Graphite crucible for sublimation growth of SiC crystal
View Patent ↗A method of forming an SiC crystal including placing in an insulated graphite container a seed crystal of SiC, and supporting the seed crystal on a shelf, wherein cushion rings contact the seed crystal on a periphery of top and bottom surfaces of the seed crystal, and where the graphite container does not contact a side surface of the seed crystal; placing a source of Si and C atoms in the insulated graphite container, where the source of Si and C atoms is for transport to the seed crystal to grow the SiC crystal; placing the graphite container in a furnace; heating the furnace; evacuating the furnace; filling the furnace with an inert gas; and maintaining the furnace to support crystal growth to thereby form the SiC crystal.
1. A graphite container and lid for use in a furnace for performing SiC crystal growth on a disk-shaped seed having a known diameter, comprising:
a graphite cylindrical container having a sidewall and an open top configured for accepting a graphite lid;
a cylindrical shelf formed on an upper part of the sidewall and having an interior diameter smaller than the diameter of the seed, the cylindrical shelf being formed at a defined distance below the open top, thereby enabling placing and supporting the seed thereupon keeping the seed sufficiently far from the graphite lid thereby forming empty space between the seed and the graphite lid and reducing the thermal influence of the graphite lid on the seed;
the graphite lid configured for forming a closure with the open top; and,
means for preventing the seed from contacting the graphite lid.
2. The graphite container of claim 1 , wherein the cylindrical shelf is formed integrally with the sidewall.
3. The graphite container of claim 1 , wherein the cylindrical shelf is formed as a ring of graphite bonded to the sidewall.
4. The graphite container of claim 1 , further comprising at least one cushion ring having a diameter smaller than the diameter of the seed and configured for placement below or above the seed.
5. The graphite container of claim 4 , wherein the at least one cushion ring comprises molybdenum or graphite.
6. The graphite container of claim 1 , wherein said means a graphite retaining ring having an exterior diameter to fit within the interior diameter of the sidewall and having an interior diameter smaller than the diameter of the seed, the retaining ring configured for placement above the seed so as to confine vertical movement of the seed inside the container.
7. The container of claim 1 , wherein the means comprises a graphite retaining ring extending from a bottom surface of the lid.
8. The container of claim 1 , wherein the cylindrical shelf comprises vertical walls.
9. The container of claim 1 , wherein the cylindrical shelf comprises slanted walls.
10. The graphite container of claim 1 , wherein said means comprises an upper cushion ring and further comprising a bottom cushion ring and wherein the upper cushion ring being thicker than the bottom cushion ring.
11. The container of claim 1 , wherein the sidewall has a diameter larger than the diameter of the seed.
12. A system for forming an SiC crystal, the system comprising:
a. a graphite cylindrical container having a sidewall and an open top configured for accepting a graphite lid; a cylindrical shelf formed on an upper part of the sidewall and having an interior diameter smaller than the diameter of the seed, the cylindrical shelf being formed at a defined distance below the open top, thereby enabling placing and supporting the seed thereupon keeping the seed sufficiently far from the graphite lid thereby forming empty space between the seed and the graphite lid and reducing the thermal influence of the graphite lid on the seed; and the graphite lid configured for forming a closure with the open top; and, means for preventing the seed from contacting the graphite lid;
b. a heater for heating an induction furnace to a temperature from 2,000° C. to 2,500° C.;
c. a pump for evacuating the induction furnace to a pressure from 0.1 Torr to >600 Torr; and
d. gas inlet for filling the induction furnace with an inert gas.
13. The system of claim 12 , wherein said means comprising at least one cushion ring allowing the seed to flex and expand while preventing the seed from contacting the lid.
14. The system of claim 13 , wherein the cushion ring comprises a first cushion ring positioned below the seed and a second cushion ring positioned above the seed.
15. The system of claim 14 , further comprising a graphite retaining ring positioned above the second cushion ring.
16. The system of claim 13 , wherein the lid comprises a graphite retaining ring extending from bottom surface of the lid.
17. The system of claim 12 , wherein the cylindrical shelf is formed integrally with the sidewall.
18. The system of claim 12 , wherein the sidewall has a diameter larger than the diameter of the seed.
19. The system of claim 12 , wherein the cylindrical shelf comprises slanted walls.