Leakage current and reliability evaluation of ultra-thin reoxidized nitride and comparison with silicon dioxides

In this work, we have conducted a systematic investigation of leakage current and reliability for re-oxidized nitride, both in planar films and deposited in the deep trenches for DRAM storage-capacitor applications. It was found that for the same equivalent thickness (Teq), the leakage current of re-oxidized nitride is anomalously higher than that Of SiO2. We demonstrate that this increase in leakage current is caused by a reduction of oxide barrier height from similar to3eV to similar to2.2eV. In addition, the species release and injection process at the anode, by the energetic electrons, is greatly enhanced by the barrier-height reduction. Within the framework of the current understanding of oxide breakdown, this reduction in oxide barrier-height can self-consistently explain the breakdown data in reoxidized nitride films in many aspects: 1) T-BD polarity and thickness dependence; 2) the disappearance of TBD polarity dependence for thinner films; 3) a much stronger T-BD(Q(BD)) thickness dependence causing a crossover effect in comparison with SiO2. This result suggests that the defect generation rate in reoxidized nitride is thickness dependent. Using a cell-based analytical model, we found that the critical defect density at breakdown extracted from the thickness dependence of Weibull slopes is higher than SiO2. The similarities and differences in T-BD (Q(BD)) voltage- and temperature- dependences between reoxidized nitrides and silicon dioxides are discussed. As compared to reoxidized nitride, it is shown that high quality SiO2 can offer a thickness scaling option for storage capacitors assuming silicon dioxide can be successfully fabricated in deep trenches with sufficiently low defect density as required by DRAM applications.