Patent ID: 7759216

Claim:
A method for forming a trench isolation, the method comprising: sequentially forming a pad oxide layer and a pad nitride layer on a semiconductor substrate; coating a photoresist layer on the pad nitride layer and selectively etching the photoresist layer to form a photoresist trench pattern layer; etching the pad oxide layer and the pad nitride layer using the photoresist trench pattern layer as a mask so that an area of the semiconductor substrate is exposed in an area corresponding to an opening of the photoresist trench pattern layer; forming a buffer oxide layer on the exposed area of the semiconductor substrate; implanting nitrogen ions into the exposed area of the semiconductor substrate and the buffer oxide layer to form a nitrogen ion-implanted layer, wherein the buffer oxide layer is provided so as to allow the nitrogen ions to be distributed substantially evenly in the area of the substrate having the nitrogen ion-implanted layer; extending the nitrogen ion-implanted layer beyond the exposed area toward both sides and bottom surface of the semiconductor substrate to form a nitride film; removing the nitride film and buffer oxide layer, leaving a recess in the semiconductor substrate in the area where the nitride film was formed; performing an etching process in the recess to form a trench including a top rounded corner portion; and filling the trench with an oxide layer to form a trench isolation.