Mechanism of Co Liner as Enhancement Layer for Cu Interconnect Gap-Fill

Cu gap-fill is enhanced by replacing the conventional Ta liner with a Co liner in a 22 nm width interconnect structure. The improvement with Co liner seen at the line-end area is attributed to a better resputtered Cu seed profile, which is thicker and exhibits no agglomeration compared to that on Ta liner. The mechanism of Co offering better Cu seed coverage than Ta was further studied and determined to be associated with its better wetting and higher sticking coefficient with Cu during the resputtering process. Similar gap-fill performance was also demonstrated with a reflow Cu seed process. The initial highly conformal Cu seed coverage profile on Co helps ensure a uniform Cu reflow process within the interconnect structure, therefore providing better top-open dimension for electrochemical plating process compared to reflow Cu seed on Ta.