Patent ID: 8536002

Claim:
A process of forming an integrated circuit having a bipolar transistor and a metal oxide semiconductor (MOS) transistor, comprising the steps of: providing a substrate comprising a semiconductor; forming a semiconductor collector layer at a top surface of said substrate, such that said collector layer has a first conductivity type; forming field oxide at said top surface of said substrate, so that said field oxide surrounds a collector active area of said bipolar transistor, the field oxide and the collector active area having a boundary therebetween; forming an MOS gate layer in an area for said MOS transistor; forming a base layer of semiconductor material on said collector active area and overlapping said field oxide adjacent to said collector active area, using a non-selective epitaxial growth process, such that said base layer has a polycrystalline region over said field oxide and has a single crystalline region on said collector active area; forming a first implant mask over said integrated circuit, so that at least a portion of said MOS gate layer is exposed, and so that the single crystalline region of said base layer is covered, and so that a first portion of the polycrystalline region of the base layer is exposed and a second portion of the polycrystalline region of the base layer is covered; performing an MOS gate layer ion implantation process so as to implant dopants of a second conductivity type opposite from said first conductivity type into portions of said MOS gate layer and said base layer which are exposed by said first implant mask, so as to form a gate implanted region in said MOS gate layer and a first base implanted region in said base layer over said field oxide; forming an emitter of said bipolar transistor on said single crystalline region of said base layer, said emitter having said first conductivity type; and performing a thermal operation on said integrated circuit, so as to cause said dopants implanted in said polycrystalline region of said base layer to diffuse toward said single crystalline region so that a base-collector junction of said bipolar transistor extends into said substrate less than one-third of a depth of said field oxide.