Carbon doped SiGe heterojunction bipolar transistors for high frequency applications

The incorporation of low concentrations of carbon (<10/sup 20/ cm/sup -3/) into the SiGe region of a heterojunction bipolar transistor (HBT) can significantly suppress boron outdiffusion caused by subsequent processing steps. This effect can be described by coupled diffusion of carbon atoms and Si point defects. We discuss the increase in performance and process margins in SiGe heterojunction bipolar technology by adding carbon. SiGe:C HBTs demonstrate excellent static parameters, exceeding the performance of state-of-the-art SiGe HBTs. C also enhances the high frequency performance, because it allows one to use a high B doping level in a very thin SiGe base layer without outdiffusion from SiGe, even if applying post-epitaxial implants and anneals.