Abstract: Different chemical mechanical polishing (CMP) slurries are used to obtain single-damascene Cu-wires with different surface fluctuations as well as pre-existing surface-defects in wires with rougher surfaces.The presence of such pre-existing defects strongly increases the rate of early failures to almost 100%,reduces electromigration lifetime rapidly to the level of early failures,and changes the multimodal failure distribution into monomodal.The activation energy (0.74±0.02eV) for the failure mechanism associated with these pre-existing defects confirms a dominant surface diffusion.It shows how a weakest link approximation analysis can be applied to a single wire by dividing the wire into relevant segments and assigning different failure mechanisms to the various segments.The analysis confirms that,although surface-defects are not the fastest early failure mechanism,the ten times higher surface-defect-density in the rougher wires is responsible for the observed high early-failure rate and unreliable performance.

Key words: early failure,  surface-defect,  weakest link approximation