Patent ID: 7811894

Claim:
A method for manufacturing a bipolar junction transistor comprising: forming a collector region having a first conductivity type in a semiconductor substrate having a second conductivity type; forming a low concentration base region having the second conductivity type in the semiconductor substrate adjacent to the collector region; etching the semiconductor substrate in the low concentration base region to form a trench; depositing a first doped polysilicon layer on an entire surface of the semiconductor substrate, and depositing a first insulating layer on the first doped polysilicon layer; etching the first insulating layer to form a first insulating spacer and etching the first doped polysilicon layer to form a first base region having the second conductivity type; forming a second insulating layer spacer on the first base region; forming an emitter region having the first conductivity type on the second insulating spacer and an exposed bottom surface of trench; forming a third insulating spacer on a sidewall of the emitter region; and forming a second base region having the second conductivity type between opposed portions of the third insulating spacer.