A comparison of SiSiO 2 interface trap properties in thin-film transistors with thermal and plasma nitrided oxides

Abstract

In this work, electrical properties of the SiSiO 2 interface have been investigated in terms of interface-trap parameters (emission time, capture cross-section, state density) by standard and three-level charge pumping techniques in n-channel thin-film (8 nm) metal-oxide-semiconductor field-effect transistors. Some of the devices have been nitrided in an ammonia plasma reactor and reoxidized in oxygen. For nitrided devices, a significant decrease of interface state density, D it, has been observed as compared with pure oxide devices. This reduction clearly corresponds to both an uniform decrease of D it over the silicon band gap and a decrease of a D it peak in the upper part of the band gap. The evolution of capture cross-sections has been also monitored and found to significantly vary for electron traps. This substantial change in electron interface-trap properties could be at the origin of the augmentation of the high field transconductance observed for these n-channel devices after such a nitridation process.