Investigation of bis-(3-sodiumsulfopropyl disulfide) (SPS) decomposition in a copper-electroplating bath using mass spectroscopy

Bis-(3-sodiumsulfopropyl disulfide) (SPS) is a well-known accelerator used to promote "bottom-up filling" in the semiconductor copper (Cu) electroplating process. However, the gap-filling capability and the defect performance of Cu electroplating are impacted as the SPS molecules are decomposed or oxidized. In this study, by-products generated from SPS decomposition and oxidation were identified and quantized using mass spectroscopy. It was found that 1,3-propanedisulfonic acid (PDS) was the most stable species among the SPS by-products. The PDS concentration increased with the increasing surface area of immersed Cu metals. The relationship between the consumption rate of SPS and the generation rate of PDS with different surface areas of Cu metals was particularly investigated. Furthermore, an equivalent circuit was developed and then examined using electrochemical impedance spectroscopy to characterize the properties of the aged bath with the decomposition of SPS.