Adherence experiments on cBN films

Abstract

Boron nitride thin films were deposited by tuned substrate rf magnetron sputtering from an h-BN target. Pure Ar, 85% Ar + 15% N2 and Ar + 10% < H2 < 30% were used as processing gases. A threshold value of momentum per deposited atom was found, around 600 eV12amu12, to obtain films with a high content of the cubic phase (between 70 and 90%). By introducing H2 into the gas mixture, an attempt was made to improve stability of the films exposed to the air atmosphere, which was achieved at 18% H2 content. However, a decrease in cBN percentage, deduced from IR spectra, was observed. A 50% Ar + 50% N2 gas mixture was also used for “in situ” deposition of hBN coatings on cBN films. The resulting films exhibited longer lifetimes and different methods of delamination, observed by SEM, than films without hBN coatings. Besides these attempts, different substrates were tested. B-doped (100)-Si showed greater stability than P-doped (100)-Si, and a buffer layer of 40 A Ni improved the adherence of 18% H2 film. However, neither buffer layers consisting of diamond nor other Ni thickness, nor mechanical scratching of silicon with diamond and cBN powders, were successful. From XPS analysis, the B/N atomic ratio was estimated to be in the range of 1.05–1.10 for films obtained with 85% Ar + 15% N2 and 1.15–1.20 for films deposited in pure Ar and in an Ar + H2 atmosphere.