Fabrication of High Tc NbN Films by Ion Beam Deposition Technique

Abstract

A new sputtering type of ion source which can generate ions of heavy metals such as niobium has been developed to use for ion beam deposition of thin films. The ion source is composed of two targets facing each other, anode and a magnetic coil, which are arranged in the same way as that in Targets Facing type of high rate sputtering method. Ion beam of high current density above 1 mA/cm² (2.5 cm in diameter) can be obtained at very low accelerating voltage below 50 V. The ion beam deposition apparatus with this ion source has the strict controllabilities over the most of film preparation conditions such as deposition rate, film composition, substrate temperature and the energy of arrival of film atoms.

Then, the authors have attempted to use this apparatus for deposition of high Tc NbN films. Film structure, and lattice constant of B1 phase depend significantly on the energy of arrival of film atoms. The authors have succeeded in fabricating the NbN films composed of single B1 phase with high Tc of 16 K at low substrate temperature below 350°C. The region of substrate temperature is much lower than that for such films deposited by means of conventional reactive sputtering. These results indicate that the ion beam deposition apparatus is very useful to prepare high NbN films at low substrate temperature.