Self-aligned dual-base semiconductor process and structure incorporating multiple bipolar device types

Abstract

A semiconductor process is disclosed which forms openings in a dielectric layer through which the base region of both high-voltage and high-gain bipolar transistors are formed. In one embodiment of the invention, the openings for the high-gain transistors are first protected by a photoresist layer that is patterned to expose the openings for the high-voltage transistors. A first base implant is performed through the exposed windows in the dielectric layer and into the exposed substrate or epitaxial layer therebelow, and then diffused to a suitable depth. The patterned photoresist is then removed to additionally expose the openings for the high-gain devices, and a second base implant is performed, this time into both base regions, and then diffused to a suitable depth. Emitter regions are then formed within the base regions of both transistor types by traditional implantation and contact techniques. Since the two base implants for each high-voltage transistor are self-aligned to a single opening through the dielectric layer, excellent control and repeatability is achieved for the high-voltage transistors. Moreover, since the second base implant is common to both types of transistors, many of the characteristics of the two types of transistors are well matched to each other.