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US-12624474-B2 - SiC single-crystal growth apparatus and method of growing SiC crystal

US12624474B2US 12624474 B2US12624474 B2US 12624474B2US-12624474-B2

Abstract

An SiC single-crystal growth apparatus and a method of growing an SiC crystal are provided capable of reducing variations in the temperature distribution in the seed crystal and/or reducing deformation of, and/or damage to, the seed crystal, thereby growing an SiC single crystal with reduced defects and/or cracks. An SiC single-crystal growth apparatus ( 1 ) includes: a heating vessel ( 10 ) including a source material-containing portion ( 12 ) adapted to contain a solid source material of SiC in one of an upper portion or a lower portion (e.g., on the bottom portion 13 ) of an interior space S defined by a cylindrical peripheral side portion ( 14 ), and including a seat ( 17 ) located in another portion located opposite to said one portion (e.g., lid ( 16 )) for allowing a seed crystal ( 2 ) of SiC to be mounted thereon; and a heating member ( 3 ) adapted to heat the solid source material M(s), where: the seed crystal ( 12 ) is mounted on the seat ( 17 ) with a first anisotropic sheet ( 41 ) positioned therebetween, the first anisotropic sheet having anisotropy in thermal conductivity; and, in the first anisotropic sheet ( 41 ), the thermal conductivity in a direction in the plane of the sheet, x, is high and the thermal conductivity in the thickness direction of the sheet, y, is low.

Inventors

  • Hiromu Shiomi

Assignees

  • SEC CARBON, LTD.

Dates

Publication Date
20260512
Application Date
20220118
Priority Date
20210331

Claims (7)

  1. 1 . A silicon carbide (SiC) single-crystal growth apparatus comprising: a heating vessel including a source material-containing portion adapted to contain a solid source material of SiC in one of an upper portion or a lower portion of an interior space defined by a cylindrical peripheral side portion, and including a seat located in another portion located opposite to said one portion for allowing a seed crystal of SiC to be mounted thereon; and a heating member adapted to heat the solid source material, wherein: the seed crystal is mounted on the seat with a first anisotropic sheet positioned therebetween, the first anisotropic sheet having anisotropy in thermal conductivity; in the first anisotropic sheet, a thermal conductivity in a direction in a plane of the sheet is high and a thermal conductivity in a thickness direction of the sheet is low; and the first anisotropic sheet is formed to have a larger surface area than each of the seed crystal and the seat so as to expand from between the seed crystal and the seat.
  2. 2 . The SiC single-crystal growth apparatus according to claim 1 , wherein a seed crystal-mounting surface of the first anisotropic sheet has an arithmetical mean roughness (Ra) not higher than 1 μm.
  3. 3 . The SiC single-crystal growth apparatus according to claim 1 , wherein the first anisotropic sheet has a thickness in a range of not smaller than 0.04 mm and not larger than 2 mm.
  4. 4 . The SiC single-crystal growth apparatus according to claim 1 , further comprising: a guide member located in the interior space and between the seed crystal and the source material-containing portion and at a peripheral side portion of the heating vessel for guiding a direction of growth of the SiC single crystal growing from a surface of the seed crystal, the guide member being located adjacent to a peripheral side surface of the SiC single crystal, wherein: a surface of the guide member facing the growing SiC single crystal is covered with a second anisotropic sheet having anisotropy in thermal conductivity; and, in the second anisotropic sheet, a thermal conductivity in a direction in a plane of the sheet is high and a thermal conductivity in a thickness direction of the sheet is low.
  5. 5 . The SiC single-crystal growth apparatus according to claim 4 , wherein the surface of the second anisotropic sheet facing the single crystal has an arithmetical mean roughness (Ra) not higher than 1 μm.
  6. 6 . The SiC single-crystal growth apparatus according to claim 4 , wherein the second anisotropic sheet has a thickness in a range of not smaller than 0.04 mm and not larger than 2 mm.
  7. 7 . A method of growing a silicon carbide (SiC) crystal, comprising growing an SiC single crystal using the SiC single-crystal growth apparatus according to claim 1 .

Description

TECHNICAL FIELD The present invention relates to an SiC single-crystal growth apparatus and a method of growing an SiC crystal. BACKGROUND ART Silicon carbide (SiC) provides excellent electric properties, namely, a dielectric breakdown field that is approximately one order of magnitude higher, and a bandgap that is approximately three times larger, than that of silicon (Si). Further, SiC provides an excellent thermal property, namely, a thermal conductivity that is approximately three times as high as that of Si. Due to these excellent properties, SiC is expected to be used in various devices, such as power devices, high-frequency devices, and high-temperature operating devices. These devices are fabricated by machining an SiC single-crystal ingot to produce an SiC single-crystal substrate and using chemical vapor deposition (CVD) and/or other methods to form an epitaxial layer that is to provide an active region of the resulting device. One known method of forming an SiC single-crystal ingot is the sublimation method. The sublimation method involves: positioning a seed crystal, composed of an SiC single crystal, inside a crucible made of graphite; heating the crucible and source material powder (i.e., source material in the crucible) to cause the source material powder (i.e., source material) in the crucible to sublimate into sublimated gas; supplying this gas to the seed crystal, thereby growing the seed crystal into a larger SiC single-crystal ingot. An SiC single crystal-manufacturing crucible used to form an SiC single crystal with the sublimation method is described in Patent Document 1, which discloses a crucible with a seed crystal mounted thereon, where the seed crystal is adsorbed onto the lid of the crucible. More specifically, Patent Document 1 discloses a crucible including a lid having through-holes, extending therethrough between the inside and the outside of the crucible, that are closed by a seed crystal adsorbed thereon during the growth of a crystal, and a seed-crystal support means located below the seed-crystal contact surface of the lid for supporting the seed crystal while retaining a clearance from the seed-crystal contact surface so that the seed crystal can be adsorbed onto the crucible lid by controlling the difference between the pressures inside and outside the crucible. Another method of manufacturing an SiC single crystal with the sublimation method is described in Patent Document 2, which discloses reducing crystal defects in an SiC single crystal by preventing the seed crystal from being subjected to stress. More specifically, Patent Document 2 discloses promoting vapor transport of gaseous source material toward the seed crystal while directing gas flow from below the seed crystal past the periphery of the seed crystal to the center of the volume between the ceiling of the heating vessel and the backside of the seed crystal to prevent the backside of the seed crystal to contact the ceiling of the heating vessel. PRIOR ART DOCUMENTS Patent Documents Patent Document 1: Japanese Patent No. 5146418Patent Document 2: Japanese Patent No. 6444890 SUMMARY OF THE INVENTION Problems to be Solved by the Invention During the growth of an SiC single crystal, portions of the seed crystal that are in contact with the seat located adjacent thereto experience thermal stress and/or distortion due to the differences in thermal expansion between the seed crystal and the seat, which may result in defects and/or cracks in the grown SiC single crystal. Further, variations in temperature in the seat adjacent to the seed crystal may cause variations in the temperature distribution in the seed crystal and thus produce thermal stress in the seed crystal, which may also result in defects in the grown SiC single crystal. To address this, the crucible of Patent Document 1 reduces thermal stress and/or distortion due to the differences in thermal expansion between the crucible lid and seed crystal by causing the seed crystal to be adsorbed onto the crucible lid to mount it on the crucible; however, the document fails to address, at least, variations in the temperature distribution in the seed crystal. The method of Patent Document 2 reduces crystal defects in an SiC single crystal by directing gas flow into the volume between the ceiling of the heating vessel and the backside of the seed crystal to keep the backside of the seed crystal floating from the ceiling of the heating vessel. However, since the seed crystal is not attached to the seat or the like in the method of Patent Document 2, thermal conductivity is not uniform across the plane of the seed crystal (i.e., varies going from the middle to the periphery), making it difficult to achieve a uniform crystal growth rate across the plane, i.e., similar rates at the middle and at the periphery. Further, in the method of Patent Document 2, the seed crystal is clamped by spacers to hold it; as such, the clamping force of the spacers may damage the seed