Charge Trapping in Interface Doped MNOS Structures

摘要

Evaporated tungsten interface dopant, oxide-nitride interface and nitride bulk traps in MNOS structures were examined using charge centroid and thermally stimulated current (TSC) techniques. Trapping in dopant traps occurred at low injected charge levels. Above a 'saturation' level trapping occurred in the nitride, and the charge centroid penetrated into the nitride. TSC measurements were made on MNS, MNOS, and interface doped MNOS devices. Analysis of TSC spectra yielded trap depths for the interface dopant and oxide-nitride interface of 1.71 - 1.86 and 0.70 - 1.34 eV respectively, and charge densities up to 6 x 10 to the 12th power/sq cm and 3 x 10 to the 13th power/sq cm respectively. A model of MNOS charging and discharging was developed. Electron charging is by Fowler-Nordheim (F-N) injection from the silicon into the oxide conduction band, trapping at the oxide-nitride interface and Poole-Frenkel (P-F) conduction in the nitride. Discharging occurs by: (1) F-N injection of holes from the silicon into the oxide valence band and recombination with trapped electrons at the oxide-nitride interface and the nitride, and (2) redistribution of trapped electrons toward the silicon via P-F conduction and F-N injection from the nitride into the silicon. Calculated write/erase and charge centroid characteristics were compared with measured data. (Author)