Investigation of Ta–RuO2 diffusion barrier for high density memory capacitor applications

Abstract

The properties of both oxygen indiffusion and oxidation resistance in a Ta+RuO2 layer for high density memory devices were investigated by using Rutherford backscattering spectroscopy, four point probe, x-ray diffraction, x-ray photoelectron spectroscopy, and planar transmission electron microscopy. The Ta+RuO2/Si system sustained up to 800 °C without an increase in resistivity. The Ta+RuO2 diffusion barrier showed a Ta amorphous microstructure and an embedded RuOx nanocrystalline structure in the as-deposited state. The Ta+RuO2 film showed the formation of RuO2 phase by reaction with the indiffused oxygen from atmosphere after annealing in an air ambient. The Ta+RuO2 diffusion barrier showed that Ta is sufficiently bound to oxygen in the as-deposited state, but RuO2 consists of Ru and Ru–O binding state. The Ta–O bonds showed little change compared to the as-deposited state with increasing annealing temperature, whereas Ru–O bonds significantly increased and transformed to conductive oxide, RuO2. Therefore, the Ta layer deposited by RuO2 addition effectively prevented the indiffusion of oxygen up to 800 °C and its oxidation resistance was superior to various barriers reported by others.