Preparation of cubic boron nitride films by use of electrically conductive boron carbide targets

This paper deals with the successful preparation of cubic boron nitride (c-BN) films by use of an electrically conducting boron carbide (B4C) target in reactive rf sputtering. It describes the influences of the most important sputter parameters. It turned out, that the B:N ratio of the sputtered layers was stabilized in the order of 1 by using Ar/N2 gas mixtures with >6 per cent N2. The carbon content in the films could be reduced to <5 at per cent by varying the Ar/N2 gas mixture. With respect to c-BN formation important parameters have been found in the ratio of target to substrate power and the negative substrate bias voltage. Almost single phase c-BN films have been deposited at substrate temperatures < 300 deg C. Characterization of the films has been performed by EPMA, IR spectroscopy, HRTEM and TED. The films revealed a nano crystalline microstructure of 10 - 40 nm in size. Hardness as determined by nanoindentation measurements was as high as 60 GPa.