Time dependent dielectric breakdown of thermally evaporated HfO ₂ for nanoscale devices

Charge trapping and time dependent dielectric breakdown (TDDB) characteristics of 50nm thermally evaporated HfO ₂ films have been investigated by applying constant current stress (CCS), Condensation of the films after anneal ruled out the existence of interfacial layer. Low effective barrier height at HfO ₂Si interface facilitated considerable F-N injection of electrons from substrate during CCS. After filling up of existing traps, neutral bulk oxide traps generation, due to interaction of energetic electrons with oxide, dominated initially. This was followed by extensive neutral interface states generation due to injection of anodic species at high oxide electric field (E _ox). E _ox thresholds for former and latter generation mechanisms have been experimentally found to be around 0.4-0.5MV/cm and 0.8-0.9MV/cm respectively. It has been observed that continuous increment of stress induced neutral traps, whose generation rate increases exponentially with stress level, lead to dielectric breakdown by creating percolating path of defects across the oxide. Weibull plot of charge to breakdown (Q _BD) distribution suggests that intrinsic breakdown is dominant.