SiO2- and ONO-induced substrate current in silicon field-effect transistors

The origin of the substrate current of a metal insulator semiconductor field effect transistor (MISFET) when electrons are injected into the gate is investigated. MISFETs with thermal SiO2 (35 Angstrom up to 170 Angstrom) or with a LPCVD SiO2-Si3N4-SiO2 triple stacked layer (with an oxide-equivalent thickness between 115 Angstrom and 130 Angstrom) as gate insulator are used. Comprehensive and accurate quantitative data fitting is presented, considering both the quantum yield and the substrate-current, It is shown that thick SiO2 data are consistent with tunneling of hot holes created at the anode by impact ionization. Nevertheless, in thin oxides substrate electron valence-band tunneling plays a dominant role. In the last case a quantitative agreement between data and model is obtained considering a smaller SiO2 electron effective-mass for valence-band electrons. In addition, it is shown that energy quantization of the silicon conduction-band does not change the analysis results. Finally, for the SiO2-Si3N4-SiO2 stacked layer, a model based on Si3N4 electron-valence band injection well explains the experimental data, and suggests an important electron-conduction in Si3N4. (C) 1998 Elsevier Science Ltd. All rights reserved.