Patent ID: 7029988

Claim:
A method of fabricating a semiconductor device, the method comprising: forming a first single crystal silicon layer on a semiconductor substrate containing a single crystal silicon-germanium layer on the surface; forming a first thermal oxide layer on the surface of said first single crystal silicon layer; forming a silicon nitride layer on said first thermal oxide layer; forming a trench region to a depth extending into said single crystal silicon-germanium layer on a multi layer structure made from said single crystal silicon-germanium layer, said first single crystal silicon layer, said first thermal oxide layer, and said silicon nitride layer; forming a second single crystal silicon layer inside said trench region; forming a second thermal oxide layer on the surface of said second single crystal silicon layer; embedding an insulator inside said trench region, thereby forming a device isolation region; and forming a device in an active region separated by said device isolation region, wherein the step of forming said device in said active region includes forming a doped region of a depth to reach within said single crystal silicon-germanium layer below said first single crystal silicon layer, and wherein the step of forming said second single crystal silicon layer includes using selective epitaxial growth.