Patent ID: 7199012

Claim:
A method for forming a trench in a semiconductor device comprising: forming a pad oxide film and a silicon nitride film on a silicon wafer; forming a first photosensitive film pattern on the region to be formed with the trench by applying, exposing, and developing a photosensitive film on the silicon nitride film; selectively etching the silicon nitride film and the pad oxide film on a region to be formed with a trench using the first photosensitive film pattern as a mask; forming a second photosensitive film pattern having an opening portion of a width narrower than that of an opening portion of the first photosensitive film pattern on the silicon nitride film and the exposed silicon wafer, the opening portion of the second photosensitive film pattern having a center axis as the opening portion of the first photosensitive film pattern; implanting oxygen ions into the silicon wafer in the region to be formed with the trench at a desired depth of the trench using the second photosensitive film pattern as a mask; forming an oxide in the silicon wafer by reacting the oxygen ions with the silicon wafer through a thermal diffusion of the oxygen ions; forming the trench by etching the silicon wafer and the oxide on the region to be formed with the trench using the silicon nitride film as a mask; forming a liner oxide film on an inner wall of the trench using a thermal diffusion process; and forming an insulation film on the liner oxide film such that the trench is filled, wherein an edge at which a side end a bottom of the trench intersect has a curved surface.