Cobalt/copper composite interconnects for line resistance reduction in both fine and wide lines

Co/Cu composite interconnect systems were studied. Since wide Cu lines require a diffusion barrier which is simultaneously applied also to fine Co lines to reduce Co volume fraction, through-Cobalt Self-Formed-Barrier (tCoSFB) was employed to thin down TaN barrier to <1 nm which works as an adhesion layer for Co lines. Line R of fine Co lines was reduced by 30% successfully. The Co/tCoSFB-Cu composite interconnect system is promising to achieve low line R for both fine and wide lines simultaneously in 7nm BEOL and beyond.