Investigation of adsorption behavior of smoothing additives in copper plating electrolytes

Abstract

Smoothing additives are the necessary component of copper plating electrolytes. Choice of the required additive is determined by the type of electrolyte and its pH values. Studies of adsorption behavior of such compounds in electrolytes with different acidities are of current interest. Adsorption activity of poly-N, N'-dimethylsafranine and poly-N, N'-diethylsafranine on the copper electrode in sulfate electrolytes was established in the present work. The dependencies of the differential capacitance of the double electric layer of the copper electrode on the potential which were obtained in acidic (pH 1.7) and neutral (pH 5.9) electrolytes indicate that acidity of the medium has a significant effect on the additive adsorption. The studied organic substances show high adsorption activity in an acidic solution. The likely cause of the established phenomenon in an acid medium is transition of these organic compounds to a protonated state with formation of positively charged amino groups. Cationic groups of the additives are responsible for an additional interaction with the cathode surface and provide stronger adsorption of poly-N, N'-dimethylsafranine and poly N, N'-diethylsafranine on the copper electrode in comparison with a neutral sulfate electrolyte. Poly-N, N'-diethylsafranine with its molecular weight higher than that of poly-N, N'-dimethylsafranine is characterized by higher adsorbability. Since the smoothing effect of additives in electrodeposition of copper coatings is determined by their adsorption properties, it should be expected that the most effective in this process will be the use of poly-N, N'-diethylsafranine at lower pH values of the copper plating electrolytes.