Enhanced Electrical Properties of an Al-Doped TiO₂ Dielectric Film on a TiN Electrode by Adopting an Atomic Layer Deposited Ru Interlayer

The physicochemical and electrical properties of Pt/Al-doped TiO2 (ATO)/Ru/TiN capacitors were investigated by adopting an atomic-layer-deposited Ru interlayer between the ATO and the TiN layers. The Ru interlayer induced local-epitaxial growth of the ATO films to the rutile phase, resulting in improved electrical properties. The work function and surface morphology of the Ru/TiN bottom electrode affected the electrical properties of the capacitors. When the Ru interlayer was too thin (<1.5 nm) to completely cover the entire TiN surface, a mixture of rutile/anatase/amorphous ATO dielectric films was grown, resulting in negligible improvement in the electrical properties. With an increased Ru interlayer thickness, the work function of the bottom electrode increased and the crystallinity of the rutile ATO film was improved. However, when the Ru interlayer was too thick, the capacitors became degraded because of the rough surface morphologies of the electrode and dielectric films. Consequently, the improvement of the electrical performances was maximized with a Ru interlayer thickness of ∼2.5 nm. The achieved minimum equivalent oxide thickness (EOT) was ∼0.52 nm with a low leakage current density (<10–7 A/cm2 at a capacitor voltage of 0.8 V). This performance was comparable to that of a bulk Ru bottom electrode.