Chemistry of active oxygen in RuO sub(x) and its influence on the atomic layer deposition of TiO sub(2) films

Rutile structured TiO sub(2) 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 RuO sub(2), 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 RuO sub(2) via RuO sub(x) (x: similar to 1.12) was used as a bottom electrode for the ALD growth of TiO sub(2) films. It was found that the growth per cycle of TiO sub(2) at the initial growth stage was drastically increased on RuO sub(x) (RuO sub(2)/Ru mixture) compared to Ru and RuO sub(2). This is attributed to the drastic increase in the chemical activity of oxygen in the mixture film of RuO sub(2)/Ru. The catalytic decomposition of RuO sub(2) with the help of Ru in the film played the crucial role for the increase in the active oxygen. Although RuO sub(2) and Ru mostly retained their structures during the ALD of TiO sub(2) or chemical etching using O sub(3) gas, the RuO sub(x) film, which was composed of 56% RuO sub(2) and 44% Ru, drastically changed its phase composition during the ALD of TiO sub(2) at 250 degree C and changed almost to Ru. Other chemical effects depending on the chemical composition and phase structure were also examined in detail.