The stress, surface morphology, superconducting characteristics, and crystal structure of sputtered Nb films were evaluated to judge their applicability to the Josephson-junction electrodes. The film qualities were compared between Nb films deposited by dc and RF magnetron sputtering. We concluded that dc sputtered Nb films are more suitable for junction electrodes, and studied the relationship between their film quality and sputtering parameters. We observed that the Nb film characteristics were determined solely by the cathode voltage during sputtering regardless of the other parameters. Thus high-quality Nb films usable for junction electrodes can be obtained by controlling the cathode voltage. The base pressure before sputtering moderately affects film quality. We discuss the changes in film characteristics during Josephson integrated circuit processing.
