Suppression Effect of Low-Concentration Bis-(3-sodiumsulfopropyl disulfide) on Copper Electroplating

Abstract

Bis-(3-sodiumsulfopropyl disulfide) (SPS) is a well-known additive that promotes "bottom-up filling" in the copper (Cu) electroplating process. In the literature, SPS has been widely investigated and has proven to have an acceleration effect on Cu electroplating. However, our results show that low-concentration SPS (∼10 ppm) has a suppression effect on the Cu electroplating rate. The suppression behavior of low-concentration SPS is demonstrated using various electrochemical analyses, including the polarization curve, cyclic-voltammetry stripping, and electrochemistry-impedance spectroscopy (EIS). The equivalent circuit simulated from the EIS data shows that the mechanism of low-concentration SPS inhibiting the Cu electroplating rate is caused by an increase in the charge-transfer resistance. This suggests that when SPS concentration is too low, the formation of Cu(I)thiolate complexes is too low to accelerate the Cu electroplating rate while the added SPS still consumes energy from the system. The acceleration effect of SPS concentration on the Cu electroplating rate exists when SPS concentration is larger than ∼100 ppm. © 2007 The Electrochemical Society.