For sub-5 nm oxides there are two different stages for breakdown; soft breakdown (SBD) and hard breakdown (HBD). It has been shown that both SBD and HBD exhibit the same statistics. Therefore, the physical mechanism governing them is the same. The major difference between them is the energy transferred from the capacitor to the localized conducting path. In this paper, a simple equivalent circuit is proposed to explain the effect of the measurement technique, oxide thickness, and test structure area on the detection of soft breakdown. Also an inelastic quantum tunneling model is proposed to discuss the current-voltage characteristics after SBD. The model is also successful in explaining the temperature dependence of SBD IV characteristics.