Interfacial Leveler-Accelerator Interactions in Cu Electrodeposition

We investigate the effect of amine-based leveler additives on the catalytic function of the accelerator at the Cu-electrolyte interface. In the presence of the bis-(sodium sulfopropyl)-disulfide (SPS) accelerator, chronopotentiometric measurements show the potential changes from inhibition of the levelers increased with molecular weight and were greater to those of glycol-based suppressors. In situ surface-enhanced Raman spectroscopy (SERS) revealed significant conformational changes of the surface-adsorbed SPS in the presence of the amine-based levelers. This leveler-induced conformational perturbation of SPS diminishes the activity of SPS. SERS also revealed decreased coverages of surface-adsorbed SPS in the presence of the high molecular weight amine-based levelers at negative potentials, indicating that the leveler limits direct contact of SPS with the surface. Decreased coverages were also found for adsorbed chloride in the presence of all levelers considered, likely contributing to the deactivation of the accelerative effect of SPS. Secondary-ion mass spectrometry (SIMS) analysis of Cu electrodeposited from solutions comprised of a linear polyethyleneimine (PEI), SPS, and Cl- show increased S, Cl, and C content in the deposit relative to solutions absent PEI, indicating the presence of PEI results in co-incorporation of these additives. This leveler-assisted incorporation of SPS and Cl- also serves to mitigate SPS acceleration.