Cu-substrate interfacial adhesion: A key factor in controlling the oxidation of Cu thin films on oxide substrates

Abstract

Despite the likelihood of H2O adsorption on the highly defective surfaces of polycrystalline Cu thin films under ambient atmospheric conditions, the influence of adsorbed H2O on the oxidation of Cu thin films has not been fully recognized. This study explored the oxidation of 16 nm-thick polycrystalline Cu thin films deposited on SiOx and ZnO substrates under conditions mimicking accelerated oxidation at 85 °C and 85% relative humidity. Through experimental evaluations and numerical calculations, we discovered that enhanced Cu adhesion to oxide substrates effectively suppresses the oxidation of Cu thin films. A notable increase in adhesion at the Cu–ZnO interface resulted in a significant decrease of Cu oxidation on ZnO substrates, starkly contrasting with the accelerated Cu oxidation on SiOx substrates. The augmented adhesion between Cu and ZnO slowed the solid-state outward diffusion of Cu ions from the Cu–ZnO interface, thus inhibiting oxidation. Conversely, the weak adhesion between Cu and SiOx stimulated the outward diffusion of Cu ions, leading to void formation at the interface. These findings challenge prevailing beliefs by revealing a strong correlation between oxidation and metal–substrate adhesion. Our results provide valuable insights for identifying the key factors governing oxidation mechanisms.