With the continued growth of photonics, silicon oxynitride (SiO xN y) is becoming a popular material for optoelectronic applications owing to its large tunable refractive index. However, with the increase in refractive index, these films tend to show poor optical transmission characteristics. In this research we have investigated the influence of growth conditions on the loss characteristics of PECVD SiO xN y films. The films are grown at 350°C substrate temperature and 1 Torr pressure with silane (SiH 4) and nitrous oxide (N 2O) precursor gases. The precursor flow rate and power input to the system are varied as the two primary parameters. It is observed that films grown at 100 kHz plasma frequency proved to be more transmissive than films grown at 13.56 MHz plasma frequency. Elastic recoil detection analysis results showed the hydrogen content is less in the low frequency films than the high frequency films, which is believed to be the reason for the low loss behavior. The details of these analysis results are discussed below. © 2005 Materials Research Society.