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

Abstract

In this work, the structural and electrical properties of amorphous and crystalline Ta 2 O 5 thin filmsdeposited on p -type Si substrates by low-pressure chemical vapor deposition from a Ta(OC 2 H 5 ) 5 precursor have been investigated. The as-deposited layers are amorphous, whereas crystalline Ta 2 O 5 was obtained after postdeposition O 2 treatment at 800 °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 (∼1 nm ) interfacial SiO 2 layer but was not sufficient to reduce the level of hydrocarbon contamination. The dominant conduction mechanism in amorphous Ta 2 O 5 is clearly due to the Poole–Frenkel effect, whereas the situation remains unclear for crystalline Ta 2 O 5 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 ∼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 N 2 and forming gas at 425 °C have been investigated for both types of films.