Trapped-electron and generated interface-trap effects in hot-electron-induced MOSFET degradation

A new experimental method is proposed to distinguish the electron-trapping effect in the gate oxide from the interface-trap generation effect in hot-electron-induced nMOSFET degradation. In this method, by selecting the appropriate bias conditions, hot electrons and/ or hot holes are intentionally injected into the oxide region above the channel outside the drain layer, which affects MOSFET characteristics such as threshold voltage and transconductance. The negative charges of electrons trapped in the oxide during hot-electron injection are completely compensated for by the positive charges of subsequently injected and trapped holes, and the trapped electron effect in the degradation is eliminated. Using this method, the causes for hot-electron-induced transconductance degradation (Δgm/gm) are analyzed. As the degradation increases, the trapped-electron effect decreases, and the generated interface-trap effect increases. The relationship of (Δgm/gm)_{it}, = (Δgm/gm) -- is obtained, where (Δgm/gm)_{it} is gmdegradation due to generated interface-traps, and and are fixed numbers. Furthermore φ_{it}/λ (the ratio of the critical value in hot-electron energy for interface-trap generation to the mean free path of hot electrons in Si) is experimentally obtained to be 5.7 × 10⁶eV/cm. Using λ = 9.2 nm [1], a value of φ_{it} = 5.2 eV is derived.