A comparative study of indium and boron implanted silicon bipolar transistors

The use of indium as base dopant offers potential advantages of high current gain and high current gain-Early voltage product due to the impurity freeze-out effect for indium, thus providing extended design space for analog and mixed signal applications. In this work, we present characteristics of indium and boron implanted base npn transistors. In particular, we discuss the potential advantages and tradeoffs by utilizing indium implant as the base dopant based on experimental results. Device performance enhancement, key device parameter sensitivity to process conditions, device scaling, and possible implications to high speed applications are addressed. Our study demonstrates that indium implanted base bipolar transistors exhibit excellent h_FE-V_A product (>24000) performance which is comparable to that of SiGe HBT´s and good collector-emitter breakdown characteristics (BV_CEO~5 V) as compared with those for boron base devices (h_FE-V_A~3600 and BV_CEO ~5.5 V). At the same time, experimental results suggest that issues associated with indium implanted base devices such as high base resistance (>x10 boron-base npn), basewidth profile, and key parameter sensitivity to implant conditions (high variations) must be addressed in order to fully utilize the potential advantages of indium implanted base bipolar devices