High purity silicon carbide 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 high purity silicon carbide structure suitable for use in high temperature silicon wafer manufacturing, the structure being a silicon carbide coated silicon carbide substrate and consisting essentially of silicon carbide, the structure having a denuded zone, the denuded zone extending from the outer surface of the silicon carbide structure to a distance of from about 5 micrometers to about 25 micrometers inward and comprising no more than about 1×10 12 atoms of iron/cm 3 .
2. The high purity silicon carbide structure as set forth in claim 1 wherein the denuded zone comprises no more than about 1×10 11 atoms of iron/cm 3 .
3. The high purity silicon carbide structure as set forth in claim 1 wherein the denuded zone has a depth of from about 5 micrometers to about 10 micrometers.
4. The high purity silicon carbide structure as set forth in claim 1 , the structure consisting of silicon carbide.
5. The high purity silicon carbide structure as set forth in claim 1 wherein the denuded zone is prepared by a 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 1 hour to about 100 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.
6. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon carbide structure is subjected to moisture by immersing the structure in water.
7. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon carbide structure is subjected to moisture by exposing the structure to humidity.
8. The high purity silicon carbide structure as set forth in claim 5 wherein in step b from about 2 micrometers to about 4 micrometers
9. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon carbide structure is exposed to the hydrogen gas for a time period of from about 10 hours to about 24 hours.
10. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon oxide layer of step d is grown at a temperature of about 1200° C.
11. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon oxide layer of step d is grown over a period of from about 6 hours to about 10 hours.
12. The high purity silicon carbide structure as set forth in claim 5 wherein the silicon oxide layer of step d is grown over a period of about 8 hours.
13. The high purity silicon carbide structure as set forth in claim 5 wherein in step b from about 1 micrometer to about 20 micrometers of silicon carbide is chemically stripped.
14. The high purity silicon carbide structure as set forth in claim 13 wherein step b is completed by etching the silicone carbide structure at a temperature of from about 20° C. to about 600° C. in an atmosphere comprising C 1 F 3 .
15. The high purity silicon carbide structure as set forth in claim 5 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.
16. The high purity silicon carbide structure as set forth in claim 15 wherein the etching temperature is from about 1000° C. to about 1350° C.
17. The high purity silicon carbide structure as set forth in claim 15 wherein the halide containing gas is selected from the group consisting of chlorine gas, hydrogen chlorine gas, SF 6 and combinations thereof.
18. The high purity silicon carbide structure as set forth in claim 15 wherein plasma is used in combination with the halide containing gas to etch the silicon carbide coated structure.
19. The high purity silicon carbide structure as set forth in claim 18 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.
20. The high purity silicon carbide structure as set forth in claim 5 wherein step b is completed by first oxidizing the silicon carbide structure and then chemically stripping the oxidized layer.
21. The high purity silicon carbide structure as set forth in claim 20 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.
22. The high purity silicon carbide structure as set forth in claim 20 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.
23. The high purity silicon carbide structure as set forth in claim 20 wherein the oxidized layer is chemically stripped off of the silicon carbide structure using an aqueous etching solution.
24. The high purity silicon carbide structure as set forth in claim 23 wherein the aqueous etching solution comprises hydrofluoric acid.
25. The high purity silicon carbide structure as set forth in claim 5 wherein the chemical stripping of step e is done with an aqueous hydrofluoric acid etchant.
26. The high purity silicon carbide structure as set forth in claim 25 wherein the aqueous hydrofluoric acid etchant comprises from about 0.05% (by weight) to about 49% (by weight) hydrofluoric acid.
27. The high purity silicon carbide structure as set forth in claim 25 wherein the stripping occurs at a temperature of from about 15° C. to about 90° C.
28. The high purity silicon carbide structure as set forth in claim 25 wherein the chemical stripping occurs over a time period of from about 1 minute to about 4 hours.