Semiconductor device having inter-poly oxide layer between gate polysilicon and shield polysilicon and method of forming a semiconductor device

Abstract

A method of forming a semiconductor device includes: disposing an isolation oxide layer and a shield polysilicon in trenches formed in a substrate, with the shield polysilicon being partially surrounded by the isolation oxide layer; etching the isolation oxide layer; disposing an inter-poly oxide (IPO) layer on an upper surface of the shield polysilicon with the IPO layer laterally surrounded in the trenches by the isolation oxide layer; etching the IPO layer and the isolation oxide layer; lining at least upper sidewalls of the trenches with a gate oxide layer; disposing a gate polysilicon on an upper surface of the IPO layer and on an upper surface of the isolation oxide layer, with the gate polysilicon laterally surrounded by the gate oxide layer; etching the isolation oxide layer so that a thickness of the isolation oxide layer tapers from the shield polysilicon a top opening of the trench.