Properties of (Nb0.35, Ti0.15)xNi1−x thin films deposited on silicon wafers at ambient substrate temperature

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Abstract
We have studied the properties of ( Nb 0.35 , Ti 0.15 ) x N 1−x filmsdeposited by reactive magnetron sputtering at ambient substrate temperature, focusing in particular on the dependence of film properties on the total sputteringpressure. As the pressure increases we observe a transition in the filmstructure from the ZT to the Z1 structural zone according to the Thornton classification. In general, the superconducting transition temperature (T c ) and residual resistance ratio have a very moderate dependence on total sputteringpressure, while the filmresistivity increases an order of magnitude as the sputteringpressure increases. A wide spectrum of material science techniques is used to characterize the films and to explain the relationship between the sputtering conditions and film properties. Transmission electron microscopy and x-ray diffraction analysis show that 160-nm-thick ( Nb 0.35 , Ti 0.15 ) x N 1−x films consist of 20–40 nm grains with good crystallinity. Filmssputtered under low pressures have a weak [100] texture, while filmssputtered under high pressures have a distinct [111] texture. A stable chemical composition and reduction in film density as the sputteringpressure increases indicate that the change of resistivity in the ZT structural zone is due to a variation in the quenched-in vacancy concentration. In contrast voids on the grain boundaries and vacancies together produce the high filmresistivities in the Z1 structural zone.