Microstructure, mechanical and electrical properties of nanocrystalline W-Mo thin films

The effect of sputtering pressure on the surface/interface microstructure, crystal phase, mechanical properties and electrical characteristics of nanocrystalline W-Mo films is reported. The W-Mo films (≈300 nm) with variable microstructure were deposited under variable argon (Ar) sputtering pressure (PAr), which is varied in the range of 3-19 mTorr. X-ray diffraction analyses indicate that the W-Mo films crystallize in thermodynamically stable α-phase of W. However, the crystal-quality degradation occurs for W-Mo films deposited at higher PAr due to difference in the adatom mobilities. The average grain size (d) of the W-Mo films was in the range of 11-24 nm; grain size decreases with increasing PAr. The effect of PAr and associated microstructure are significant on the mechanical characteristics; the hardness (H) and modulus of elasticity (Er) of W-Mo films deposited at lower PAr were higher but decreases continuously with increasing PAr. The W-Mo films deposited under optimum sputtering pressure exhibit superior mechanical characteristics: H=40 GPa, Er=275 GPa, H/Er=0.8, and H3/Er2=0.145 GPa, which are higher compared to pure, α-phase W-films. The W-Mo films deposited at PAr=3-9 mTorr exhibit high resistivity≈350-400 μΩ-cm, which decreases to 150-200 μΩ-cm for films deposited at higher PAr. Based on the results, structure-mechanical-electrical property correlation in W-Mo films is established.