Patent ID: 7202136

Claim:
A method of forming a bipolar transistor comprising: forming a collector region in a wafer; forming an isolation structure in said collector region; forming a semiconductor layer on said wafer, wherein said forming comprises: epitaxially growing said semiconductor layer so that a single crystalline region is formed above said collector region and a polycrystalline region is formed above said isolation structure; and during said eptiaxially growing, doping said semiconductor layer with carbon so that said carbon extends from a bottom surface of said semiconductor layer to a level below a top surface of said semiconductor layer; forming an emitter on said single crystalline region such that an emitter diffusion region extends below said top surface of said single crystalline region above said level of said carbon; and implanting a portion of said single crystalline region adjacent to said polycrystalline region with a dopant, wherein said carbon limits outdiffusion of said dopant within said semiconductor layer.