Infrared spectroscopy and X-ray diffraction studies on the crystallographic evolution of La2O3 films upon annealing

Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La2O3 films are promising for integration into future NVMs because they are expected to crystallize above 400 degrees C in the hexagonal phase (h-La2O3) which has a higher K value than the cubic phase (c-La2O3) in which most of REOs crystallize. In this work, La2O3 films are grown on Si by atomic layer deposition using La(C5H5)(3) and H2O. Within the framework of the h-La2O3 formation, we systematically study the crystallographic evolution of La2O3 films versus annealing temperature (200-600 degrees C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)(3) occurs. Vacuum annealing of sufficiently thick (> 100 nm) La(OH)(3) layers induces clear changes in FTIR and GIXRD spectra: c-La2O3 gradually forms in the 300-500 degrees C range while annealing at 600 degrees C generates h-La2O3 which exhibits, as inferred from our electrical data, a desirable k similar to 27. A quick transformation from h-La2O3 into La(OH)(3) occurs due to H2O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La2O3 formation. (C) 2008 Elsevier B.V. All rights reserved.