Quaternary ammonium-based levelers for high-speed microvia filling via Cu electrodeposition

Abstract

Shortening the Cu gap-filling time at microvias by electrodeposition is critical for increasing the productivity of printed circuit board (PCB) fabrication. Additives that can facilitate accelerated Cu bottom-up filling should be developed, and a method to increase the operating current density for Cu electrodeposition without compromising the performance of the additives is necessary to realize a highly productive electrodeposition process. Although it is well known that the behavior of levelers is critical for Cu bottom-up filling, the relationship between the levelers' structure and gap-filling performance is not completely understood, which is the main hurdle to developing a high-speed Cu filling process. This study analyzes the effects of the number of quaternary ammoniums in the levelers on their suppression and synergetic or antagonistic behavior with accelerator and microvia filling. The suppression of the levelers increases with the number of quaternary ammoniums. The highest bottom-up filling performance is achieved when the leveler contains three quaternary ammoniums in the presence of a polymeric suppressor and an accelerator. However, when the operating current density increases two-fold, the leveler-suppressor-accelerator combination loses its ability for bottom-up filling. This study proposes a method to restore the behavior of the additives to obtain successful gap-filling at microvias at a two-fold higher current density.