The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating

The inhibition effect of different polyether suppressors on the nucleation and growth of copper during galvanostatic deposition was investigated as a function of deposition current density and suppression strength. An increase in the deposition current density resulted in higher island density, (Np). The copper island density increased significantly in the presence of suppressor additive while keeping the other parameters constant. Modification of the polyether molecular weight (Mw) and structure exhibited different inhibition behavior, which in turn affected the island density. Analysis of the potential-time transients shows that an exponential relationship exists between the island density, Np, and the actual deposition overpotential. Interestingly, the same exponential dependence between copper island density and overpotential as those in the additive free CuSO4 solutions was found. This relationship provides a universal equation for Np on RuTa surface and thus, the island density can be estimated from the actual deposition overpotential irrespective of the Cu2+ concentration, suppressor kind and current density. High Np can be achieved by controlling the overpotential which can be manipulated by increasing the current density, lowering the Cu2+ concentrations and adding a strong suppressor to the plating solution. These observations imply that a better solution composition can be tailored to fulfill the requirements for direct plating applications.