Chemistry of active oxygen in RuOx and 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 RuO2via RuOx (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 RuOx (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 RuOx 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.