Adhesion improvement of cBN film by B-C-N gradient layer system

Adhesion of cBN films on silicon substrate was vastly improved by the introduction of a compositional gradient layer which contains B, C and N. The cBN films were prepared by reactive sputtering using a boron carbide (B4C) target. By employing this gradient layer, deposition of thick (up to similar to 1.6 mu m) and stable cBN films was realized. Infrared (IR) spectra of thick films showed that, the films contain a large amount of cBN. Secondary ion mass spectroscopy (SIMS) measurements confirmed that the gradient layer system starts from a B4C layer on the substrate followed by a subsequent step-like increase in the amount of N, while the amount of B and C decreased. Measurement of hardness by nano-indentation showed that these films have hardness up to 60 GPa. Superior performance against abrasive wear compared to hard nitride coatings was clearly demonstrated by the abrasive wear tests.