Invasion percolation model for abnormal TDDB characteristic of ULK dielectrics with Cu interconnect at advanced technology nodes

With the continuing aggressive scaling of interconnect dimensions and introduction of new lower k materials, dielectric TDDB reliability margin is greatly reduced. In this paper, a comprehensive investigation on an abnormal low-k TDDB characteristic, a systematic degradation of Weibull slopes at lower stress voltages, was conducted for Cu and CuMn alloy interconnect with porous ultra low-k (ULK) CVD dielectric (k = 2.4). Based on extensive electrical and physical evidences, such abnormal TDDB characteristic was attributed to slow metallic diffusion in bulk ULK induced by Mn and Cu segregation. A new TDDB model based on invasion percolation was proposed to successfully model the observed abnormality. CuMn interconnect with robust liner to assure metal free ULK has become important for TDDB reliability.