Electromigration threshold for Cu/low k interconnects

Electromigration (EM) statistics and critical current-density line-length product (jL)(c) were investigated for Cu interconnects integrated with oxide, CVD low k, porous MSQ, organic polymer dielectrics. The EM activation energy was found to be about 0.8 to 1.0 eV, which is commonly associated with mass transport at the Cu/SiNx cap-layer interface. The lower EM lifetime and threshold product (jL)(c) can be attributed to a smaller back stress due to less thermomechanical confinement in the low k structures. The confinement effect can be expressed in terms of an effective modulus B to account for EM behavior and threshold products of low k structures. For all the ILDs studied, (jL)(c) showed no temperature dependence but for the organic polymer, j dependence was observed.