Redistribution Layer (RDL), composed of layered dielectrics and electroplated copper materials, is a basic structure to rearrange numerous I/O pads on the chip surface in wafer-level advanced packaging. As the key chemicals in electrolyte baths, electroplating additives have undergone continuous development to meet the industrial needs for high-speed and fine-line/fine-pitch applications. Meanwhile, the intricate relationships between additive chemical structures and electroplated copper properties are yet to be well understood. In this work, a pair of triphenylmethane-based dye molecules, i.e., gentian violet (GV) and methyl green (MG), was comparatively investigated as levelers for high-speed RDL copper electroplating. Compared to GV, significantly stronger electrochemical polarization and tunable deposit morphology can be achieved by MG with just one extra quaternized amine terminal. Combining quantum chemical computations, in situ spectroelectrochemical analyses, and microstructural characterization, it is found that MG possesses enhanced electrostatic adsorption, surface coverage and multi-additive synergies, enabling tailored copper trace morphology. This study elaborates the adsorption mechanism and screening criteria of triphenylmethane-derived levelers, and presents a candidate additive structure for high-speed copper electroplating.
Song et al. (Sat,) studied this question.