Reduction of Base Resistance and Increase in Cutoff Frequency of Si Bipolar Transistor Using Rapid Vapor-Phase Doping

Abstract

The shallow intrinsic base region of a double poly-Si self-aligned bipolar transistor was formed by rapid vapor-phase doping (RVD) in order to increase the high-frequency performance, compared to that provided by low-energy BF2 ion implantation. RVD produced a transistor with fT of 50-GHz and rb of 400-Ω. These parameters are 20% higher and 15% lower than those of a transistor produced by BF2 implantation. Low base resistance also led to an increase in the maximum oscillation frequency fmax to over 40 GHz in transistors with longer emitter. A two-dimensional profile simulation clarified that RVD can form a shallower intrinsic base profile and a deeper link base profile than those formed by BF2 ion implantation. These doping profiles made it possible to increase fT and fmax, and to reduce rb simultaneously.