Influence of Reducing Agent on Chemical Decomposition of Bis(3- sulfopropyl) Disulfide (SPS) in Cu Plating Bath

Abstract

In this study, we investigated the effect of reducing agents to decrease the chemical decomposition of SPS. We added reducing agents (hypophosphite, formaldehyde, glyoxylic acid, hydrazine, and oxalic acid) into the Cu plating bath and examined their effects on the voltammetric response, bath performance, and stability of SPS. Among these, hydrazine and oxalic acid resulted in the formation of precipitates, and thus could not be used for accurate analysis. Hypophosphite was electrochemically active in the cathodic region due to the reduction of metallic phosphite, which led to errors in the CVS analysis. Therefore, it was determined that only formaldehyde and glyoxylic acid could be used as reducing agents in Cu electrolytes. Formaldehyde reduced the rate of SPS decomposition more effectively. The bath performance with and without formaldehyde was evaluated by performing a via-fill test. Consequently, when formaldehyde was not present, SPS was rapidly decomposed by Cu+, and the filling performance became poor after aging for 3 h. However, when formaldehyde was present, the filling performance was maintained for up to 9 h and SPS decomposition in the open-circuit condition rarely occurred. These results indicate that formaldehyde reduces the number of active radicals, thereby reducing the chemical oxidation of SPS.