Patent ID: 7226844

Claim:
A method for manufacturing a bipolar transistor in a semiconductor substrate of a first conductivity type, comprising the steps of: forming on the substrate a single-crystal silicon-germanium layer; forming a heavily-doped single-crystal silicon layer of a second conductivity type overlying the single-crystal silicon-germanium layer; forming a silicon oxide layer overlying the single-crystal silicon layer; opening a window in the silicon oxide and silicon layers, thereby exposing a portion of the silicon-germanium layer at bottom of the window; forming on walls of the window a silicon nitride spacer; removing the silicon-germanium layer from the bottom of the window to provide a cavity extending beyond the bottom of the window into areas under the silicon layer; forming in the cavity a heavily-doped single-crystal semiconductor layer of the second conductivity type; and forming in said window an emitter of the transistor.