In this paper, we report a process for the preparation of high quality amorphous tantalum oxynitride (TaOxNy) via ammonia annealing of Ta2O5 followed by wet reoxidation for use in gate dielectric applications. Compared with tantalum oxide(Ta2O5), a significant improvement in the dielectric constant was obtained by the ammonia treatment followed by light reoxidation in a wet ambient. We confirmed nitrogen incorporation in the tantalum oxynitride (TaOxNy) by Auger Electron Spectroscopy. By optimizing the nitridation and reoxidation process, we obtained an equivalent oxide thickness of less than 1.6nm and a leakage current of less than 10mA/cm2 at -1.5V. Compared with NH3 nitridation, nitridation of Ta2O5 in ND3 improve charge trapping and charge-to-breakdown characteristics of tantalum oxynitride.