In semiconductor copper (Cu) metallization, external organic additives including bis(3-sodiumsulfopropyl disulfide) (SPS) and polyalkylene glycols (PAG) are necessary and widely used to improve the gap-fill capability of Cu electroplating for high-aspect-ratio features. In this study, the interaction of SPS and PAG (SPS-PAG) in the electrolytes was investigated. The results not only show the antisuppression effects of SPS in the presence of PAG, but also indicate the competitive adsorption between SPS and PAG. The proposed mechanism is that when SPS-PAG are added to a plating bath, the Cu-electroplating rate is influenced by competing adsorptions of SPS-PAG and SPS, which disperses PAG species far away from the Cu surface to enhance electroplating rates. The elements (charge-transfer resistance, adsorption-layer resistance, and inductance) of the equivalent circuit simulated using the electrochemistry-impedance spectroscopy data also demonstrate the behavior of SPS-PAG competing reactions. (C) 2008 The Electrochemical Society.