Integratable and low base resistance Si/Si1-xGex heterojunction bipolar transistors using selective and non-selective rapid thermal epitaxy

We report a new Si/SiGe HBT device structure using selective and non-selective rapid thermal epitaxy. The structure has the potential to simultaneously provide for high level integration and a high Ge fraction strained alloy base which allows high base doping. We used an in-situ As doped polysilicon emitter contact to provide low R_E (9 to 12 Ω for A_E=0.5×10 μm²) without the enhanced diffusion effects associated with direct implantation or phosphorous doped poly emitters. In addition, we studied the effects of the extrinsic base implant position on the device I-V characteristics, junction capacitances, and high frequency performance. The collector current increased by over 3 decades as the extrinsic base implant position moved from the single crystal region to an adjacent poly region due to the containment of damage. S-parameter measurements of a 0.5×10 μm² device yielded a cutoff frequency of 54 GHz for V_CE=1.5 V and I_C=14.8 mA