Thermal decomposition mechanisms of hafnium and zirconium silicates at the atomic scale

The hafnium and zirconium silicates, (MO2)(x)(SiO2)(1-x), with M=Hf/Zr, are being considered as high-k gate dielectrics for field-effect transistors as a compromise between high permittivity and thermal stability during processing. Using atomic-scale models of silicates derived from hafnon/zircon, stability before and after simulated thermal annealing is calculated within a density-functional approach. These silicates are found to be thermodynamically unstable with respect to decomposition into SiO2 and MO2 (M=Hf/Zr). Segregation mechanisms on the atomic scale are studied leading to an insight as to an why SiO2-rich mixtures undergo spinodal decomposition and why, by contrast, MO2-rich phases are metastable, decomposing below typical process temperatures. (C) 2005 American Institute of Physics.