Quantitative investigation of titanium/amorphous-silicon multilayer thin film reactions

Growth of amorphous-titanium-silicidc and crystalline C49 TiSi₂ in titanium/amorphous-silicon multilayer films was investigated using a combination of differential scanning calorimetry (DSC), thin film x-ray diffraction, Auger depth profiling, and cross-sectional transmission electron microscopy. The multilayer films had an atomic concentration ratio of 1Ti to 2Si and a modulation period of 30 nm. In the as-deposited condition, a thin amorphous-titanium-silicide layer was found to exist between the titanium and silicon layers. Heating the multilayer film from room temperature to 700 K caused the release of an exothermic heat over a broad temperature range and an endothermic heat over a narrow range. The exothermic hump was attributed to thickening of the amorphous-titanium silicide layer, and the endothermic step was attributed to the homogenization and/or densification of the amorphous-silicon and amorphous-titanium-silicide layers. An interpretation of previously reported data for growth of amorphous-titanium-silicide indicates an activation energy of 1.0 ± 0.1 eV and a pre-exponential coefficient of 1.9 × 10⁻⁷ cm²/s. Annealing at high temperatures caused formation of C49 TiSi₂ at the amorphous-titanium-silicide/amorphous-silicon interfaces with an activation energy of 3.1 ± 0.1 eV. This activation energy was attributed to both the nucleation and the early stages of growth of C49 TiSi₂. The heat of formation of C49 TiSi₂ from a reaction of amorphous-titanium-silicide and crystalline titanium was found to be –25.8 ± 8.8 kJ/mol and the heat of formation of amorphous-titanium-silicide was estimated to be –130.6 kJ/mol.