Design considerations of high-performance narrow-emitter bipolar transistors

The control of the lateral diffusion of the extrinsic base is a key issue in the downscaling of high-speed bipolar transistors for achieving the lowest base resistance without altering the shallow impurity profile of the intrinsic region. This letter will present the effects of lateral encroachment of the extrinsic-base dopant on the characteristics of transistors with submicrometer emitter stripe width, measurement of the amount of encroachment, and its relationship to the vertical profile.