Plasma-induced pre-oxidation of ultrathin aluminum layers for enhanced oxidation resistance of copper nanofilms

Abstract

Ultrathin copper (Cu) films are indispensable in micro- and nano-electronic devices but suffer from severe environmental oxidation due to their high surface-to-volume ratio. Here, we report a plasma-induced pre-oxidation strategy that enhances the environmental stability of Cu nanofilms using an ultrathin aluminum (Al) layer with a critical thickness as low as ~3 nm. Al layers were physically vapor deposited onto Cu surfaces (Cu@Al) and subsequently exposed to low-power plasma treatment (Cu@Al-P), enabling controlled in situ formation of a compact and structurally uniform Al2O3 barrier. Electrical measurements under ambient air, high temperature and high-temperature & high-humidity conditions show that Cu@Al-P films with 3 nm Al exhibit significantly improved oxidation resistance. Under these conditions, the resistance variation of Cu@Al-P is ~2.9 times, ~9.34 times, and ~5.75 times lower than that of Cu@Al, respectively. Compared to bare Cu, the improvements are even more significant, with Cu@Al-P exhibiting resistance variations that are ~5.84 times, ~27.19 times and ~23.93 times lower. X-ray photoelectron spectroscopy, scanning Kelvin probe microscopy characterization and parallel resistance model calculation confirm that plasma treatment enables the rapid formation of a more uniform and stable Al2O3 barrier, which effectively suppresses oxygen diffusion and stabilizes the electrical properties of the Cu films. This work establishes a critical thickness criterion for ultrathin barrier design and provides a simple, scalable and fabrication-compatible strategy to enhance the environmental stability of copper-based nanoscale electronic systems and other ultrathin metallic nanostructures.