Room Temperature Evolution of Microstructure and Resistivity In Electroplated Copper Films

We demonstrate that at room temperature (21° C), electroplated Cu films undergo microstructural changes which are manifested by a large decrease in resistivity. The electroplated, 1um thick films were monitored in situ using resistance and stress analysis and ex situ using focused ion beams (FIB), theta-theta x-ray diffraction (XRD) and pole figure analysis. The films, while held at 21° C, undergo a 20 to 25% decrease in resistivity and a decrease in compressive stress to near zero values. The resistance and stress changes are dirven by complete recrystallization of the film where grains grow in size by over and order of magnitude. The recrystallization leads to a microstructure which has a stronger Cu(111) fiber texture. The effective activation energy for the process was calculated using the Kissinger analysis method applied to plots of in situ resistance as a function of temperature with varied heating ramp rates. The processes involved in the evolution of the new microstructure in the electroplated Cu films have an effective activation energy of 0.92 ± 0.04 eV, which is consistent with grain boundary diffusion as the dominant mechanism.