SIO2-INDUCED 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 17 0 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 da ta fitting is presented, considering both the quantum yield and the su bstrate-current, It is shown that thick SiO2 data are consistent with tunneling of hot holes created at the anode by impact ionization. Neve rtheless, in thin oxides substrate electron valence-band tunneling pla ys a dominant role. In the last case a quantitative agreement between data and model is obtained considering a smaller SiO2 electron effecti ve-mass for valence-band electrons. In addition, it is shown that ener gy quantization of the silicon conduction-band does not change the ana lysis results. Finally, for the SiO2-Si3N4-SiO2 stacked layer, a model based on Si3N4 electron-valence band injection well explains the expe rimental data, and suggests an important electron-conduction in Si3N4. (C) 1998 Elsevier Science Ltd. All rights reserved.