Boron nitride films were deposited by unbalanced RF magnetron sputtering of a sintered hexagonal boron nitride (h-BN) target in an argon and nitrogen mixture working atmosphere with a pulsed DC bias applied to the substrate. The microstructure of the films was analyzed by reflective Fourier transform infrared (FTIR) spectroscopy. The three main absorption peaks observed on the FTIR spectra, i.e. the two h-BN peaks at approximately 1380 and 780 cm(-1), and the cubic phase (c-BN) peak at approximately 1080 cm(-1), were used to characterize the film structure. The variation of the 17TIR spectra with different deposition parameters, including substrate bias voltage, substrate temperature, working gas composition and RF target power, was systematically investigated. It was observed that there existed a threshold bias voltage above which the c-BN started-to form. The c-BN content in the film increased with the increase of the bias voltage. A relatively higher substrate temperature favored the c-BN formation. In the range of the deposition conditions investigated, the highest c-BN content, up to 75%, was obtained in the film deposited at 400 degreesC under a bias voltage of 150 V in the working atmosphere of N-2 to Ar ratio of 1:5 using RF target power of 800 W (C) 2003 Elsevier Science B.V. All rights reserved.