Chemical reduction and wet etching of CeO₂ thin films

Cerium oxide is stable to commonly used aqueous etching agents and can be reliably etched only by a combination of chlorine and fluorine plasma. This hinders practical applications of pure and doped ceria thin films in bulk and surface micromachining. In the present work, the reasons for the chemical stability of cerium oxide in aqueous media were analyzed and two etching solutions were investigated. In the absence of stirring, the etching rate dropped with time. In an ultrasonic bath, etching was isotropic with a constant rate of ∼10 nm/min. This permits patterning of ceria films using chromium as a mask and demonstrates practical applicability of the proposed etching solutions.