Superconducting nanobridges prepared by a self-limiting wet chemical etching process

An optimized patterning process of thin films resulting in superconducting nanobridges is reported. The process is based on conventional electron beam lithography (EBL, 20 keV) combined with wet chemical etching using dilute phosphoric acid. This etching is found to be self-limiting and, thus, the minimum width of the bridge becomes independent of the etching time and is determined only by the electron dose applied for EBL. For the self-limiting to be effective, the dilution of the acid is essential. With the above procedure, nanobridges of a well-defined geometry and lateral dimensions down to 60 nm could be reproducibly fabricated exhibiting superconducting transition temperatures K.