On the narrow-emitter effect of advanced shallow profile bipolar transistors

This paper presents a detailed study on the narrow-emitter effect of advanced shallow-profile bipolar transistors. The physical mechanisms behind both the base current and collector current modifications caused by the lateral encroachment of the extrinsic base are investigated. It is shown that in addition to a reduction in the active device area due to the lateral encroachment of extrinsic base into the intrinsic base area, the emitter polysilicon-single crystal interface (bulk property of the polysilicon emitter) and the junction curvature of the emitter/extrinsic-base intercept (perimeter property) also play important roles in determining the current gain for narrow emitter bipolar transistors. The implications on the device and process design for future scaled-down devices are discussed.