Patent ID: 7465638
Filing Date: 2008-12-16
Classification: H01L

Abstract:
1. A method of forming a bipolar transistor, said method comprising: forming a base region of a first conductivity type in a collector region of a second conductivity type, wherein the collector region is formed on a substrate of the first conductivity type; forming a first silicon layer of the second conductivity type on the base region using a first formation process; forming a second silicon layer of the second conductivity type on the first silicon layer using a second formation process which is different than the first formation process; wherein the secon silicon layer of the second conductivity type barely influences the formation of the emitter region outdiffusing impurities from the first silicon layer into the base region to form an emitter region, wherein outdiffusion of impurities of the second silicon layer into the base region is inhibited by the first silicon layer interposed between the second silicon layer and the base region.