Nucleation and Growth of Copper on Ru-Based Substrates: I. The Effect of the Inorganic Components

The effect of the inorganic components, namely copper sulfate (CuSO4), sulfuric acid (H2SO4) and hydrochloric acid (HCl) on the nucleation and growth of copper on Ru-based substrate is reported in the absence and the presence of a suppressor molecule, polyethylene glycol (PEG). In the absence of PEG it was found that the island density, Np was the highest when CuSO4 and HCl concentrations were low while H2SO4 concentration was high. The effect of each component remained similar when all components were mixed together. In the presence of PEG, the effect of CuSO4 and H2SO4 remained similar. However, for the HCl, an optimal concentration was found where Np reached a maximum value. The study illustrates the importance of an optimal bath composition toward faster coalescence of the Cu islands into a continuous Cu film for direct plating applications.