Charge trapping properties in Ti-doped Ta2O5 films on nitrided Si

The trapping of charge carriers in Ti-doped Ta₂O₅ (6 nm) stacks on nitrided Si during constant current stress of metal-insulator-semiconductor capacitors has been investigated. Both, the charge buildup on pre-existing traps as well as on traps generated by the stress have been taken into account to explain the observed evolution of the gate voltage during the measurement. The cross section of pre-existing traps has been estimated by applying the first order kinetic model. Two types of neutral trapping sites with cross sections of 2.8·10^-18 cm² and 3.7·10^-19 cm² were identified to exist simultaneously in each of the four technologically different Ti-doped Ta₂O₅ stacks. One of these traps (σ = 3.7·10^-19 cm²) is inherent for the Ta₂O₅ structure itself, while the other one (σ = 2.8·10^-18 cm²) originates from the presence of Ti. Evidences are presented which support the idea that Ti-related center might be neutral complex obtained by coupling Ti-atoms with an oxygen vacancy.