Method 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 method of forming silicon carbide comprising:
i) 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, wherein the insulation comprises a plurality of layers of fibrous thermally insulating material, the hot zone including:
a) a crucible having an upper region, a lower region, and one or more vent holes;
b) a crucible cover sealing the crucible;
c) a substantially solid silicon carbide precursor contained within a source module that is positioned in the lower region of the crucible, wherein the silicon carbide precursor is porous, further wherein the source module is removable from the crucible;
d) a stand-alone seed module, removable from the crucible, that, when suspended in the upper region of the crucible, forms a space between the crucible cover and an entire top surface of an upper section of a seed holder of the seed module, the seed module having a plurality of vapor release openings and a silicon carbide seed disposed within the seed holder, wherein the silicon carbide seed has a top surface that is exposed to the upper region of the crucible and a bottom surface that faces the substantially solid silicon carbide precursor, and wherein the plurality of vapor release openings are formed in the seed holder below the bottom surface of silicon carbide seed as a plurality of holes around a center axis that is perpendicular to the bottom surface of the silicon carbide seed; and
e) at least one vapor release ring having one or more holes, wherein the at least one vapor release ring is positioned between the seed holder and the crucible, with at least one of the holes of the vapor release ring aligned with at least one of the vent holes of the crucible;
ii) disposing the seed between the upper section and a lower section of the seed holder;
iii) disposing the seed holder between the crucible cover and the lower region of the crucible;
iv) after positioning the source module in the lower region of the crucible and disposing the seed holder between the crucible cover and the lower region of the crucible, heating the hot zone with the at least one heating element to sublimate the substantially solid silicon carbide precursor contained within the source module;
v) forming the silicon carbide on the bottom surface of the silicon carbide seed;
vi) removing the seed module including the formed silicon carbide on the bottom surface of the silicon carbide seed; and
vii) removing the source module including the sublimated substantially solid silicon carbide precursor.
2. The method of claim 1 , wherein the source module comprises a precursor chamber and wherein the substantially solid silicon carbide precursor is contained within the precursor chamber.
3. The method of claim 1 , wherein the substantially solid silicon carbide precursor has a density that is less than a density of silicon carbide.
4. The method of claim 1 , wherein the top surface of the silicon carbide seed comprises a seed protection layer.
5. The method of claim 4 , wherein the seed protection layer has a thickness of less than 250 microns.
6. The method of claim 4 , wherein the seed protection layer has a thickness of less than 100 microns.
7. The method of claim 4 , wherein the seed protection layer comprises at least two coating layers.
8. The method of claim 4 , wherein the seed protection layer comprises at least one cured coating layer.
9. The method 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.
10. The method 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.
11. The method of claim 1 , wherein the hot zone is positioned along a center axis inside the furnace shell.
12. The method of claim 1 , wherein the fibrous thermally insulating material is graphite felt.
13. The method of claim 1 , wherein the crucible has a substantially cylindrical shape.
14. The method of claim 1 , wherein the upper region of the crucible has a substantially cylindrical shape having an upper diameter and the lower region of the crucible has a substantially cylindrical shape having a lower diameter, and wherein the upper diameter is larger than the lower diameter.
15. The method of claim 1 , wherein the at least one heating element is an induction heater.
16. The method of claim 1 , wherein the silicon carbide formed is a silicon carbide boule having a substantially circular cross-sectional shape in a direction parallel to the silicon carbide seed.
17. The method of claim 1 , wherein the silicon carbide has a total defect count of less than 8000/cm 2 .