Complementary Adsorption of Binary Levelers for Highly Uniform Cu Micropillars

Highly uniform Cu micropillars were electrodeposited on a Cu seed layer in a micropatterned photoresist in the presence of binary levelers containing pyrrolidine and pyridine functional groups. The adsorption behaviors of binary levelers, i.e., 3-hydroxy-6-(tert-butyl)pyridine and pyridinium tribromide in an electroplating bath were investigated by chronopotentiometry with sequential injection of levelers and linear sweep voltammetry with a rotating disk electrode. From electrochemical analysis, pyridinium tribromide composed of a positively charged pyridine ring was strongly adsorbed on the Cu seed surface, relative to 3-hydroxy-6-(tert-butyl)pyridine. Additional microscopy, surface roughness, and nitrogen concentration analyses revealed that the binary levelers were preferentially adsorbed on the center and the edge region of the Cu seed, resulting in a uniform Cu pillar profile. The possible mechanism of highly uniform Cu pillar deposition was discussed in terms of the adsorption behaviors of the levelers dependent on their molecular structures.