Patent ID: 6864532

Claim:
A semiconductor device comprising: a semiconductor substrate having a surface in which a trench is formed, wherein the trench has a wall; a heavily doped region, which is formed in the wall at an end of the trench, wherein the heavily doped region is doped with an impurity to increase the oxidization speed of the heavily doped region; a stack of films formed on the wall, wherein the stack includes: a first silicon oxide film, wherein the thickness of the first silicon oxide film is greater at the end of the trench than elsewhere; a silicon nitride film; and a second silicon oxide film, and a gate electrode formed on the films an entrance silicon oxide film, the thickness of which is greater than that of the stack, wherein the entrance silicon oxide film is located at an entrance of the trench; and a bottom film, the thickness of which is greater than that of the stack, wherein the bottom film is located at a bottom of the trench.