The influence of surface fluctuations on early failures in single-damascene Cu wires: A Weakest Link Approximation analysis

Different CMP slurries are used to obtain single-damascene Cu wires with different surface fluctuations as well as ´intentional´ surface defects in the lines with rougher surface. The presence of such intentional defects strongly increases the rate of early failures up to almost 100%, reduces electromigration lifetime rapidly to the level of early failures, and changes the multimodal failure distribution into a monomodal one. The activation energy (0.74 ± 0.02 eV) for the failure mechanism associated With these intentional defects confirms a dominant surface diffusion. We show how a Weakest Link Approximation analysis can be applied to single lines by dividing the lines into relevant segments and assigning different failure mechanisms to the various segments. The WLA analysis confirms that, although surface defects are not the fastest early failure mechanism, the 10 times higher surface-defect density in the rougher lines is responsible for the observed high early-failure rate and poor reliability performance.