An isothermal annealing study of spontaneous morphology change in electrodeposited copper metallization

A systematic investigation of the effect of annealing time and temperature on the incubation period for spontaneous morphology change (SMC) in electrodeposited copper metallization is reported. Based on an additivity principle derived by Mittemeijer for transformations with an Arrhenius-type dependence of kinetics on temperature, it is shown that the remaining incubation time for SMC at room temperature following annealing at a given temperature should be linearly related to the annealing time. By repeatedly scanning atomic-force microscopy images at room temperature, the time at which SMC occurred was determined for films annealed for various times at temperatures ranging from 32 to 60°C. At each temperature studied, the remaining incubation time at room temperature was found to decrease approximately linearly with increasing annealing time, thus experimentally verifying the behavior predicted by the additivity principle. An Arrhenius plot of the measured rates of decrease showed good linearity and yielded a value of 0.48 eV for the activation energy. This is consistent with a vacancy diffusion mechanism for the process occurring during the incubation period, and supports our proposed mechanism for SMC.