Thickness dependent native oxidation kinetics observation and prediction for Cu films using spectroscopic ellipsometry

Abstract Long-term native oxidation of polycrystalline Cu films with different thicknesses is investigated using spectroscopic ellipsometry. In order to more accurately determine the thickness of the oxide layer, a three-phase Maxwell-Garnett effective medium approximation model has been proposed to fit both the ellipsometric parameters and reflectance. X-ray photoelectron spectroscopy and transmission electron microscopy have been used to verify the rationality of the proposed model and measured results. The results demonstrate the Cabrera-Mott rule, and both the oxidation rate and the initial oxide thickness show significant dependencies on the thickness of Cu film. When thickness increases from 15 nm to 400 nm, the oxidation rate, defined as the slope in the inverse logarithmic correlation, decreases from 0.11/(nm·day) to 0.03/(nm·day) following an exponential function. Meanwhile, the initial oxide thickness, i.e. the intercept in the inverse logarithmic correlation, decreases from 0.73/nm to 0.3/nm in the light of a parabolic function. In the end, the oxidation evolution of a Cu film with arbitrary thickness is further predicted based on the obtained thickness-dependency, which is expected to provide a reference for better application of Cu films.