Kinetics of the formation of C49 TiSi2 from Ti-Si multilayers as observed by in situ stress measurements

Abstract

The formation of C49 TiSi2 from sputter-deposited amorphous Ti-Si multilayers on Si(100) substrates was studied during isochronal and isothermal heat treatment. The formation process was analyzed for multilayer periodicities (i.e., the thickness of one Ti and one Si layer) of 1, 5, and 12 nm, respectively, by in situ stress measurements and differential scanning calorimetry (DSC). A strong correlation between the evolution of the stress and the formation of the C49 TiSi2 phase was found. During heat treatment an abrupt change of the stress in the film was observed. DSC and x-ray diffraction experiments revealed that this change of the stress coincides with the formation process of the C49 TiSi2 phase. The transition temperature of the Ti-Si multilayer to the C49 TiSi2 phase shifts from ∼295 to ∼550 °C with increasing multilayer periodicity. From kinetic analysis of the experiments the activation energy of the C49 TiSi2 phase formation process was acquired. For the smallest periodicity of 1 nm an effective activation energy of 170±25 kJ/mol was found, for multilayers with 12 nm periodicity the activation energy was 280±40 kJ/mol. The difference in activation energy is explained by different rate-limiting steps during silicide formation as a function of the multilayer periodicity. DSC measurements revealed two processes during the formation of the C49 TiSi2 phase: mixing and crystallization. The enthalpy for mixing for Ti-Si multilayers with periodicities of 1 and 12 nm was −38 and −33 kJ/mol, respectively. The crystallization enthalpy was comparable for both periodicities: −5 kJ/mol.