Electromigration reliability of dual damascene Cu/CVD SiOC interconnects

Electromigration (EM) characteristics were evaluated for multilevel copper test structures embedded in a CVD SiOC low k inter-metal dielectric. After electromigration stress testing, Cu extrusion along the interface between SiOC and the SiN dielectric diffusion barrier was revealed as the primary cause of EM failure. No evidence of cracking or mechanical weak points was observed in the bulk SiOC film; thus improved EM lifetime is expected from enhancement in the adhesion strength of SiN to SiOC. The calculated EM activation energies for 0.35 μm via chains and 0.5 μm via chains are 0.82 eV and 0.93 eV, respectively. The current density exponent (n) was measured to be about 1, which is consistent with the void growth mechanism in Cu. The critical length was found to decrease with increasing current density, and the j·L _c product was determined to be approximately 7500 A/cm.