Microstructure of & lt;111 & gt;-Textured Cubic Boron Nitride Film Deposited under Oxygen-Containing Atmosphere

The cross-sectional and planar microstructures of a cubic boron nitride (cBN) thin film with a <111>-preferential orientation are observed using transmission electron microscopy. The cBN films are deposited by unbalanced magnetron sputtering under the condition that oxygen is added to a 20 sccm Ar-N2(25%) gas mixture. Thecross-sectional view of the cBN film deposited with the addition of 0.4 sccm of oxygen shows a dual-phase structure: turbostratic boron nitride (tBN) layers are filled between cBN columns, and the planar view shows that cBN crystals were surrounded by a tBN matrix. The films deposited under less than 0.4 sccm of oxygen addition show a single-phase structure with no tBN layers between the cBN columns. The difference between dual- and single-phase structures is that they have preferred <111> and <220> orientations. This texture variation is interpreted as being due to the low residual stress of the dual-phase-structured cBN film and the low surface energy of the cBN (111) plane. The residual stress of the dual-phase structure is significantly lower than that of the single-phase structure. This is attributed to the compressive residual stress relieved by the tBN layers formed between the cBN columns.