Elimination of oxynitride (ONO) etch residue and polysilicon stringers through isolation of floating gates on adjacent bitlines by polysilicon oxidation

摘要

A method for fabricating a first memory cell and a second memory cell having floating gates electrically isolated from each other. A first polysilicon (poly I) layer is formed on an oxide coated substrate, portions of the poly I layer to serve as future floating gates for the first and second memory cells. An interpoly dielectric layer is formed over the poly I layer. At least a portion of the interpoly dielectric layer is etched to expose at least a portion of the poly I layer so as to pattern the floating gates on either side of the exposed portion of the poly I layer. The exposed portion of the poly I layer is transformed into an insulator via thermal oxidation such that the insulator electrically isolates a floating gate of the first memory cell from a floating gate of the second memory cell. A second polysilicon (poly II) layer is formed substantially free of abrupt changes in step height.