Characterization of micrometric and superficial residual stresses using high frequency surface acoustic waves generated by interdigital transducers.

Controlling thin film deposition of materials and property gradients is a major challenge for the implementation of applications in microelectronics or glassmaking. It is essential to control the level of residual stress and thus important to have the right tools to characterize this stress in terms of scale and nature of the deposits. In this context, dispersion of ultrasound surface waves caused by the presence of a residual micrometric surface stress was studied in an amorphous medium for different superficial fields of residual stress. The design and implementation of SAW-IDT MEMS sensors enabled quasi-monochromatic Rayleigh-type surface waves to be generated and the dispersion phenomenon to be studied over a wide range of frequencies. The thicknesses of the stressed cortical zones as well as the level of stress were estimated with good accuracy using an inverse method.