Emitter Scaling of Single-Polysilicon SiGe:C HBTs with Highly Doped Base Layers

We demonstrate that single-polysilicon SiGe:C heterojunction bipolar transistors with a very thin, highly doped SiGe layer can be scaled in the emitter width to 0.4 μm and in the emitter overlap to 0.2 μm without any indications of B outdiffusion from the SiGe:C base. Thus, transistors can be fabricated with excellent low-power performance, reaching an fmax of 40 GHz at a collector current of 10 μA. We report also a reduction in the IB-driven Early voltage for devices with small overlap due to a perimeter component of the base current, originating from the external base, or the base contact region.