Patent ID: 7078315

Claim:
A method for fabricating a semiconductor DRAM device, comprising: providing a first conductivity type semiconductor substrate; depositing a pad layer over the semiconductor substrate, the pad layer having an opening exposing the semiconductor substrate; etching the semiconductor substrate through the opening to form an isolation trench and an active island in the semiconductor substrate; depositing a non-doped sacrificial layer over the active island and the non-doped sacrificial layer filling the isolation trench; etching back the non-doped sacrificial layer to a depth of the isolation trench, thereby exposing a corner portion of the active island; depositing a dielectric layer doped with first conductivity type dopants over the remaining non-doped sacrificial layer and covering the exposed corner portion of the active island; and performing a thermal diffusion to diffuse the first conductivity type dopants of the dielectric layer into the corner portion of the active island to form a first conductivity type diffusion region at the periphery of the active island in a channel width direction.