Effect of hydrogen addition on the residual stress of B–C–N films with cubic boron nitride phase prepared by r.f. magnetron sputtering of a B4C target

Abstract

The effect of hydrogen on the compressive residual stress of B–C–N films composed of amorphous B4C, hexagonal boron nitride (hBN), and cubic boron nitride (cBN) phases has been investigated. The films were basically deposited on silicon (100) substrates by sputtering of a B4C target with a gas mixture of Ar (25sccm), N2 (5sccm), and H2 (0–5sccm) at a chamber pressure of 0.27Pa. To improve the adhesive strength of the films, a compositional gradient B–C–N buffer layer, which was prepared by step-wise deposition with an increasing nitrogen flow rate from 0sccm to 4.5sccm in Ar/N2 mixed gas with a constant Ar flow rate of 25sccm, was adopted before the nucleation stage of the cBN phase. Up to 5sccm hydrogen was added to the Ar/N2 reactive gas after the deposition of the B4C layer with pure Ar gas. For all deposition conditions, hBN and cBN phases were observed to form in the B–C–N films. The cBN fraction in these films remained around 65%, irrespective of the amount of hydrogen added. However, the compressive stress of the B–C–N films was observed to rapidly decrease from 9.5GPa to 4.2GPa, with increasing the hydrogen flow from 0sccm up to 5sccm. The stress reduction is discussed in terms of the relation between the penetration probabilities of hydrogen and argon ions into the films, which was the main origin of the compressive residual stress of the compositional gradient B–C–N layer with hBN structure.