Adhesion assessment of copper thin films

Nano-indentation testing has been used to quantitatively assess the adhesion of thin copper films, sputtered to thicknesses of 150 nm to 1500 nm. Copper films of low residual stress were deposited via RF diode cathode sputtering onto SiO₂/Si substrates. Overlayers of DC magnetron sputtered high residual stress tungsten, 850 nm thick, were additionally used to provide a driving force for delamination. All films tested exhibited buckle-driven delamination, from which the interfacial toughness was estimated to be 0.2 - 2 J/m², which is comparable to the thermodynamic work of adhesion. The use of an overlayer requires extensions of existing models, but otherwise does not change the interfacial adhesion, allowing measurements of films that would not otherwise delaminate.