Ammonium Fluoride as an Inhibitor of Liquid Acid Etching of YBCO

Among classical applications of superconductivity, various microelectronic devices are of key importance. As a rule, such devices represent a thin superconductor film on a substrate, structured in the shape controlled by the device design. Structuring can be performed by various methods; simplest and most commonly used one is the liquid acid etching over the photoresist mask. In this work, we study the etching process of thin films of high-temperature superconductor YBa2Cu3O7 – δ using an etchant based on a 0.2% of nitric acid aqueous solution modified by an ammonium fluoride addition. The latter inhibits the etching process to a value convenient for manual treatment. As the addition concentration increases, the etching rate decreases to the total process shutdown. At an NH4F concentration of 0.3‰, an etching rate of 6 ± 2 nm/s was reached, which can be considered as optimum for manual treatment of films to 100 nm thick.