Fabrication of Nb/Al, AlO sub(x)/Al/Nb Josephson tunnel junctions using reactive ion etching in SF sub(6)

High quality Nb/Al,AlO sub(x)/Al/Nb Josephson tunnel junctions have been made with the help of a fabrication process based on reactive ion etching of Nb in SF sub(6). The V sub(m) value of these junctions is typically 60-70 mV at 4.2 K. At 1.6 K, a V sub(m) of 4.1 V has been measured, which is the highest value that has ever been reported for this type of junction. The area of the junctions ranges from 1 to 25 mu m super(2). By burying the Nb/Al,AlO sub(x)/Al/Nb trilayer in the substrate, a planarized junction configuration has been obtained. Reactive ion etching of Nb in SF sub(6) plasmas has been studied in detail. Anisotropic etch profiles can be obtained because of the formation of a resistant layer during etching, which prevents etching of Nb under the photoresist. The etching process has been monitored with a spectrometer. The fluorine emission at 703.7 nm is shown to be suitable for end point detection.