Josephson tunnel junctions with Pb counterelectrodes have been fabricated on magnetron‐sputtered Al5 Nb3X(X=Al,Ge) thin films using a CF4plasma cleaning process (CFCP) in conjuction with standard photolithographic processing. The fabrication conditions necessary to produce optimized junctions and their tunneling properties have been investigated. The junction quality rapidly decreases with the increase in the discharge cathode self‐bias voltage (VCSB) during the plasma oxidation as well as the CF4cleaning. The optimum voltage for the cleaning necessary to obtain high‐quality junctions with a uniform current distribution is common to both compounds and exists in the narrower range of 120–140 V than for Nb/Pb junctions. Nevertheless, high‐quality Nb3X/Pb junctions withVm>20 mV can be highly reproducibly fabricated for a wide range of the critical current density (1–103A/cm2). Such junctions show high barrier height values of 0.8–1.0 eV and good aging stability, which is also the case for the Nb/Pb junctions fabricated using CFCP. X‐ray photoelectron spectroscopy (XPS) and ellipsometric measurements on the CF4‐cleaned base electrode surface indicate the presence of an ultrathin fluoride overlayer which is composed of Nb‐F and X‐fluorides. The former also show that the tunnel barrier is a mixture of Nb2O5, Nb‐F‐O, and X‐F‐O. These results, in addition to those for barrier height measurements, suggest that F atoms prevent the defect creation in the barrier and the selective Nb oxidation. They, thus, play an important role in the formation of the highly insulating barriers as well as a nearly ideal barrier‐electrode interface without a substantial proximity layer.