Cubic boron nitride films were successfully prepared on Si(100) substrates by radio frequency (rf) bias sputtering of a hexagonal boron nitride target in pure Ar discharge with the aid of a magnetic field and with the phase regulation of the rf voltages applied to the target and substrate electrodes. Above the threshold of the negative substrate bias voltage (Vs), the infrared (IR) absorbance corresponding to the cBN TO mode showed a linear increase proportional to deposition time, while that of the sp(2) phase kept a nearly constant value. The resulting dependency indicated that the cBN films consisted of a double-layered structure caused by an initial deposition of the sp2 phase and the subsequent growth of a cBN single phase, and did not consist of a two-phase mixed layer. The layered structure was also confirmed by observing the depth dependence of the IR spectra. The growth rate of the cubic phase and the thickness of the initial sp(2) bonded layer were estimated to be approximately 1 nm/s and 40 nm, respectively, for cases where V-s ranged from 250 to 300 V at p=16 m Torr. This rate was relatively high compared with those of other techniques used for cBN deposition.