Investigation of Disilane-Based SiGe-HBT Layers for Low External Base Resistances

Abstract

In this work we study different SiGe epitaxial processes for the base realization of a heterojunction bipolar transistor. In particular we investigate the poly SiGe layer of external base contact region. Silane (SiH4) and disilane (Si2H6) based precursors were used for a chemical vapour deposition (CVD) process of the Si/SiGe/Si layer stack. Sheet resistances of the poly SiGe layer as well as the boron doping and germanium distribution before and after different rapid thermal annealing steps were analyzed. We show that for equal doping profiles in the single crystalline region and minor differences in the thickness of the poly SiGe region the use of a disilane based precursor is beneficial for a reduced external base resistance. Sheet resistance measurements a decrease by more than 60% with respect to the standard silane based SiGe layer.