Ad/desorption mechanism of amine-terminated polyoxypropylene suppressor in advanced acid copper electroplating

Acid copper electroplating is a fundamental process in modern integrated circuits and printed-circuit boards industries, where micro- to nano- sized interconnect patterns (e.g., line, pad or via structures) can be bottom-up manufactured with excellent service reliability and cost performance. Organic additives are indispensable in acid copper electroplating, which not only affects the electrocrystallization process, but also controls the deposit morphologies. However, the interfacial adsorption mechanism of some industrial additives is not clearly understood. For example, suppressor wtih ethylene oxide (EO) and propylene oxide (PO) block copolymers (EPE). In this work, amine-terminated PO and EO suppressors were comparatively studied in acid copper electroplating, formulated with bis-(sodium sulfopropyl)-disulfide (SPS) accelerator and Janus green (JGB). Ad/desorption mechanism of PO in acid copper plating system and its interaction with other additives are revealed by electrochemical and quantum chemical analyses. The morphologies and crystal orientations of copper films electroplated at different current densities (1, 5 and 10 ASD) are characterized. The results demonstrate that due to existence of hydrophobic methyl groups, PO shows dynamic ad/desorption alternation and limited surface coverage. The unique ad/desorption mechanism of PO is believed to synergize with EO in adsorption of EPE suppressors.