Reversibility of trapped hole annealing

Annealing under negative bias of metal-oxide-semiconductor field-effect transistors (MOSFETs) previously irradiated and annealed under positive bias is studied as a function of oxide field and time. Using three different sets of samples ranging from hard to soft, it is possible to observe a considerable reversal of the oxide trapped charge component in the two harder sets and essentially none in the soft set. These results are interpreted in terms of electrons tunneling back and forth from the Si substrate to electron traps associated with the simple oxygen vacancy (an E´ center) in the oxide. Some of these compensating electrons do reform the Si-Si bonds broken by the trapped holes. The results are consistent with a large body of previous work. In addition, the data suggest that the energy level of the hole trap is below the valence band edge of Si