Understanding and mitigating oxidation-induced electrical instability in sputtered Sc thin films

Scandium (Sc) thin films are promising candidates for advanced electronic applications due to their excellent electrical and thermal properties. However, the reliability is challenged by oxidation-induced instability. This study identifies and decouples two distinct oxidation mechanisms: transient oxidation during the deposition phase, driven by residual oxygen at plasma ignition, and ambient-induced oxidation postdeposition. Sequential wafer analysis reveals a pronounced first-wafer effect, with elevated sheet resistance (Rs) and nonuniformity (NU%) in early wafers. Grazing incidence x-ray diffraction and long-term statistical process control confirm surface oxidation and its temporal evolution. An in situ 5 nm Ru capping layer effectively suppresses ambient oxidation, stabilizing Rs, though NU% remains high due to deposition variability. These findings highlight the importance of both surface passivation and precise process control to ensure the electrical stability of Sc thin films.