Abstract Cubic boron‐nitride (c‐BN)/hexagonal boron nitride (h‐BN) thin films were grown in situ on (100) oriented silicon substrates by r.f. (13.56 MHz) magnetron sputtering technique. In order to obtain the highest fraction of the c‐BN phase, a negative d.c bias voltage, varying from 0 to –200 V was applied to the substrate during deposition. Another set of boron nitride thin films was deposited in situ on (100) oriented silicon substrates under r.f. bias voltage. The substrate holder was biased from 0 to –350 V by connecting such to an auxiliary r.f. generator (operated at 13.56 MHz). Films were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) and Atomic Force Microscope (AFM). Well‐defined peaks at 787 cm –1 , 1100 cm –1 and 1387 cm –1 , corresponding to the 2 Au (out‐plane bending of B–N–B bond) h‐BN vibration mode, the F2 (stretching) c‐BN Transversal Optical (TO) mode and the E 1u (in‐plane stretching of B–N bond) vibration mode of the h‐BN, respectively, were observed in the FTIR spectra. A maximal fraction of the c‐BN phase close to 85% was obtained under a bias voltage of –150 V at substrate temperature of 300 °C and a total pressure of 4 × 10 –2 mbar. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)