Leakage current reduction of chemical-vapor-deposited Ta2O5 films on rugged polycrystalline silicon electrode for dynamic random access memory application

Abstract

In this paper we describe the electrical and physical characterizations of Ta2O5 films on rapid thermal nitrided (RTN) rugged polycrystalline silicon electrodes for 256 M dynamic random access memory (DRAM) application. To overcome the higher leakage on Ta2O5 films with rugged poly-Si bottom electrodes, we have successfully employed a light oxidation on rugged poly-Si grains for improving the acute angle of surface morphology, and a post-treatment with rapid thermal nitridation of N2O on Ta2O5 films to reduce the leakage. In addition, a RTN pre-treatment is also applied to prevent rugged poly-Si oxidation during a Ta2O5 film deposition that compromises the effective Ta2O5 thickness. Our results show that Ta2O5 film with an effective thickness of 1.4 nm (physical thickness=10 nm) and a low leakage current density of less than 1 X 10(-8) A/cm(2), suitable for 256 M DRAM application, can be achieved. Our results also show that while a light oxidation on rugged poly-Si grains could improve the acute angle between the rugged poly-Si and its congruent amorphous silicon sub-layer, over oxidation on rugged poly-Si grains could degrade the leakage current and the time dependent dielectric breakdown (TDDB) characteristics of the stacked capacitor.