Fluorinated silicon nitride films deposited from SiF4/NH3 gas mixtures by PACVD at two different frequencies have been investigated. At 13.56 MHz, low deposition rate was detected and no appreciable changes were observed when the deposition parameters varied in a wide range. On the contrary, higher deposition rates were achieved when a 35 KHz frequency was applied. These low frequency silicon nitride films showed an increase in the fluorine content In their structure when the SiF4 flow ratio in the gas mixture was increased, as detected by analytical resolution of the IR spectra. In addition, analysis of the plasma emission spectra has been performed in order to explain the effect of the plasma frequency in the deposition process.