Plasma-enhanced CVD synthesis and structural characterization of Ta2N3

Microcrystalline tantalum nitride films were prepared on various substrates from TaCl5 precursor and nitrogen gas using the plasma-enhanced chemical vapor deposition (PECVD) method. Syntheses carried out at 600-650 degreesC led to single-phase samples of the tantalum nitride Ta2N3 with a defect fluorite-type structure. The anion vacancies were found to order resulting in a 2 x 2 x 2 cubic superstructure of the C-Ln(2)O(3) type (space group Ia (3) over bar, Z = 16) with a = 9.8205(4) Angstrom according to a Rietveld refinement of the X-ray powder diffraction data. At higher deposition temperatures (650-700 degreesC) formation of highly textured orthorhombic Ta3N5 was observed. The samples were additionally studied by high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The details of the new crystal structure for Ta2N3 as well as a possible nitrogen nonstoichiometry are discussed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.