Influences of film composition and annealing on the mechanical and electrical properties of W–Mo thin films

In this article, the mechanical and electrical characteristics of co-sputtered W–Mo thin films investigated for the application to microelectromechanical systems are described. W–Mo thin films with various compositions were deposited by co-sputtering onto a cover glass and silicon oxide (SiOx) film-coated Si wafer. The internal stress measured by Newton-ring method depended on film composition and Ar pressure, but were independent on annealing at 623 K. The hardness gradually decreased with an increase in Ar pressure, whereas the effective Young’s modulus stayed constant throughout Ar pressures ranging from 0.2 to 0.4 Pa. Both the mechanical properties showed no dependences of film composition and annealing. The resistivity was proportional to Ar pressure, but was not related to film composition. Annealing slightly affected the resistivity. Auger spectroscopy clarified that, by annealing, an oxide layer of approximately 10 nm thick was produced on the top surface, but film composition did not change. From the experimental results obtained, annealing at 623 K did not affect the mechanical and electrical properties of W–Mo films. This indicates that the co-sputtered film is very stable at temperatures ranging from RT to 623 K. By controlling Ar pressure, stress-free W–Mo films with superior mechanical characteristics and low resistivity can be produced regardless of film composition.