Advanced characterization of oxide traps: The dynamic time-dependent defect spectroscopy

An accurate understanding of oxide traps is essential for a number of reliability issues, including the bias temperature instability, hot carrier degradation, time-dependent dielectric breakdown, random telegraph and 1/f noise. Recent results have demonstrated that hole capture and emission into oxide traps in pMOS transistors are more complicated than the usually assumed Shockley-Read-Hall-like process. In particular, both charging and discharging proceed via a non-radiative multiphonon (NMP) mechanism involving metastable defect states. The existence of these metastable states can be demonstrated by extending the previously introduced time-dependent defect spectroscopy (TDDS) to a more general dynamic case by employing AC stresses and precisely timed discharge pulses during recovery. Application of AC stresses clearly reveals a frequency-dependence of the effective capture time, which confirms the existence of an intermediate metastable state. Application of pulses during recovery, on the other hand, allows extraction of the effective emission time also in depletion as well as in accumulation, thereby clearly revealing a metastable switching state. While all investigated traps show a frequency-dependent capture time constant, suggesting them to be of the same microscopic origin, we find two different kinds of emission behavior, namely fixed positive and switching traps. We finally demonstrate that our multi-state NMP model perfectly captures both cases.