We investigated Ta2O5 films grown by chemical vapor deposition of Ta(N(CH3)(2))(5) and O-2 both bare and SiOxNy-passivated Si(100) using x-ray photoelectron Spectroscopy, time-of-flight secondary-ion-mass spectroscopy (TOF-SIMS), and electrical measurements. The SiOxNy-passivated layer was formed by nitric oxide exposure to the Si substrate. Chemical composition of the Ta2O5 films is strongly dependent on the oxygen flow rate during film deposition; lower carbon levels and higher O/Ta ratios are observed for the films grown at higher O-2 flow rates. A corresponding leakage current decrease is observed for the films grown at a high O-2 flow rate. Compared to Ta2O5 films deposited on bare Si(100), the films deposited on SiOxNy-passivated layers show better electrical properties; with smaller equivalent thickness (Delta t(eq) similar to 6 Angstrom) one order of magnitude lower leakage current was measured. TOF-SIMS data indicate that SiOxNy layers (similar to 9 Angstrom) incorporate some oxygen during Ta2O5 deposition; however, regions where x=2, y=0 were not detected. Postdeposition annealing of Ta2O5/SiOxNy samples results in displacement of N by O in SiOxNy layers and oxidation of the Si substrate, forming SiO2.