JP2007197274A - Method for producing silicon carbide single crystal - Google Patents

Abstract

A method for producing a silicon carbide single crystal having a desired crystal structure with a high growth rate by a solution method is provided.
In a method for producing a hexagonal silicon carbide single crystal, the method includes contacting a silicon carbide seed crystal substrate with a melt obtained by melting a raw material containing Si and C, and growing a silicon carbide single crystal on the substrate. When a hexagonal silicon carbide single crystal substrate is used as the seed crystal substrate, the (000-1) carbon surface is used, the seed crystal temperature is set to 1700-1900 ° C., and the surface in contact with the seed crystal substrate from the melt is used. Crystals are grown with a temperature gradient in the range of 1 to 5 ° C./mm. On the other hand, when a rhombohedral silicon carbide single crystal substrate is used as the seed crystal substrate, the (0001) silicon surface is used, and the crystal is grown at a seed crystal temperature of 1700 to 1900 ° C.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a silicon carbide single crystal, and more particularly to a method for efficiently manufacturing a silicon carbide single crystal having a desired crystal structure by a solution method.

  Silicon carbide is used as an environmentally resistant semiconductor material because it is very stable thermally and chemically and has excellent heat resistance and mechanical strength. Silicon carbide is known to have a crystalline polymorphic structure. This crystal polymorphism is a phenomenon that takes many different crystal structures even if the chemical composition is the same. When the molecule in which the Si and C are bonded in the crystal structure is considered as one unit, this unit structure molecule Is caused by the difference in the periodic structure when stacked in the c-axis direction ([0001] direction) of the crystal.

  Representative crystal polymorphs include 2H, 3C, 4H, 6H and 15R. Here, the first number represents the repetition period of the lamination, the alphabet represents the crystal system, H represents the hexagonal system, R represents the rhombohedral system, and C represents the cubic system. Each crystal structure has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 4H is used as a substrate wafer for high frequency, high withstand voltage electronic devices, etc., and 6H is used as a light emitting element material for blue LEDs because of its large band gap of about 3 eV. 3C has high crystal symmetry, Because of its high mobility, it is expected as a semiconductor element material that operates at high speed.

  Conventionally, as a method for growing a silicon carbide single crystal, a vapor phase growth method, an atchison method, and a solution growth method are known.

As the vapor phase growth method, there are a sublimation method (modified Lerry method) and a chemical reaction deposition method (CVD method). The sublimation method is a method in which silicon carbide powder is used as a raw material and is sublimated at a high temperature of 2000 ° C. or higher, and Si, Si ₂ C, and SiC ₂ gas are supersaturated on a low-temperature seed crystal substrate to precipitate a single crystal It is. The CVD method is a method of epitaxially growing a silicon carbide single crystal by a chemical reaction on a heated substrate such as Si using a silane gas and a hydrocarbon-based gas, and is used for manufacturing a silicon carbide single crystal thin film.

  The Atchison method is a method for producing an artificial abrasive by heating silicic acid anhydride and carbon to a high temperature of 2000 ° C. or more, and a single crystal is produced as a by-product.

  The solution method uses a crucible made of a material containing carbon (generally graphite), melts silicon in the crucible to form a melt, dissolves carbon from the crucible in the melt, and is placed in a low temperature part. In this method, silicon carbide is crystallized on a crystal substrate and the crystal is grown.

  However, it is known that a single crystal produced by the above-described sublimation method has various lattice defects such as hollow through defects and stacking faults called micropipe defects. Furthermore, since the crystal growth conditions and polymorphic transition are closely related in the sublimation method, it is difficult to achieve both lattice defect control and polymorph control, and crystal polymorphism tends to occur.

  In addition, in the CVD method, since the raw material is supplied by gas, the raw material supply amount is small, and the generated silicon carbide single crystal is limited to a thin film, and it is difficult to produce a bulk single crystal as a substrate material for a device.

  In the Atchison method, there are many impurities in the raw material, and it is difficult to achieve high purity, and large crystals cannot be obtained.

  On the other hand, in the solution method, since there are few lattice defects and crystal polymorphism rarely occurs, it is said that a single crystal with good crystallinity can be obtained (see, for example, Patent Documents 1 and 2).

JP 2000-264790 A JP 2002356563 A

  The production of a single crystal by the sublimation method has a drawback that micropipe defects are likely to occur as described above. A single crystal is produced by growing (stacking) crystals in a specific direction, but a crystal polymorphic transformation occurs in which a single crystal having a property different from that of the past grows at a certain stack. Therefore, in order to grow a single crystal having the same properties as the seed crystal, it is necessary to prevent the transformation of the crystal polymorph in the stack, but the sublimation method as described above cannot prevent the transformation of the crystal polymorph. On the other hand, the solution method can prevent the occurrence of micropipe defects and further prevent the transformation of crystal polymorphism, but the flatness on the growth surface of the obtained single crystal is not sufficient and the crystal growth rate is satisfactory. It wasn't going to be good.

  An object of the present invention is to solve such problems and to provide a method for producing a silicon carbide single crystal having a desired crystal structure with a high growth rate and good flatness on a crystal growth surface by a solution method. And

In order to solve the above problems, according to a first invention, a silicon carbide seed crystal substrate is brought into contact with a melt obtained by melting a raw material containing Si and C, and a silicon carbide single crystal is grown on the substrate. In the manufacturing method of the hexagonal silicon carbide single crystal containing,
When a hexagonal silicon carbide single crystal substrate is used as the seed crystal substrate, the (000-1) carbon surface is used, the seed crystal temperature is set to 1700-1900 ° C., and the surface in contact with the seed crystal substrate from the melt is used. When growing a crystal with a temperature gradient in the range of 1 to 5 ° C./mm, or when using a rhombohedral silicon carbide single crystal substrate as a seed crystal substrate, use the (0001) silicon surface and use a seed crystal Growing the crystal at a temperature of 1700-1900 ° C.,
It is characterized by.

In order to solve the above problems, according to a second invention, a silicon carbide seed crystal substrate is brought into contact with a melt obtained by melting a raw material containing Si and C, and a silicon carbide single crystal is grown on the substrate. In the manufacturing method of the hexagonal silicon carbide single crystal containing,
First, using a rhombohedral silicon carbide single crystal substrate as a seed crystal substrate, using the (0001) silicon surface, growing the crystal at a seed crystal temperature of 1700 to 1900 ° C. to obtain a hexagonal silicon carbide single crystal, Next, using the (000-1) carbon surface of the obtained hexagonal silicon carbide single crystal, the temperature of the hexagonal silicon carbide single crystal is set to 1700 to 1900 ° C., and the surface is in contact with the single crystal from the melt. The crystal is grown by setting the temperature gradient toward 1 to 5 ° C./mm.

In order to solve the above problem, according to a third invention, a silicon carbide seed crystal substrate is brought into contact with a melt obtained by melting a raw material containing Si and C, and a silicon carbide single crystal is grown on the substrate. In the manufacturing method of the rhombohedral silicon carbide single crystal containing,
A rhombohedral silicon carbide single crystal substrate is used as a seed crystal substrate, its (000-1) carbon surface is used, the seed crystal temperature is set to 1700 to 1900 ° C., and the surface in contact with the single crystal from the melt is used. The crystal is grown by setting the temperature gradient toward 1 to 5 ° C./mm.

In order to solve the above problems, according to a fourth invention, a silicon carbide seed crystal substrate is brought into contact with a melt obtained by melting a raw material containing Si and C, and a silicon carbide single crystal is grown on the substrate. In the manufacturing method of the cubic silicon carbide single crystal containing,
A rhombohedral silicon carbide single crystal substrate is used as a seed crystal substrate, its (000-1) carbon surface is used, the seed crystal temperature is set to 1700-1900 ° C., and the surface is in contact with the single crystal from the melt. The crystal is grown by setting the temperature gradient toward to within a range of 5 to 50 ° C./mm.

  According to the present invention, a silicon carbide single crystal having a desired crystal structure excellent in flatness is obtained at high speed by selecting a crystal polymorph of a seed crystal and growing the crystal on a predetermined surface at a predetermined temperature. be able to.

  Hereinafter, the method for producing a silicon carbide single crystal of the present invention will be specifically described. First, the structure of the manufacturing apparatus used for the manufacturing method of the silicon carbide single crystal of this invention is demonstrated with reference to FIG. This manufacturing apparatus includes a chamber 1, and a crucible 2 can be inserted into the chamber 1. A seed crystal 3 is arranged on the bottom surface inside the crucible 2, and a raw material 4 containing silicon grains, carbon, and, if necessary, additional elements is placed inside the crucible 2. When a crucible made of carbonaceous material, for example, graphite, is used as the crucible 2, the carbon melts from the crucible 2 and therefore does not need to be added to the raw material. A heating device 5 such as a high frequency device is disposed around the chamber 1, and a cooling plate 6 is disposed on the outer bottom surface of the crucible 2.

  A method for producing a silicon carbide single crystal using this production apparatus will be described. First, a seed crystal is put on the bottom of the crucible 2 and then the raw material 4 is filled inside. After that, the crucible 2 is inserted into the chamber 1 and the inside of the chamber 1 is evacuated. Then, an atmosphere of an inert gas such as Ar is used, and the inside of the chamber 1 is pressurized to atmospheric pressure or higher. Next, the crucible 2 is heated by the heating device 5, the raw material 4 is melted, a melt containing silicon and carbon is formed, and the melt is brought into contact with the seed crystal 3.

  The temperature of the melt may be equal to or higher than the melting point of the raw material in order to secure the melt state, and the most stable silicon carbide single crystal can be obtained in a temperature range of 1700 ° C. or higher. The melt temperature is preferably 2300 ° C. or lower. This is because if the temperature exceeds 2300 ° C., there will be a problem that Si evaporates violently from the melt.

  After the melt and the seed crystal are brought into contact in this way, the cooling plate 6 is cooled, and the temperature of the seed crystal 3 is set to 1700 to 1900 ° C., so that the melt is directed from the inside to the surface in contact with the seed crystal. Thus, a temperature gradient is formed, and the crystal grows on the seed crystal 3.

  FIG. 2 shows the configuration of another manufacturing apparatus used in the method for manufacturing a silicon carbide single crystal of the present invention. In this manufacturing apparatus, a carbon supply raw material die 8 is placed on a tray 7, a raw material 9 plate (silicon and silicon alloy) is placed thereon, and a seed crystal 3 is placed thereon. An inner susceptor 10 is disposed on the die 8, and an inner punch 11 is disposed in contact with the seed crystal 3. This is placed in the die 12 and the heating device 5 is disposed under the tray 7.

  A method for producing a silicon carbide single crystal using this production apparatus will be described. After the inside of the die 12 is evacuated, an inert gas atmosphere such as Ar is used, and the inside of the die 12 is pressurized to atmospheric pressure or higher. Next, the material is heated by the heating device 5 to melt the raw material 9, and the carbon in the die is dissolved in the melt. On the other hand, by cooling seed crystal 3 from inner punch 11, a temperature gradient is generated, and a silicon carbide single crystal can be grown on the seed crystal.

  Whichever apparatus is used, the method of the present invention is characterized in that the surface on which the crystal is grown is changed depending on the crystal form of the seed crystal. That is, when a hexagonal silicon carbide single crystal is used as a seed crystal, the crystal is grown on the (000-1) carbon surface. That is, in the apparatus shown in FIG. 1, the seed crystal 3 is placed in the crucible 2 so that the side in contact with the raw material 4 is a (000-1) carbon surface, and in the apparatus shown in FIG. Place the side so that it is the (000-1) carbon surface. At this time, the temperature of the seed crystal is set to 1700 to 1900 ° C., and the temperature gradient is set to 1 to 5 ° C./mm. With such a configuration, the hexagonal silicon carbide single crystal grows at a high rate on the seed crystal of the hexagonal silicon carbide single crystal, and the flatness is excellent.

  When a rhombohedral silicon carbide single crystal is used as a seed crystal, the crystal is grown on the (0001) silicon surface. That is, in the apparatus shown in FIG. 1, the seed crystal 3 is placed in the crucible 2 so that the side in contact with the raw material 4 is a (0001) silicon surface, and in the apparatus shown in FIG. [0001] Place the silicon surface. At this time, the temperature of the seed crystal is 1700 to 1900 ° C., but the temperature gradient may be 5 ° C./mm or more. With such a configuration, the hexagonal silicon carbide single crystal grows at a high rate by transformation on the seed crystal of the rhombohedral silicon carbide single crystal.

  Further, when a rhombohedral silicon carbide single crystal is used as a seed crystal, the crystal may be grown on the (000-1) carbon surface. At this time, the temperature of the seed crystal may be 1700 to 1900 ° C., and the temperature gradient may be 5 ° C./mm or more. When the temperature gradient is 1 to 5 ° C./mm, the rhombohedral silicon carbide single crystal grows on the rhombohedral silicon carbide single crystal at a high rate, while when the temperature gradient is 5 ° C./mm or more, the rhombohedral silicon carbide. A cubic silicon carbide single crystal grows at a high rate on the single crystal seed crystal.

  Further, by combining the above methods, using a rhombohedral silicon carbide single crystal as a seed crystal, transforming on the (0001) silicon surface to grow a hexagonal silicon carbide single crystal, and then obtaining the obtained hexagonal silicon carbide single crystal The (000-1) carbon surface can be used to grow a crystal, and a hexagonal silicon carbide single crystal can be grown at a high rate.

Example 1
Using a 6H silicon carbide single crystal produced by the Lerry method as a seed crystal using the apparatus shown in FIG. 1, the (000-1) carbon surface of this seed crystal is placed on the bottom of a graphite crucible and placed in the crucible. A predetermined amount of silicon grains was added, silicon carbide was melted at an ambient temperature of 1750 ° C., a temperature gradient was set to 3 ° C./mm, and a silicon carbide single crystal was grown on the seed crystal. FIG. 3 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was the same 6H as the seed crystal, its growth rate was 21 μm / hr, and the surface flatness was good.

Comparative Example 1
A silicon carbide single crystal was grown in the same manner as in Example 1 except that the 6H silicon carbide seed crystal was placed in the crucible with its (0001) silicon surface facing up. FIG. 4 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was the same 6H as the seed crystal, but the growth rate of the single crystal was 8 μm / hr, which was slower than that of Example 1, and the surface flatness was also deteriorated.

Example 2
As in Example 1, except that a 15R silicon carbide single crystal produced by the Lerry method is used as the silicon carbide seed crystal, and the seed crystal is placed at the bottom of the graphite crucible with the (0001) silicon surface as the upper surface. A silicon carbide single crystal was grown. FIG. 5 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was transformed to 6H, and the growth rate was 12 μm / hr.

Example 3
A 21R silicon carbide single crystal produced by the Lely method is used as the silicon carbide seed crystal, and the same is applied as in Example 1 except that the (0001) silicon surface of this seed crystal is used as the top surface and placed at the bottom of the graphite crucible. A silicon carbide single crystal was grown. FIG. 6 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was transformed to 6H, and the growth rate was 15 μm / hr.

Example 4
A silicon carbide single crystal was grown in the same manner as in Example 2 except that the 15R silicon carbide seed crystal was placed in the crucible with its (000-1) carbon surface facing up. FIG. 7 shows a cross section of the obtained silicon carbide single crystal. The growth rate of the single crystal was 20 μm / hr, and the surface flatness was good, but the crystal polymorph was 15R, the same as the seed crystal, without transformation.

Example 5
Using the apparatus shown in FIG. 2, a 15R silicon carbide single crystal produced by the Lerry process is used as a seed crystal, and the seed crystal is placed so that the (0001) silicon surface is in contact with the raw material, and the raw material is used at an ambient temperature of 1870 ° C. And a temperature gradient of 10 ° C./mm was set, and a silicon carbide single crystal was grown on the seed crystal. FIG. 8 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was transformed to 4H.

Example 6
A silicon carbide single crystal was grown in the same manner as in Example 4 except that the ambient temperature was 1890 ° C. FIG. 9 shows a cross section of the obtained silicon carbide single crystal. The obtained single crystal was transformed to 6H.

Comparative Example 2
A silicon carbide single crystal was grown in the same manner as in Example 4 except that a 6H single crystal was used as a seed crystal, and the (000-1) carbon surface was disposed downward. The obtained silicon carbide single crystal was 6H, but the surface flatness was deteriorated.

Example 7
A 15R single crystal was used as a seed crystal, and a silicon carbide single crystal was grown in the same manner as in Example 4 except that the (000-1) carbon surface was placed downward. The obtained single crystal was transformed to 3C.

The above results are summarized in the following table.

  As is clear from the above results, when a hexagonal silicon carbide single crystal was used as the seed crystal, growth from the carbon surface was faster than that from the silicon surface, and surface flatness was good. However, when the temperature gradient is larger than 5 ° C./mm, the surface flatness tends to decrease, and the temperature gradient is preferably 1 to 5 ° C./mm. On the other hand, when a rhombohedral silicon carbide single crystal was used as a seed crystal, it was transformed into a hexagonal crystal from the silicon surface and was not affected by the temperature gradient. Moreover, it did not transform from the carbon surface at a temperature gradient of 1 to 5 ° C./mm, but transformed to 3C at a temperature gradient higher than 5 ° C./mm.

1 is a schematic diagram showing the configuration of a manufacturing apparatus used in the method for manufacturing a silicon carbide single crystal of the present invention. 1 is a schematic diagram showing the configuration of a manufacturing apparatus used in the method for manufacturing a silicon carbide single crystal of the present invention. It is the photograph replaced with drawing which shows the cross section of the single crystal formed by this invention. It is the photograph replaced with drawing which shows the cross section of the single crystal formed in the comparative example. It is the photograph replaced with drawing which shows the cross section of the single crystal formed by this invention. It is the photograph replaced with drawing which shows the cross section of the single crystal formed by this invention. It is the photograph replaced with drawing which shows the cross section of the single crystal formed in the comparative example. It is the photograph replaced with drawing which shows the cross section of the single crystal formed by this invention. It is the photograph replaced with drawing which shows the cross section of the single crystal formed by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Crucible 3 Seed crystal 4 Raw material 5 Heating device 6 Cooling plate 7 Tray 8 Die 9 Raw material 10 Inner susceptor 11 Inner punch 12 Die

Claims (4)

A method for producing a hexagonal silicon carbide single crystal, comprising bringing a silicon carbide seed crystal substrate into contact with a melt obtained by melting a raw material containing Si and C, and growing a silicon carbide single crystal on the substrate,
When a hexagonal silicon carbide single crystal substrate is used as the seed crystal substrate, the (000-1) carbon surface is used, the seed crystal temperature is set to 1700-1900 ° C., and the surface in contact with the seed crystal substrate from the melt is used. When growing a crystal with a temperature gradient in the range of 1 to 5 ° C./mm, or when using a rhombohedral silicon carbide single crystal substrate as a seed crystal substrate, use the (0001) silicon surface and use a seed crystal Growing the crystal at a temperature of 1700-1900 ° C.,
A method for producing a hexagonal silicon carbide single crystal. A method for producing a hexagonal silicon carbide single crystal, comprising bringing a silicon carbide seed crystal substrate into contact with a melt obtained by melting a raw material containing Si and C, and growing a silicon carbide single crystal on the substrate,
First, using a rhombohedral silicon carbide single crystal substrate as a seed crystal substrate, using the (0001) silicon surface, growing the crystal at a seed crystal temperature of 1700 to 1900 ° C. to obtain a hexagonal silicon carbide single crystal, Next, using the (000-1) carbon surface of the obtained hexagonal silicon carbide single crystal, the temperature of the hexagonal silicon carbide single crystal is set to 1700 to 1900 ° C., and the surface is in contact with the single crystal from the melt. A method for producing a silicon carbide single crystal, wherein the crystal is grown with a temperature gradient toward 1 in a range of 1 to 5 ° C./mm. A method for producing a rhombohedral silicon carbide single crystal, comprising bringing a silicon carbide seed crystal substrate into contact with a melt obtained by melting a raw material containing Si and C, and growing a silicon carbide single crystal on the substrate,
A rhombohedral silicon carbide single crystal substrate is used as a seed crystal substrate, its (000-1) carbon surface is used, the seed crystal temperature is set to 1700 to 1900 ° C., and the surface in contact with the single crystal from the melt is used. A method for producing a rhombohedral silicon carbide single crystal, wherein the crystal is grown with a heading temperature gradient in a range of 1 to 5 ° C / mm. A method for producing a cubic silicon carbide single crystal comprising bringing a silicon carbide seed crystal substrate into contact with a melt obtained by melting a raw material containing Si and C, and growing a silicon carbide single crystal on the substrate,
A rhombohedral silicon carbide single crystal substrate is used as a seed crystal substrate, its (000-1) carbon surface is used, the seed crystal temperature is set to 1700-1900 ° C., and the surface is in contact with the single crystal from the melt. A method for producing a cubic silicon carbide single crystal, wherein the crystal is grown with a temperature gradient toward the range of 5 to 50 ° C./mm.