Silicon nitride films were prepared at low mixed Ar-N-2 pressure in the substrate temperature range of 17-700 degreesC by reactive magnetron sputtering. X-Ray reflectivity, atomic force microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the films. It was found that these films had almost the same structure, composition (Si3N4) and density although they were prepared at quite different substrate temperatures. These films had a very high density (similar to3.1 g/cm(3)) and a very low surface roughness (similar to 0.2 nm). Analyses of the results suggest that at low pressure, the bombardment of energetic particles, together with the effect of an angle between the target and the substrate normal, may provide more contribution to the mobility of deposited ad-species than substrate temperatures. So at both low and high temperatures, smooth and dense Si3N4 films can be prepared by radio frequency magnetron sputtering.