Optical and in situ characterization of plasma oxidized Al for magnetic tunnel junctions

An optical polarization modulation technique was adapted to provide a simple, fast, and flexible method for studying the kinetics and growth characteristics of thin oxide layers, using ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_3$ as an example. The optical technique allows precise determination of the amount of remaining metallic Al as a function of the initial Al thickness, while scanning a laser spot across the wedge. Optical data suggest that the oxide growth rate for the ultrathin layers may be dependent on the specific microstructure. In situ x-ray photoelectron spectroscopy performed on homogenous samples confirmed the interpretation of the optical results.