This paper addresses fabrication aspects of SiGe heterojunction bipolar transistors which record high-speed performance. We previously reported fT values of 505 GHz, fMAX values of 720 GHz, and ring oscillator gate delays of 1.34 ps for these transistors. The impact of critical process steps on radio frequency performance is discussed. This includes millisecond annealing for enhanced dopant activation and optimization of the epitaxial growth process of the base layer. It is demonstrated that the use of a disilane precursor instead of silane can result in reduced base resistance and favorable device scalability.
