Method for purifying silicon carbide coated structures
View Patent ↗Processes for the purification of silicon carbide structures, including silicon carbide coated silicon carbide structures, are disclosed. The processes described can reduce the amount of iron contamination in a silicon carbide structure by 100 to 1000 times. After purification, the silicon carbide structures are suitable for use in high temperature silicon wafer processing.
1. A process for purifying a silicon carbide structure suitable for use in high temperature silicon wafer processing, the process comprising:
a. subjecting the silicon carbide structure to moisture;
b. chemically stripping at least about 1 micrometer of silicon carbide from the silicon carbide structure;
c. exposing the silicon carbide structure to hydrogen gas at a temperature of at least about 1200° C. for a time period of from about 10 hours to about 24 hours;
d. growing a silicon oxide layer having a thickness of from about 2 nanometers to about 400 nanometers on the surface of the silicon carbide structure at a temperature of from about 1150° C. to about 1250° C.;
e. chemically stripping the silicon oxide layer from the silicon carbide structure using an aqueous etchant; and
f. repeating steps c, d, and e from about 1 to about 4 times.
2. The process as set forth in claim 1 wherein the silicon carbide structure is subjected to moisture by immersing the structure in water.
3. The process as set forth in claim 1 wherein the silicon carbide structure is subjected to moisture by exposing the structure to humidity.
4. The process as set forth in claim 1 wherein in step b from about 1 micrometer to about 20 micrometers of silicon carbide is chemically stripped.
5. The process as set forth in claim 1 wherein in step b from about 2 micrometers to about 4 micrometers of silicon carbide is chemically stripped.
6. The process as set forth in claim 1 wherein step b is completed by etching the silicon carbide structure at a temperature of at least about 1000° C. for a time period of from about 10 minutes to about 2 hours in a halide containing gas.
7. The process as set forth in claim 6 wherein the etching temperature is from about 1000° C. to about 1350° C.
8. The process as set forth in claim 6 wherein the halide containing gas is selected from the group consisting of chlorine gas, hydrogen chloride gas, SF 6 and combinations thereof.
9. The process as set forth in claim 6 wherein plasma is used in combination with the halide containing gas to etch the silicon carbide structure.
10. The process as set forth in claim 9 wherein the plasma is created using a gas selected from the group consisting of organic or inorganic fluorides, organic or inorganic chlorides and organic and inorganic bromides.
11. The process as set forth in claim 4 wherein step b is completed by etching the silicon carbide structure at a temperature of from about 20° C. to about 600° C. in an atmosphere comprising ClF 3 .
12. The process as set forth in claim 1 wherein step b is completed by first oxidizing the silicon carbide structure and then chemically stripping the oxidized layer.
13. The process as set forth in claim 12 wherein the oxidation comprises exposing the silicon carbide structure to a mixture of dichloroethylene and oxygen at a temperature of at least about 1000° C.
14. The process as set forth in claim 12 wherein the oxidation comprises exposing the silicon carbide structure to a mixture of hydrogen chloride gas and oxygen at a temperature of at least about 1000° C.
15. The process as set forth in claim 12 wherein the oxidized layer is chemically stripped off of the silicon carbide structure using an aqueous etching solution.
16. The process as set forth in claim 15 wherein the aqueous etching solution comprises hydrofluoric acid.
17. The process as set forth in claim 1 wherein the silicon oxide layer of step d is grown at a temperature of about 1200° C.
18. The process as set forth in claim 1 wherein the silicon oxide layer of step d is grown over a period of from about 6 hours to about 10 hours.
19. The process as set forth in claim 1 wherein the silicon oxide layer of step d is grown over a period of about 8 hours.
20. The process as set forth in claim 1 wherein the chemical stripping of step e is done with an aqueous hydrofluoric acid etchant.
21. The process as set forth in claim 20 wherein the aqueous hydrofluoric acid etchant comprises from about 0.05% (by weight) to about 49% (by weight) hydrofluoric acid.
22. The process as set forth in claim 20 wherein the stripping occurs at a temperature of from about 15° C. to about 90° C.
23. The process as set forth in claim 20 wherein the chemical stripping occurs over a time period of from about 1 minute to about 4 hours.
24. The process as set forth in claim 1 wherein the silicon carbide structure comprises a silicon carbide base structure having a high purity silicon carbide coating.