Semiconductor device and a method of fabricating the same

Abstract

A semiconductor fabrication process for forming a shield-plate electrode or a gate electrode in a trench to have the same conductivity type with each of adjacent p- and n-well regions includes steps for forming a trench in a semiconductor substrate by using a silicon nitride mask, forming an oxide film on the bottom of the trench, and filling a polysilicon film on the oxide film. In a selected region, outside the trench, an impurity of a desired conductivity type is doped by ion implantation to a predetermined depth of the semiconductor substrate. An impurity of the same conductivity type is further doped into the polysilicon film by shallowing the implantation level. In the adjacent region, an impurity of the opposite conductivity type is also doped into the polysilicon film and the semiconductor substrate outside the trench at different implantation levels. Annealing is performed to form a trench filled with p-type polysilicon in the p-well region and a trench filled with n-type polysilicon in the n-well region. The polysilicon in each trench is processed into a shield-plate electrode or a gate electrode.