The electrochemical behavior of levelers was studied and compared for two commercial Cu plating chemistries in an effort to correlate the electrochemical behaviors with their impacts on bottom-up filling, impurity incorporation, and grain structures. While a strong complexing between leveler and accelerator resulted in a leveler-sensitive bottom-up filling rate and low impurity level in the deposit, a traditional non-interacting leveler showed little impact on the filling performance and yielded a high impurity incorporation. An oscillatory behavior was reported for the strongly-interacting leveler chemistry during galvanostatic plating, this oscillation manifested itself in both the potential and impurity incorporation. High impurity incorporation is known to inhibit the Cu grain growth; a laminated structure with alternating layers of big and fine Cu grains was obtained by annealing the Cu films plated with the oscillatory behavior.
The effects of suppressor and accelerator on the superfilling of copper are studied for two commercial chemistries. The potential transients during galvanostatic plating were obtained for injections of the industrially recommended dose of accelerator and various doses of suppressor. The potential increase immediately after the injection was found to be strongly dependent on the type of suppressor as well as the amount of suppressor injected. While the transient of the full dose of suppressor represents what happens at the mouth of the feature and the field outside the feature, the bottom of the feature can be simulated by the case in which a fraction of suppressor is injected. The filling results in sub-100 nm lines are well correlated with the differences observed in the potential transients.
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