This work addresses the preparation of ultrathin (effective oxide thickness, 42 Angstrom) interpoly-oxynitride (SiOxNy) films by annealing thin nitride films with high density N2O plasma and N2O rapid thermal annealing. The proposed oxynitride dielectrics formed using N2O plasma annealing exhibited low gate leakage current, high breakdown electric field, long ten-year lifetime, and large effective barrier height. These superior properties can be attributed to the high concentration of oxygen incorporated in the poly-II/nitride interface and a reduction of the trap density of the interpoly-oxynitride films. The dielectric is a suitable substitute for the inter-polyoxide of electrically-erasable programmable read only memory. (C) 2003 The Electrochemical Society.