Surface-Directed Spinodal Decomposition In The Pseudobinary Alloy (Hfo2)(X)(Sio2)(1-X)

Hf silicate films (HfO2)(0.25)(SiO2)(0.75) with thicknesses in the range 4-20 nm were grown on silicon substrate by atomic layer deposition at 350 degrees C. Hf distributions in as-grown and 800 degrees C annealed films were investigated by high resolution transmission electron microscopy (HRTEM), angle-resolved x-ray photoelectron spectroscopy (ARXPS), and medium energy ion scattering (MEIS). HRTEM images show a layered structure in films thinner than 8 nm. The ARXPS data also reveal a nonuniform distribution of Hf throughout the film depth. Diffusion of SiO2 to the film surface after a longer time anneal was observed by MEIS. All these observations provide evidence for surface-directed spinodal decomposition in the pseudobinary (HfO2)(x)(SiO2)(1-x) alloy system. (C) 2010 American Institute of Physics. [doi:10.1063/1.3448232]