Scaling Effect on Electromigration in On-Chip Cu Wiring

Electromigration in on-chip plated Cu damascene interconnection has been investigated for metal linewidths form 0.24 um to 1.3 um. Void growth at the cathode end and protrusions at the anode end of the lines have been found to be the main causes of failure. The failure lifetime was found to decrease linearly with decrease in the cross sectional area of the line. This behavior can be explained by interfact diffusion as the dominant path for mass transport and by the bamboo-like nature of the microstructure. The factor of n for the lifetime dependece on current density for 0.28 um wide line, t = t_o j^-n was found to increase from 1 to 2 as j increased beyond 25 mA/um².