Trap-assisted conduction in nitrided-oxide and re-oxidized nitrided-oxide n-channel metal-oxide-semiconductor field-effect transistors

Abstract

The off-state leakage characteristics of n-channel metal-oxide- semiconductor field-effect transistors with pure oxide, low-partial pressure nitrided (LPN) oxide, re-oxidized LPN, and nitrogen-annealed LPN oxide as the gate insulator, were investigated over the temperature range 300-400 K. In the high-field region (above 7 MV/cm), the gate-induced drain leakage was found to be due to band-to-band tunneling for all samples. Low-field conduction was determined to be due to a gate current which was many orders of magnitude higher than the Fowler-Nordheim current observed in capacitors on the same wafers. A trap-assisted tunneling model was employed, using a trap energy of 0.7 eV determined from the activation data, in order to explain the low-field gate current. The most likely cause of this enhanced conduction is oxide degradation in the gate-to-drain overlap region created during the source/drain implant.