Roles of Additives in Damascene Copper Electropolishing

Abstract

This study explores how the dissolution of damascene Cu depends on accelerators of organic acids in alcohol-containing electropolishing electrolytes. Four two-additive electrolytes that contain different accelerators, acetic, citric, citrazinic, and benzoic acids, are evaluated. At the bottom of damascene features, an esterification reaction between alcohols and organic acids efficiently forms a highly resistive layer and reduces the acidity of the solution. Accordingly, outside the damascene features, the rate of removal of Cu is dominated by the acidity of electrolytes but, inside the features, it is also determined by the resistance of the viscous layer. For a weak acidic additive, acetic acid, an extremely high additive concentration is introduced to sustain the moderate acidity of the solution to initiate intense esterification. Therefore, acetic-acid-based two-additive electrolytes exhibit excellent Cu planarization capability.