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

The hafnium and zirconium silicates, (M O2) x (Si O2) 1-x, with M=HfZr, 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 Si O2 and M O2 (M=HfZr). Segregation mechanisms on the atomic scale are studied leading to an insight as to an why Si O2 -rich mixtures undergo spinodal decomposition and why, by contrast, M O2 -rich phases are metastable, decomposing below typical process temperatures.