TEMPERATURE-DEPENDENT POSITIVE OXIDE CHARGE ANNEALING BY ELECTRON-TUNNELING

The charge transfer processes between hole traps in SiO2 and the adjac ent Si have been investigated. The annealing of positive oxide charge in the Si/SiO2/Al structures can be described by a modified tunnelling model. The main topics are the correct description of the wavevector in the whole oxide bandgap using a two-band approximation and the cons ideration of the temperature-dependent occupation of tunnel states at the silicon interface. Holes are generated and trapped in the oxide ne ar the Si/SiO2 interface during vacuum ultraviolet irradiation (10.2 e V) at positive gate voltage. Subsequent annealing is observed in the t emperature range from 80 K to 420 K. Measurements and calculations are in good agreement for a hole trap energy E(t0) = 6.5 +/- 0.2 eV above the oxide valance band edge. In our model the temperature influence c an be explained by the Fermi occupation function of the silicon states which are the initial states for tunnelling transitions. The bias dep endence of oxide charge annealing is also consistent with this model a nd reflects the dependence of the tunnelling rate on the applied field due to the shift of hole trap states relative to the silicon Fermi le vel.