Selective SiGeC epitaxy by RTCVD for high performance self-aligned HBT

Selective SiGeC epitaxy is desirable for forming the base of self aligned HBTs. Carbon, incorporated into substitutional sites (C/sub s/), should suppress boron outdiffusion in the base. We show that C/sub s/ incorporation is decreased as temperature or total C concentration is increased, leading to defects in the epitaxy and degradation of the base current. Nevertheless, we were able to grow, selectively, high quality SiGeC films with a C dose high enough to block boron diffusion. This is confirmed by the comparison of static and dynamic results between a C-free and a C-doped SiGe HBT Finally, a state of the art 175 GHz ft/180 GHz f/sub MAX/ HBT with a selective epitaxial SiGeC base is presented.