Semiconductor memory device having isolation structure and method of fabricating the same

Abstract

A fabrication method for a semiconductor memory device having an isolation structure which includes the steps of forming a pad oxide film on a semiconductor substrate, forming a first nitride film on the pad oxide film, patterning the first nitride film and the pad oxide film, forming an oxynitride film on a portion of the substrate externally exposed by the patterning step, forming side walls of a second nitride film on sides of the first nitride film, removing a portion of the oxynitride film using the side walls as a mask, forming a field oxide film on an exposed portion of the substrate, and removing the remaining pad oxide film, first nitride film, second nitride film, and oxynitride film. The first nitrate film and the pad oxide film may be patterned such that the pad oxide film is undercut to expose more of the substrate and to allow formation of the oxynitride film under the first nitride film. As such, the first nitride film can be used as a mask, rendering unnecessary the formation of side walls. The method simultaneously employs an oxide film and an oxynitride film to decrease a bird's beak generation while minimizing stress resulting from the oxynitride film.