Interfacial reaction induced phase separation in La{sub x}Hf{sub y}O films

Amorphous La{sub x}Hf{sub y}O films containing La at concentrations (x) of 50 and 20% were prepared by atomic layer deposition on ultrathin SiO{sub 2} films (1 nm). We examined the electronic structures and microstructures of the La{sub x}Hf{sub y}O 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 La{sub 2}O{sub 3} and HfO{sub 2} was observed in the La{sub x}Hf{sub y}O films subjected to annealing temperatures over 900 deg. C, although the mixture of La{sub 2}O{sub 3} and HfO{sub 2} 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 La{sub 2}O{sub 3} content in the La{sub x}Hf{sub y}O films, which has a significant influence on the phase separation process and resulting film structure.