Abstract: A method for fabricating a silicon dioxide/silicon nitride/silicon dioxide (ONO) stacked composite having a thin silicon nitride layer for providing a high capacitance interpoly dielectric structure. In the formation of the ONO composite, a bottom silicon dioxide layer is formed on a substrate such as polysilicon. A silicon nitride layer is formed on the silicon dioxide layer and is thinned by oxidation. The oxidation of the silicon nitride film consumes some of the silicon nitride by a reaction that produces a temporary silicon dioxide layer. The temporary silicon dioxide layer is removed with a hydrofluoric acid dilution. The silicon nitride layer is again thinned by re-oxidization as a top silicon dioxide layer is formed on the silicon nitride layer. A layer of polysilicon is deposited over the silicon nitride, forming an interpoly dielectric.