Influence of oxidation temperature on the microstructure and electrical properties of Ta2O5 on Si

The effect of the oxidation temperature (673-873 K) on the microstructural and electrical properties of thermal Ta2O5 thin films on Si has been studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that the films are non-stoichiometric in the depth; an interfacial transition layer between tantalum oxide and Si substrate, containing presumably SiO2 was detected. It has been found by X-ray diffraction that the amorphous state of Ta2O5 depends on both the oxidation temperature and the thickness of the films-the combination of high oxidation temperature (> 823 K) and thickness smaller than 50 nm is critical for the appearance of a crystal phase. The Ta2O5 layers crystallize to the monoclinic phase and the temperature of the phase transition is between 773 and 823 K for the thinner layers (< 50 nm) and very close to 873 K for the thicker ones. The electrical characterization (current/voltage; capacitance/voltage) reveals that the optimal oxidation temperature for achieving the highest dielectric constant (similar to32) and the lowest leakage current (10(-8) A/cm(2) at 1 MV/cm applied field) is 873 K. The results imply that the poor oxidation related defects are rather the dominant factor in the leakage current than the crystallization effects. (C) 2002 Elsevier Science Ltd. All rights reserved.