Ultrathin oxide reliability after combined constant voltage stress and substrate hot electron injection

An experimental investigation on ultra-thin oxides under combined substrate hot-electron injection (SHEI) and tunnelling electrical stress (CVS) is reported. We study the electrical properties of 2.5-1.5 nm-thick SiO2 oxides in N-channel metal-oxide-semiconductor (NMOS) field effect transistors. CVS stress at VG = +3.5 V does not affect the transistor operating parameters but does increase, up to a factor of 10, the gate current. We have verified that the critical parameter of CVS stress is the gate voltage bias, consequently we suggest a model based on energetic electrons creating damage, which, correctly describes the reliability of ultra-thin SiO2 at CVS condition. In comparison SHEI is observed to be not only dependent on gate bias but also on the electric field in the oxide. A comparison of each parameter either injected charge or current, gate and substrate voltage or oxide field is experimentally done. Based on these and previous results, the defect creation probability for CVS and SHEI stress is fitted over gate voltage to resolve two defect generation mechanisms.