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Mechanical and thermal properties of Cu/Al2O3 systems; effects of substrate surface ion bombardment etching

Nominal-contact-area analysis is combined with x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and measurements of the scratch test critical load (Lc) to study interfacial properties in thin-film adhesion and heat transfer. This work complements an earlier investigation of the enhancement of adhesion strength and thermal contact resistance (Rc) produced by ion bombardment of the substrate surface before deposition. In this study, we have investigated Cu films deposited by radio-frequency sputtering onto alumina substrates. Extended ion bombardment etching leads to three related effects: the nominal contact area is increased significantly; Rc and Lc are decreased and increased respectively; XPS shows a greater penetration of the film material into the substrate and the formation of a complex interface. These results are interpreted as confirmation that ion bombardment leads to the formation of microcavities in the interface layer and, consequently, to increased adhesion strength and heat transfer by allowing mechanical interlocking between the film and the substrate.