Molecular content of the deposition flux during reactive Ar∕O2 magnetron sputtering of Al

The deposition flux obtained during reactive radio frequency magnetron sputtering of an Al target in Ar∕O2 gas mixtures was studied by mass spectrometry. The results show significant amounts of molecular AlO+ (up to 10% of the Al+ flux) in the ionic flux incident onto the substrate. In the presence of ∼10−4Pa H2O additional OH+ and AlOH+ were detected, amounting to up to about 100% and 30% of the Al+ flux, respectively. Since the ions represent a small fraction of the total deposition flux, an estimation of the neutral content was also made. These calculations show that, due to the higher ionization probability of Al, the amount of neutral AlO in the deposition flux is of the order of, or even higher than, the amount of Al. These findings might be of great aid when explaining the alumina thin film growth process.