Patent ID: 9698237
Date: 2017-07-04
CPC Classifications: H01L

Claim:
1. A method for fabricating a lateral bipolar transistor, comprising: providing a semiconductor substrate of a first conductivity type; forming a first buried layer of the first conductivity type and a second buried layer of a second conductivity type in the substrate, the second conductivity type being opposite the first conductivity type, the first buried layer being located under a trench isolation structure and the second buried layer being located under a base region; forming an epitaxial layer of the second conductivity type on the substrate; forming a dielectric masking layer over the epitaxial layer; forming first and second trenches in the dielectric masking layer and the epitaxial layer; removing the dielectric masking layer; forming a second dielectric layer over the epitaxial layer and in the first and second trenches; isotropically etching the second dielectric layer to leave the second dielectric layer on a top surface of the epitaxial layer and on a bottom portion of each trench; forming a polysilicon layer over the second dielectric layer and in each trench, the polysilicon layer being heavily doped with the first conductivity type; patterning the polysilicon layer to form polysilicon regions associated with each trench and to form an extended portion of the polysilicon layer of the first trench over the second dielectric layer and extending over a portion of the base region, the extended portion of the polysilicon layer of the first trench formed over the dielectric layer functioning as a field plate for the base region to shield the base region from electrostatic build-up in the overlying dielectric layer; and annealing the epitaxial layer and the polysilicon layer to form by dopant out-diffusion first and second diffusion regions of the first conductivity type in the epitaxial layer surrounding only the sidewalls of respective first and second trenches, the polysilicon layer of each trench being in electrical contact with the respective diffusion region surrounding sidewalls of the respective trench, wherein an emitter region is formed in the first trench and the first diffusion region, a collector region is formed in the second trench and the second diffusion region, the base region being formed in the epitaxial layer between the first and second diffusion regions associated with the first and second trenches.