Patent ID: 8871599

Claim:
A method of manufacturing an integrated circuit comprising a bipolar transistor, the method comprising: providing a substrate comprising a pair of first isolation regions separated from each other by an active region comprising a collector impurity of said bipolar transistor; forming a base layer stack over said substrate; forming a further stack of a migration layer having a first migration temperature and an etch stop layer over said base layer stack; forming a base contact layer having a second migration temperature over the further stack, the second migration temperature being higher than the first migration temperature; etching an emitter window in the base contact layer over the active region, said etching step terminating at the etch stop layer; at least partially removing the etch stop layer, thereby forming cavities extending from the emitter window in between the base contact layer and the migration layer; and exposing the resultant structure to the first migration temperature in a hydrogen atmosphere, thereby filling the cavities with the migration layer material; wherein the migration layer is formed on the etch stop layer, and wherein said etching step further comprises removing the migration layer from over the active region.