Abstract
In copper-plating baths for filling of submicron features, a combination of additives regulates the distribution of deposition rate, and in the proper concentrations produces superconformal filling. The present study is built on the competitive adsorption model of superconformal filling in which an adsorbed suppressor, in this instance benzyl viologen or polyethylene glycol, is displaced from the surface by the accelerant 3-mercapto-1-propane sulfonic acid (MPS) during copper electrodeposition. The change in deposition current after progressive additions of suppressor or accelerant was used to determine the surface coverage of each additive as a function of its concentration in solution and of temperature. The data were fitted to the Langmuir isotherm, and the free energy and enthalpy of adsorption or displacement were determined. It was shown that adsorption of PEG or BV is a spontaneous exothermic process, and the displacement of PEG or BV by MPS is a spontaneous endothermic process. Although the suppressors form stronger bonds with the surface, the accelerant displaces them due to the resulting increase in surface-excess entropy.
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