Optimisation of a Link Base Implant for Reducing the Access Base Resistance of Single-Poly Quasi Self-Aligned Bipolar Transistors

In this paper we will present and discuss the improvements on electrical performances that can be obtained in single-polysilicon quasi self-aligned BJTs of a 0.5¿m BiCMOS technology by adding a link base implant (LB), i.e. a boron implant self aligned to the polysilicon emitter edge before the formation of sidewall spacers. An accurate and extensive electrical characterization has been carried out: statistical measurements, DC, AC, and high frequency measurements, base resistance extraction based on the impact ionization method will be widely discussed. By adding the LB implant, a good decrease in the base resistance is observed, which in turn improves the BJT noise performances. The reliability of the LB devices remains unchanged compared to the reference ones, as well as the high frequency performances.