Bipolar transistor process using sidewall spacer for aligning base insert

Abstract

An improved method for fabricating a bipolar transistor reduces base current resistance which heretofore has limited the switching frequency and current handling ability of bipolar transistors. The transistor base and emitter are formed as a diffusion through an emitter contact pedestal formed on an epitaxial layer over a substrate. Access to the n-type emitter is through the emitter contact pedestal while access to the lightly doped p-type base is through a nearby heavily doped p-type base insert. Electrical isolation between the pedestal and the base insert is ensured by forming oxide sidewall spacers on the emitter contact pedestal during the implant used to form the base insert. Defining the isolation with sidewall spacers permits reliable isolation of emitter and base insert while minimizing their physical separation. The minimized physical separation provides a base current path with considerably less total resistance than is found in the background art in which the isolation is defined photo-lithographically.