Method for growing a SiC crystal by vapor deposition onto a seed crystal provided on a supporting shelf which permits thermal expansion
View Patent ↗A method of forming an SiC crystal, the method including: placing a SiC seed in a growth vessel, heating the growth vessel, and evacuating the growth vessel, wherein the seed is levitated as a result of a temperature and pressure gradient, and gas flows from a growth face of the seed, around the edge of the seed, and into a volume behind the seed, which is pumped by a vacuum system.
1. A method of forming an SiC crystal using a seed crystal having a given diameter, the method comprising:
a. providing a graphite container having an interior diameter which is larger than the diameter of the seed crystal and having a shelf on an interior sidewall of the graphite container with an inner diameter which is smaller than the diameter of the seed crystal;
b. placing a source of silicon and carbon atoms in the insulated graphite container, wherein the source of silicon and carbon atoms is for transport to the seed crystal to grow the SiC crystal;
c. placing the seed crystal on the shelf and placing a lid on the graphite container to form a ceiling while preventing an exposed back surface of the seed from contacting the ceiling, thereby defining a volume between ceiling of the graphite container and the exposed back surface of the seed;
d. providing means for directing gas flow from a periphery of the seed crystal to the volume;
e. placing the graphite container inside a furnace;
f. evacuating the furnace and filling with inert gas to a pressure above 600 torr;
g. heating the furnace to a temperature from about 2,000° C. to about 2,500° C.; and,
h. evacuating the induction furnace to a pressure of from about 0.1 Torr to about 100 Torr, while directing gas flow from below the seed crystal through a periphery of the seed crystal and to a center of the volume between ceiling of the graphite container and the back surface of the seed, to thereby facilitate vapor transport from the source of silicon and carbon atoms to the seed while preventing the back surface of the seed from contacting the ceiling.
2. The method of claim 1 , further comprising flowing dopant gas into the furnace.
3. The method of claim 2 , wherein the temperature and pressure are maintained to enable growth of from 0.1 to 50 mm thick SiC crystal with a nitrogen concentration from 1×10 15 to 1×10 19 /cm 3 .
4. The method of claim 2 , wherein the seed crystal is a 4H-SiC crystal with offcut from 0 to 4 degrees toward (11-20) crystalline orientation and wherein a nitrogen concentration of the seed crystal is from about 1×10 16 /cm 3 to about 8×10 18 /cm 3 .
5. The method of claim 1 , wherein preventing the back surface of the seed from contacting the ceiling comprises inserting a retaining ring above the seed.
6. The method of claim 5 , wherein providing the means for directing gas flow comprises inserting a gas channel ring between the seed and the retaining ring.
7. The method of claim 6 , further comprising inserting a second gas channel ring between the seed and the shelf.
8. The method of claim 1 , wherein the seed crystal has a diameter of greater than or equal to 76 mm.
9. The method of claim 8 , wherein the seed crystal has a diameter of greater than or equal to 150 mm.
10. The method of claim 8 , wherein the seed crystal has a diameter of greater than or equal to 76 mm and less than or equal to 150 mm.