CVD Co capping layers for Cu/low-k interconnects: Cu EM enhancement vs. Co thickness

Co films with various thicknesses were selectively deposited as Cu capping layers by chemical vapor deposition technique. Selectivity of the Co deposition between Cu and dielectric surfaces was improved by both raising the deposition pressure and adopting a pre-clean process prior to the Co deposition. Degree of electromigration resistance enhancement was observed to be dependent on the deposited Co thickness. Compared to the no-Co control, significant EM lifetime enhancement was observed when the Co cap is thicker than 6nm.