Design Tools for Copper Deposition in the Presence Additives

摘要

Considerations for the development of a plating tool that predicts the spatial uniformity of metallization rates are discussed. Models that attempt to account for the effect of additives on electrode kinetics, which may affect metal deposition rates, must be based upon significant experimental work. The mechanism of two of these additives, polyethylene glycol (PEG) and chloride ions, is investigated via an electrochemical quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS) to understand how a plating tool should account for their effects. The addition of polyethylene glycol (PEG) and Cl~- to an acid copper electrolyte inhibits the deposition reaction for cathodic overpotentials of up to about 150 mV. Adding Cl~- only promotes the deposition reaction, while adding PEG alone has a relatively small effect on electrode kinetics. Frequency shifts of an electrochemical quartz crystal microbalance suggest the adsorption of a monolayer of PEG molecules that are collapsed into spheres provided chloride ions are present, with little adsorption occurring when Cl~- is absent. This behavior is the same for gold and copper surfaces. Simulated results from a model that assumes the adsorption of a nearly complete monolayer of PEG in the presence of chloride ions and no adsorption without Cl~- agree with experimental steady state and EIS results. The primary effect of PEG adsorption, which does not appear to vary with time during an EIS measurement, is a blocking of available surface sites for charge transfer.