A Comprehensive Study of Low-k SiCOH TDDB Phenomena and Its Reliability Lifetime Model Development

In the course of Cu/low-k technology development and qualification, low-k time-dependent dielectric breakdown (TDDB) is rapidly becoming one of the most important reliability issues. In order to accurately predict low-k TDDB reliability, it is crucial to clarify the electric field dependence and temperature dependence of time-to-breakdown. In this study, bias-temperature stresses of CVD low-k SiCOH dielectric at the 65nm technology node were conducted over a wide range of fields and temperatures. Based on the extensive long-term test results (longer than one year), it was found that the "square-root of E" (radicE) dependence seems to be the best choice for modeling field dependent TDDB data. It was also determined that the TDDB activation energy is dependent on electric field, and that the field acceleration parameter for the radicE model decreases with increasing temperature. The physical mechanism behind radicE and the role of Cu diffusion during bias-temperature-stress are discussed, and an electron-fluence-driven, Cu-catalyzed SiCOH breakdown model is introduced. Finally, it is emphasized that great care must be taken in evaluating low-k dielectric TDDB when different stress fields and temperatures are used for chip operational lifetime projections