Self-assembly of surfactant mixtures for a versatile control of the rate of the heterogeneous reaction: Case study in Cu electrodeposition

• Surfactant mixtures are versatile controllers for the rate of heterogeneous reactions. • The mixture can increase or decrease the rate of Cu electrodeposition. • Various surfactant assemblies are formed in the plating electrolyte. • The formation of assemblies affects the surfactant coverage and the reaction rate. • Surfactant mixture can realize the effective deep via fill. This study introduces surfactant mixtures as versatile controllers for the rate of heterogeneous reactions. Contrary to the use of a single surfactant, a mixture of cationic surfactant and anionic surfactant allows for a more diverse change on the rate of Cu electrodeposition as a typical example of a heterogeneous reaction. Dodecyltrimethylammonium bisulfate (DTABS) as a cationic surfactant suppresses the rate via adsorption on the reaction surface whereas sodium dodecyl sulfate (SDS) anionic surfactant exhibits a weak enhancement. Small-angle X-ray scattering analyses identify various types of surfactant assemblies present in the electrolyte containing DTABS and SDS. Their formation was associated with the change in the rate: the addition of SDS enhances the suppressing effect of DTABS in DTABS-rich mixed micelle phase; however, further addition of SDS neutralizes this effect with the formation of precipitates, vesicles, and SDS-rich micelles. The corresponding changes in the coverage of the surfactant adsorbates on the reaction surface are analyzed electrochemically. The ability of DTABS-SDS mixture can be utilized for Cu electrodeposition on a patterned structure, and it realizes the effective deep via fill. To the best of our knowledge, this is the first demonstration of controlling the rate of heterogeneous reactions using surfactant mixtures.