Bipolar junction transistors having an increased safe operating area

Abstract

A bipolar junction transistor includes a semiconductor substrate having a surface, a base region of first conductivity type in the substrate, and an emitter region of second conductivity type extending from the surface into the base region to form a generally concave semiconductor junction having an apex oriented towards the surface. The emitter region preferably includes a plurality of contiguous emitter subregions extending from the surface into the base region in an arcuate manner and merging to form the generally concave semiconductor junction. The transistor preferably includes an emitter terminal electrically contacting the emitter region at an emitter contact area on the surface, the emitter contact area having a central portion substantially centered with respect to the apex of the semiconductor junction. To produce the bipolar junction transistor, a base layer of first conductivity type is provided in a semiconductor substrate, ions of second conductivity type implanted through the base layer surface in portions of the base layer surface increasing in area from a central portion of the base layer surface laterally towards outer portions of the base layer surface, and the implanted ions diffused into the base layer to thereby create the emitter region and the concave semiconductor junction. Preferably, the ions are implanted by depositing an oxide or other masking layer on the base layer, selectively etching the masking layer to expose the plurality of surface portions, and then implanting the ions into the exposed surface portions.