The effects of methane in the deposition of superconducting niobium nitride thin films at ambient substrate temperature

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Abstract
Thin films of the niobium‐carbon‐nitrogen system have been prepared at ambient substrate temperature by rf diode reactive sputtering in an argon‐nitrogen atmosphere with controlled amounts of methane added to the sputter gas. Superconducting transition temperatures ranged from approximately 11 to 15.85 °K. Auger and x‐ray diffraction analysis indicate that all films were of the single phase B1 structure with a small amount of β‐phase hexagonal structure in the very low carbon containing films. A correlation of the superconducting properties, room temperature sheet resistance, preferred crystallite orientation, and film composition was observed. The results of this investigation show that high Tc niobium nitride/niobium carbonitride thin films can be prepared at ambient substrate temperatures with the proper amount of nitrogen and methane partial pressures during film deposition. These films have potential application for the fabrication of high Tc Josephson tunnel junctions.