AN AES STUDY OF LPCVD TA2O5 FILMS ON SI

Methods of evaluation of the chemical composition of tantalum oxide films and of the interface between tantalum oxide films and Si substrates were studied by means of sputter-assisted Auger electron spectroscopy (AES). Tantalum oxide films 10-50 nm thick were grown on Si single-crystal substrates by low-pressure chemical vapour deposition (LPCVD). It has been found that reduction of the oxides is induced by ion sputtering during Auger depth profiling. Therefore we optimized the ion-sputtering conditions to minimize the reduction rate. Then, using stoichiometric-beta-Ta2O5 as reference, it was confirmed that as-deposited tantalum oxide films were oxygen-deficient and that the oxygen content of these films was increased by subsequent annealing in an O2 ambient. By means of Auger depth profiling, we evaluated the thickness of silicon native oxides formed at the Ta2O5/Si interface as 1.5-2 nm. Moreover, we revealed the oxidation mechanism of a silicon nitride intermediate layer (e.g. 10 nm thick) deposited between tantalum oxide film and an Si substrate during heat treatment at 900-1000-degrees-C in O2.