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

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.