Degradation mechanism of protected ultrathin silver films and the effect of the seed layer

摘要

In this work, we characterize the oxidation and degradation of protected silver thin films through the Kirkendall effect. We then present a solution to reduce the degradation of silver films exposed to a reactive oxidizing environment. In particular, we study the growth of silver deposited by magnetron sputtering on glass substrates pre-coated with three different underlayers: SiO2, ZnO and a self-assembled monolayer of (3-mercaptopropyl) trimethoxysilane (MPTMS). The films are then covered with a 2-nm barrier titanium film and exposed to reactive oxygen plasma. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy reveal that the degradation process begins with the migration of silver through the top titanium barrier. We quantify the degradation by comparing the atomic content of silver present at the top of the degraded samples. We find that in the case of the ZnO and SiO2, a significantly higher amount of silver migrates through the top barrier and onto the surface, as compared to the MPTMS-treated surface. We attribute this difference to the chemisorption of silver atoms to the MPTMS layer.