WO2014137072A1

WO2014137072A1 - Apparatus and method for growing silicon carbide single crystals

Info

Publication number: WO2014137072A1
Application number: PCT/KR2014/000587
Authority: WO
Inventors: Jung Gyu Kim; Jong Hwi Park; Kap Ryeol Ku; Myung Ok Kyun; Jung Woo Choi
Original assignee: SKC Co Ltd
Current assignee: SKC Co Ltd
Priority date: 2013-03-07
Filing date: 2014-01-21
Publication date: 2014-09-12
Anticipated expiration: 2015-09-07
Also published as: KR101458183B1; KR20140110266A

Abstract

The present invention relates to an apparatus and a method for growing high-quality silicon carbide single crystals by coating the inner wall of the existing graphite crucible with tungsten (W). In accordance with the present invention, high-quality silicon carbide single crystals can be grown by coating the inner wall of the existing graphite crucible with tungsten (W).

Description

APPARATUS AND METHOD FOR GROWING SILICON CARBIDE SINGLE CRYSTALS

The present invention relates to an apparatus and a method for growing silicon carbide single crystals, more particularly to an apparatus and a method for growing high-quality silicon carbide (SiC) single crystals by coating the inner wall of a crucible or a seed holder with tungsten (W).

With the physical limitations of silicon (Si), the representative semiconductor material, wide-bandgap semiconductor materials such as SiC, GaN, AlN, ZnO, etc., are emerging as next-generation semiconductor materials. Among them, SiC exhibits better thermal stability and oxidation resistance than GaN, AlN and ZnO. In addition, since SiC has superior thermal conductivity of about 4.6 W/cmºC and can be produced into a large-sized substrate with a diameter of 2 inches or greater, it is favored over GaN, AlN or ZnO substrates. SiC crystals are classified based on their growth temperature. 6H-SiC single crystal is used in LED devices and 4H-SiC single crystal is used in power devices. At present, 4H-SiC single-crystal substrates are favored in the aspects of environment friendliness and power loss reduction.

To prepare a 4H-SiC or 6H-SiC substrate of 2 inches or greater, a seed (4H-SiC or 6H-SiC) is attached on a seed holder and a 4H-SiC or 6H-SiC single crystal is grown on the seed (4H-SiC or 6H-SiC). For this, the seed (4H-SiC or 6H-SiC) is attached so as to be in contact with the seed holder. Then, the 4H-SiC or 6H-SiC single crystal is grown on the seed (4H-SiC or 6H-SiC) as time goes on.

As the existing patents on a method of growing silicon carbide single crystals, PCT/US2000/41076 discloses use of a graphite crucible coated with a thin coating of a metal carbide, particularly a carbide selected from a group consisting of tantalum carbide, hafnium carbide, niobium carbide, titanium carbide, zirconium carbide, tungsten carbide, and vanadium carbide.

PCT/US2005/006058 discloses a Czochralski (CZ) system for growth of a single-crystal silicon ingot from a molten silicon feedstock, including: a low low-aspect-ratio, wide-diameter crucible including a base and side walls for holding a quantity of molten silicon at a melt/crystal interface with respect to a seed crystal for growing an ingot from the molten material; a pre-melter for providing a continuous source of molten silicon feedstock to the crucible, such that the melt/crystal interface is maintained at a desired level without vertical travel of the crucible; a plurality of pull chambers rotatably disposed with respect to the crucible for pulling the seed crystal so as to form an ingot such that the crucible for each pull chamber is replenished at a desired level by the pre-melter; and an annular heating means disposed beneath the base of the crucible with a fixed distance for providing a uniform thermal distribution across the crucible and at the melt/crystal interface for optimal crystal growth.

However, the existing arts are problematic in that coating of thin film is difficult, manufacturing cost is high and crystal quality is affected by the feedstock. Tungsten is advantageous in that manufacturing cost is lower as compared to the previously used material and can prevent inclusion of carbon, which negatively affects crystal quality, since it can act as carbon getter by reacting with free carbon in the crucible.

At present, a graphite crucible is used to grow silicon carbide single crystals. During the growth of silicon carbide single crystals, the graphite crucible is heated by induction heating. The reaction occurring on the surface of the crucible varies depending on the material of the crucible. In the case of the graphite crucible, carbon is supplied as a source for the growth of silicon carbide single crystals, resulting in defects as the increased carbon acts as impurity. Also, loss of the graphite crucible occurs as the sublimed silicon etches the graphite crucible. In addition, seed back etching or other problem occurs at the portion where the seed is attached to the graphite. To solve these problems, the present invention is directed to providing an apparatus and a method for growing high-quality silicon carbide single crystals capable of preventing formation of defects caused by inclusion of carbon from a graphite crucible and capable of preventing crucible etching and seed back etching by coating the graphite crucible with tungsten.

In an aspect, the present invention provides an apparatus for growing silicon carbide single crystals using a seed holder coated with tungsten (W) and a method for growing silicon carbide single crystals using same.

In another aspect, the present invention provides an apparatus for growing silicon carbide single crystals using a graphite crucible coated with tungsten (W) and a method for growing silicon carbide single crystals using same.

More particularly, the present invention provides an apparatus for growing silicon carbide single crystals, including: a crucible comprising a hollow portion inside thereof and a tungsten film layer covering all or part of an inner wall thereof; an insulating material covering all or part of an outer wall of the crucible; and a heating means disposed outside the insulating material, and a method for growing silicon carbide single crystals using same.

In accordance with the present invention, silicon carbide single crystals of higher quality than the single crystals grown using the existing graphite crucible can be produced.

Figs. 1a and 1b are respectively a cross-sectional view and a plan view of a seed attached to a seed holder.

Figs. 2a and 2b are respectively a cross-sectional view and a plan view of silicon carbide single crystals grown from a seed attached to a seed holder.

Fig. 3 is a cross-sectional view of an apparatus for growing silicon carbide single crystals according to an exemplary embodiment of the present invention.

Fig. 4 is a plan view of silicon carbide single crystals (ingot) grown in Comparative Example.

Fig. 5 is a plan view of silicon carbide single crystals grown in Example.

Fig. 6 is a longitudinal cross-sectional view of silicon carbide single crystals (ingot) grown in Comparative Example.

Fig. 7 is a longitudinal cross-sectional view of silicon carbide single crystals grown in Example.

Fig. 8 shows Si-face rocking curves of silicon carbide single crystals grown in Comparative Example.

Fig. 9 shows Si-face rocking curves of silicon carbide single crystals grown in Example.

The present invention provides an apparatus for growing silicon carbide single crystals, including: a crucible including a hollow portion inside thereof and a tungsten film layer covering all or part of an inner wall thereof; an insulating material covering all or part of an outer wall of the crucible; and a heating means disposed outside the insulating material.

In an exemplary embodiment, the apparatus for growing silicon carbide single crystals includes a seed holder located above the hollow portion, the seed holder having a tungsten film layer formed on one surface thereof to which the seed is attached.

The present invention also provides a method for growing silicon carbide single crystals using a seed holder coated with tungsten or a graphite crucible coated with tungsten.

The method for growing single crystals according to the present invention is a method for growing 4H-SiC or 6H-SiC single crystals on a 4H-SiC or 6H-SiC seed using a graphite crucible coated with tungsten and includes coating an existing graphite crucible with tungsten and growing silicon carbide single crystals on a seed attached to one surface of a seed holder.

In the present invention, the seed holder made from high-density graphite may be coated with tungsten and a seed may be attached thereto. The seed holder with the seed attached may be disposed at an upper portion in the graphite crucible and silicon carbide single crystals may be grown on the seed.

In the present invention, a coating of tungsten, which has the highest melting point of all metals, is used to capture carbon during growth of single crystals. The melting points of metals that serve similar roles are described in Table 1.

Carbon-capturing materials	Melting point [ºC]	Boiling point [ºC]
Tantalum (Ta)	2,990	5,400
Niobium (Nb)	2,468	4,927
Tungsten (W)	3,380	5,927

Use of tungsten as in the present invention is advantageous in that a) inclusion of the metal during the growth of silicon carbide single crystals is reduced because of high melting point, b) the material is easily available than the existing carbon-capturing materials and thus is less costly, c) the temperature of the seed can be lowered by about 100 ºC because of low infrared emissivity of 0.5 (graphite: 0.85-0.95), d) crucible etching caused by sublimed silicon source can be prevented, and e) seed back etching and inclusion of carbon into ingot can be prevented.

Hereinafter, the present invention will be described in more detail through examples referring to the attached drawings. However, the present invention is not limited by the following examples but can be embodied in various forms. The following examples are provided so that the disclosure of the present invention is complete and the scope thereof is fully informed to those of ordinary skill in the art.

An apparatus for growing silicon carbide single crystals according to an exemplary embodiment of the present invention includes a tungsten film layer 600 formed on one surface of a seed holder 100. A seed 200 is attached on the tungsten film layer 600.

The seed holder 100 may be formed of graphite, but is not particularly limited in its material.

The tungsten film layer 600 may be formed by thermal spray coating, chemical vapor deposition (CVD), etc., but is not particularly limited in the formation method. The tungsten film layer 600 may be formed to cover all or part of one surface of the seed holder, and may also be formed to cover the side surface of the seed holder. Specifically, the tungsten film layer 600 may have a thickness of 50-500 μm, but is not particularly limited in its thickness.

The seed 200 may have different crystal structures depending on the crystal desired to grow, e.g., 4H-SiC, 6H-SiC, 3C-SiC or 15R-SiC.

Referring to Fig. 3, simultaneously with or separately from the tungsten film layer 600 formed on the seed holder 100, a tungsten film layer 600 may be formed inside the crucible.

That is to say, an apparatus for growing silicon carbide single crystals according to an exemplary embodiment of the present invention may include a crucible 510 in which a feedstock is loaded, a seed holder 100 to which a seed 200 is attached, an insulating material 520 surrounding the crucible 510, a quartz tube 530 and a heating means 540 disposed outside the quartz tube 530 for heating the crucible 510. In addition, the apparatus may further include a controller (not shown) for independently operating the heating means 540.

The crucible 510 is prepared from a material having a melting point higher than the sublimation temperature of silicon carbide. For example, it may be made from graphite and the tungsten film layer 600 may be present on an inner wall of the crucible 510.

Further, the feedstock A loaded in the crucible 510 may include, e.g., silicon carbide powder.

The seed holder 100 is prepared using high-density graphite. As described above, the seed 200 is attached to the seed holder 100 having the tungsten film layer 600 formed thereon. The seed holder 100 with the seed 200 attached is disposed at an upper portion in the crucible 510 so as to grow single crystals 300 on the seed 200.

The insulating material 520 and the quartz tube 530 are disposed outside the crucible 510 and maintain the temperature of the crucible 510 at a crystal growth temperature. Since the crystal growth temperature of silicon carbide is very high, a graphite felt prepared by compressing graphite fiber into a tubular cylinder with a predetermined thickness may be used as the insulating material 520. Also, the insulating material 520 may be formed as a plurality of layers to surround the crucible 510.

The heating means 540 is disposed outside the quartz tube 530. For example, a high-frequency induction coil may be used as the heating means 540. The crucible 510 may be heated by allowing a high-frequency current to flow in the high-frequency induction coil and, consequently, the feedstock A may be heated to a desired temperature.

Hereinafter, a method for growing silicon carbide single crystals according to an exemplary embodiment of the present invention will be described in detail.

A method for growing single crystals according to an exemplary embodiment of the present invention is a method for growing single crystals 300 on a seed 200. For this, a seed 200 is prepared first. Although 4H-SiC or 6H-SiC was used as the seed 200 in Example, other various kinds of seeds (3C-SiC, 15R-SiC, etc.) may be used without being limited thereto. Specifically, the seed 200 may have a circular shape with a diameter of 2 inches or greater. As will be described later, the seed 200 is attached onto a seed holder 100.

Referring to Fig. 2a and Fig. 2b, the seed 200 is attached onto a seed holder 100 having a tungsten film layer 600 formed thereon. The seed 200 may be attached on the seed holder 100 using a carbon paste or a photoresist. Also, various adhesives capable of attaching the seed 200 on the seed holder 100 may be used without being limited thereto.

The seed holder 100 having the seed 200 attached is inserted in an apparatus for growing single crystals and then single crystals 300 are grown on the seed 200. The seed holder 100 having the seed 200 attached may be inserted into the apparatus using a guide ring. At this time, a lower surface of the seed holder 100 is attached to an upper portion inside a crucible 510, such that an upper surface of the seed holder 100 having the seed 200 attached faces an upper side of the crucible 510. Then, a feedstock A, e.g., SiC powder, is loaded in the crucible 510.

After the seed holder 100 and the feedstock A are loaded, impurities contained in the crucible 510 are removed by heating for 2-3 hours at 1300-1500 ºC in vacuo. Subsequently, air remaining inside the crucible 510 and between the crucible 510 and an insulating material 520 is removed by injecting an inert gas, e.g. argon (Ar) gas. Then, after raising pressure to atmospheric pressure, the crucible 510 is heated to 2000-2300 ºC using a heating means 540. The reason why atmospheric pressure is maintained is to prevent polymorphism, i.e., formation of unwanted crystals in the early stage of crystal growth. That is to say, the feedstock A is first heated to the crystal growth temperature while maintaining atmospheric pressure. Then, single crystals 300 are grown by subliming the feedstock A by lowering the pressure inside the crucible to 5-30 Torr and maintain the pressure.

The silicon carbide single crystals grown using the crucible and the seed holder having the tungsten film layers 600 exhibit fewer defects than the single crystals grown using the existing graphite crucible and seed holder. Accordingly, by growing single crystals using a graphite crucible having a tungsten film layer 600 formed thereon, silicon carbide single crystals having fewer defects can be grown.

[Example]

Silicon carbide single crystals were grown using a graphite crucible having a tungsten film layer and a seed holder having a tungsten film layer. The tungsten film layers were formed by thermal spray coating to a thickness of 100 μm.

Specifically, after loading the seed holder and SiC powder as a feedstock, impurities contained in the graphite crucible were removed by heating for 2-3 hours at about 1400 ºC in vacuo. Subsequently, air remaining in the graphite crucible and between the graphite crucible and the insulating material was removed by injecting argon (Ar) gas. Then, after raising pressure to atmospheric pressure, the graphite crucible was heated to about 2200 ºC using a heating means. Subsequently, silicon carbide single crystals were grown for 70 hours by lowering the pressure inside the graphite crucible to about 10 Torr.

[Comparative Example]

Silicon carbide single crystals were grown in the same manner as in Example, except that a graphite crucible without a tungsten film layer and a seed holder without a tungsten film layer were used.

Fig. 4 is a plan view of the silicon carbide single crystals (ingot) grown in Comparative Example, and Fig. 5 is a plan view of the silicon carbide single crystals grown in Example. As shown in Fig. 4 and Fig. 5, when the crucible and the seed holder having the tungsten film layers were used (Example), the quality of the single crystals was very superior.

Fig. 6 is a longitudinal cross-sectional view of the silicon carbide single crystals (ingot) grown in Comparative Example, and Fig. 7 is a longitudinal cross-sectional view of the silicon carbide single crystals grown in Example.

As shown in Fig. 6 and Fig. 7, when the crucible and the seed holder having the tungsten film layers were used (Example), there were very few micropipe defects. In Fig. 6 and Fig. 7, the micropipe defects are shown as black lines.

Fig. 8 shows Si-face rocking curves of the silicon carbide single crystals grown in Comparative Example, and Fig. 9 shows Si-face rocking curves of the silicon carbide single crystals grown in Example.

The Si-face rocking curve is used to evaluate the quantity or quality of grown single crystals. A smaller full width at half maximum (FWHM) indicates better quantity or quality of single crystals. The FWHM of the silicon carbide single crystals prepared in Comparative Example was 38-55 arcsec, suggesting low crystallinity. In contrast, the FWHM of the silicon carbide single crystals prepared in Example was 38-40 arcsec, suggesting much superior crystallinity.

As described, an apparatus and a method for growing silicon carbide single crystals according to the present invention can grow high-quality silicon carbide single crystals by preventing etching of a graphite crucible by a tungsten film layer formed on an inner wall of the crucible and by preventing seed back etching at a portion where a seed is attached to a seed holder by a tungsten film layer formed on at least one surface of the seed holder.

[Description of Main Elements]

100: seed holder

200: seed

300: single crystal

510: crucible

520: insulating material

530: quartz tube

540: heating means

600: tungsten film layer

A: feedstock

Claims

An apparatus for growing silicon carbide single crystals, comprising:
a crucible comprising a hollow portion inside thereof and a tungsten film layer covering all or part of an inner wall thereof;
an insulating material covering all or part of an outer wall of the crucible; and
a heating means disposed outside the insulating material.
The apparatus for growing silicon carbide single crystals according to claim 1, which comprises a seed holder located above the hollow portion, present on the inner wall of the crucible and having a tungsten film layer formed on one surface thereof.
A method for growing silicon carbide single crystals using a crucible, a seed holder to which a seed is attached, an insulating material surrounding the crucible, a quartz tube, and a heating means present outside the quartz tube, comprising disposing the seed holder having a tungsten film layer at an upper portion inside the crucible.
The method for growing silicon carbide single crystals according to claim 3, wherein the crucible comprises a hollow portion inside thereof and a tungsten film layer covering all or part of an inner wall thereof.
The method for growing silicon carbide single crystals according to claim 3, which comprises, after said disposing the seed holder having a tungsten film layer at an upper portion inside the crucible:
removing impurities contained in the crucible by heating for 2-3 hours at 1300-1500 ºC in vacuo;
removing air remaining inside the crucible and between the crucible and the insulating material by injecting an inert gas;
raising pressure to atmospheric pressure;
heating the crucible to 2000-2300 ºC using the heating means; and
growing silicon carbide single crystals by lowering the pressure inside the crucible to 5-30 Torr.