Patent ID: 6905943

Claim:
A method for forming a semiconductor structure in manufacturing a semiconductor device, comprising: providing a pad layer on a surface of a substrate; providing a nitride layer on the pad layer; providing a sacrificial oxide layer on the nitride layer; in a first etching step, etching at least the sacrificial oxide and nitride layers to define opposing substantially vertical surfaces of at least the sacrificial oxide and nitride layers; in a second etching step, etching the nitride layer such that the opposing substantially vertical surfaces of the nitride layer are recessed from the opposing substantially vertical surfaces of the sacrificial oxide layer, the sacrificial oxide layer substantially preventing the nitride layer from decreasing in thickness as a result of the etching of the nitride layer; and in a third etching step, etching the substrate to form a trench extending into the substrate for purposes of defining one or more isolation regions adjacent the trench; wherein the first etching step comprises etching the pad layer, in addition to etching sacrificial oxide and nitride layers, to define opposing substantially vertical surfaces of the pad layer; and wherein the first etching step comprises etching a portion of the substrate, in addition to etching the sacrificial oxide, nitride, and pad layers, to define opposing substantially vertical surfaces of the substrate.