We have studied silicon nitride films a-SiN:H deposited at a substrate temperature of 350°C by means of the Low frequency (LF) PECVD from silane and nitrogen as stock gases. Film properties as hydrogen bonding and content, nitrogen content, refractive index and etch rate are reported and analyzed. Our deposited films show physical properties similar to those that are obtained deposition temperatures of 700°C by the low pressure chemical vapor deposition (LPCVD) technique. An investigation of bonding structures for the deposited films was performed, and quantitative results for hydrogen bonding based on Fourier Transform Infrared (FTIR) analysis are presented. It was observed that low hydrogen content in the films is in good correlation with low etch rate in 10% buffered HF solution, therefore these films present a material with good etch selectivity in respect to others materials (as phosphosilicate glass PSG, Al etc). Selectivity which makes these films very promising in surface micromachining for fabrication of sensors and device structures, e.g. microbolometers. Additionally, the Si-N bond at 830-840cm-1 was analyzed because of its big absorption produced at 12μm; therefore these films can be used as absorber layers in uncooled microbolometres.