Electrochemical study of electroless Co-W-P alloy deposition

The electrochemical mechanism of electroless Co-W-P deposition, in a chloride based solution, with hypophosphite as reducing agent using polarization measurements was studied. The overall mechanism and transfer coefficient of Co-W-P electroless plating was determined by the technique based on the application of the mixed potential theory to rotating disk electrode. The partial anodic polarization and partial cathodic polarization curves at various pH and various compositions of metal ions and reducing agent show that the Co-W-P electroless deposition reaction still follows the mixed potential theory even in a 3-component system. This electrochemical experiment also describes that the reaction rate determining step is the oxidation reaction of hypophosphite under normal operating condition. The conclusion of this experiment is that the electroless Co-W-P deposition can be explained by the mixed potential theory as a combination of oxidation of hypophosphite and the reduction of Co W and P complex ions. The deposition rate is higher at higher pH and higher concentration of hypophosphite. Results of this study were used for a high quality Co-W-P thin film deposition for barrier formation in 0.25 μm ULSI technology.