Sputtering yields and surface chemical modification of tin-doped indium oxide in hydrocarbon-based plasma etching

Sputtering yields and surface chemical compositions of tin-doped indium oxide (or indium tin oxide, ITO) by CH⁺, CH₃⁺, and inert-gas ion (He⁺, Ne⁺, and Ar⁺) incidence have been obtained experimentally with the use of a mass-selected ion beam system and in-situ x-ray photoelectron spectroscopy. It has been found that etching of ITO is chemically enhanced by energetic incidence of hydrocarbon (CH_x⁺) ions. At high incident energy incidence, it appears that carbon of incident ions predominantly reduce indium (In) of ITO and the ITO sputtering yields by CH⁺ and CH₃⁺ ions are found to be essentially equal. At lower incident energy (less than 500 eV or so), however, a hydrogen effect on ITO reduction is more pronounced and the ITO surface is more reduced by CH₃⁺ ions than CH⁺ ions. Although the surface is covered more with metallic In by low-energy incident CH₃⁺ ions than CH⁺ ions and metallic In is in general less resistant against physical sputtering than its oxide, the ITO sputtering yield by incident CH₃⁺ ions is found to be lower than that by incident CH⁺ ions in this energy range. A postulation to account for the relation between the observed sputtering yield and reduction of the ITO surface is also presented. The results presented here offer a better understanding of elementary surface reactions observed in reactive ion etching processes of ITO by hydrocarbon plasmas.