Stress Evolution During Reactive Film Formation

Reactive film formation is widely used in the processing of micro- and nano-devices. Common examples include oxidation of silicon and formation of metal silicides through reactions between metallic films and silicon. The latter is an example of solid-state reactive film formation. During reactive film formation, the molar or atomic volume of the substrate material is significantly changed as it is incorporated into the reaction product. This volume change should lead to a large stress that would affect both the reaction rate and the stress state of the reaction product. The stress generated during reactive film formation may also affect what phase forms as a reaction product. We have studied stress evolution during reactive formation of nickel silicide films, using substrate curvature measurements. We find that the stress generated during reactions is partially relieved through mechanical relaxation, as the reaction proceeds. We have independently characterized the rates of stress generation and stress relaxation as a function of temperature, in order to better understand the stress conditions at the reacting interface. This allows determination of a lower bound for the instantaneous stress generated at the interface where the reaction is occurring. This was found to be 2 GPa in the case of nickel silicide formation.