Patent ID: 10043825

Abstract:
A method comprises forming shallow trenches in an intrinsic base semiconductor layer and forming a first base layer thereon; applying a first mask to the layer; etching the first base layer; forming a second base layer on the intrinsic base semiconductor layer adjacent the first base layer; removing the first mask; applying a second mask to the base layers; simultaneously etching the layers to produce extrinsic bases of reduced cross dimensions, a length of the second extrinsic base layer being different from a length of the first extrinsic base layer; disposing spacers on the extrinsic bases; etching around the bases leaving the intrinsic base semiconductor layer under the bases and spacers; implanting ions into sides of the intrinsic base semiconductor layer under the extrinsic bases to form emitter/collector junctions; depositing semiconductor material adjacent to the junctions and the trenches; and removing the applied second mask.