Self-aligned, planar heterojunction bipolar transistor

Abstract

A heterojunction bipolar transistor (HBT) is formed with self-aligned base-emitter and base-collector junctions by forming a two-level mask over a doped base layer, sequentially forming openings in registration through the two mask layers, and using the opening in one mask layer to define the collector region and the opening in the other mask layer to define the emitter. A buried conductive layer formed by a dopant implant establishes an electrical contact to the collector region, and connects to the surface via another conductive implant that extends through a lateral extension of the collector region. The collector region itself is formed by a dopant implant, while the active base region which forms junctions with the emitter and collector is thinner than the remainder of the base layer; the latter feature reduces the resistivity associated with connections to lateral base contacts. Parasitic capacitances are minimized when the collector and buried conductive layers are implanted into a semi-insulating substrate such that only the active junction regions overlap.