Evolution of stress-induced surface damage and stress-relaxation of electroplated Cu films at elevated temperatures

Evolution of stress-induced surface damage after annealing in various temperature over 200 degrees C was observed. Deformation mechanisms of electroplated Cu thin films on TaN/SiO2/Si were investigated by performing isothermal annealing between 200 degrees C and 400 degrees C. During heating, fast relaxation and subsequent slow relaxation processes were observed. In contrast, during cooling, only slow relaxation process was observed. Stress relaxation behavior during isothermal annealing was analyzed in terms of power-law creep and diffusional creep. The large variation of exponent n in power-law creep means that those are not main mechanism. The both fast and slow relaxation curve fit well exponential decay function, which can indicate grain-boundary creep is the most plausible mechanism of stress-induced surface damages and stress-relaxation.