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Boron nitride thin films have been deposited on silicon by tuned substrate r.f. magnetron sputtering from a sintered hexagonal BN target using a mixture of Ar (90%) and N 2 (10%) as sputtering gas at different substrate bias conditions. The deposited films have been characterized by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Both FTIR and XPS results show that the formation of nearly pure cubic boron nitride films were achieved when the films were deposited by a two-step process at a lower substrate bias voltage after the initial formation of the cubic boron nitride layer. Also, as indicated by FTIR measurements, this two-step process caused a reduction of the residual stress in the deposited films and no re-sputtering effects were present during the cubic BN growing process.

The substrate tuning technique was applied to a radio frequency magnetron sputtering system to obtain a variable substrate bias without an additional source. The dependence of the substrate bias on the value of the external impedance was studied for different values of chamber pressure, gas composition and rf input power. A qualitative explanation of the results is given, based on a simple model, and the role of the stray capacitance is clearly disclosed. Langmuir probe measurements show that this system allows independent control of the ion flux and the ion energy bombarding the growing film. For an argon flow rate of 2.8 sccm and a radio frequency power of 300 W ͑intermediate values of the range studied͒ the ion flux incident on the substrate was 1.3ϫ10 20 m Ϫ2 s Ϫ1 . The maximum ion energy available in these conditions can be varied in the range 30-150 eV. As a practical application of the technique, BN thin films were deposited under different ion bombardment conditions. An ion energy threshold of about 80 eV was found, below which only the hexagonal phase was present in the films, while for higher energies both hexagonal and cubic phase were present. A cubic content of about 60% was found for an ion energy of 120 V.

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