Scaling effect on electromigration reliability for Cu/low-k interconnects

We investigated the scaling effects due to line width and barrier thickness on electromigration in Cu/low-k (porous MSQ) interconnects. Multilink test structures were used to measure the statistics of the weak-mode early failures and the strong-mode failures as a function of line width. Three line widths: 0.25, 0.175 and 0.125 /spl mu/m, were studied corresponding to the 180, 130 and 90 nm nodes. Results from our studies revealed intrinsic scaling effects through the line width dependence of the strong-mode EM statistics which are as expected. However, process-related issues were observed leading to decreasing early failure lifetime and reliability degradation for the 0.125 /spl mu/m interconnects. The effect of barrier thickness scaling on the (jL)/sub c/ product was studied using Ta barriers ranging from 75 /spl Aring/ to 175 /spl Aring/ in thickness. The (jL)/sub c/ product was found to decrease with decreasing barrier thickness and the trend can be attributed to a decreasing confinement effect which was estimated using an effective elastic modulus.