Surface uniform wet etching of ZnO films and influence of oxygen annealing on etching properties

Wet etchings of ZnO films with HCl, H₃PO₄ and NH₄Cl as etchants were systematically studied. The etching morphology and etching rate were focused on and reported in details. The investigation shows that the NH₄Cl aqueous solution can provide uniform etching rate in the entire regions exposed to the etchant, and the etching rate always changes linearly with NH₄Cl solution concentrations in a wide range. The etching rate will be stable if a constant concentration is applied. We also took the influence of different annealing conditions on etching properties into accounts. Under a certain annealing condition, the NH₄Cl aqueous solution still provides uniform etching properties and controllable etching rates. These properties of NH₄Cl aqueous solution as etchant will bring wide design window to real applications. The above results indicate NH₄Cl is a promising etchant for ZnO wet etching.