Lifetime Modeling And Characteristics Of TDDB In VLSI Copper Interconnection

With the continued scaling of advanced VLSI circuits and application of low-k dielectric materials, the time-dependent dielectric breakdown (TDDB) has become one of the most serious reliability issues. The existence of the barriers make the TDDB failure mechanism in Cu interconnects so different from the Al interconnects without barriers. The traditional TDDB failure mechanism is no longer applicable. In this paper, analyzing the TDDB failure phenomena and establishing the physics mechanism for TDDB degradation. The general continuity equation on Cu+ diffusion and drift is investigated. An improved Cu interconnect TDDB lifetime model was acquired. The improved model presented here introduces a correctional factor and takes into account the effects of electric fields, temperature, and interconnect line spacing. The predictions of the new model regarding TDDB lifetime vs. temperature agree will with the previously published experimental data in the dielectric of SiOX and SiNX. Further more, contrasting to the E model, it is find that the E model overestimates about 40% of the lifetime for SiOX at high electric field (10MV/cm).In additional, in this proposed physics mechanism, taking the interconnect line spacing into the electric acceleration factor make the TDDB reliability issue need to be inspected again. The improved lifetime model with the effect of the interconnect line spacing can provide more accurate prediction. Finally, from the improved lifetime model, an interconnect line spacing of 70nm which maybe result in serious reliability issue is proposed. At the last, some advice for the TDDB reliability is given.