Mechanical performance and growth characteristics of boron nitride films with respect to their optical, compositional properties and density

We present a study of the growth processes of sputtered BN films, deposited on c-Si (001) substrates, at room temperature (RT) by rf magnetron sputtering. Nanoindentation (hardness ∼21 GPa), density (∼2.6 g/cm3) and roughness by X-ray reflectivity and stress measurements indicated the existence of sp3-bonded BN with properties similar to those of crystalline BN being superior for optical applications due to their homogeneity offering a single refractive index and smooth surfaces. The growth mechanism of sputtered BN films is sensitive to the Ar partial pressure and the bias voltage applied to the substrate during deposition inducing bombardment of the film with Ar+ ions. There is a narrow ion energy window where sp3-bonded BN is predominant providing dense, hard- and wear-resistant films. The fact that they are produced at RT and they are homogeneous with no gradient refractive index and smooth surfaces are correct for processes, such as optical applications on polymers or soft substrates.