Plasma enhanced chemical vapor deposition (PECVD) allows low temperature processing and so it is widely used, but it causes instability of devices due to serious amount of impurities within the film. In this paper, electrical and chemical characteristics of the PECVD oxynitride film formed by different N$_{2}$O to N$_{2}$O+NH$_{3}$ gas ratio is studied. It has been found that hydrogen concentration of PECVD oxynitride film was decreased from 4.25*10$^{22}$ [cm$^{-2}$ ] to 1.18*10$^{21}$ [cm$^{-2}$ ] according to the increase of N$_{2}$O gas. It was also found that PECVD oxynitride films have low trap density in the oxide and interface in comparison with PECVD nitroxide films, and has higher refractive index and capacitance than oxide films. In particular, oxynitride film formed in gas ratio of N$_{2}$O/(N$_{2}$O+NH$_{3}$)= 0.88 shows increased capacitance and decreased leakage current due to small portion of hydrogen in oxide and the accumulation of nitrogen about 4[atm.%] at the interface.