We investigated annealing effects on yttrium oxide films elaborated at 350 degrees C by pulsed injection plasma-enhanced metallorganic chemical vapor deposition. A certain amount of carbon is present in the as-deposited layers due to incomplete metallorganic precursor decomposition. Because the carbon is known to be disadvantageous for the dielectric permittivity, several annealing post-treatments (under Ar or O-2 at 700 degrees C and under H-2 at 450 degrees C during 30 min at atmospheric pressure) were performed. Chemical modifications in the yttrium oxide layer and also at the interface were investigated combining several analyses [as infrared spectroscopy, (angle-resolved) X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy, and Rutherford backscattering spectrometry] carried out on thick and thin films (respectively, similar to 40 and similar to 5 nm). High-temperature post-treatments result in a significant reduction of carbon content. However, the presence of oxygen at high temperature (even for low residual oxygen partial pressure) involves SiO2 formation at the interface and leads to the transformation of the yttrium oxide into Y-based silicates, which, for the thin films, results in the absence of Y2O3 crystalline phase. The H-2/450 degrees C anneal does not modify the film's chemical nature except for a significant reduction of hydrogen content. After annealing under H-2/450 degrees C, a strong improvement of the capacitance behavior is observed, especially on the thin films. (c) 2005 The Electrochemical Society. All rights reserved.