Use of polysilicon field plates to improve high voltage bipolar device breakdown voltage

Abstract

A method for fabricating a buried layer pinched collector bipolar, (BPCB), device, sharing several process steps with simultaneously formed CMOS devices, has been developed. The BPCB device fabrication sequence features the use of polysilicon field plates,. placed on field oxide regions, in an area of an N well region in which the field oxide regions are located between subsequent P type, base and N type, collector regions. The use of the polysilicon field plates results in an increase in collector—emitter breakdown voltage, as a result of a reduction in the electric field at the surface underlying the polysilicon field plates. The ability to increase collector —emitter breakdowns, via use of only polysilicon field plates, allows the use of higher N well dopant concentrations, thus resulting in increased frequency responses, (Ft), of the BPCB device, when compared to counterparts fabricated with the lower N well dopant concentrations, where the lower N well dopant concentration is needed to achieve the desired, increased collector emitter breakdowns.