Photoemission and glancing-angle extended x-ray absorption fine-structure studies of vacuum-deposited Al/Cu bilayers

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Abstract
The effects of oxygen exposure and substrate temperature on the structure and chemical composition of vacuum-deposited Al/Cu and Al/O2/Cu bilayers are studied using photoemission and glancing-angle extended x-ray absorption fine-structure (EXAFS) measurements. Use of these complementary techniques permits detailed atomic-level characterization of thin-film structure and chemical composition during thin-film deposition in vacuum or thin-film modification by heat treatment in air. In absence of oxygen contamination, photoemission indicates significant interfacial reaction at room temperature at the Al/Cu interface. Glancing-angle EXAFS shows that an Al-rich Cu–Al alloy forms at the interface at room temperature. Heat treatment promotes alloy formation and CuAl2 forms at temperatures from 120 to 150 °C. For interfaces formed after substrate oxygen exposure significant alloying is still observed and Al reduces the Cu–O substrate leading to the formation of Cu–Al and Al2O3 compounds at room temperature. Annealing the oxygen exposed interface leads to the formation of a CuAl2 phase but at higher temperatures than was observed for samples produced in ultrahigh vacuum.

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