Charge trapping during constant current stress in Hf-doped Ta 2O 5 films sputtered on nitrided Si

Abstract

Metal–insulator–silicon structures containing Hf-doped Ta 2O 5 dielectric films sputtered on rapid thermally nitrided Si are shown to have very good reliability properties. Stress-induced leakage currents are low, both at low and at high-fields. It is found that charge trapping during the stress is the dominant wear-out mode for very long stress times of 500 s even for injected current densities J s as high as 100 mA/cm 2. Stress curves approach saturation at long stress time, indicating that the trap generation rate is very low, even compared to the observed reduced trapping at pre-existing traps. Applying a trapping kinetics model, two trapping sites with characteristic trapping times τ 1 = 3.2 s and τ 2 = 49 s were determined and attributed to pre-existing defects in the bulk Hf:Ta 2O 5 layer and not in the interfacial SiO xN y layer. It was found that both τ 1 and τ 2 do not depend on J s, which may be explained by the presence of a mechanism of charging the active sites through field activated emission of charge from them.