Effect of Al gate on the electrical behaviour of Al-doped Ta2O5 stacks

Abstract

The electrical behaviour of Al-doped Ta2O5 films on nitrided silicon and implemented in Al-gated MIS capacitors has been studied. The dopant was introduced into the Ta2O5 through its surface by deposing a thin Al layer on the top of Ta2O5 followed by an annealing process. The HRTEM images reveal that the initial double-layer structure of the stacks composed of doped Ta2O5 and interfacial SiON layer undergoes changes during the formation of the Al gate and transforms into a three-layer structure with an additional layer between the Al electrode and the doped Ta2O5. This layer, being a result of reaction between the Al gate and the Al-doped Ta2O5, affects the overall electrical properties of the stacks. Strong charge trapping/detrapping processes have been established in the vicinity of the doped Ta2O5/SiON interface resulting in a large C–V hysteresis effect. The charge trapping also influences the current conduction in the layers keeping the current density level rather low even at high electric fields (J < 10−6 A cm−2 at 7 MV cm−1). By employing a three-layer model of the stack, the permittivity of both, the Al-doped Ta2O5 and the additional layer, has been estimated and the corresponding conduction mechanisms identified.