Stress in copper films for interconnects

As the scaling down of integrated circuits progresses the demands for the interconnect material will reach a point where aluminium and its alloys can not be used any longer. Copper has the potential to meet future requirements, especially with its low electrical resistivity and high resistance against electromigration. Developing deposition processes for copper it is important to investigate the properties of the deposited films. Mechanical stress in films has a negative influence on the adhesion of the interconnects and the lifetime because of stress migration. Following a simple theory, stress can be traced back to internal stress and thermal stress. Thermal stress can only be reduced with lower deposition temperatures. In this paper sputtered and CVD produced copper films are compared and the reason for stress is discussed. Additionally the change of stress over time was investigated.