Vertical scaling of the polysilicon emitter/implanted base structure

Some of the limitations and consequences of scaling the polysilicon-emitter/implanted-base structure in advanced bipolar transistors are explored. It is found that ion implantation for the base below 10 keV is unattractive. It is also found that the collector current of bipolar devices is not independent of the base doping density and/or distribution. For identical base pinch resistances a reduction in collector current is observed for thinner bases. To reduce the emitter depth, the use of low-temperature anneals, possibly in conjunction with rapid thermal annealing, for the emitter outdiffusion is preferred. A higher dopant activation in the polysilicon is obtained, for similar junction depths, than with the use of RTA exclusively, and a better emitter efficiency is obtained