Stress development and relaxation during reactive film formation of Ni₂Si

Using continuous wafer-curvature measurements, stress generation was monitored as nickel thin films reacted with silicon substrates to form Ni₂Si during isothermal anneals. A large compressive force developed during the reaction, but gradually relaxed after the reaction was complete. From a model for reactive film formation, a lower limit for the instantaneous stress associated with compound formation was found to be −2.00 ± 0.75 GPa. This instantaneous stress can be explained by a volumetric strain of 1.65 ± 0.62%, which is much smaller than the theoretical volume expansion of 62% in this system. These results suggest that significant inelastic deformation occurs during silicide formation. It was also found that diffusive creep relaxes the growth stress after the reaction. The observed instantaneous stress indicates that the energy of deformation associated with the reaction is of the same order as the energy that drives it, suggesting that stress generation and stress relaxation can play a significant role in the kinetics of reactive film formation.