Comparison of Dielectric Characteristics of Ta ₂O ₅ Thin Films on RuO ₂ and Ru Bottom Electrodes

Dielectric properties of Ta ₂O ₅ thin films with RuO ₂ and Ru as the bottom electrodes were investigated. The Ta ₂O ₅ thin films were reactively sputtered on the bottom electrodes and then annealed in oxygen ambient at 700°C for 30 min. Using X-ray diffraction and Auger electron spectrometry, it has been found that the Ru bottom electrode was partially oxidized during annealing, while the RuO ₂ electrode remained its structure. However, the annealed Ta ₂O ₅ exhibited a higher dielectric constant, as well as a smaller leakage current, on the Ru electrode than on the RuO ₂ electrode. Accordingly, the Ru bottom electrode is satisfactory for Ta ₂O ₅ storage capacitors, even in a high temperature, oxidizing environment. The divergent electrical performances of two electrodes are attributed to the different crystallinity of annealed Ta ₂O ₅ on Ru and RuO ₂.