Beyond interfacial anion/cation pairing: The role of Cu(I) coordination chemistry in additive-controlled copper plating

Abstract This study reinvestigates the electrochemical characteristics of three different suppressor additives that are used in context of industrial copper plating (Damascene, Through-Silicon-Via). It is the particular aim of this contribution to further substantiate our recently introduced classification scheme of suppressor chemistries that relies on their antagonistic and synergistic interplay with MPS (mercaptopropane sulfonic acid/sulfonate). The latter appears as intermediate species in the course of copper electrodeposition in the presence of SPS (bis-(sodium-sulfopropyl)-disulfide). Both the linear sweep voltammetry and potential transient experiments reveal a purely antagonistic interaction between PAG (polyalkylene glycol) based suppressor ensembles and the SPS (MPS precursor) which is rationalized in terms of the coordinative dissolution of a hyper-branched PAG-Cu(I)-Cl coordination network by the MPS. Such purely antagonistic suppressor/MPS interplay is our criterion for a so-called type-I suppressor . A purely synergistic suppressor/MPS interaction is observed for the PEI (polyethylene-imine) which can be considered as a prototypical type-II suppressor . Beyond classical interfacial anion/cation pairing the partly protonated, poly-cationic PEI is capable to form MPS-stabilized Cu(I) adducts. Their suppressing effect relies on an in situ hyper-branching achieved by a combination of Cu(I) coordination and an inner salt formation. Polymerizates of imidazole and epichlorohydrin (Imep) actually show both an antagonistic and a synergistic MPS/suppressor interaction. While free MPS acts as antagonist with respect to the formed Imep-Cu(I)-MPS suppressor adduct it is the MPS coordinated to Cu(I) which serves as crucial co-additive for the Imep suppressor ensemble. It is this interplay of antagonistic and synergistic MPS/suppressor interactions which introduces an extra feedback loop into the reaction cycle of those plating additives thus giving rise to the appearance of non-linear temporal instabilities into the plating characteristics under galvanostatic control.