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US-12618171-B2 - Large diameter silicon carbide single crystals and apparatus and method of manufacture thereof

US12618171B2US 12618171 B2US12618171 B2US 12618171B2US-12618171-B2

Abstract

In an apparatus and method growing a SiC single crystal, a PVT growth apparatus is provided with a single crystal SiC seed and a SiC source material positioned in spaced relation in a growth crucible. A resistance heater heats the growth crucible such that the SiC source material sublimates and is transported via a temperature gradient that forms in the growth crucible in response to the heater heating the growth crucible to the single crystal SiC seed where the sublimated SiC source material condenses forming a growing SiC single crystal. Purely axial heat fluxes passing through the bottom and the top of the growth crucible form a flat isotherm at least at a growth interface of the growing SiC single crystal on the single crystal SiC seed.

Inventors

  • Xueping Xu
  • Iiya ZWIEBACK
  • Avinash Gupta
  • Varatharajan Rengarajan

Assignees

  • II-VI ADVANCED MATERIALS, LLC

Dates

Publication Date
20260505
Application Date
20240117

Claims (20)

  1. 1 . A Physical Vapor Transport (PVT) growth apparatus for PVT growing a SiC single crystal comprising: a growth chamber; a growth crucible positioned in the growth chamber, the growth crucible configured to be charged with a SiC source material at a bottom of the growth crucible and a single crystal SiC seed at a top or lid of the growth crucible with the SiC source material and the single crystal SiC seed in spaced relation; a growth guide positioned on either side of the single crystal SiC seed and extending from the top of the growth crucible toward the bottom of the growth crucible, terminating above a top level of the SiC source material; thermal insulation surrounding the growth crucible inside of the growth chamber, the thermal insulation including a side insulation piece between a side of the growth crucible and a side of the growth chamber, a bottom insulation piece between the bottom of the growth crucible and a bottom of the growth chamber, a top insulation piece between the top of the growth crucible and a top of the growth chamber, and an insulation insert positioned in an opening in the top insulation piece; and a heater positioned between the bottom of the growth crucible and the bottom insulation piece, wherein a geometry of the insulation insert is tuned to control heat flux in the SiC single crystal that grows on the single crystal SiC seed in use of the PVT growth apparatus, and wherein the insulation insert includes a top surface and a bottom surface, and the bottom surface of the insulation insert includes a concave surface portion or a convex surface portion that is configured to support a growth interface of the SiC single crystal that is concave or convex.
  2. 2 . The PVT growth apparatus of claim 1 , wherein at least an interior facing surface of the top of the growth chamber that faces the insulation insert is black in color.
  3. 3 . The PVT growth apparatus of claim 2 , wherein the growth chamber is made from a metal or metal alloy.
  4. 4 . The PVT growth apparatus of claim 2 , wherein the growth chamber is made from stainless steel.
  5. 5 . The PVT growth apparatus of claim 2 , wherein the apparatus includes an exterior facing surface that faces away from the insulation insert, and wherein the exterior facing surface is black in color.
  6. 6 . The PVT growth apparatus of claim 1 , wherein the growth guide is spaced from an interior of the side of the growth crucible.
  7. 7 . The PVT growth apparatus of claim 1 , wherein the side, top, and bottom insulation pieces each have a thickness greater than or equal to the thickness of the insulation insert.
  8. 8 . The PVT growth apparatus of claim 7 , wherein the side, top, and bottom insulation pieces each have a thickness that is at least two times the thickness of the insulation insert.
  9. 9 . The PVT growth apparatus of claim 1 , wherein the heater comprises a resistance heater.
  10. 10 . The PVT growth apparatus of claim 1 , wherein the heater has a largest dimension greater than a largest dimension of the bottom of the growth crucible.
  11. 11 . The PVT growth apparatus of claim 1 , wherein the heater resides exclusively between the bottom of the growth crucible and the bottom insulation piece.
  12. 12 . The PVT growth apparatus of claim 1 , wherein a ratio of an outside diameter of the growth crucible over a height of the growth crucible is between 1 and 3.
  13. 13 . The PVT growth apparatus of claim 1 , wherein a ratio of an outside diameter of the growth crucible over a height of the growth crucible is between 1.5 and 4.
  14. 14 . The PVT growth apparatus of claim 1 , wherein the heater is a three-phase resistive heater.
  15. 15 . The PVT growth apparatus of claim 1 , wherein: the top surface of the insulation insert includes a planar surface that extends along a first geometric plane; and the concave surface portion or the concave surface portion is an outer segment of the bottom surface, and the bottom surface of the insulation insert includes a central segment surrounded by the outer segment, and the central segment is a planar surface that extends along a second geometric plane that is parallel with the first geometric plane.
  16. 16 . The PVT growth apparatus of claim 15 , wherein the concave surface portion of the outer segment extends further away from the top surface than the central segment of the bottom surface.
  17. 17 . The PVT growth apparatus of claim 1 , wherein the insulation insert has a thickness between 20 mm and 50 mm and a diameter between 90% and 120% of a diameter of the single crystal SiC seed.
  18. 18 . A PVT growth apparatus for PVT growing a SiC single crystal comprising: a growth crucible having a side, a top, and a bottom, the top of the growth crucible configured to support a single crystal SiC seed in an interior of the growth crucible, and the bottom of the growth crucible configured to support a SiC source material; a growth guide positioned on either side of the single crystal SiC seed and extending from the top of the growth crucible toward the bottom of the growth crucible, terminating above a top level of the SiC source material; insulation surrounding an exterior of the growth crucible, said insulation including side, top, and bottom insulation pieces positioned adjacent the respective side, top, and bottom of the growth crucible, the insulation further including an insulation insert positioned in an opening in the top insulation piece, wherein the insulation insert has a thickness less than a thickness of any one of the side, top, and bottom insulation pieces; and a heater positioned between the bottom of the growth crucible and the bottom insulation piece, wherein a geometry of the insulation insert is tuned to control heat flux in the SiC single crystal that grows on the single crystal SiC seed in use of the PVT growth apparatus, and wherein the insulation insert includes a top surface and a bottom surface, and the bottom surface of the insulation insert includes a concave surface portion or a convex surface portion that aids in generating isotherms that have a radial temperature variation in the growth crucible of less than 10° C. between a central axis of the growth crucible and an outside diameter of the single crystal SiC growing on single crystal SiC seed.
  19. 19 . The PVT growth apparatus of claim 18 , further including a growth chamber in which the growth crucible, insulation, and heater are positioned, the growth chamber including a top in spaced relation to the top of the growth crucible, wherein at least an interior facing surface of the top of the growth chamber is black in color.
  20. 20 . The PVT growth apparatus of claim 18 , wherein the growth guide is spaced from an interior of the side of the growth crucible.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 17/249,597, filed Mar. 5, 2021, which is a divisional of U.S. patent application Ser. No. 16/458,385, filed Jul. 1, 2019, now U.S. Pat. No. 11,035,054, which is a divisional of U.S. patent application Ser. No. 15/584,583, filed on May 2, 2017, which claims the benefit of U.S. Provisional Patent Application No. 62/332,731, filed on May 6, 2016, the disclosures of each of which are incorporated herein by reference in their entireties. BACKGROUND Field of the Invention Disclosed herein is high-quality, large-diameter silicon carbide (SiC) single crystals, and an apparatus and method of growth thereof. Description of Related Art SiC single crystals find their use in a variety of semiconductor, electronic, and optoelectronic devices where SiC wafers serve as substrates for the growth of epitaxial layers of SiC or GaN. The epilayers are then fabricated into devices, such as power switching devices, RF/microwave devices and LEDs. Compared to traditional Si-based devices, SiC-based and GaN-based devices can operate at much higher temperature, power level, frequency—all combined with improved efficiency. Wide-spread application of SiC-based and GaN-based devices is hampered by the high cost the SiC substrate, which is a major contributor to the overall device cost. Currently, the largest 4H-SiC and 6H-SiC substrates available commercially are of 100 mm and 150 mm in diameter, while development of 200 mm SiC substrates has been announced. Implementation of large-size SiC substrates, such as of 200 mm, 250 mm or 300 mm in diameter in the device technology can substantially reduce the cost of SiC- and GaN-based devices. Crystal defects in the SiC substrate are harmful to the device performance, especially in the SiC-based power switching devices formed on N-type 4H-SiC substrates. It is known that threading dislocations cause charge leakage and device degradation, while basal plane dislocations and stacking faults can cause terminal device failure. Stress and strain in the SiC substrate are negative factors in device processing. Industrial-size SiC single crystals, e.g., 100 mm and 150 mm in diameter, are grown by the technique of Physical Vapor Transport (PVT). A sectional view of a conventional PVT growth apparatus is shown schematically in FIG. 1, wherein a graphite growth crucible 1 charged with a SiC source material 2 and a single crystal SiC seed 3 in spaced relation is placed in a growth chamber 20. A heating means 4, for heating the interior of crucible 1 to a sublimation growth temperature, e.g., between 2000° C. and 2400° C., can be provided about the exterior of chamber 20, which can be water-cooled and formed from fused silica. In this example, heating means 4 can be an exterior RF heating coil. However, heating means in the form of a resistance heater inside chamber 20 is envisioned. For the purpose of this description, heating means 4 will be described as being an RF heating coil. However, this is not to be construed in a limiting sense. Crucible 1 is surrounded by thermal insulation 5 inside of chamber 20. A top window 5a having a relatively small diameter is provided in thermal insulation 5. This window 5a is provided for heat dissipation from the backside of SiC seed 3 attached to a top or lid 22 of growth crucible 1. Window 5a can also serve for measuring the temperature of the crucible top using an optical pyrometer via a sealed viewing port 30 in top or lid 22 of chamber 20. In preparation for growth of a SiC single crystal 6 on SiC seed 3, chamber 20 and, hence, growth crucible 1 are evacuated via a vacuum pump and are filled to a desired pressure with a suitable process gas or gases, e.g., argon, nitrogen, boron, supplied through an inlet 36. By controlling the flow of process gas introduced into chamber 20 and, hence, growth crucible 1, via gas inlet 36, and controlling the operation of a vacuum pump connected to an outlet 38 of chamber 20, the gas pressure inside of chamber 20 and, hence, growth crucible 1, can be controlled to a pressure suitable for growth of SiC single crystal 6 on single crystal SiC seed 3. In an example, this pressure can be between 5 and 300 Torr. A window 5b can be provided in thermal insulation adjacent a bottom of growth crucible 1 for temperature measurement of crucible 1 using an optical pyrometer via a sealed viewing port 30 in a bottom 24 of crucible 20. In use, crucible 1 is heated by heating means 4 to a temperature between 2000° C. and 2400° C. sufficient to vaporize the SiC source material 2 and fill the crucible material with vapor species 7 of SiC2, Si2C and Si in the presence of a suitable pressure of the process gas within chamber 20 and, hence, growth crucible 1. Because growth crucible 1 is formed of porous graphite, process gas introduced into chamber 20 appears almost immediately in the interior of growth crucible 1. Similarly, a vacuum applied