Smoothing method for semiconductor material and wafers produced by same
A smoothing method for semiconductor material and semiconductor wafers produced by the method are disclosed. Semiconductor wafers with reduced atomic steps, as well with reduced scratches and subsurface defects can be produced. Such wafers feature an improved growth surface that can provide for the growth of an epilayer with reduced macroscopic defects and defect densities. A method of smoothing the surface of a wafer according to example embodiments of the invention includes planarizing the surface of a semiconductor wafer, and then oxidizing the wafer to achieve a specified thickness of oxide on the surface of the wafer. The oxide can then be stripped from the surface of the semiconductor wafer.
1. A wafer comprising:
a substrate with a surface wherein an appearance of atomic steps is reduced by at least 50% compared to the surface after chemical mechanical planarization and an arithmetic mean surface roughness less than 0.2 nm over a 1×1 micron or greater area of the surface; and
an epitaxial layer on the substrate, wherein the epitaxial layer is free of defects from 10 to 5000 microns in size that are characterized by localized morphological changes, and has a defect density of less than 5×10 7 cm −2 .
2. The wafer of claim 1 wherein the substrate further comprises silicon carbide.
3. The wafer of claim 2 wherein the epitaxial layer further comprises silicon carbide or a group III-V compound.
4. The wafer of claim 3 wherein the surface is free of scratches and atomic steps.
5. A die cut from the silicon carbide wafer of claim 3 .
6. A device made from the die of claim 5 .
7. A semiconductor wafer comprising a substrate with a surface wherein an appearance of atomic steps is reduced by at least 50% compared to the surface after mechanical material removal and chemical mechanical planarization, the surface also having an arithmetic mean surface roughness less than 0.2 nm over a 1×1 micron or greater area and the semiconductor wafer also having an epitaxial layer with a defect density of less than 5×10 7 cm −2 , and being prepared by a process comprising:
planarizing a surface of the semiconductor wafer;
oxidizing the semiconductor wafer; and
growing the epitaxial layer on the substrate so as to be free of defects from 10 to 5000 microns in size that are characterized by localized morphological changes.
8. The semiconductor wafer of claim 7 wherein the planarizing of the surface of the wafer further comprises chemical mechanical planarization.
9. The semiconductor wafer of claim 8 wherein the process further comprises stripping from the semiconductor wafer an oxide formed by the oxidizing of the semiconductor wafer.
10. The semiconductor wafer of claim 9 wherein the semiconductor wafer further comprises silicon carbide.
11. The semiconductor wafer of claim 10 wherein the oxidizing of the semiconductor wafer further comprises thermally oxidizing the wafer at a temperature of between 1225 C and 1800 C for a time sufficient to achieve a specified thickness of oxide.
12. The semiconductor wafer of claim 11 wherein the oxidizing is accomplished by dry oxidation and the specified thickness of oxide is at least 500 angstroms.
13. The semiconductor wafer of claim 12 wherein the epitaxial layer further comprises at least one of silicon carbide and a group III-V compound.