicon carbide raw material powder (2) is heated. ) Lower temperature silicon carbide single crystal layer (5)
It is effective to grow the silicon carbide single crystal (7) on the surface of the substrate because the thickness of the silicon carbide single crystal (7) can be increased.

The silicon carbide single crystal layer (12) formed on the sapphire substrate (8) has the same diameter as the underlying sapphire substrate (8). For example, 4-6
When an inch sapphire substrate (8) is used, 4 to
A 6-inch large-diameter silicon carbide single crystal (7) can be obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a graphite crucible 1 as a crystal growth apparatus used in the present embodiment. The graphite crucible 1 sublimates the silicon carbide raw material powder 2 provided in the graphite crucible 1 by heat treatment to grow a silicon carbide single crystal 7 on a silicon carbide single crystal layer 5 as a seed crystal. is there.

The graphite crucible 1 comprises a crucible body 1a having an open upper surface, and a lid 1b for closing the opening of the crucible body 1a. Then, in this graphite crucible 1, the lid 1b serves as a pedestal for supporting the silicon carbide single crystal layer 5 as a seed crystal. The graphite crucible 1 can be heated by a heater in a vacuum vessel into which an arcon gas can be introduced. By adjusting the power of the heater, the temperature of the silicon carbide single crystal layer 5 as a seed crystal can be reduced. The temperature is kept at about 100 ° C. lower than the temperature of silicon carbide raw material powder 2.

Next, a method for producing a silicon carbide single crystal is shown in FIG.
A description will be given based on (a) to (e). First, FIG.
As shown in (1), a sapphire substrate 8 having a (0001) plane as a substrate surface is prepared. Since silicon carbide single crystal layer 5 and silicon carbide single crystal 7 have a (0001) crystal plane,
By making the surface of the sapphire substrate 8 the (0001) plane, the atomic arrangement becomes the same, and the silicon carbide single crystal layer 5 and the silicon carbide single crystal 7 without defects can be formed more effectively.

Then, a silicon carbide single crystal layer 5 serving as a seed crystal is grown on the surface of sapphire substrate 8 by chemical vapor epitaxy (CVD). More specifically,
A chemical vapor deposition method is used by a chemical reaction between a raw material gas for supplying carbon such as propane and a raw material gas for supplying silicon such as silane, so that the silicon carbide single crystal layer 5 has a thickness of about 20 μm. .

At this time, since the difference in lattice constant between sapphire substrate 8 and silicon carbide single crystal layer 5 is small, silicon carbide single crystal layer 5 is formed by using sapphire substrate 8 to form silicon carbide single crystal layer 5. Cracks can be prevented. Furthermore, since the melting point of sapphire is 2053 ° C. and higher than the melting point of silicon (1414 ° C.), the temperature is higher at a higher temperature than when a silicon single crystal substrate (silicon wafer) is used as a substrate.
That is, silicon carbide single crystal layer 5 can be formed at a temperature equal to or higher than the melting point of silicon and lower than the melting point of sapphire.

That is, when the silicon carbide single crystal layer 5 is formed at a high temperature, a high quality silicon carbide single crystal having a 6H crystal structure can be formed. Therefore, by using sapphire substrate 8, high-quality 6H silicon carbide single crystal layer 5 can be formed directly on sapphire substrate 8. Next, as shown in FIG. 2 (b), the sapphire substrate 8 is removed, and then, as shown in FIG. 2 (c), the silicon carbide single crystal layer 5 is joined to the lid (base) 1b of the graphite crucible 1. Silicon carbide single crystal layer 5 is fixed to lid 1b by bonding with adhesive 6 as an agent. Here, silicon carbide single crystal layer 5 is covered with lid material 1b.
When fixing to silicon carbide, polycrystalline silicon or polycrystalline silicon carbide may be formed in silicon carbide single crystal layer 5 to reinforce it.

Further, lid material 1b to which silicon carbide single crystal layer 5 is fixed is arranged in the opening of graphite crucible body 1a.
Then, the pressure in the graphite crucible 1 was set to 1 Torr in an argon gas atmosphere, and the temperature of the silicon carbide raw material powder 2 was set to 23.
30 ° C., the temperature of the silicon carbide single crystal layer 5 as a seed crystal is 22
While maintaining the temperature at 10 ° C., silicon carbide single crystal 4 is sublimated and recrystallized on silicon carbide single crystal layer 5.

At this time, since silicon carbide single crystal layer 5 has a 6H crystal structure as described above, silicon carbide single crystal 7 having a similar crystal structure is easily formed. In other words, as described above, when a solid phase transition is performed from the cubic (3C) silicon carbide single crystal to the 6H silicon carbide single crystal, crystal defects are induced. Therefore, 6H silicon carbide single crystal 7 can be formed without inducing crystal defects due to solid phase transition.

As a result, as shown in FIG. 2 (d), a bulk-shaped silicon carbide single crystal layer 5 having a diameter of 4 inches and a thickness of 2 mm having substantially the same diameter as the sapphire substrate 8 is formed on the silicon carbide single crystal layer 5 as a seed crystal. Silicon carbide single crystal (silicon carbide single crystal ingot) 7
Is formed. When sapphire substrate 8 having a diameter of 4 to 6 inches is used, silicon carbide single crystal 8 having a large diameter of 4 to 6 inches can be obtained.

Further, as shown in FIG. 2 (e), the silicon carbide single crystal (silicon carbide single crystal ingot) 7 is removed from the lid 1b of the graphite crucible, and the obtained crystal is sliced.
The semiconductor substrate is completed by polishing. The crystal plane orientation and the crystal structure (polymorphism) of this substrate were determined by X-ray diffraction and Raman spectroscopy.
It was confirmed that it had an H-type (0001) plane orientation. As described above, by using sapphire substrate 8 to form silicon carbide single crystal layer 5 serving as a seed crystal, induction of crystal defects due to solid phase transition can be prevented, and high quality silicon carbide single crystal 7 can be formed. Can be formed.

Incidentally, using the substrate thus completed,
A semiconductor device such as a vertical MOSFET, a pn diode, and a Schottky diode for high power can be manufactured. (Second Embodiment) In the first embodiment, the sapphire substrate 8
The silicon carbide single crystal layer 5 was formed by directly growing a crystal thereon. However, as shown in FIG. 3, a silicon single crystal 10 was first grown on a sapphire substrate 8, and this silicon single crystal 10 was further carbonized. Thus, cubic silicon carbide single crystal layer 11 is formed, and 6H silicon carbide single crystal layer 3 is formed on cubic silicon carbide single crystal layer 11.

Hereinafter, a method for producing a silicon carbide single crystal will be described with reference to FIG.
A description will be given based on (a) to (f). First, (000
1) A sapphire substrate 8 having a surface as a substrate surface is prepared, and a silicon single crystal 10 is grown on the sapphire substrate 8 as shown in FIG. Then, the silicon single crystal 10 is carbonized in an atmosphere of a raw material gas for carbon supply such as propane, and FIG.
A cubic silicon carbide single crystal layer 11 is formed as shown in FIG. The thickness of the silicon single crystal 10 is set to such a thickness that the entire silicon single crystal 10 is carbonized during the carbonization. That is, if silicon single crystal 10 having a relatively low melting point remains, silicon carbide single crystal layer 5 cannot be formed at a high temperature. Therefore, with such a thickness, high-quality silicon carbide single crystal layer 5 can be formed in a later step.

Next, as shown in FIG. 3C, a silicon carbide single crystal layer 5 serving as a seed crystal is grown on the cubic silicon carbide single crystal layer 11 by a CVD method. At this time, silicon carbide single crystal layer 5 is formed at a temperature higher than the melting point of silicon and lower than the melting point of sapphire. In other words, silicon carbide single crystal layer 5 can be formed with a 6H crystal structure by forming silicon carbide single crystal layer 5 by a CVD method capable of performing stable crystal growth at such a high temperature.

After removing the sapphire substrate 8 as shown in FIG. 3D, the cubic silicon carbide single crystal layer 11 is covered with the adhesive 6 as shown in FIG.
Glue to Thereafter, a bulk silicon carbide single crystal (silicon carbide single crystal ingot) 7 is formed by a sublimation recrystallization method as shown in FIG.
As shown in FIG. 3 (g), bulk silicon carbide single crystal 7 is obtained by removing silicon carbide single crystal 7 from graphite crucible lid 1b.

As described above, the silicon single crystal 10 is first grown on the sapphire substrate 8, and
To form a cubic silicon carbide single crystal layer 11 and a 6H silicon carbide single crystal layer 5 formed on cubic silicon carbide single crystal layer 11. Since silicon carbide single crystal 5 can be formed, silicon carbide single crystal 7 can be formed using silicon carbide single crystal layer 5 as a seed crystal, as in the first embodiment, without causing crystal defects due to solid phase transition. Silicon carbide single crystal 7 can be formed.

In this embodiment, a silicon single crystal 10 is grown on a sapphire substrate. However, an SOS (silicon-on-sapphire) substrate in which a silicon single crystal is formed in advance on a sapphire substrate is used. May be used. (Other Embodiments) In the first and second embodiments, the silicon carbide single crystal layer 5 is formed by the CVD method, but may be formed by another method.

Further, in the first and second embodiments, the silicon carbide single crystal is formed by the sublimation recrystallization method, but may be formed by other methods. That is, the source gas to be supplied is not limited to a sublimation gas generated by a method of sublimating a material to be a single crystal by heating and sublimation (sublimation method), and may be a gas of a raw material to be a single crystal adjusted by a method other than the sublimation method. However, when a silicon carbide single crystal is formed by the sublimation recrystallization method, it is preferable to form the silicon carbide single crystal using the sublimation recrystallization method because the silicon carbide single crystal is easily grown.

Although a crucible made of graphite is used, a material other than graphite, such as a refractory metal such as tungsten or tantalum, may be used as the material of the crucible. Further, in the first and second embodiments, powdered silicon carbide raw material powder 2 was used as the silicon carbide raw material, but other forms such as a sintered body were used instead of powder as the silicon carbide raw material. Is also good.

[Brief description of the drawings]

FIG. 1 is a schematic view of a graphite crucible used in an embodiment of the present invention.

FIG. 2 is a cross sectional view for illustrating a manufacturing process of a silicon carbide single crystal.

FIG. 3 is a cross-sectional view for illustrating a manufacturing process of a silicon carbide single crystal in a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Graphite crucible, 1a ... Crucible body, 1b ... Lid member,
2 silicon carbide raw material powder, 5 silicon carbide single crystal layer having a 6H crystal structure, 7 silicon carbide single crystal, 8 sapphire substrate, 10 silicon single crystal, 11 silicon carbide single crystal layer.

Claims (5)

[Claims] 1. A step of preparing a sapphire substrate (8) and growing a silicon carbide single crystal layer (5) on the surface of the sapphire substrate (8) at a temperature equal to or higher than the melting point of silicon and lower than the melting point of sapphire. Removing the sapphire substrate (8), fixing the silicon carbide single crystal layer (5) to a pedestal (1b), and mounting the pedestal (1b) to a crystal growth apparatus (1); Producing a silicon carbide single crystal (7) on the silicon carbide single crystal layer (5) using the silicon carbide single crystal layer (5) as a seed crystal. Method. 2. A cubic silicon carbide single crystal layer is prepared by preparing a substrate on which a silicon single crystal (10) is grown on the surface of a sapphire substrate (8) and carbonizing the silicon single crystal (10). Forming (11) at a temperature equal to or higher than the melting point of silicon and lower than the melting point of sapphire;
Growing an α-type silicon carbide single crystal layer (5) on the cubic silicon carbide single crystal layer (11); removing the sapphire substrate (8); A) fixing the α-type silicon carbide single crystal layer (5) to a pedestal (1b) through the above-mentioned method, and mounting the pedestal (1b) on a crystal growth apparatus (1); Using layer (5) as a seed crystal, silicon carbide single crystal (7) is formed on α-type silicon carbide single crystal layer (5).
And a step of growing a silicon carbide single crystal. 3. The silicon single crystal (10) has a thickness such that all of the silicon single crystal (10) is carbonized during the carbonization. Of producing a silicon carbide single crystal. 4. The surface of the sapphire substrate (8)
The method for producing a silicon carbide single crystal according to any one of claims 1 to 3, wherein the method is constituted by a (0001) plane. 5. The apparatus for growing a crystal according to claim 1, wherein the crystal growing apparatus comprises
In the step of forming the silicon carbide single crystal (7) on the α-type silicon carbide single crystal layer (5), the graphite crucible (1)
The silicon carbide raw material powder (2) is heated and sublimated in an inert gas atmosphere in the inside thereof, and the silicon carbide single crystal layer is formed on the surface of the silicon carbide single crystal layer (5) at a lower temperature than the silicon carbide raw material powder (2). 5. The method for producing a silicon carbide single crystal according to claim 1, wherein (7) is grown.