Growth process of cubic boron nitride films in bias sputter deposition

Intending to study phase evolution of cubic boron nitride (cBN) films during RF bias sputter deposition, surfaces of the cBN films in different growth stages were examined systematically. Argon content at the film surface increased during the deposition of initial sp^2 bonded layer growth, and saturated at about 1.5 at.%, and remained constant after the formation and growth of cubic phase, accompanied with an increase of compressive stress up to 5 GPa. This increase of stress is confirmed to be the result of averaging film stress over the double-layered cBN film, that is, over low-stressed initial layer and high-stressed cubic layer. Atomic force microscope (AFM) observations in tapping mode revealed self-affine fractal nature and kinetic roughening of film surface during the growth, and root mean square (rms) roughness changed from 0.3 nm of an initial layer, to 0.9 nm accompanied with peculiar surface smoothing at the initial stage of cBN formation. Moreover, the evolution of the surface roughness was clearly characterized by the change of modes in each growth process, that is, an initial layer growth stage, a transition stage, and a cubic layer growth stage