Crystallographic study on self-annealing of electroplated copper at room temperature

Self-annealing in electroplated Cu films is the dramatic evolution of the microstructure in electroplated Cu near room temperature, and it occurs during a transient period of hours following the electroplating process. This study discusses the change of grain size and orientation in self-annealing of Cu films electroplated by an additive-free sulfate bath using X-ray diffraction and electron backscatter diffraction techniques. We found that the self-annealing started at the interface between the substrate and the electroplated Cu film. Immediately after the electroplating process, orientation of the Cu grains in the region near the interface was similar to that of the substrate. This indicates that the grain growth was affected by the substrate. Then, grain growth and change in orientation of the electroplated Cu film at room temperature became independent from the orientation of the substrate. The electroplated Cu film had many high-angle-grain boundaries (HAGBs) before incubation, and the fraction of HAGBs reduced as incubation time increased. Self-annealed Cu grains in the electroplated Cu film had many multiple twins, which came from low stacking-fault energy of Cu.