Patent ID: 8404547

Claim:
A manufacturing method for a semiconductor device including a field effect transistor having a LOCOS offset, the manufacturing method comprising: forming a sacrificial oxide film on a semiconductor substrate having a first conductivity type; forming a nitride film on the sacrificial oxide film, etching only a target region of the nitride film; forming an offset diffusion layer having a second conductivity type through ion implantation; forming a LOCOS oxide film on the region in which the nitride film is etched; removing the nitride film and the sacrificial oxide film; forming a gate oxide film on a surface of the semiconductor substrate, forming a polycrystalline silicon film on the gate oxide film, and etching only a target region of the polycrystalline silicon film; forming a heavily-doped diffusion layer having a second conductivity type through ion implantation, the heavily-doped diffusion layer serving as a drain diffusion layer; etching a part of the LOCOS oxide film adjacent to the drain diffusion layer so as to reduce a film thickness of the LOCOS oxide film toward the drain diffusion layer, wherein an end of the LOCOS oxide film on a drain diffusion layer side is formed in a round shape; and wherein an end of the drain diffusion layer adjacent to the LOCOS oxide film is formed to extend into the offset diffusion layer to cover a region where the part of the LOCOS oxide film is etched, and an impurity concentration of the end of the drain diffusion layer adjacent to the LOCOS oxide film is lower than an impurity concentration of a center portion of the drain diffusion layer.