Spinodal decomposition in amorphous metal–silicate thin films: Phase diagram analysis and interface effects on kinetics

Abstract

Among several metal silicate candidates for high permittivity gate dielectric applications, the mixing thermodynamics of the ZrO2–SiO2 system were analyzed, based on previously published experimental phase diagrams. The driving force for spinodal decomposition was investigated in an amorphous silicate that was treated as a supercooled liquid solution. A subregular model was used for the excess free energy of mixing of the liquid, and measured invariant points were adopted for the calculations. The resulting simulated ZrO2–SiO2 phase diagram matched the experimental results reasonably well and indicated that a driving force exists for amorphous Zr–silicate compositions between ∼40 mol % and ∼90 mol % SiO2 to decompose into a ZrO2-rich phase (∼20 mol % SiO2) and SiO2-rich phase (>98 mol % SiO2) through diffusional phase separation at a temperature of 900 °C. These predictions are consistent with recent experimental reports of phase separation in amorphous Zr–silicate thin films. Other metal–silicate systems were also investigated and composition ranges for phase separation in amorphous Hf, La, and Y silicates were identified from the published bulk phase diagrams. The kinetics of one-dimensional spinodal decomposition normal to the plane of the film were simulated for an initially homogeneous Zr–silicate dielectric layer. We examined the effects that local stresses and the capillary driving force for component segregation to the interface have on the rate of spinodal decomposition in amorphous metal–silicate thin films.