FABRICATION OF NB AL,ALOX/AL/NB JOSEPHSON TUNNEL-JUNCTIONS USING REACTIVE ION ETCHING IN SF6/

High quality Nb/Al,AlO(x)/Al/Nb Josephson tunnel junctions have been m ade with the help of a fabrication process based on reactive ion etchi ng of Nb in SF6. The V(m) value of these junctions is typically 60-70 mV at 4.2 K. At 1.6 K, a V(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 mum2. By burying the Nb/ Al,AlO(x)/Al/Nb trilayer in the substrate, a planarized junction confi guration has been obtained. Reactive ion etching of Nb in SF6 plasmas has been studied in detail. Anisotropic etch profiles can be obtained because of the formation of a resistant layer during etching, which pr events etching of Nb under the photoresist. The etching process has be en monitored with a spectrometer. The fluorine emission at 703.7 nm is shown to be suitable for end point detection.