Electrochemical Investigation of Pd-Free Electroless Co-Based Capping Layers on Cu Surfaces

Electroless Co-based capping layers with dimethylamine borane (DMAB) and hypophosphite as reductants on Cu lines were achieved without Pd activation. The oxidation process of electroless Co-based deposition was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation of DMAB was greatly suppressed with the addition of hypophosphite during electroless CoBP deposition. At low [OH - ], an obvious oxidation peak of hypophosphite was attained due to insufficient formation of BH 3 OH - , which showed slow charge transfer on the Cu surface; at high [OH - ], distinct competition between hypophosphite and OH - and sufficient BH 3 OH - formed enhanced the oxidation of DMAB, indicating fast charge transfer. The selectivity of electroless Co-based deposition was also strongly influenced by [DMAB], [hypophosphite], and [OH - ].