Process for forming device isolation region

摘要

A process for forming a device isolation region comprising the steps of: forming a pad oxide film and a silicon nitride film on a semiconductor substrate; removing the pad oxide film and the silicon nitride film on a region for device isolation and forming a trench in the semiconductor substrate by etching using the remaining pad oxide film and silicon nitride film as an etching mask; forming a first oxide film at least on the bottom and sidewalls of the trench and below the pad oxide film under an end portion of the silicon nitride film using the silicon nitride film as a mask resistant to oxidization; forming a gap between the silicon nitride film and the semiconductor substrate by removing the first oxide film on the bottom and the sidewalls of the trench and the first oxide film and the pad oxide film below the end portion of the silicon nitride film by etching using the silicon nitride film as an etching mask; forming a second oxide film at least on the bottom and the sidewalls of the trench and in the gap using the silicon nitride film as a mask resistant to oxidization; and forming a third oxide film so as to fill the trench, thereby to form a device isolation region.