Properties of amorphous and crystalline Ta2O5 thin films deposited on Si from a Ta(OC2H5)5 precursor

In this work, the structural and electrical properties of amorphous and crystalline Ta2O5 thin films deposited on p-type Si substrates by low-pressure chemical vapor deposition from a Ta(OC2H5)(5) precursor have been investigated. The as-deposited layers are amorphous, whereas crystalline Ta2O5 was obtained after postdeposition O-2 treatment at 800 degrees C. As evidenced by x-ray diffraction, a hexagonal structure was obtained in the latter case. Physicochemical analysis of our layers shows that the O-2-annealing step leads to the growth of a thin (similar to 1 nm) interfacial SiO2 layer but was not sufficient to reduce the level of hydrocarbon contamination. The dominant conduction mechanism in amorphous Ta2O5 is clearly due to the Poole-Frenkel effect, whereas the situation remains unclear for crystalline Ta2O5 for which no simple law can be invoked to correctly describe its conduction properties. From capacitance-voltage measurements, the dielectric constant was found to be similar to 25 for amorphous samples, but values ranging from 56-59 were found for crystalline layers, suggesting a particularly high anisotropic character of the crystalline phase. Finally, the effects of postdeposition annealing in Nz and forming gas at 425 degrees C have been investigated for both types of films. (C) 1998 American Institute of Physics.