Cu导线表面起伏程度对早期失效的影响

使用两种化学机械抛光剂得到的单层大马士革Cu导线表面起伏程度不同.扫描电镜观察到明显的缺陷出现在大起伏的Cu导线表面.这种表面缺陷导致早期失效比率剧增至几乎100%、电迁移寿命猛降至早期失效的量级、失效时间分布从多模变为单模,其相应的失效机制激活能为0.74±0.02 eV,这说明失效主要是由Cu原子沿导线表面扩散引起的.最弱链接近似被用来分析单根Cu导线:Cu导线被适当均分为若干相互串联、失效机制不同的Cu块,任何一个Cu块的失效都会使整根Cu导线失效.分析结果表明,虽然表面缺陷不是最快的失效机制,但大起伏Cu导线的表面缺陷密度是另一种的10 倍以上,这是其早期失效比率高和可靠性较低的主要原因.

Impact of Cu-Wire Surface Fluctuations on Early Failures

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 the lines with rougher surface.The presence of such pre-existing 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 monomodal.The activation energy (0.74±0.02 eV) for the failure mechanism associated with these pre-existing 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 analysis confirms that,although surface-defects are not the fastest early failure mechanism,the 1-magnitude higher surface-defect-density in the rougher lines is responsible for the observed high early-failure rate and poor reliability performance.