Growth of high-density Ru- and RuO2-composite nanodots on atomic-layer-deposited Al2O3 film

Growth of Ru- and RuO₂-composite (ROC) nanodots on atomic-layer-deposited Al₂O₃ film has been studied for the first time using ion-beam sputtering followed by post-deposition annealing (PDA). X-ray photoelectron spectroscopy analyses reveal that RuO₂ and Ru co-exist before annealing, and around 10% RuO₂ is reduced to metallic Ru after PDA at 900 °C for 15 s. Scanning electron microscopy measurements show that well-defined spherical ROC nanodots are not formed till the PDA temperature is raised to 900 °C. The mean diameter of the nanodots enlarges with increasing PDA temperature whereas the nanodot density decreases, which is attributed to coalescence process between adjacent nanodots. It is further illustrated that the resulting nanodot size and density are weakly dependent on the annealing time, but are markedly influenced by the decomposition of RuO₂. In this article, the ROC nanodots with a high density of 1.6 × 10¹¹ cm⁻², a mean diameter of 20 nm with a standard deviation of 3.0 nm have been achieved for the PDA at 900 °C for 15 s, which is promising for flash memory application.