Patent ID: 8048723

Claim:
A method of forming a semiconductor structure, the method comprising: providing a composite substrate comprising a bulk silicon substrate and a silicon germanium (SiGe) layer over and adjoining the bulk silicon substrate; performing a first condensation to the SiGe layer to form a condensed SiGe layer, wherein the condensed SiGe layer has a substantially uniform germanium concentration; etching the condensed SiGe layer and a top portion of the bulk silicon substrate to form a composite fin, wherein the composite fin comprises a silicon fin and a condensed SiGe fin over the silicon fin; oxidizing a portion of the silicon fin, wherein the step of oxidizing comprises: filling a dielectric material to embed a bottom portion of the silicon fin therein; forming a mask to cover a top surface and sidewalls of the condensed SiGe fin, wherein the portion of the silicon fin is exposed; and performing an oxidation to oxidize the portion of the silicon fin and to form an oxide region; and performing a second condensation to the condensed SiGe fin.