The incorporation of low concentrations of C (<1020/cm3) into the SiGe region of a heterojunction bipolar transistor could significantly suppress B out-diffusion caused by subsequent processing steps. This effect could be described by coupled diffusion of C atoms and Si point defects. An increase in performance and process margins in SiGe heterojunction bipolar technology due to adding C was examined. SiGe:C HBTs demonstrate excellent static parameters, exceeding the performance of state-of-the-art SiGe HBTs. Carbon also enhanced the high frequency performance, because it allows one to use a high B doping level in a very thin SiGe base layer without out-diffusion from SiGe, even if applying post-epitaxial implants and anneals. The first modular integration of SiGe:C HBTs into a 0.25μm, epi-free, dual-gate CMOS platform was demonstrated.

Dopant Diffusion Control by Adding Carbon to Si and SiGe - Principles and Device Application. H.J.Osten, D.Knoll, H.Rücker: Materials Science and Engineering B, 2001, 87[3], 262-70