Mechanical behavior of thin films

The mechanical properties of thin films differ significantly from those of bulk materials due, largely, to the effects of interfaces, microstructure, and thick underlying substrates. Specialized experimental techniques have been developed to determine mechanical properties and the strain and stress states of both free-standing films and films bonded to substrates. In this review, recent innovations in measurement of thin film properties are considered. Included are discussions of nanoindentation, bulge testing, substrate curvature, X-ray diffraction, micro-Raman spectroscopy, and electron diffraction contrast imaging. Selected recent advances in the understanding of continuous thin film and patterned thin film mechanical behavior are also presented. Examples include low-temperature and high-temperature plastic flow in Al and Cu films, strain energy effects on film morphology, hardness enhancement in multilayers, and stress in passivated Al lines.