Effects of hydrogen ion irradiation on zinc oxide etching

Mechanisms of zinc oxide (ZnO) etching by hydrocarbon plasmas were investigated both experimentally and theoretically with the use of a mass-selected ion beam system and first-principle quantum mechanical (QM) simulation based on the density functional theory. The mass-selected ion beam experiments have shown that the sputtering yield of ZnO increases by a pretreatment of the ZnO film by energetic hydrogen (H) ion injections prior to heavy ion bombardment, suggesting that chemically enhanced etching of ZnO by hydrocarbon plasmas is closely related to hydrogen storage and/or formation of damage in the ZnO layer by energetic hydrogen injections. In this study, the effects of hydrogen storage in ZnO are examined. First-principle QM simulation of ZnO interacting with H atoms has shown that H atoms in ZnO form hydroxyl (OH) groups (or partially convert ZnO to ZnOH), which results in the weakening or breaking of the Zn–O bonds around H atoms and thus makes the ZnO film more prone to physical sputtering. The formation of hydroxyl groups in ZnO is also expected to occur in ZnO etching by hydrocarbon plasmas and increase its sputtering yields over those by inert-gas plasmas generated under similar conditions.