The attainment of cubic boron nitride by physical vapour deposition methods is influenced by several parameters. We present new results obtained at about 343 K on the system boron-nitrogen with an RF sputtering machine, adopting both DC and RF bias and in argon or argon plus nitrogen atmospheres. We also prepared samples by reactive ion assisted deposition (LEAD). The films were deposited on silicon substrates, and characterized by Auger electron spectroscopy (AES) infrared (IR) and Raman spectroscopies and nanoindentation. Significant differences are found between DC and RF biased samples, in particular concerning film structure. Evidence of sp(3) bonded phase formation, as given by IR spectroscopy, is found only in samples produced with a RF bias. Raman spectra of all films show a broad band typical of a completely disordered structure. Strong Raman signals from the substrate prove that the films, except the IBAD ones, are highly transparent in the visible.