Patent ID: 7049198

Claim:
A method for fabricating a MOSFET semiconductor device, comprising the steps of: a) forming a first semiconductor layer, which is made of Si 1-y Ge y (0<y<1), on a substrate; b) forming a second semiconductor layer made of Si including carbon in contact with the first semiconductor layer; and c) annealing the substrate, wherein the carbon suppresses movement of at least one constituent of the first semiconductor layer into the second semiconductor layer, wherein the step b) further comprises the steps of: b-1) forming a second semiconductor layer, which is made of Si, on the first semiconductor layer; b-2) forming an intrinsic Si layer on the second semiconductor layer; b-3) doping the second semiconductor layer with carbon; and b-4) forming an oxide film substantially reaching the Si layer by oxidizing the intrinsic Si layer after the step b-3) has been performed.