Interfacial reaction induced phase separation in LaxHfyO films

Amorphous LaxHfyO films containing La at concentrations (x) of 50 and 20% were prepared by atomic layer deposition on ultrathin SiO2 films (1 nm). We examined the electronic structures and microstructures of the LaxHfyO films by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). Phase separation into La2O3 and HfO2 was observed in the LaxHfyO films subjected to annealing temperatures over 900 deg. C, although the mixture of La2O3 and HfO2 is thermodynamically stable. The structural changes that occurred as the result of phase separation were dependent on the concentrations of La and Hf in the films. During the annealing treatment, silicate was produced due to interfacial reactions and the interfacial reactions were found to be dependent on the La2O3 content in the LaxHfyO films, which has a significant influence on the phase separation process and resulting film structure.