AlN films have been deposited by RF (1.78 MHz) and DC reactive magnetron sputtering (argon and nitrogen) on glass substrates at low temperatures (< 150 degrees C) and with 16, 21 and 30% nitrogen ratios. We have found optically and structurally distinguishable characteristics for films (both opaque and transparent), obtained using these two experimental methods. We suggest that these differences are due to plasma effects in the substrate during growth, resulting from the different ionic bombardment rates of the two sputtering modes.