NEW INSIGHT INTO HIGH-FIELD MOBILITY ENHANCEMENT OF NITRIDED-OXIDE N-MOSFETS BASED ON NOISE MEASUREMENT

The mobility crossover phenomenon observed in NH3-nitrided N-MOSFET's has been interpreted by the reduced acceptor-type interface states which are located near and above the conduction band edge. However, a direct confirmation of such a hypothesis is not available from the conventional electrical measurement techniques. In this work, for the first time, we used both 1/f noise and random telegraph signal (RTS) measurements which are capable of probing those oxide traps near and above Si conduction band of energy, to study the modification of interface traps induced by N2O nitridation. The 1/f noise measurement results confirm that thermal nitridation decreases the near-interface oxide trap density at the higher energy levels, as a result, trapping of the mobile electrons is decreased. The RTS measurement further suggests that thermal nitridation moves the oxide traps farther away from the Si/SiO2 interface and thus suppresses the Coulombic scattering of mobile electrons by the trapped charges. Both nitridation-induced interfacial modifications result in enhanced high-field mobility of nitrided-oxide devices over the standard MOS devices.