Experimental study of PVD Cu/CVD Co bilayer dissolution for BEOL Cu interconnect applications

Abstract

In this study, we characterize the anodic dissolution behavior of thin PVD Cu/CVD Co bilayer films using linear sweep amperometry in a potassium nitrate electrolyte. The Co and Cu dissolution peaks are well separated, enabling an assessment of the continuity of the Cu overlayers. Complete coverage of the Co film is attained at a PVD Cu overlayer nominal thickness of ∼20 nm. Exposing the bilayer films to various wet solutions (as a "pretreat") followed by a linear potential sweep allows measurement of the Co loss during pretreatment. The impact of a pretreat in Cu plating chemistries with different cupric ion concentrations and various organic additive packages is characterized on the Cu/Co bilayer stack. Electrical data are presented for 24 nm CD dual Damascene BEOL test structures for Cu plating chemistries with different Cu contents. The influence of the plating bath Cu concentration on yield is discussed with respect to the observed dependency of Co loss on the pretreat solution Cu content.