Quasi self-aligned single polysilicon bipolar active device with intentional emitter window undercut

摘要

An emitter stack for a quasi-self-aligned bipolar (NPN or PNP) transistor is formed where two layers over the emitter of a silicon substrate are windowed in a manner to under cut the top layer thereby exposing the substrate material. The emitter polysilicon structure is then formed over the window and conformally extends into the undercut region thereby widening the emitter region and so reducing the distance between the edge of the emitter and the extrinsic base (the base link distance) and therefore reducing the total base resistance of the transistor.