We incorporated significant density of nitrogen only near the top surfaces of the thermally grown oxides by the fluorination at room temperature followed by atomic nitrogen treatment around 550°C. Average nitrogen concentration of more than 6 percent was obtained in the nitrided layer with thickness below 1 nm. We fabricated MOS devices using the nitrided oxide films without hydrogenation, and measured capacitance-voltage characteristics. The density of nitridation-induced interface defects in the MOS device was estimated to be below 2×1010 cm−2. The proposed technique identifies a unique process for obtaining high quality ultrathin dielectrics.