Low-temperature formation of metastable cubic tantalum nitride by metal condensation under ion irradiation

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Abstract
Nitrogen containing tantalum was grown on silicon by electron-beam evaporation of the metal under simultaneous irradiation with highly energetic nitrogen ions from an ion source. Phase analysis by means of x-ray diffraction revealed that at low irradiation intensities the deposited material is tantalum metal with dissolved nitrogen. At high intensities a phase transformation to tantalum nitride takes place. By contrast to the stable TaN in the phase diagram, which is hexagonal, the material grown under ion bombardment exhibits a metastable cubic structure of the NaCl type. The crystallographic orientation of the grains is directly dependent on the ion irradiation intensity. Initially, the films show a [111] texture. With increasing ion irradiation intensity the [100] orientation appears additionally. This orientation is independent of the substrate. The lattice spacings are also dependent on the irradiation intensity. With increasing ion irradiation the lattice is widened, then the spacings decrease again. The results are discussed in comparison to data from the literature on sputter deposition with low-energy ions.

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