Unraveling Adsorption Behaviors of Levelers for Bottom-Up Copper Filling in Through-Silicon-Via

A leveler is one of the most important additives for achieving defect-free Cu-filled through-silicon-via (TSV). In this study, we experimentally investigated TSV filling performance in the presence of three levelers, i.e., pyrrolidone, imine and diazonium. A detailed analysis of the mass change in the levelers from EQCM conclusively verified that the diazonium was strongly adsorbed on the copper surface at a current density of 10 mA/cm2. This behavior was attributed to its unique molecular structure, with a positively charged nitrogen and a carbocation from resonance structure. Observations of via filling suggested that the bottom-up fill performance was obtained in the presence of diazonium. The possible mechanism responsible for defect-free TSV filling is discussed in terms of the adsorption behaviors of levelers, which is dependent on their molecular structures.