Properties of NbN thin films deposited on ambient temperature substrates

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Abstract
The preparation of cubic NbN films by reactive dc magnetron sputtering is described. These superconductive films are deposited at a sufficiently low temperature (2–85% Ar and 1.06 Pa total pressure. The resistivity ratio of these films is close to unity. Structural studies by transmission electron microscopy and electron diffraction show that films 100‐nm thick or less are randomly oriented, and noncolumnar with a crystallite diameter of 5 nm and a lattice parameter of 4.46 Å, which is significantly higher than the bulk value for cubic NbN. The films are dense with void diameters no larger than 0.7 nm. Films 300‐400 nm thick show a small degree of texturing in x‐ray studies with a Read camera. Auger analysis shows a monotonic increase in the N/Nb ratio with increase in the N2/Ar ratio in the sputtering ambient up to 30% N2. From 30% to 50% N2 in the sputtering mixture the N/Nb ratio is constant. Small amounts of carbon impurity are found in all films.