Electromigration reliability in nanoscale Cu interconnects

Abstract

Electromigration behavior in Cu damascene wires was studied for various Cu grain structures. The grain size was modulated by Cu linewidth and thickness, and by adjusting the wafer annealing process step after Cu electroplating and before Cu chemical mechanical polishing. A larger variation of Cu grain size between the samples was achieved on CMOS 65 nm node technology than previous nodes which was due to the finer line width and thinner metal thickness. The Cu lifetime and mass flow in samples with bamboo, near bamboo, bamboo- polycrystalline mixture, and polycrystalline grain structures were measured. The effects of a Cu(2.5 wt.% Ti) alloy seed, Cu surface pre-clean, and selective electroless CoWP deposition techniques on Cu electromigration were also observed and a significantly improved Cu lifetime was found. The electromigration activation energies for Cu in Cu(Ti) alloy, along Cu/amorphous α-SiC xNyHz interface and grain boundary were found to be 1.3, 0.95 and 0.79 ± 0.05 eV, respectively. In addition the Cu line size effect on the Cu conductivity for Cu area less than 4×104 nm2 was found to be a linear function of the Cu line area. © 2008 Materials Research Society.