Charge Trapping at Deep States in Hf–Silicate Based High- κ Gate Dielectrics

We have observed charge trapping during constant voltage stress in Hf-based high-K dielectrics at deep traps as well as at the shallow traps. ΔV FB and leakage current dependence on these deep traps further suggest that trapping at deep levels inhibits fast ΔV T recovery. The earlier findings where charge trapping seemed to be very transient due to the presence of a large number of shallow traps and trapped charge could be eliminated by applying a reverse direction electric field may no longer be valid. The experimentally observed trap energy levels from low-temperature measurements establish a relationship between the origin of the deep traps and their dependence on O vacancy formation in Hf-silicate-based films. Substrate hot electron injection gives rise to significant electron trapping and slow post-stress recovery under negative bias conditions, which confirms that O-vacancy-induced deep defects determine the transient behavior in Hf-silicate-based high-K gate dielectrics. It is further shown that negative-U transition to deep defects is responsible for trap-assisted tunneling under substrate injection. A fraction of the injected electrons remains trapped at the deep defects and gives rise to significant ΔV FB . This has the potential to be the ultimate limiting factor for the long-term reliability of Hf-based high-K gate dielectrics.