Improvements in the Electromigration Performance of an Aluminium-Copper Alloy Metallization by Optimization of the Copper Distribution

The alloying of Al interconnects with Cu has been shown [1] to give a vast improvement in electromigration performance over pure-Al interonnects. In the work presented here it has been demonstrated that there is an optimum degree of Cu distribution at which the resistance to electromigration of an aluminium-copper alloy metallization can befur-ther enhanced. This microstructure is achieved using a relatively simple temperature ageing step to promote the coating of the aluminium grain boundaries with segregated copper atoms. Electromigration lifetimes are shown to be increased by a factor of 2. Measurements on n-MOSFETS have show that such a temperature ageing step has negligible effect on device performance. It is concluded that temperature ageing is a viable method of achieving enhanced interconnect electromigration performance.