Characterization of nano-crystalline Ti–W–N thin films for diffusion barrier application: a structural, microstructural, morphological and mechanical study

Ti–W–N thin films with various W contents are deposited on the glass and 304 steel substrates, kept at 150 °C, using the reactive magnetron co-sputtering system. The films were deposited with simultaneous sputtering of Ti and W targets where they powered by DC and RF sources, respectively. The effect of W content on the structure, microstructure and mechanical properties of Ti–W–N thin films are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and nanoindentation tester. The results show that all films have NaCl-type structure with (200) or (111) preferred orientation, depending on the W content. Furthermore, cross-sectional images corroborate the formation of columnar structure and reduction in distance between the columns with increasing W content. The grains’ size calculated from XRD patterns and SEM micrographs revealed that increasing W content results in increasing their values in the films. Study of the surface morphology and the surface roughness of the films confirm the increase of surface roughness as a function of W content, and this is in agreement with the increase seen in the grain size. Incorporation of W to Ti–N system results in dramatic reduction in electrical resistivity. Addition of W to the films has significant effects on the film stoichiometry. With increasing RF power, the hardness of the films increases and reaches a maximum value of about 26.5 GPa at a RF power of 80 W while in higher values of power the hardness decreases.