Effects of N2O Plasma Annealing on the Characteristics of Tantalum Oxide Thin Films Deposited on TaN/Ta Electrode

Abstract

The effects of N2O plasma annealing on the structural and leakage current characteristics of amorphous and crystallized TaOx thin films deposited on a TaN/Ta bottom electrode by chemical vapor deposition at 350°C were investigated. An interfacial Ta(O,N) layer was formed following the oxidation of the TaN electrode after plasma annealing the TaOx films of ∼25 nm thickness, which decreased the effective capacitance of the thin film capacitors, and the Ta(O,N) layer grew with increasing annealing time or temperature. The growth of the Ta(O,N) layer up to a thickness of 38 nm followed a linear oxidation law with an activation energy of ∼0.74 eV for the annealing of the amorphous TaOx films in a temperature range of 300°C–450°C. However, an activation energy of ∼1.18 eV was found for the linear oxidation of TaN within an oxidation thickness of 22 nm, and then, the oxidation switched to a parabolic process with an activation energy of ∼0.8 eV for annealing the crystallized TaOx films. The current–voltage (I–V) relation of the TaOx films was asymmetric with respect to the biasing polarity, and the leakage current decreased with increasing annealing time or temperature due to the formation and growth of a Ta(ON) layer. Barrier heights of 1.08 and 0.74 eV were evaluated from the temperature dependence of the I–V characteristics for the Schottky emission in the amorphous and crystalline 50-nm-thick TaOx films annealed in N2O plasma at 350°C for 10 min, respectively.