Characterization of Soft Breakdown in Thin Oxide NMOSFETs Based on the Analysis of the Subs.pdf

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 6, JUNE 2001 1109 Characterization of Soft Breakdown in Thin Oxide NMOSFETs Based on the Analysis of the Substrate Current Felice Crupi, Giuseppe Iannaccone, Isodiana Crupi, Robin Degraeve, Guido Groeseneken, Senior Member, IEEE, and Herman E. Maes, Fellow, IEEE Abstract—We have investigated the properties of soft break- increase of the direct tunneling current component due to the down (SBD) in thin oxide (4.5 nm) nMOSFETs with measurements formation of a localized conducting filament which extends of the gate and substrate leakage currents using the carrier separa- into the oxide within 3 nm from the SiO /Si interface. On tion technique. We have observed that, at lower gate voltages, the level of the substrate current exhibits a plateau. We propose that the other hand, Halimaoui et al. [5] found that the best fit of the observed plateau is due to the Shockley-Hall-Read (SHR) gen- the current–voltage ( ) characteristic after SBD with a di- eration of hole-electron pairs in the space charge region and at the rect tunneling mechanism requires a potential barrier height Si-SiO2 interface. At higher voltages, the substrate current steeply of 6.2 eV, which is not realistic. Therefore, they suggested increases with voltage, due to a tunneling mechanism, trap-assisted that SBD coincides with the generation of conducting paths or due to a localized effective thinning of the oxide, from the sub- strate valence band to the gate conduction band, which becomes between the electrodes, in which the transport mechanism is pos