Growth of RuO₂ Thin Films by Pulsed-Chemical Vapor Deposition Using RuO₄ Precursor and 5% H₂ Reduction Gas

Abstract

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/H2 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 N2/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/H2 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).