Relationship between substrate temperature, structure, and superconducting properties of reactively sputtered niobium nitride thin films

Niobium nitride thin films have been reactively sputtered at substrate temperatures of 300 ° and 700 °C. The background pressure was in the low 10−7-Torr range, total sputtering pressure was kept at 2×10−3 Torr and partial pressures of argon and nitrogen were monitored and controlled with a residual gas analyzer. The structure was examined by reflection electron diffraction and Jc-H characteristics were measured using a pulsed field and pulsed current technique. Substrate temperature and Ar/N2 partial-pressure ratio strongly influenced the crystallographic structure which in turn determined the superconducting properties of the films. Consequently, a clear relationship between deposition parameters, particular nitride phases and their mixtures and superconducting properties has been established. The highest Tc of 14.9 K has been observed for a film deposited at 700 °C which exhibited the δ NbN phase.