Coherent growth of α-W film on Si wafer and its thickness dependent mechanical and electrical properties

By means of template effect the α-W thin films were successfully coherent grown on pre-deposited Mo seed-layer on Si substrate at ambient temperature by magnetron sputtering. Microstructures have been studied by XRD, FESEM and HRTEM. Residual stress and electric resistance of the thin films were investigated by wafer curvature method and standard four-probe technique. Observations show the stable α-W with equiaxial-grain shape is preferred on Mo layer by template effect while the metastable α-W with non-equiaxed grain structure appeared on Si substrate. With increasing W film thickness, the resistivity and residual stress increase for above two series of samples. For the case of α-W, the thickness dependent properties indeed resulted from increasing grain boundary. Whereas, for α-W case, the constraint of coherent interface between α-W and Mo will dominate electric resistance and residual compressive stress, especially at film thicknesses equal to or smaller than tens of nanometers.