Investigation of bilayer period and individual layer thickness of CrN/TiN superlattices by ellipsometry and X-ray techniques

CrN/TiN superlattice (SL) coatings were prepared employing reactive magnetron sputtering in unbalanced configuration. The coatings were deposited in a mixed Ar/N2 atmosphere rotating the substrate holder, located at the centre of the deposition chamber. Through the rotation, the substrate was sequentially exposed in two diametrically located Cr and Ti targets (purity 99.95%) leading to the deposition of the CrN and TiN single layers, respectively. The deposition was carried out at various values of substrate bias voltage and substrate rotation speed. The microstructure of the SL coatings was investigated in terms of the thickness of the individual CrN and TiN single layers and the bilayer period Λ, namely the sum of the thickness of two sequentially CrN and TiN layers. Λ values were calculated employing X-ray diffraction (XRD) at both low and high diffraction angles. Moreover, the high-angle XRD patterns enabled the determination of the single CrN and TiN layer thickness. In addition, the thickness of the single layers was determined from Spectroscopic Ellipsometry using the Bruggeman effective medium approximation. The results reveal good agreement between the various techniques.