Effect of repetition of plasma nitride oxide integration was examined, because plasma nitrided oxide can be repeatedly used for multiple gate oxide structure and modified substrate technique. More localization of nitrogen on the oxide surface and re-arrangement of nitrogen-less interface are obtained by repetition of plasma nitride oxide integration. The structural and molecular changes in Si/oxide stack result in the improved channel mobility and the comparable saturated drive current. A 70% of gate leakage current density reduction is also obtained without drive current degradation, which is equivalent to about 5% of drive current improvement at a given gate leakage current density. The increase in nitride layer and oxide/interface layer could be estimated by using a schematic oxide thickness model. (c) 2006 Elsevier B.V. All rights reserved.