Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature–stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.