Mass-selected ion beam study on etching characteristics of ZnO by methane-based plasma

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In reactive ion etching (RIE) of ZnO by methane-based plasmas, the predominant ion–surface interactions are considered to occur through small hydrocarbon ions such as CH+ and CH3+. In this study, the sputtering yields of ZnO etched by incident CH+, CH3+, He+, Ne+, and Ar+ ions have been obtained as functions of incident ion energy with the use of a mass-selected ion beam system. Modification of chemical compositions of ZnO surfaces after ion bombardment has also been examined with an in-situ X-ray photoelectron spectroscopy (XPS) system. It has been found that etching of ZnO by CH3+ ions is chemically enhanced, exhibiting a sputtering yield much higher than the corresponding purely physical sputtering yield. The sputtering yield of ZnO depends strongly on the amount of hydrogen supplied by incident hydrocarbon ions. Hydrogen adsorbed on a ZnO surface tends to impede carbon deposition and therefore exposes ZnO directly to energetic incident ions. On the other hand, if a SiO2 or SiN surface is exposed to hydrocarbon ion beams of the same kinds and energies, carbon deposition always takes place and no etching of the material occurs. Therefore, both SiO2 and SiN may serve as ideal hard mask materials for selective etching of ZnO by methane-based plasmas.