Activation mechanism of ruthenium etching by Cl-based radicals in O2/Cl2 plasma

The Ru etching mechanism was investigated using O2/Cl2 plasma with O, ClO, and Cl radicals. The etch rate drastically increased with a 10%–20% addition of Cl2 to O2 and was lower when using pure O2 or Cl2-rich gas in an ECR etcher. Experimental results indicate that chemical reactions involving Cl-based radicals contributed to the etching reactions. The chemical role of the Cl-based radicals was investigated by density functional theory simulations. The hypothesis tested was that O, ClO, and Cl adsorb on the RuO2 surface when it is irradiated with O-rich plasma. The reactivities of the topmost Ru atoms, where O, ClO, and Cl adsorbed, were compared in terms of the d-band structures. The ClO and Cl were found to enhance the reactivity of the Ru atoms more than O. These findings suggest that Cl-based radicals activate surface Ru atoms, resulting in the formation of volatile RuO4 or RuClxOy.