Wet chemical etching of Zn-containing oxide and HfO₂ films

The etch rates and surface morphologies of Zn-containing oxide and HfO ₂ films after wet chemical etching were investigated. ZnO could be easily etched using each of the acids tested in the present study: sulfuric, formic, oxalic, and HF. The etch rate of In-Ga-Zn-O (IGZO) was strongly dependent on the etchant used, and the highest measured etch rate (500 nm/min) was achieved using a buffered oxide etchant at room temperature. There was a lag in the etching rate of IGZO when oxalic and sulfuric acids were used as etchant, which increased significantly when sulfuric acid was used at a concentration greater than 1.5 M. Furthermore, the etching of HfO₂ films by BF (BOE + formic acid) acid proceeded through lateral widening and merging of the initial irregular pits. Additionally, when the BF solution was used as the etchant, the selectivity of IGZO relative to HfO₂ was increased to as high as 122 with an etching time of 10 min.