MECHANISMS OF INTERFACE TRAP-INDUCED DRAIN LEAKAGE CURRENT IN OFF-STATE N-MOSFETS

An interface trap-assisted tunneling and thermionic emission model has been developed to study an increased drain leakage current in off-sta te n-MOSFET's after hot carrier stress. In the model a complete band-t rap-band leakage path is formed at the Si/SiO2 interface by hole emiss ion from interface traps to a valence band and electron emission from interface traps to a conduction band. Both hole and electron emissions are carried out via quantum tunneling or thermal excitation. In this experiment, a 0.5 mu m n-MOSFET was subjected to a de voltage stress t o generate interface traps. The drain leakage current was characterize d to compare with the model. Our study reveals that the interface trap -assisted two-step tunneling, hole tunneling followed by electron tunn eling, holds responsible for the leakage current at a large drain-to-g ate bias (V-dg) The lateral field plays a major role in the two-step t unneling process. The additional drain leakage current due to band-tra p-band tunneling is adequately described by an analytical expression D elta I-d = A exp (B-it/F). The value of Bit about 13 mV/cm was obtaine d in a stressed MOSFET, which is significantly lower than in the GIDL current attributed to direct band-to-band tunneling. As V-dg decreases , a thermionic-field emission mechanism, hole thermionic emission and electron tunneling, becomes a primary leakage path. At a sufficiently low V-dg, our model reduces to the Shockley-Read-Hall theory and therm al generation of electron-hole pairs through traps is dominant.