Mechanical and electrical properties of electroplated copper thin films used for thin film interconnection

Micro-texture dependences of both the mechanical and electrical properties of electroplated copper thin films were discussed experimentally considering the change of their micro texture caused by thermal history after electroplating. Both the static and fatigue strength of the films changed drastically depending on their micro texture and it was found that there were two fatigue fracture modes in the films. One was a typical ductile intragranular fracture and the other was brittle intergranular one. The reason for the variation of the strength of the electroplated copper thin films was attributed to the variation of the average grain size and the characteristics of grain boundaries. In addition, the electrical reliability of the electroplated copper interconnections was discussed under electromigration tests. Though abrupt fracture mode due to the local fusion appeared in the as-electroplated films, the life of the interconnections was improved significantly after the annealing at temperatures higher than 200°C. However, typical change of the surface morphology of the film due to the stress-induced migration appeared on the annealed narrow interconnections. This was because of the high tensile residual stress occurred in the film caused by the constraint of the shrinkage of the films by rigid oxide around them during annaeling. These results clearly indicated that the control of both the micro-texture and residual stress is indispensable for improving the reliability of the interconnections.