Off-Axis Texture and Crystallographic Accommodation in Multicomponent Nitride Thin Films Deposited by Pulsed Magnetron Sputtering

The study of texture in thin films is one of the possibilities to obtain information on the fundamental physical processes which govern the thin film growth. Near the substrate, the crystalline orientation of the coating layer will usually be influenced by the surface state of the substrate (grain orientation and dimensions, roughness etc.). However, during the film deposition, the texture of the coating can evolve. This evolution is a particular interesting phenomenon in order to unravel the atomic movements occurring during the deposition. To gain an overall picture for the evolution of texture and development of microstructure with film thickness and substrate material in nanostructured nitride films, a variety of analytical x-ray diffraction (XRD) techniques like θ–2θ scan, pole figure, and residual stress by sin2ψ method were utilized. The coatings of Ti1-xAlxN from different target compositions were deposited onto various substrates (WC-Co, glass, Si(100)). Based on the results obtained, Ti0.5Al0.5N films on WC-Co and glass reveal that surface energy minimization at low thickness leads to the development of (002) orientation. On the other hand, the competitive growth promotes the growth of (111) planes parallel to film surface at higher thickness. However, despite the prediction of growth models, the (002) grains are not completely overgrown by (111) grains at higher thickness. Rather, the (002) grains still constitute the surface, but are tilted away from the substrate normal showing substantial in-plane alignment to allow the (111) planes remain parallel to film surface. Conversely, films on Si had a dominant (002) texture nearly parallel to the surface for all samples, not changing with thickness. This indicates that the surface and interface energy anisotropies provide the driving force for texture development. For films on WC-Co, the stress along (002) which was compressive at low thickness decreases with gradual tilt of (002) and changes to tensile at higher thickness. Tilting of (002) is to minimize the overall energy of the system as the (111) planes develop with thickness store very high compressive stress. On the contrary, the stress state in (002) grains on Si remained compressive through the film thickness. Morphological and roughness observation by SEM and AFM reveal that films on WC-Co and glass display higher roughness than on Si. This confirms that the development of orientation is accompanied by an increase in surface roughness of the film. In contrast, cross- sectional TEM observations reveal a smooth surface region, and the SAED patterns and HR-TEM image support the crystallographic results regarding the texture formation for films on Si. Film hardness was measured by nanoindentation and a correlation between (111) texture, stress, hardness and the type of substrate is obtained. However, for Ti0.67Al0.33N films, the texture growth mechanism is similar to Ti0.5Al0.5N, but the final dominant orientation at higher thic