Boron nitride films were deposited at different substrate temperatures (623-773 K) on Si and quartz (fused silica) substrates by RF plasma chemical vapour deposition technique using borane-ammonia and nitrogen as the precursor gases. FTIR studies indicated the films to contain mixed phases of c-BN and h-BN and the percentage of c-BN (35-53%) was dependent on the deposition environment. The optimum deposition condition for obtaining higher c-BN phase was ascertained. The surface textures of the films were observed by scanning electron microscope and atomic force microscope. The optical properties of the films were studied to determine the optical constants (refractive index and bandgap). (C) 2002 Elsevier Science B.V. All rights reserved.