Evaluation of elastic properties of SiO2 thin films by ultrasonic microscopy

This paper describes evaluation of stiffnesses of SiO₂ thin films when the anisotropy in elasticity is taken into account. The authors measured the propagation direction θ dependence of the water-loaded surface acoustic waves (SAW) velocity, and tried to estimate stiffnesses of SiO₂ films from the measured θ dependence. The result indicates that SiO₂ films possess the strong 6mm anisotropy. Namely, stiffnesses normal to the surface are significantly lager than those along the surface. This anisotropy may be induced during the deposition or caused by variation of film properties in the thickness direction.