Fabrication of Nb/AlO/sub x//Nb tunnel junctions using focused ion beam implanted Nb patterning (FINP) technique

The focused ion beam implanted Nb patterning (FINP) technique was applied to the fabrication process of Nb/AlO/sub x//Nb tunnel junctions. The essence of this technique is that Ga-ion-implanted layers in Nb films serve as a masking layer during reactive ion etching in CF/sub 4/ plasma. Uniform and reproducible patterns of 0.3*0.3 mu m/sup 2/ have been formed by this technique. The tunnel junction fabricated with a 60-keV ion beam had the quality parameter Vm of 48 mV, which indicates no degradation of junction characteristics by focused ion beam irradiation. The authors also investigated the CF/sub 4/ plasma etching characteristics of Ga-ion-implanted Nb films and found that an improvement in the characteristics is achieved by lowering beam energy and raising CF/sub 4/ gas pressure.>