Ellipsometric Evaluation of the Optical Constants of Zirconium Oxynitride Thin Films Deposited by Reactive Pulsed Magnetron Sputtering

Three different zirconium oxynitride films were deposited onto glass and Si (100) substrates at room temperature by pulsed reactive dc magnetron sputtering of a metallic Zr target in an $Ar//O_2//N_2$ atmosphere. The structural, compositional and optical properties of the deposited films were found to depend on the ratio of nitrogen partial pressure to the total reactive gas partial pressure. Energy-dispersive X-ray spectroscopy measurements revealed that as the nitrogen amount increased in the reactive gas the nitrogen content was found to increase in the film. The film structure was determined by X-ray diffraction. The X-ray diffraction patterns of the analyzed samples revealed a strong dependence of the $ZrO_xN_{y}$ film structure on composition. A two layer model, the Bruggeman effective medium approximation and both Drude absorption edge and Lorentz oscillators were used to describe the surface roughness layer and the main $ZnO_xN_{y}$ layer, respectively, was used to describe the experimental ellipsometric data. The optical band gap was decreased from 3.56 to 3.45 eV with changing nitrogen content, while refractive index at 650 nm simultaneously was increased from 1.98 to 2.11.