WO2009098997A1 - Process for producing silicon carbide single crystal - Google Patents

Abstract

A powder of an a-form silicon carbide raw material which has been produced by the precursor method using low-nitrogen-content phenol and has a boron content of 0.5 ppm or lower or a nitrogen content of 10 ppm or lower is supplied to the inside of a crucible (3). A seed crystal (4) and the powder of a silicon carbide raw material (2) are disposed face to face. This crucible (3) is placed in a heating furnace (7). The crucible (3) is heated in an inert-gas atmosphere to thereby sublimate the silicon carbide raw material (2) and recrystallize the raw material (2) as a silicon carbide single crystal on the surface of the seed crystal (4).

Description

Method for producing silicon carbide single crystal

The present invention relates to a method for producing a silicon carbide (SiC) single crystal suitable for a substrate of a high-frequency semiconductor device.

In recent years, it is expected that a silicon carbide single crystal is used as a substrate for a high-frequency semiconductor device. In general, a substrate of a high-frequency semiconductor device is required to have a semi-insulating (high resistance) characteristic exhibiting a resistivity of about 10 ⁵ to 10 ¹² [Ω · cm].

Therefore, conventionally, by producing a silicon carbide single crystal using a β-type (3C type) silicon carbide raw material powder having a low boron and nitrogen content produced by a CVD (Chemical Vapor Deposition) method, Impurity concentration in the silicon carbide single crystal is reduced.
JP 2003-73194 A

The silicon carbide raw material powder produced by the CVD method is very expensive. Moreover, the powder of the silicon carbide raw material manufactured by CVD method is flake shape, and the particle size of powder is a submicron unit. Therefore, the crucible for single crystal growth cannot be filled with high density. In addition, since the silicon carbide raw material powder produced by the CVD method is β-type, the crystalline state is not stable in a high temperature atmosphere. Therefore, it is decomposed before reaching the growth temperature of the single crystal. In a high temperature atmosphere, α-type (6H-type) single crystals are crystallized. Therefore, it has been difficult to stably control the growth of the single crystal by the CVD method.

The present invention has been made to solve the above problems. The purpose is to produce a silicon carbide single crystal having a low impurity content at a low cost. Moreover, it is filling the powder of a silicon carbide raw material with high density in the crucible for growing a single crystal. Furthermore, it is providing the manufacturing method of the silicon carbide single crystal which can control the growth of a silicon carbide single crystal stably.

The silicon carbide single crystal production method according to the present invention is a powder of an α-type silicon carbide raw material having a boron content of 0.5 ppm or less or a nitrogen content of 10 ppm or less produced by a precursor method using low nitrogen phenol. Supplying the body into the crucible, placing the seed crystal and silicon carbide raw material powder facing each other, placing the crucible in a heating furnace, and heating the crucible in an inert gas atmosphere By sublimating the silicon carbide raw material to recrystallize the silicon carbide single crystal on the surface of the seed crystal.

According to the method for producing a silicon carbide single crystal according to the present invention, a silicon carbide single crystal having a low impurity content is produced at a low cost, and a silicon carbide raw material powder is filled at a high density, and silicon carbide is produced. Single crystal growth can be stably controlled.

FIG. 1 is a schematic view showing an apparatus for producing a silicon carbide single crystal according to an embodiment of the present invention.

Hereinafter, a silicon carbide single crystal manufacturing apparatus and a manufacturing method thereof according to an embodiment of the present invention will be described.

As shown in FIG. 1, a silicon carbide single crystal manufacturing apparatus 1 according to an embodiment of the present invention includes a graphite crucible 3, a lid 5, a porous heat insulating material 6, a heating furnace 7, and an argon A gas cylinder 8.

In the crucible 3, the powder of the silicon carbide raw material 2 is accommodated. The lid 5 covers the opening of the crucible 3. A seed crystal 4 is attached to the back surface of the lid 5. The heat insulating material 6 covers the entire crucible 3 including the lid 5. The heating furnace 7 accommodates the entire heat insulating material 6 including the crucible 3. The argon gas cylinder 8 supplies argon gas (inert gas) into the heating furnace 7.

When manufacturing a silicon carbide single crystal using the manufacturing apparatus 1, first, the powder of the silicon carbide raw material 2 is supplied into the crucible 3. Next, the seed crystal 4 attached to the back surface of the lid 5 is opposed to the powder of the silicon carbide raw material 2, and the opening of the crucible 3 is covered with the lid 5. Next, argon gas is supplied from the argon gas cylinder 8 into the heating furnace 7. Thereafter, the crucible 3 is heated to a temperature (about 2500 ° C.) at which the silicon carbide raw material 2 sublimes in an argon gas atmosphere. Thereby, the silicon carbide raw material 2 is sublimated. The sublimated source gas is recrystallized on the surface of the seed crystal 4 to grow a silicon carbide single crystal.

The boron content in the powder of the silicon carbide raw material 2 before recrystallization and the boron content in the silicon carbide single crystal obtained by recrystallization are substantially the same. Therefore, in order to give the silicon carbide single crystal a semi-insulating characteristic (high resistance value) suitable for a substrate of a high-frequency semiconductor device, the boron content in the powder of the silicon carbide raw material 2 is 0.5 ppm or less, preferably 0.1 ppm or less.

Further, when the nitrogen content in the powder of the silicon carbide raw material 2 is 10 ppm or more, the semi-insulating characteristics (high resistance value) of the silicon carbide single crystal are not suitable values. Therefore, the nitrogen content in the powder of the silicon carbide raw material 2 is set to 10 ppm or less. The powder of the silicon carbide raw material 2 is an α-type silicon carbide raw material powder produced by a precursor method using low nitrogen phenol.

When recrystallizing a silicon carbide single crystal using powder of a β-type silicon carbide raw material produced by a CVD method, before reaching the temperature at which a single crystal of 4H type or α type (6H type) grows, There was a drawback that the powder of the β-type silicon carbide raw material was decomposed.

In contrast, the α-type silicon carbide raw material powder does not decompose before reaching the temperature at which the single crystal grows, so that the growth of the silicon carbide single crystal can be controlled stably.

〔Example〕
Hereinafter, the manufacturing method of the powder of the said silicon carbide raw material 2 is demonstrated in detail based on an Example.

[Example 1]
In Example 1, ethyl silicate 40 (ES40) was used as the silicon source, and liquid phenol resin PL-2818 was used as the carbon source. A liquid mixture containing ethyl silicate 40 (ES40), phenol resin PL-2818, and maleic acid as a polymerization or crosslinking catalyst was supplied into the container, and the container was placed under a reduced-pressure atmosphere. Phenol resin PL-2818 is synthesized without using an amine catalyst, and therefore does not contain nitrogen (amine) inside. Therefore, the nitrogen content in the liquid mixture can be significantly reduced as compared with the case where a phenol resin synthesized using an amine catalyst is used as a carbon source.

Next, an inert gas such as argon gas was bubbled in the liquid mixture, and the exhaust gas was exhausted. According to this step, nitrogen in the liquid mixture is replaced with the inert gas component and exhausted as exhaust gas. Therefore, the nitrogen content in the liquid mixture can be further reduced.

Next, the container was introduced into a drying chamber under a reduced pressure atmosphere, and the liquid mixture was cured and dried with microwaves (electromagnetic waves) in the drying chamber to generate a solid.

Next, the solid material generated was introduced into a crucible in a heating furnace configured with a carbon member having a low boron content as a main member. Thereafter, the solid was heated and carbonized under an inert gas atmosphere other than nitrogen at about 900 [° C.] to produce a temporarily fired powder. The calcined powder was further calcined in an inert gas atmosphere of about 1800 to 2300 [° C.] to obtain silicon carbide powder. Finally, the silicon carbide powder was pulverized by a jet mill to a predetermined particle size.

By the above operation, an α-type silicon carbide powder having a boron content of 0.2 ppm, a nitrogen content of 5 ppm, and a content of other impurity elements of 0.1 ppm or less was obtained. The particle size of the silicon carbide powder obtained by firing is about several tens to several hundreds μm. Therefore, it can be easily pulverized to a particle size of several to several tens of μm by a jet mill without causing contamination of metals and the like. Thereby, the filling density to the crucible 3 is stably increased, and the filling height can be controlled.

[Example 2]
In Example 2, the same process as in Example 1 was performed except that the baking process was performed after the heating furnace was heated for 4 hours under vacuum. As a result, an α-type silicon carbide powder having a boron content of 0.5 ppm, a nitrogen content of 1 ppm, and a content of other impurity elements of 0.1 ppm or less was obtained.

[Comparative Example 1]
In Comparative Example 1, the same treatment as in Example 1 was performed, except that SR-101 (manufactured by Sumikin Air Water Chemical Co., Ltd.) was used as the phenol resin. As a result, an α-type silicon carbide powder having a boron content of 2 ppm, a nitrogen content of 50 ppm, and a content of other impurity elements of 0.1 ppm or less was obtained.

[Comparative Example 2]
In the comparative example 2, the heating furnace comprised as a main member the carbon member with little boron content was not used. Except this, the same processing as in Example 1 was performed. An α-type silicon carbide powder having a boron content of 0.15 ppm and a nitrogen content of 1 ppm was obtained.

[Evaluation of resistivity]
A silicon carbide single crystal was produced using the silicon carbide powders of Examples 1 and 2 and Comparative Examples 1 and 2. The packing density in the crucible of the silicon carbide single crystals of Examples 1 and 2 was 2.0 g / cm ³ . Each also packing density in the crucible of a silicon carbide single crystal of Comparative Examples 1 and 2 1.98 g ^/ cm 3, was 1.78 g / cm ^3.

The specific resistance of the manufactured silicon carbide single crystal was evaluated. As shown in Table 1, the silicon carbide single crystals produced from the silicon carbide powders of Examples 1 and 2 exhibited semi-insulating properties. Silicon carbide single crystals produced from the silicon carbide powders of Comparative Examples 1 and 2 did not exhibit semi-insulating properties.

As mentioned above, although the embodiment to which the invention made by the present inventor is applied has been described, the present invention is not limited by the description and the drawings that constitute a part of the disclosure of the present invention according to this embodiment. That is, it is needless to say that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

Note that the entire contents of Japanese Patent Application No. 2008-029300 (filed on Feb. 8, 2008) are incorporated herein by reference.

As described above, the method for producing a silicon carbide single crystal according to the present invention produces a silicon carbide single crystal having a low impurity content at a low cost, and fills the silicon carbide raw material powder with a high density, and Since the growth of the silicon carbide single crystal can be stably controlled, it is useful in the field of semiconductor manufacturing.

Claims (1)

Supplying an α-type silicon carbide raw material powder having a boron content of 0.5 ppm or less or a nitrogen content of 10 ppm or less, produced by a precursor method using low nitrogen phenol, to the inside of the crucible;
Arranging the seed crystal and the silicon carbide raw material powder to face each other;
Placing the crucible in a heating furnace;
Heating the crucible under an inert gas atmosphere to sublime the silicon carbide raw material to recrystallize the silicon carbide single crystal on the surface of the seed crystal. Production method.

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