Self-aligned Ti germanosilicide formation on a polycrystalline Si/SiGe/Si extrinsic base for SiGe heterojunction bipolar transistors

This work reports our investigation of a microstructure of self-aligned Ti germanosilicide made on polycrystalline Si/SiGe/Si multilayers. The existence of the SiGe layer restricted the growth of the Ti germanosilicide layer and produced protrusions penetrating the underlying polycrystalline layer. Each protrusion corresponded to a stacking-faulted single grain of the C49 phase. The microstructure of the thin Ti germanosilicide layer and the deep protrusions caused an increase of the sheet resistance and the contact resistivity of the extrinsic base region. The raised contact resistivity led to a degradation of radio frequency (RF) and noise characteristics of the SiGe heterojunction bipolar transistor (HBT).