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

摘要

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 -C, 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 between100 and300 V was applied during the initial nucleation process and50 to100 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 between50 and250 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 cm1 referred to as ‘‘out-of-plane’’ h-BN vibration mode; another peak at 1100 cm1 corresponds to the c-BN TO mode and the ‘‘in-plane’’ vibration mode of the h-BN at 1400 cm1. BN films deposited at 300 -C at a pressure of 4.0 Pa and under150 Vof 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-Am-thick c-BN film with adequate mechanical properties and good adhesion to the substrate.