We demonstrate that there is an optimum distribution of copper within the aluminium-copper alloy at which the electromigration performance is optimised. We show how this optimum distribution can be achieved using a relatively simple temperature ageing step. This step is devised so as to promote the coating of the grain boundaries with segregated copper atoms. Measurements on MOS transistors are used to confirm that such a step has negligible effect on device performance. We conclude that temperature ageing is a viable method of achieving enhanced interconnect electromigration performance.
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