Hole trapping in SiO₂ films annealed in low-pressure oxygen atmosphere

Abstract

The generation of hole traps in thermal SiO2 films on Si(100) has been characterized as a function of O2 partial pressure in the annealing ambient in order to address the chemistry associated with the hole traps. The annealing treatments were carried out in ultrahigh vacuum (base pressure∼5×10-9 Torr) without and with the presence of an intentional (controlled) partial pressure of O2 in the range 10-6-5×10-2 Torr. Hole trapping was characterized using the avalanche injection technique. Annealing in vacuum results in an increased hole trapping rate similar to that observed for high-temperature (T>900 °C) furnace annealing in N2. The hole trapping is reduced upon annealing in O2 containing ambients if the O2 partial pressure exceeds the SiO vapor pressure by at least one order of magnitude. Thus, the presence of sufficient O2 in the postoxidation annealing process suppresses hole trapping. These results appear analogous to the reduction in low-field breakdown when O2 is present, as recently reported. In both cases, it is likely that the O2 serves to reoxidize a defect related SiO product which is generated by Si-SiO 2 reaction at the interface.