Real-time monitoring of plasma oxidation dynamics of subnanometer Al2O3 barriers for magnetic tunnel junctions

Abstract

We show that over-oxidation of sub-nm thin Al2O3 barriers of magnetic tunnel junctions can be observed in real time using in situ differential ellipsometry measurements. The change in ellipsometry signal of Al layers grown on CoFe films is proportional to the amount of oxidized metallic material. As a result, the derivative of this signal is a direct measure of the oxidation rate. Further analysis of this oxidation rate allows us to determine the onset of the CoFe oxidation. We found the onset to be proportional to the deposited Al layer thickness. The amount of CoO determined from in situ x-ray photoelectron spectroscopy data on identical samples was found to be proportional to that obtained from ellipsometry.