Deposition of B4C/BCN/c-BN multilayered thin films by r.f. magnetron sputtering

Thin films of cubic boron nitride (c-BN) and B4C/BCN/c-BN multilayers, were deposited by r.f. (13.56 MHz) multi-target magnetron sputtering from high-purity (99.99%) h-BN and a (99.5%) B4C targets, in an Ar (90%)/N2 (10%) gas mixture. Films were deposited onto silicon substrates with (100) orientations at 300 oC, with r.f. power density near 7 W/cm2. In order to obtain the highest fraction of the c-BN phase, an r.f. substrate bias voltage between - 100 and - 300 V was applied during the initial nucleation process and - 50 to - 100 V during the film growth. Additionally, B4C and BCN films were deposited and analyzed individually. For their deposition, we varied the bias voltage of the B4C films between - 50 and - 250 V, and for the BCN coatings, the nitrogen gas flow from 3% to 12%. A 300-nm-thick TiN buffer layer was first deposited to improve the adhesion of all samples. X-ray diffraction patterns revealed the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements indicate the presence of a peak at 780 cm-1 referred to as 'out-of-plane' h-BN vibration mode; another peak at 1100 cm-1 corresponds to the c-BN TO mode and the 'in-plane' vibration mode of the h-BN at 1400 cm-1. BN films deposited at 300 deg. C at a pressure of 4.0 Pa and under - 150 V of nucleation r.f. bias, applied for 35 min, presented the highest c-BN fraction, near 85%. By using 32 layers, it was possible to deposit a 4.6-μm-thick c-BN film with adequate mechanical properties and good adhesion to the substrate