Electromigration comparison of selective CVD cobalt capping with PVD Ta(N) and CVD cobalt liners on 22nm-groundrule dual-damascene Cu interconnects

Alternate metallization schemes for copper interconnect using selective CVD Co capping at the 22nm technology node are investigated. Control splits fabricated with PVD Ta(N) barrier/liner layers and CuMn alloy seedlayers are compared against interconnects fabricated using a PVD TaN barrier/CVD Co liner scheme with selective CVD Co capping. Secondary ion mass spectroscopy (SIMS) studies of PVD TaN barrier/CVD Co liner structures indicates that top-surface segregation of the Mn-dopant in alloy seedlayers is suppressed in the presence of the CVD Co Liner. Alternate metal capping in the form of selective CVD Co layers is evaluated in combination with CVD Co liners. Good electrical yields are obtained in-line with the Co liner/Co cap scheme. The PVD TaN/Co-Liner/Selective CVD Co cap combination is seen to have greatly enhanced electromigration performance over PVD Ta(N)/PVD CuMn controls, with T50 fail times for the former being ~100x longer than the controls. Kinetics studies of the CVD Co liner/selective Co cap samples show electromigration activation energies of 1.7 eV, a substantial enhancement over the 1.0 eV obtained for the PVD Ta(N)/CuMn controls.