Experimental considerations for indentation-induced adhesion measurement of multilayered thin films

Nanoindentation of thin films is an especially attractive technique for the quantitative assessment of the adhesion energy of thin films, in that the film can be measured in the as-processed condition with almost no sample preparation. Linear elastic fracture mechanics calibrations have been previously developed to quantify the strain energy release rate as a function of film properties, film residual stress and indentation volume. However, this test is limited by the practical difficulty of producing a suitable delamination for either strong interfaces or ductile films. Modified mechanics suitable for a multilayer film have recently been developed. One particularly useful application of this calibration is discussed, namely the use of a highly stressed refractory superlayer that acts to promote delamination of the underlying film (assuming said interface is the weaker). Delamination is ensured by triggering the fracture process through nanoindentation. Such superlayers can be deposited over the as-processed film of interest, producing no significant changes in that film's microstructure or interfacial character. Experimental results using this method are reviewed with particular attention to experimental consideration, along with recent results using copper and tungsten thin films on SiO₂.