Anodic Oxidation of SPS Resulting in PDS Formation and the Influence of PDS on Electrolytic Copper Via Filling Performance

Electrolytic copper via filling based on three additive component copper sulfate bath chemistry has been and currently is widely used in electronic packaging. Progression in copper sulfate plating chemistry continues to promote device densification, which is vital to development of smart phones among other devices. Bath maintenance is an important aspect of ensuring filling performance, where in addition to additive concentration, additive decomposition product concentrations also require management. In order to further elucidate bath chemistry and possibly methods to improve performance, degradation of the disodium 3,3'-dithiobis(1-propanesulfonate) (SPS) additive, which is employed as brightener, during copper via filling by electrodeposition and the influence of a byproduct on plating were investigated. Oxidative decomposition of SPS and formation of disodium 1,3-propanedisulfonate (PDS) at an IrO₂ coated Ti insoluble anode during electrolysis were confirmed by NMR analysis. Furthermore, formation of PDS by chemical oxidation of SPS was also observed, suggesting anodic oxidation as the mechanism for PDS formation in the plating bath during electrolysis. By addition to a fresh bath, PDS was then shown to compromise via filling performance, where increase in PDS concentration resulted in a proportional performance decrease. This study clarified the anodic oxidation of SPS to PDS under electrolytic filling conditions and that the PDS concentration correlated to the filling ability of the copper plating bath.