Conversion from Al to Al2O3 of subnanometer barriers for magnetic tunnel junctions monitored in real time

In situ differential ellipsometry measurements are used to investigate the plasma oxidation dynamics of subnanometer Al layers in real time. An analysis of the measured oxidation rate allows us to monitor the conversion from Al to Al2O3 in real time and mark the onset of the CoFe electrode oxidation. In situ x-ray photoelectron spectroscopy (XPS) measurements of identical samples that were plasma oxidized for 3s are used to confirm the ellipsometry results. A linear relationship was found between the amount of Al2O3 determined from the XPS data and the amount of oxidized Al derived from the ellipsometry data. From this, we conclude that the conversion from Al to Al2O3 of subnanometer thin barriers for magnetic tunnel junctions can be observed by using the derivative of the ellipsometer signal.