Understanding the effect of additives in electroless copper deposition: Correlating deposition rates with absorption complexation and

Electroless copper plating has potential in ultra-large scale integrated technology (ULSI) to provide a breakthrough for interconnect scaling, which is the performance limiting factor for further miniaturization of electronic devices. The effect of additives on electroless copper plating has been attributed to either complexation related to charge transfer resistance or adsorption related to double layer capacitance and charge transfer resistance. However, the relative contributions remain to be investigated. In this paper, we studied the effects of additives 2,2'-dipyridine, sodium thiosulfate and rhodanine by AC impedance spectroscopy. The double layer capacitance and charge transfer resistance were calculated from the AC impedance spectra. The electroless copper deposition rates were also measured. Based on these results and the stability constants of additive-Cu(I) complexes, there appear to be two effects of the addition of 2,2'dipyridine in electroless copper deposition: complexation and adsorption. The effect of sodium thiosulfate mainly arises from the strong complexation of thiosulfate with Cu(I). The effects of rhodanine are related to the strong adsorption of rhodanine onto the substrate surface. These results should be useful for predicting the operating mechanism for various additives in electroless copper plating.