Synthesis of Quaternary Ammonium Gemini Levelers and Their Action Mechanisms in Microvias Void-Free Copper Filling

Developing a highly efficient leveler in acid copper electroplating solution is one of the primary tasks necessary for achieving superconformal filling of microvias and interconnections in printed circuit boards (PCBs). Two triethylenediamine-based Gemini levelers, both with terminal quaternary ammonium groups, are synthesized and named as GL1 (C8) after reaction of triethylenediamine with 1,8-dichlorooctane and GL2 (C6 with two C–O linkages) after triethylenediamine with 1,2-bis(2-chloroethoxy) ethane. Electrochemical experiments indicate that at 100 rpm and 1000 rpm GL2 combines with a suppressor and accelerator to exhibit greater potential difference of 23 mV than GL1 in 9 mV for Cu2+ reduction, demonstrating that GL2 has a stronger synergistic convection-dependent adsorption (CDA) effect. Microvias copper electroplating experiments confirm that acid copper electroplating solution containing GL2 achieve more effective superconformal void-free filling as it results in FP = 96.1%, while the solution containing GL1 results in FP = 70%. Theoretical calculations indicate that adsorption energy of GL2 is −1037.54 kJ·mol−1, which is lower than GL1 (−1019.06 kJ·mol−1). GL2 displays lower electron density compared to GL1, which facilitates its displacement by accelerator at the bottom. The lower adsorption energy of GL2 suggests the weaker adsorption ability and the stronger CDA behavior.