Apparatus for producing bulk silicon carbide
A method of producing silicon carbide is disclosed. The method comprises the steps of providing a sublimation furnace comprising a furnace shell, at least one heating element positioned outside the furnace shell, and a hot zone positioned inside the furnace shell surrounded by insulation. The hot zone comprises a crucible with a silicon carbide precursor positioned in the lower region and a silicon carbide seed positioned in the upper region. The hot zone is heated to sublimate the silicon carbide precursor, forming silicon carbide on the bottom surface of the silicon carbide seed. Also disclosed is the sublimation furnace to produce the silicon carbide as well as the resulting silicon carbide material.
1. A sublimation furnace for forming silicon carbide comprising a furnace shell, at least one heating element positioned outside the furnace shell, and a hot zone positioned inside the furnace shell surrounded by insulation, the hot zone comprising:
a) a crucible having an upper region and a lower region;
b) a crucible cover sealing the crucible;
c) a solid silicon carbide precursor positioned in the lower region of the crucible;
d) a seed module disposed in the upper region of the crucible, the seed module comprising:
(1) a silicon carbide seed having a top surface and a bottom surface, the top surface exposed to the upper region of the crucible, the bottom surface facing the solid silicon carbide precursor and the lower region of the crucible, and
(2) a seed holder having an upper section and a lower section that hold the silicon carbide seed therebetween, the seed holder comprising a plurality of vapor release openings formed around a center axis of the seed holder; and
e) a vapor release ring disposed above the upper section of the seed holder, the vapor release ring comprising one or more holes that align with one or more vent holes formed in the crucible,
wherein the plurality of vapor release openings of the seed holder, the one or more holes of the vapor release ring, and the one or more vent holes of the crucible, in combination, form a path for vapors to pass out of the crucible.
2. The sublimation furnace of claim 1 , wherein the solid silicon carbide precursor is contained within a precursor chamber of a source module positioned in the lower region of the crucible.
3. The sublimation furnace of claim 1 , wherein the solid silicon carbide precursor is porous.
4. The sublimation furnace of claim 1 , wherein the one or more holes of the vapor release ring changeably align with the one or more vent holes of the crucible.
5. The sublimation furnace of claim 1 , wherein the plurality of vapor release openings are formed in both of the upper and lower sections of the seed holder.
6. The sublimation furnace of claim 1 , wherein the top surface of the silicon carbide seed comprises a seed protection layer.
7. The sublimation furnace of claim 6 , wherein the seed protection layer has a thickness of less than 250 microns.
8. The sublimation furnace of claim 6 , wherein the seed protection layer has a thickness of less than 100 microns.
9. The sublimation furnace of claim 6 , wherein the seed protection layer comprises at least two coating layers.
10. The sublimation furnace of claim 6 , wherein the seed protection layer comprises at least one cured coating layer.
11. The sublimation furnace of claim 1 , wherein the silicon carbide seed has a silicon face and a carbon face, and wherein the top surface is the silicon face.
12. The sublimation furnace of claim 1 , wherein the silicon carbide seed has a silicon face and a carbon face, and wherein the top surface is the carbon face.
13. The sublimation furnace of claim 1 , wherein the hot zone is positioned along a center axis inside the furnace shell.
14. The sublimation furnace of claim 1 , wherein the insulation comprises a plurality of layers of fibrous thermally insulating material.
15. The sublimation furnace of claim 14 , wherein the fibrous thermally insulating material is graphite felt.
16. The sublimation furnace of claim 1 , wherein the crucible has a cylindrical shape.
17. The sublimation furnace of claim 1 , wherein the upper region of the crucible and the lower region of the crucible differ in cross-sectional area.
18. The sublimation furnace of claim 1 , wherein the upper region of the crucible has a cylindrical shape having an upper diameter and the lower region of the crucible has a cylindrical shape having a lower diameter, and wherein the upper diameter is larger than the lower diameter.
19. The sublimation furnace of claim 1 , wherein the at least one heating element is an induction heater.
20. The sublimation furnace of claim 1 , wherein the hot zone further comprises at least one thermal sight tube positioned through the crucible cover and above the silicon carbide seed.
21. The sublimation furnace of claim 1 , wherein the seed module with the silicon carbide seed therebetween is removable separately from a crucible lid.