Photoelectron spectroscopy study of Al–Cu interfaces

Reactions at Al–Cu interfaces were investigated by ultraviolet and monochromatized X-ray photoelectron spectroscopy (UPS–HeI/II, MXPS). Al was deposited step by step on high purity Cu substrates at various substrate temperatures by RF magnetron sputtering. The oxygen contamination as determined by MXPS was always below 5%. For the ambient and 100°C substrate temperatures both UPS and MXPS results indicate the formation of a thin Al-rich alloy of a few monolayers at the interface. A totally different behaviour was observed for 200 and 300°C substrate temperatures. A reaction at the interface was still present after a nominal Al coverage of more than 100 monolayers. Presumably, Cu-rich intermetallic compounds were formed, the stoichiometry depending on both the substrate temperature and deposition rate.