Effect of substrate bias voltage on amorphous Si–C–N films produced by PVD techniques

Abstract

SixCyNz thin films were deposited by reactive magnetron sputtering in glass and steel substrates. The films were grown in a rotation mode over a carbon and a silicon targets in a mixed Ar/N2 atmosphere. The substrates were held at a substrate temperature of 573 K. The argon flow was kept constant (100 sccm) and the nitrogen flow was 20 sccm or 25 sccm, in each one of the two series of produced films, resulting in a working pressure around 0.5 Pa. The substrate bias varied between grounded and -100 V. The films were analysed with respect to microstructure, state of chemical bonding and optical properties by X-Ray Diffraction (XRD), Raman Spectroscopy (RS), optical reflectance and transmittance. Raman spectroscopy was used as a probe of microstructural modifications induced by deposition conditions. The main features observed in RS spectra are the well-known D- and G-bands characteristic of amorphous carbon materials. The position, widths and intensity ratio of these bands are found to be dependent of the films deposition conditions. The refractive index, absorption coefficient, optical band gap and also the thickness were calculated from transmittance spectra obtained between 200 nm and 2500 nm.The residual stress of the coatings depends on deposition conditions and was calculated by measuring the substrate curvature before and after film deposition. The curvature of the samples was measured by laser triangulation in two series of two orthogonal directions. All coatings were in a state of compressive residual stress. The average hardness and Young’s modulus of the produced coatings is about 16 GPa and 170 GPa, respectively. The nano-hardness of the grounded produced samples presented values about 30% lower.