X-ray photoelectron spectroscopy characterization of the oxidation of electroplated and sputter deposited copper surfaces

Abstract

X-ray photoelectron spectroscopy (XPS) was used to study the surface oxidation of sputtered and electroplated copper films following exposure to ambient air and chemical processing reagents used during the fabrication of interconnect structures. Exposure of both sputtered and electroplated copper films to ambient air and deionized (DI) water resulted in the formation of thin copper oxide layers. For ambient exposed copper films, the topmost layer contains Cu2+ oxide species, and the next Cu+ oxides. For DI water exposure, only Cu+ oxide species were observed. Oxidation was more rapid for the electroplated compared to the sputtered copper films as measured by copper oxide to copper metal concentration ratios calculated from XPS curve fitting results and photon-induced Auger peak height measurements. For the electroplated copper films, oxygen uptake was slower as a result of exposure to ambient compared to DI water treatments. Electroplated copper films exposed to common wet chemical etchants also show indications of oxidation of the copper surface region with evidence of mechanical instability between the formed oxide and underlying copper film, resulting in adhesion loss. A method for the removal of the oxide layer has also been investigated to improve adhesion to overlying passivation films.