Effects of moisture on the breakdown strength and lifetime of low permittivity dielectric for nanometer scale interconnects



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Advanced integrated circuit (IC) technology has implemented new materials for necessary and timely performance improvements. New materials are now required at both the front-end-of-line (FEoL) and back-end-of-line (BEoL) of the device because simple dimensional scaling with standard materials has come with performance costs that negate dimensional scaling performance improvements. At the FEoL, high-[kappa]/metal gate processes are being developed to reduce gate oxide leakage. At the BEoL, Cu-based metallization and low-[kappa] dielectric materials have been developed to reduce BEoL contribution to RC-propagation delay. Cu-based metallization has required change in integration strategy, which has led to concerns about new material reliability performance. Furthermore, continuing pressure to improve device performance requires that a new, more advanced low-[kappa] dielectric be used, which are mechanically and electrically inferior. These performance demands and greater reliability concerns must be balanced. This kind of balance requires that better understanding of the extrinsic threats to device reliability be understood and is the general area of interest for this work. In particular, this study examines the extent of degradation found in low-[kappa] dielectric when it is exposed to ambient moisture and the potential impact of this degradation on intrinsic reliability performance under electrical stress. The integration method is described for low-[kappa] dielectric processing so that potential damages during process can be explained. Local damages can allow moisture incorporation at the expense of additional dielectric performance and reliability degradation. The molecular form of moisture incorporation into low-[kappa] dielectric and potential process methods to reduce moisture incorporation are also discussed. The electrical reliability performance is shown using interdigitated structures through voltage ramped dielectric breakdown study of inter-metal dielectric (IMD). Clear evidence of dielectric degradation is found after extreme moisture incorporation. Moisture penetration impact is also examined on the long-term reliability of integrated low-[kappa] dielectric using time-dependent dielectric breakdown (TDDB). Results show a dramatic change in the observed field acceleration parameter through moisture exposure that is not easily explained in a standard way according to proposed dielectric breakdown models for low-[kappa] dielectrics. A simple modification of the thermochemical [Epsilon]-model is proposed to explain the results.