Electroanalytical Study of Organic Additive Interactions in Copper Plating and Their Correlation with Via Fill Behavior

In this study, individual interactions between various classes of organic additives in electrolytic copper plating solutions are characterized by electroanalytical methods. Cyclic voltammetry and chronopotentiometry were used to compare cases of sequential and competitive adsorption of additive combinations to the Cu cathode. Of the polyalkylene glycol (PAG) suppressors investigated, polypropylene glycol was in general a weaker suppressor than polyethylene glycol, showing weaker polarization of the Cu cathode and faster depolarization when combined with bis(sodium sulfopropyl)disulfide (SPS). The rapid depolarization of PAG with SPS resulted in a conformal Cu filling behavior in blind-vias. By itself, the leveler molecule polyvinyl pyrrolidone (PVP) shows very weak and slow suppression compared to the PAG-type suppressors, but depolarization of the Cu cathode is prevented when combined with SPS. The weak polarization of PVP combined with SPS resulted in sub-conformal filling behavior in blind-vias. The potential response of SPS, PAG, and PVP combined was found to be the sum of their individual interactions: PAG adsorbs rapidly to strongly polarize the cathode, but PVP prevents depolarization with time from SPS. This strong and consistent polarization outside the vias resulted in a superconformal filling behavior, with more than twice the thickness of Cu plated in the vias than outside.