Hydrolysis corrosion of alumina thin films produced by pulse DC reactive magnetron sputtering at various operating pressures

Alumina thin films were prepared by pulsed DC reactive magnetron sputtering using operating pressures that were varied from 3 to 20 mTorr. The films were immersed in DI water at temperatures of 55 degrees C and 65 degrees C for 30 min to study their hydrolysis corrosion behaviors. Unlike bulk crystalline Al2O3 materials, sputtered alumina films fabricated at operating pressures of 7 mTorr and higher were found to react with DI water within minutes, even under mild conditions. X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) showed that the as sputtered films had amorphous structures with various degrees of porosity within the films. The calculated porosity was found to increase from 17% to 25% as the operating pressure increased from 3 to 20 mTorr, respectively. Field-emission scanning electron microscopy (SEM) was employed to characterize the morphologies of the corroded films. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy showed the presence of hydroxide-containing functional groups on surfaces of alumina films, suggesting that the corrosion was due to a hydrolysis reaction. X-ray photoelectron spectroscopy (XPS) revealed distinct features in the non-corroded and corroded sample groups. For the corroded group (7-20 mTorr), the Al 2p peak showed two transitions, at 74.2 and 75.5 eV, attributed to Al-O and Al-OH, respectively. The O 1s peak intensities associated with the hydroxide content of samples in this group were found to be stronger than those associated with the lattice oxygen. The O 1s signal from adsorbed water at 533.7 eV became much stronger in corroded samples. The results also show that films fabricated at higher operating pressures yielded higher levels of pre-adsorbed hydroxide. Corrosion may progress through collective processes, including the formation of soluble aluminum hydroxide complex species and Al-O bond breaking during the proton transfer reactions between adsorbed water and hydroxide.

Automated summary

Alumina thin films prepared by pulsed DC reactive magnetron sputtering at different operating pressures exhibited hydrolysis reactions in DI water. The corrosion process involved the presence of hydroxide-containing functional groups on the film surfaces, with increasing porosity at higher operating pressures.