Dominant factors in TDDB degradation of Cu interconnects

The field acceleration factor (γ) for the E-model of time-dependent dielectric breakdown (TDDB) in various Cu interconnect structures has been studied. The γ for pSiCN structures is larger than that of pSiN structures and independent of the kind of interlayer dielectric material or other processes used to make it. The relationship between the breakdown electric field strength (E_BD) and the TDDB lifetime has been investigated. It has been demonstrated that the TDDB lifetime can be predicted from experimentally measured E_BD and γ. An E_BD of at least 4.2 MV/cm is necessary to assure ten-year reliability under 0.2 MV/cm operation. Moreover, the important factors influencing the TDDB lifetime for Cu interconnects have been discussed. These include the Cu chemical-mechanical polishing (CMP), the post-CMP annealing, line edge roughness, and fine line effect.