Leakage current in thin-films Ta₂O₅ on Si – is it a limiting factor for nanoscale dynamic memories?

Abstract

A critical review of leakage current values and reliability issues for Ta₂O₅ thin films as high-k storage insulators in gigascale dynamic random access memories (DRAMs) is presented. The challenges for reaching the leakage current limits allowable for 1–4 Gbit DRAMs are discussed. The implications for the conduction mechanisms in Ta₂O₅, and their dependence on the parameters of the system Ta₂O₅/Si, are presented. The results of high-temperature oxygen annealing on the conduction mechanism of r.f.-sputtered Ta₂O₅ are illustrated. A leakage current density as low as 10⁻⁸ A cm⁻² at a 1 MV cm⁻¹ applied field has been obtained. It is concluded that the dominant conduction mechanism in the intermediate fields (0.8–1.3 MV cm⁻¹) can be effectively controlled by appropriate technological steps.