Competitive adsorption between bromide ions and bis(3-sulfopropyl)-disulfide for Cu microvia filling

Abstract

A three–additive combination of an accelerator, a polymeric suppressor, and an organic leveler is typically utilized in the electrodeposition process to achieve Cu bottom–up filling of microvias on printed circuit boards. The use of several organic chemicals makes maintaining the performance of the electrolyte and additives more complicated due to the decomposition of the organic additives. As a replacement for the organic levelers, inorganic levelers, such as bromide ions, can avoid this problem since halide ions cannot produce organic by–products. This study investigates the effects of bromide ions on the adsorption of polymeric suppressors and accelerators and the influence of the concentration ratio of bromide ions and the accelerator on the bottom–up filling of microvias. The electrochemical analyses reveal that the bromide ions are adsorbed on the Cu surface and interact with the polymeric suppressor, increasing the suppression effect. In addition, bromide ions combined with the polymeric suppressor retard adsorption of the accelerator, and forced convection enhances the inhibitory effect of bromide ions. Electrochemical analyses also suggest that the accelerator to bromide ion concentration ratio is critical for controlling the surface activity for Cu electrodeposition and dictates the bottom–up filling characteristics. Microvia filling experiments indicate that in the optimum concentration ratio range (i.e., 0.2 < [SPS]/[Br‒] < 0.7), Cu electrodeposition starts at the bottom corners of the microvias and is effectively inhibited outside the microvias, leading to successful Cu bottom–up filling at the microvias.