Structural and electrical characterizations of yttrium oxide films after postannealing treatments

We investigated annealing effects on yttrium oxide films elaborated at 350°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 O₂ at 700°C and under H₂ at 450°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, ∼40 and ∼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°C anneal does not modify the film's chemical nature except for a significant reduction of hydrogen content. After annealing under H ₂/450°C, a strong improvement of the capacitance behavior is observed, especially on the thin films.