Patent ID: 7566919

Claim:
A method for forming an epitaxial base layer in a bipolar device, comprising: providing a structure having a field isolation oxide region ( 12 ) adjacent to an active silicon region ( 10 ), forming a silicon nitride/silicon stack ( 14 , 16 ) above the field isolation oxide region ( 12 ), wherein the silicon nitride/silicon stack includes a top layer of silicon ( 14 ) and a bottom layer of silicon nitride ( 16 ); performing an etch to the silicon nitride/silicon stack ( 14 , 16 ) to form a stepped seed layer, wherein the top layer of silicon ( 14 ) is etched laterally at the same time the bottom layer of silicon nitride ( 16 ) is etched; and growing an Si/SiGe/Si stack ( 20 ) over the stepped seed layer and active silicon region.