Patent ID: 6767798
Filing Date: 2004-07-27
Classification: H01L

Abstract:
A method of forming a bipolar transistor, comprising:providing a substrate; forming a first epitaxial layer over the substrate to form a base region having an intrinsic base region and an extrinsic base region; forming an emitter stack over the substrate including forming a first oxide layer over the first epitaxial layer, forming a first nitride layer over the first oxide layer, forming a second oxide layer over the first nitride layer, patterning an emitter mask layer over the second oxide layer, selectively etching the second oxide layer and the first nitride layer to form an emitter window, ion implanting through the emitter window, wherein the ion implant is a self-aligned collector implant, forming a polysilicon layer over the substrate, etching back the polysilicon layer, wherein the top surface of the polysilicon layer is coplanar with or recessed below the top surface of the second oxide layer, and selectively removing the second oxide layer to expose an emitter polysilicon structure; and, raising the extrinsic base region by forming a second epitaxial layer on the first epitaxial layer.