On the impurity profiles of down scaled bipolar transistors

This paper presents the design and reliability issues unique to the scaled bipolar devices, which are caused by the close proximity of the heavily doped emitter and extrinsic base region and by the contradicting heat cycle requirement for the extrinsic base and intrinsic base. Issues related to the premature punchthrough, leakage around the emitter perimeter, long-term current gain degradation and the control of thin base are discussed.