Thin films of several transition metal oxynitrides such as titanium, zirconium, hafnium, niobium and tantalum oxynitride have been produced at room temperature by direct current reactive magnetron sputtering. These films were characterized by a variety of methods including X-ray diffraction, X-ray reflectometry, Rutherford backscattering, optical spectroscopy, spectroscopic ellipsometry and wafer curvature measurements of the deposition stress in the thin films. The resulting film properties show a strong correlation with the deposition conditions. We frequently observed a substantial increase in growth rate and refractive index and a reduced roughness, but still maintained a sufficient transparency in the visible range compared with pure oxides. These attractive features are obtained even though the films contain only a small amount of nitrogen. A simulation package was developed that reproduces the variation of the deposition rate, target voltage and film stoichiometry with reactive gas flow. Based on the results, a scientific understanding is sought that explains both the film formation mechanism as well as the remarkable improvement in film properties. (c) 2005 Elsevier B.V. All rights reserved.