Effects of Thiourea and Allyl Thioura on the Electrodeposition and Microstructures of Copper from Methanesulfonic Acid Baths

This work mainly focuses on the effects of two additives, thiourea (TU) and allyl thioura (ATU), on the electrodeposition behavior and microstructure development of copper deposits plated from the methane-sulfonic acid (MSA) bath. Three variables, including additive types, additive concentration, and current density, have been investigated in order to observe the variation in the crystallographic texture of Cu deposits. From the polarization behavior through the rotating ring disk electrode (RRDE) voltammograms and chronopotentiometric (CP) steady state electrode potential analyses, TU and ATU show the suppression ability of Cu deposition and the interaction strength between Cu 2+ and ATU is weaker than that between Cu 2+ and TU. The operating current density range of the preferential (111) Cu deposition becomes wider with the introduction of TU and ATU additives in the plating bath. The influences of TU and ATU on the nucleation and growth of Cu grains are significantly different, leading to the very different surface morphologies and surface roughness of resultant Cu films although both additives are of the similar molecular structures and show a suppression ability on Cu deposition.