The Role of SPS, MPSA, and Chloride in Additive Systems for Copper Electrodeposition

This paper documents an experimental study to compare the behavior of bis-(3-sodiumsulfopropyl) disulfide (SPS)–Cl–polyethylene glycol (PEG) and 3-mercaptopropanesulfonic acid sodium salt (MPSA)-Cl-PEG additive systems during copper electrodeposition. These systems are analogous to those used industrially to plate copper lines onto integrated circuits. Galvanostatic experiments show that in the absence of chloride ion, either SPS or MPSA added to the plating solution inhibited copper deposition. Upon the addition of , a rapid transition from inhibition to acceleration was observed for both additives, illustrating the critical role played by the chloride ion in these systems. Potentiostatic experiments performed for the Cl–PEG–SPS and Cl–PEG–MPSA additive systems show that the potential dependency of the Cl–PEG–SPS system was much stronger than that of the MPSA–Cl–PEG system. Differences between the SPS and MPSA additive systems suggest that acceleration may occur through an MPSA pathway. Finally, results with chemical compounds similar to MPSA indicate that the thiol group is associated with inhibition and that a synergistic accelerating relationship exists between the sulfonate group and chloride, presumably due to complex formation.