Elastic and structural properties of nanometer scale-thick refractory metal films

In this work, we investigate thickness-dependent elastic and structural properties of refractory W, Ta and Mo thin films fabricated by radio-frequency magnetron sputtering on silicon substrates. Elastic properties of studied hard thin coatings are measured by non-destructive nanosecond laser pulse induced surface acoustic wave technique, while their structural and dimensional properties are analysed using X-ray diffraction (XRD) and scanning electron microscopy, respectively. It was found that the Young's modulus of these films increase with their nanoscale thickness. Young's modulus of hard metals (W, Mo) was consistently higher than those of their bulk. However, the modulus of Ta films was higher than that of the corresponding bulk metal except for the film with the lowest thickness (22 nm). XRD analysis revealed that all films are under compressive stress, but this stress is diminished in thicker films.