Chemistry of active oxygen in RuO_xand its influence on the atomic layer deposition of TiO₂ films

Rutile structured TiO₂ films have received great attention as dielectric materials in capacitors of the next-generation dynamic random access memory (DRAM) due to their high dielectric constant (80-150). Ru or RuO₂, which is one of the most promising electrode materials in DRAM capacitors, is indispensable to form the rutile structure. In this work, a series of the Ru-related layers with compositions ranging from Ru to RuO₂ via RuO_x (x: ∼1.12) was used as a bottom electrode for the ALD growth of TiO₂ films. It was found that the growth per cycle of TiO₂ at the initial growth stage was drastically increased on RuO_x (RuO₂/Ru mixture) compared to Ru and RuO₂. This is attributed to the drastic increase in the chemical activity of oxygen in the mixture film of RuO₂/Ru. The catalytic decomposition of RuO₂ with the help of Ru in the film played the crucial role for the increase in the active oxygen. Although RuO₂ and Ru mostly retained their structures during the ALD of TiO₂ or chemical etching using O₃ gas, the RuO_x film, which was composed of 56% RuO₂ and 44% Ru, drastically changed its phase composition during the ALD of TiO₂ at 250 °C and changed almost to Ru. Other chemical effects depending on the chemical composition and phase structure were also examined in detail.