Bromide Ion as a Leveler for High-Speed TSV Filling

Abstract

Organic levelers have been essential additives for Cu electrodeposition to achieve defect-free filling of through-silicon vias (TSVs). They selectively inhibit Cu deposition on top of TSVs, avoiding the occlusion of TSV openings and concentrating Cu deposition inside the TSVs. We recently reported that iodide ions (I−) can act as an inorganic leveler to induce defect-free TSV filling. However, it was found that I− considerably decreased the efficiency of Cu electrodeposition because of the formation of an unstable CuI suppression layer on top of the wafer. The CuI layer easily detached from the wafer, and additional electrons were consumed to reestablish the suppression layer during gap-filling. This study introduces a TSV filling process with bromide ions (Br−) as an alternative to I−. Although the suppression strength of Br− to Cu electrodeposition is weaker than that of I−, Br− forms a more stable suppression layer that does not reduce the efficiency of Cu electrodeposition, enabling high-speed TSVs filling. As a result, the filling rate with Br− was twice as fast as that with I− at the same applied current density; thereby TSVs 60 μm deep and 5 μm in diameter were completely filled in 500 s.