Abnormal Cu Grain Growth by External Stress on Electroplated Cu Films

In this study, the effect of external stress on the Cu microstructure evolution of electroplated Cu films was studied. We found that, with applying external compressive stress, abnormal grain growth occurred in the electroplated Cu films during thermal annealing. By studying the crystalline orientation mapping, we found the abnormal grain growth was attributed to the fast grain growth of the favorable Cu grains. We conclude that Cu grains with the (201) preferred orientation are the most favorable for the abnormal grain growth model under the external stress of 150 MPa and 300 MPa. Typically, subgrains (polygonization) formed by the dislocation rearrangement do not likely form in Cu, which is known to have a low stacking fault energy. Yet, by applying external stress, the energy barrier for the dislocation motion in Cu reduces. Subgrains and subgrain boundaries are observed in the Cu grains of electroplated Cu film when applying external stress.