Mechanisms of interface trap-induced drain leakage current in off-state n-MOSFET's

An interface trap-assisted tunneling and thermionic emission model has been developed to study an increased drain leakage current in off-state n-MOSFET's after hot carrier stress. In the model, a complete band-trap-band leakage path is formed at the Si/SiO/sub 2/ interface by hole emission 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 /spl mu/m n-MOSFET was subjected to a dc voltage stress to generate interface traps. The drain leakage current was characterized to compare with the model. Our study reveals that the interface trap-assisted two-step tunneling, hole tunneling followed by electron tunneling, holds responsibility for the leakage current at a large drain-to-gate bias (V/sub dg/). The lateral field plays a major role in the two-step tunneling process. The additional drain leakage current due to band-trap-band tunneling is adequately described by an analytical expression /spl Delta/I/sub d/=Aexp(B/sub it//F). The value of B/sub it/ about 13 mV/cm was obtained in a stressed MOSFET, which is significantly lower than in the GIDL current attributed to direct band-to-band tunneling. As V/sub dg/ decreases, a thermionic-field emission mechanism, hole thermionic emission and electron tunneling, becomes a primary leakage path. At a sufficiently low V/sub dg/, our model reduces to the Shockley-Read-Hall theory and thermal generation of electron-hole pairs through traps is dominant.<
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