Growth of RuO₂ thin films by pulsed-chemical vapor deposition using RuO₄ precursor and 5% H₂ reduction gas

RuO₂ thin films were grown on thermal SiO₂(100 nm) and Ta₂O₅(4 nm)/SiO₂(100 nm) substrates at 230 °C by pulsed-chemical vapor deposition using a RuO₄ precursor dissolved in blend of chosen organic solvent (with fluorinated solvents) and 95% N₂/5% H₂ mixed gas as the Ru precursor and reactant gas, respectively. The phase of the deposited film, either being RuO₂ or Ru, was controlled by the N₂/H₂ mixed gas feeding time. This was due to the fact that the time constant of the N₂/H ₂ mixed gas for oxygen atom removal from the reaction surface was related to the reaction kinetics even under identical thermodynamic conditions. High-quality RuO₂ films could be deposited at the N ₂/H₂ gas feeding time of 1-10 s, whereas a Ru film was grown with longer N₂/H₂ gas feeding times of >15 s. The saturated growth rate and resistivity of the RuO₂ thin films were 0.24 nm/cycle and ∼250 μΩ cm, respectively. Although the fundamental growth mechanism of the RuO₂ film was based on self-decomposition of the RuO₄ precursor, the N₂/H ₂ reactant feeding served to enhance RuO₂ growth by the surface hydroxyl group-mediated chemisorption of the RuO₄ precursor. The RuO₂ film showed excellent step coverage inside a capacitor hole structure with an aspect ratio of 10 (opening diameter: 100 nm).