Role of oxygen in defect-related breakdown in thin SiO2 films on Si (100)
Abstract
The influence of annealing in vacuum and in controlled low-pressure oxygen ambient on breakdown characteristics of thin (∼500 Å) SiO2 films on Si (100) has been studied under ultrahigh vacuum conditions for temperatures 750-900 °C and controlled O2 partial pressures in the range 10-6-5×10-2 Torr. Dark current-voltage measurements on Al-gate capacitors show that vacuum annealing causes low-field self-healing breakdown by the formation of local defects in the oxide. This degradation of breakdown characteristics is suppressed by the presence of sufficient O2 in the annealing ambient, such that the O2 partial pressure must exceed the SiO equilibrium partial pressure by a factor of ∼100×. This behavior suggests that low-field breakdown is a consequence of oxide decomposition (Si+SiO 2→2SiO↑) at defects in the oxide, which is suppressed by reoxidation of the volatile SiO reaction product.