Method of fabricating a shallow trench isolation by using oxide/oxynitride layers

Claim 1

A method of forming trench isolations in a silicon wafer, said method comprising: forming a first oxide layer on said silicon wafer to act as a pad oxide layer; forming a silicon nitride layer on said pad oxide; forming a second oxide layer on said silicon nitride layer; forming a silicon oxynitride layer on said second oxide layer; patterning said silicon oxynitride layer, said second oxide layer and said silicon nitride layer to expose said first oxide layer to define areas for forming said trenches; forming oxide spacers on the side walls of said said second oxide layer and said silicon nitride layer, wherein said silicon oxynitride layer being removed during the formation of said oxide spacers; etching said wafer to generate said trenches by using said second oxide layer, said silicon nitride layer and said oxide spacers as an etching mask; removing said oxide spacers and said second oxide layer, leaving said silicon nitride layer and said first oxide layer over said wafer; performing a thermal oxidation step for rounding the corners of said trenches; forming a gap filling material refilled into said trenches and over said silicon nitride and said first oxide layer; performing a chemical mechanical polishing to remove a portion of said gap filling material and leaving a portion of said silicon nitride layer and said first oxide layer over said wafer; removing said portion of said silicon nitride layer; and immersing said wafer in a wet etching solution to remove a portion of said gap filling material over a surface of wafer, and removing said portion of said first oxide layer, thereby generating said trench isolations with rounding corners.

Claim 2

A method of forming trench isolations in a silicon wafer, said method comprising: forming a first oxide layer on said silicon wafer to act as a pad oxide layer; forming a silicon nitride layer on said pad oxide; forming a second oxide layer on said silicon nitride layer; forming a silicon oxynitride layer on said second oxide layer; patterning said silicon oxynitride layer, said second oxide layer and said silicon nitride layer to expose said first oxide layer to define areas for forming said trenches; forming oxide spacers on the side walls of said said second oxide layer and said silicon nitride layer, wherein said silicon oxynitride layer being removed during the formation of said oxide spacers; etching said wafer to generate said trenches by using said second oxide layer, said silicon nitride layer and said oxide spacers as an etching mask; removing said oxide spacers and said second oxide layer, leaving said silicon nitride layer and said first oxide layer over said wafer; performing a thermal oxidation step for rounding the corners of said trenches; forming a gap filling material refilled into said trenches and over said silicon nitride and said first oxide layer; performing a chemical mechanical polishing to remove a portion of said gap filling material and leaving a portion of said silicon nitride layer and said first oxide layer over said wafer; removing said portion of said silicon nitride layer; and immersing said wafer in a wet etching solution to remove a portion of said gap filling material over a surface of wafer, and removing said portion of said first oxide layer, thereby generating said trench isolations with rounding corners.