The effect of germanium sublayer on the native corrosion of ultrathin copper films

TL;DR

This study investigates how a germanium sublayer affects the native corrosion process of ultrathin copper films, revealing that germanium significantly slows corrosion and enhances long-term stability, with potential applications in EMI shielding.

Contribution

It introduces a model explaining copper oxidation behavior and demonstrates that germanium sublayers improve corrosion resistance of ultrathin copper films.

Findings

Copper oxide layer growth follows a parabolic law contrary to existing theories.

Germanium sublayers slow down corrosion and resist degradation.

Cu/Ge/SiO2 films maintain properties longer, suitable as gold replacements.

Abstract

To examine the process of native corrosion of ultrathin (about 10 nm) copper films deposited on quartz glass substrates $(SiO_2)$ with and without a germanium sublayer, the time dependences of the microwave reflection coefficient $R$ and direct current electrical resistivity $\rho$ of such samples exposed to air at room temperature have been studied. Under these conditions, the thickness of the oxide layer $d$ on $Cu/SiO_2$ films was found to increase over time $t$ according to a parabolic law, which is in contradiction with the predictions of existing theories of copper oxidation. A model is proposed that explains this behavior of $d(t)$ by the diffusion of atomic oxygen along the boundaries of oxide grains towards the copper film with its subsequent oxidation. The $R$ and $\rho$ of $Cu/Ge/SiO_2$ films were found to degrade much more slowly than similar characteristics of $Cu/SiO_2$ films of the same thickness. The high corrosion resistance of $Cu/Ge/SiO_2$ films is explained by the peculiarities of $Ge$ redistribution during the growth of the copper film on a germanium sublayer. The long-term retention by $Cu/Ge/SiO_2$ films of their characteristics allows them to be recommended as a cheap replacement for gold coating in electromagnetic interference protection devices.