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

Abstract

We have studied the properties of (Nb0.35, Ti0.15)xN1−x films deposited by reactive magnetron sputtering at ambient substrate temperature, focusing in particular on the dependence of film properties on the total sputtering pressure. As the pressure increases we observe a transition in the film structure from the ZT to the Z1 structural zone according to the Thornton classification. In general, the superconducting transition temperature (Tc) and residual resistance ratio have a very moderate dependence on total sputtering pressure, while the film resistivity increases an order of magnitude as the sputtering pressure 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 (Nb0.35, Ti0.15)xN1−x films consist of 20–40 nm grains with good crystallinity. Films sputtered under low pressures have a weak [100] texture, while films sputtered under high pressures have a distinct [111] texture. A stable chemical composition and reduction in film density as the sputtering pressure 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 film resistivities in the Z1 structural zone.