Improvement of the adhesion of sputtered cubic boron nitride films

Cubic boron nitride (cBN) films were prepared by reactive r.f.-sputtering in an Ar-N2 discharge using an electrically conducting boron carbide (B4C) target. The substrate table was either powered by a r.f.-generator or connected to a d.c. power supply. The films were deposited on polished Si(001) and high speed steel substrates. As a measure of th cBN content the ratio of the infrared absorption bands near 1100 cm(exp -1) (cBN) and 1400 cm(exp -1) (hBN) was used. The temperature during cBN growth did not exceed 400 deg C. The thickness of the sputtered films was in the range < 0.4 mu m. A variation of the d.c. substrate bias showed, that in the range between -130...-200 V a window was found where it was possible to turn from the growth of the hexagonal-(hBN) to cubic BN (cBN). Improved adhesion even under humid conditions was found by sputtering an hBN interlayer buffer while adding 2 per cent of hydrogen to the nitogen sputter gas. The subsequent grown cBN-film was sputter deposited i n pure nitrogen. Nevertheless we found 3 at per cent of hydrogen diffused from the hBN- into the cBN-film. The hydrogen could be removed after heating the films up to 600 deg C.