Influence of magnetron sputtering conditions on the chemical bonding, structural, morphological and optical behavior of Ta1 − xOx coatings

Abstract

In this work Ta1 − xOx coatings were deposited by DC magnetron sputtering in an Ar + O2 atmosphere. The influence of the oxygen partial pressure on the morphology (SEM), structure (XRD), chemical bonding (XPS), thermal oxidation and optical response (FTIR and spectroscopic ellipsometry) of Ta-based films was study. Cross-section morphology revealed that the increase of oxygen content in the coatings change the columnar morphology to featureless. Likewise, structural results showed that the small increase of oxygen amount leads to a change from Ta stable phase (α-Ta: bcc) to a mixture of phases achieving oxide phases with large amounts of oxygen. Whereas at room temperature the oxide coatings mainly revealed an amorphous character, at 700 °C the coating reached the crystallization Ta2O5 orthorhombic phase, which is promoted by the temperature. Further, although not observed in XRD, for the coatings deposited close to the reactive mode threshold IR showed absorption bands corresponding to amorphous phase containing some crystals embedded on it, while for the coatings deposited in the poisoned regime the IR suggests a marked amorphous nature. Refractive index varied between 2.09 and 2.27 at 0.65 μm, within the range reported for Ta2O5 thin films. The changes in refractive index are correlated with the different crystallinity of the coatings, which is corroborated with the IR results.