Patent ID: 7514337

Claim:
A method of forming a semiconductor device, comprising the steps of: forming a pad oxide film and a nitride film on a semiconductor substrate; exposing the semiconductor substrate by selectively etching the pad oxide film and the nitride film; forming a trench in the exposed semiconductor substrate; forming a gap-fill dielectric film in the trench; removing the nitride film by wet etching; forming a plurality of ion implantation regions by performing a well ion implantation, a channel-stop ion implantation, and a punch through ion implantation into the semiconductor substrate after forming the gap-fill dielectric; exposing an active area of the semiconductor substrate by removing the pad oxide film; forming an epitaxial layer containing a dopant in the exposed active area by epitaxial growth, the epitaxial layer interfacing with the gap-fill dielectric film and containing sufficient dopant to control a threshold voltage of the semiconductor device; forming a gate conductive layer on a gate dielectric film on the epitaxial layer; forming a gate electrode by patterning the gate conductive layer; and forming a source region and a drain region in the active area beside the gate electrode.