Reactive Ion Etching Mechanism of RuO₂ Thin Films in Oxygen Plasma with the Addition of CF₄, Cl₂, and N₂

Abstract

In this study, we thoroughly investigated the reactive ion etching mechanism of RuO 2 film in oxygen plasma with the addition of CF 4 , Cl 2 , and N 2 . The etch rate of RuO 2 was examined as functions of flow rates of input gases, substrate temperature, DC bias applied to the substrate, and pressure. The concentrations of the etching species in the plasma were determined using optical emission spectroscopy (OES) and a quadrupole mass spectrometer (QMS). The etch products were determined with a QMS and the etched surface of RuO 2 film was examined with X-ray photoelectron spectroscopy (XPS). RuO 4 and RuO 3 , which are formed by the reactions between RuO 2 film and oxygen radicals, are the only etch products regardless of the kind of additive gas. The additive gases (CF 4 , Cl 2 , and N 2 ) are not directly involved in the chemical reaction with the RuO 2 film, but they increase the concentration of oxygen radicals and accordingly, appreciably increase the etch rate of the RuO 2 films. The etch rate is limited by the formation rate of the etch products, which is enhanced by the bombardment of energetic ions. Therefore, the etch rate depends not only on the concentration of oxygen radicals, but also on the flux and energy of the ions bombarding the film surface. In this study, for the first time, we introduced the use of the O 2 /N 2 plasma system in RuO 2 etching.