Improvement of the adhesion of sputtered cubic boron nitride films

Abstract

Cubic boron nitride (cBN) films were prepared by reactive r.f. sputtering in an Ar–N 2 discharge using an electrically conducting boron carbide (B 4 C) target. The substrate table was either powered by an 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 the cBN content the ratio of the IR absorption bands near 1100 cm −1 (cBN) and 1400 cm −1 (hexagonal BN (hBN)) was used. The temperature during cBN growth did not exceed 400 °C. The thickness of the sputtered films was in the range <0.4 μm. A variation of the d.c. substrate bias showed that in the range between −130 and −200 V a window was found where it was possible to move from the growth of hBN to that of cBN. Improved adhesion even under humid conditions was found by sputtering an hBN buffer layer while adding 2% of hydrogen to the nitrogen sputter gas. The subsequent grown cBN film was sputter deposited in pure nitrogen. Nevertheless we found 3 at.% of hydrogen diffused from the hBN into the cBN film. The hydrogen could be removed after heating the films up to 600 °C.