Cubic boron nitride films prepared by reactive r.f. and d.c. sputtering from different boron containing targets

Cubic boron nitride (c-BN) films have been deposited by reactive r.f. sputtering in Ar-N-2 mixtures, using both insulating hexagonal boron nitride (h-BN) and electrically conducting boron carbide (B4C) targets. The relative nitrogen-flow in the sputter gas was varied between 0% and 100%. The substrate electrode was operated either with an r.f. or d.c. power supply. As a measure for the c-BN content the ratio of the infrared absorption bands near 1100 cm(-1) (c-BN) and 1400 cm(-1) (h-BN) was used. A simple approximation allows estimation of the real content of the cubic phase from these ratios. For the h-BN target, maximum values of the c-BN content occurred in the range 1%-10% N-2. For the B4C target, more than 10% N-2 was needed to obtain c-BN containing films. For both target materials the growth of the cubic phase is correlated to a B/N ratio near to unity. Many films with high c-BN contents tended to peel off from the substrate. A well adhering film exhibited a very high hardness of 50-60 GPa measured with a nanoindentor set-up. First experiments using a d.c. magnetron sputter apparatus with a B4C target revealed that c-BN can also be prepared by d.c. sputtering.