Dielectric Breakdown in High-K Gate Dielectrics - Mechanism and Lifetime Assessment

Dielectric breakdown in high-k gate dielectrics is discussed from the viewpoints of its mechanism and accurate TDDB lifetime assessment. As for the dielectric breakdown mechanism, we have proposed the generated subordinate carrier injection (GSCI) model. The GSCI model considers that injected subordinate carriers degrade the dielectrics and that breakdown occurs when their number reaches a threshold value. Due to the existence of the trap-assisted conduction current component which does not contribute to breakdown in the measured subordinate carrier current, accurate decomposition into each current component is important for precise lifetime prediction. For this purpose, we have proposed a universal relationship between the voltage acceleration factory of lifetime and the stress gate voltage, the so-called 7-universality. We show that the GSCI model combined with the 7-universality makes possible the precise prediction of the TDDB lifetime. This paper also discusses a new definition of device lifetime limited by the time-dependent device-level leakage current due to multiple soft breakdowns in EOT-scaled regime. Modeling of the statistics of multiple soft breakdowns is proposed for the prediction of the device lifetime defined by this criterion.