A comparative study of indium and boron implanted silicon bipolar transistors

The use of indium as base dopant offers potential advantages of high curren t gain and high current gain-Early voltage product due to the impurity free ze-out effect for indium, thus providing extended design space for analog a nd mixed signal applications. In this work, we present characteristics of i ndium and boron implanted base npn transistors. In particular, we discuss t he potential advantages and tradeoffs by utilizing indium implant as the ba se dopant based on experimental results. Device performance enhancement, ke y device parameter sensitivity to process conditions, device scaling, and p ossible implications to high speed applications are addressed. Our study de monstrates that indium implanted base bipolar transistors exhibit excellent h(FE)-V-A product (> 24000) performance which is comparable to that of SiG e HBT's and good collector-emitter breakdown characteristics (BVCEO similar to 5 V) as compared with those for boron base devices (h(FE)-V-A similar t o 3600 and BVCEO similar to 5.5 V). At the same time, experimental results suggest that issues associated with indium implanted base devices such as h igh base resistance (> x 10 boron-base npn), basewidth profile, and key par ameter sensitivity to implant conditions (high variations) must be addresse d in order to fully utilize the potential advantages of indium implanted ba se bipolar devices.