Small geometry effects in CMOS compatible self-aligned `etched-polysilicon' emitter bipolar transistors

This paper presents a detailed study of the small geomety effects of advanced CMOS compatible polysilicon emitter bipolar transistors. The current gain increase associated with a reduction in device width is a LOCOS proximity effect, leading to a reduction in base doping concentration under the bird's beak. The current gain modification for small emitter lengths has two major causes.: first, a local variation in the emitter-base dopant concentrations introduced by the oxidation step before spacer formation, and the L.D.E.B.(Lightly Doped Extrinsic Base) implantation; second, a geometrical effect due to the recess of the silicon substrate around the emitter.