Thin films of tantalum oxynitride were prepared by reactive magnetron sputtering using a tantalum target and argon mixed with nitrogen and oxygen as reactive gases. The nitrogen flow was kept constant, while the oxygen flow was turned on and off periodically. This process prevents the complete target oxidation and controls the chemical composition of the films by varying the oxygen pulse duration. The choice of the process parameters was made by studying the evolution of the target potential during the sputtering process. The film composition evolves progressively from TaO0.46N1.34 to TaO2.04N0.5 while increasing the oxygen pulse duty cycle without any abrupt change in the elemental content. The optical transmission spectra collected on films deposited on glass show a blueshift of the absorption edge with increasing oxygen content. X-ray diffraction (XRD) patterns of all films exhibit broad peaks typical for nanocrystalline materials, which makes the phase identification difficult. Cross-section film morphology and surface topography observations support the results obtained by XRD. The optical and mechanical properties of the films are very sensitive to the chemical composition of the films and show a systematic evolution with the duty cycle. (c) 2006 American Vacuum Society.