Properties of Al doped Ta2O5 based MIS capacitors for DRAM applications

Al doped Ta₂O₅ (4; 11; 15 nm) stacks on nitrided Si obtained by rf sputtering were studied with respect to their structural, dielectric and electrical properties. Results show that the initial double-layer structure (doped Ta₂O₅ and interfacial SiON layer) transforms during the formation of the top Al electrode into a three-layer structure, which contains an additional layer between the Al electrode and the doped Ta₂O₅. It affects the dielectric properties of the stacks, deteriorating the equivalent oxide thickness (EOT). A satisfactory low level of leakage current (<;10^-7 A/cm² at 1 MV/cm) is obtained in all samples. The current is mainly governed by Poole-Frenkel effect with high level of compensation, reflecting the influence of Al incorporation into the Ta₂O₅ films on their leakage properties.