Silicon-carbon nitride (SiCN) thin films were deposited on Si substrate at room temperature by r.f. reactive sputtering. Fourier transform infrared spectroscopy (FTIR), optical absorption spectra (alpha(lambda)) and electrical conductivity (sigma) were studied for the thin films. The effect of the annealing on IR and sigma was investigated at different temperatures. IR analysis indicates that Si-H, C-N, Si-C, Si-N, C-N and CdropN bonds are present in a-SiCN:H films. A shift of the stretching mode for Si-H bond to the high-wavenumber side is observed with increasing the nitrogen flow ratio gamma(N2) (=N-2/(Ar + H-2 + N-2 + CH4)). The shift is from 2000 to 2190 cm(-1) when gamma(N2) = 13.7%. The study shows that the film structure and optical and electrical properties are obviously modified readily by controlling the process parameters of deposition. The improvement in the film properties, e.g., good thermal stability, is explained mainly in terms of the cross-linked structure between the Si, C and N atoms. (C) 2002 Elsevier Science B.V. All rights reserved.