Patent ID: 6872619

Claim:
A method for forming a semiconductor device having a trench top isolation layer, comprising the steps of: providing a substrate having at least one trench therein; forming a collar insulating layer over the sidewall of a lower portion of the trench; forming a first conductive layer protruding to the collar insulating layer in the lower portion of the trench; forming a second conductive layer overlying the first conductive layer and covering the collar insulating layer; forming an insulating spacer over an upper portion of the sidewall of the trench and separated from the second conductive layer by a gap; thermally oxidizing a portion of the second conductive layer to form an oxide layer thereon whereby the gap is filled; removing the oxide layer to expose the second conductive layer; forming a reverse T-shaped insulating layer by chemical vapor deposition to serve as the trench top isolation layer; and removing the insulating spacer.