Interfacial reactions in Al2O3/Ti, Al2O3/Ti3Al and Al2O3/TiAl bilayers

Interfacial reactions were studied at three different heat-treated oxide/metal bilayers (oxide: amorphous a-Al(2)O(3) and metal: crystalline c-Ti, Ti(3)Al or TiAl) by means of AES depth profiling. The different oxide/metal bilayers were sputter deposited on smooth silicon substrates, covered with a TiN thin-film diffusion barrier. The reactions at the oxide/metal interfaces were activated in a differential scanning calorimeter by heating the samples in an argon atmosphere at a linear heating rate of 40 degrees C/min, between room temperature and different final temperatures (350 to 700 degrees C). In order to characterize the reaction products, i.e. solid solution of oxygen in the cu-Ti and the newly formed alpha(2)-Ti(3)Al phase, XPS and TEM investigations were performed on selected samples. The thermal stability of three interfaces was investigated in dependence of aluminium content and consequently with respect to the solubility of atomic oxygen in the metallic layers. Thermodynamic calculations revealed that the heat of solution of oxygen in the metallic layers is crucial for the interfacial reactions. The experimental results are consistent with thermodynamic data: the a-Al(2)O(3)/c-Ti interface shows the highest reactivity, followed by the a-Al(2)O(3)/c-Ti(3)Al interface. In the a-Al(2)O(3)/c-TiAl bilayer no reaction was detected at the interface, indicating thermal stability up to 700 degrees C. The mechanism of the chemical reaction at the interfaces of the different bilayers is discussed. (C) 1999 Elsevier Science S.A. All rights reserved.