Fabrication of a bipolar transistor with a polysilicon ribbon

Abstract

In the fabrication of bipolar transistors by the single poly process, polysilicon sidewalls are formed along portions of a polysilicon layer that functions as a device contact. The sidewalls serve both as dopant sources which determine the width of underlying base and emitter regions, and as contacts to those devices. Since the thickness of the polysilicon sidewalls, and hence the width of the underlying device regions, are precisely controllable through conventional polysilicon deposition techniques, relatively relaxed design rules can be employed while making possible the formation of emitters having widths less than one-half of a micron.