A new oxide degradation mechanism for stresses in the Fowler-Nordheim tunneling regime

In this study, voltage and current stress measurements in the Fowler-Nordheim regime, performed on gate oxides (9 nm-28 nm), indicated that a ramped pre-stress prior to a constant stress can increase the time to breakdown in some cases. In the literature oxide breakdown is said to be related to a fixed amount of trapped oxide charge or to a fixed amount of generated traps in the oxide. However, these models cannot explain our experimental observations. Current-time, current-charge, voltage-time characteristics and results of high frequency pre-stresses have been extensively studied in order to gain information about the charge trapping properties of the virgin and pre-stressed oxides. It is concluded from experimental results that the rate of initial positive charge build up in the oxide during the constant stress is a key factor for oxide degradation and breakdown.