Temperature-dependent positive oxide charge annealing by electron tunnelling

Abstract

The charge transfer processes between hole traps in SiO2 and the adjacent 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 consideration of the temperature-dependent occupation of tunnel states at the silicon interface. Holes are generated and trapped in the oxide near the Si/SiO2 interface during vacuum ultraviolet irradiation (10.2 eV) at positive gate voltage. Subsequent annealing is observed in the temperature range from 80 K to 420 K. Measurements and calculations are in good agreement for a hole trap energy E10=6.5+or-0.2 eV above the oxide valance band edge. In our model the temperature influence can be explained by the Fermi occupation function of the silicon states which are the initial states for tunnelling transitions. The bias dependence of oxide charge annealing is also consistent with this model and reflects the dependence of the tunnelling rate on the applied field due to the shift of hole trap states relative to the silicon Fermi level.