Optical properties of tantalum nitride films fabricated using reactive unbalanced magnetron sputtering

Coatings of tantalum nitride with various compositions were deposited on silicon substrates using unbalanced reactive magnetron sputtering. An optical emission spectrometer was used to monitor the ratio of tantalum to nitrogen particles in the plasma in real time. The coatings were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). The primary nitride phases (⁠$Ta$⁠, $Ta2N$⁠, $TaN$⁠) in the films were determined using XRD and XPS. The elemental composition was revealed from XPS measurements. The refractive indices were deduced from analysis of the SE data, which were subsequently simulated using the Drude–Lorentz model. The resistivity and electron mean free paths were deduced from this simulation and were correlated to the film composition and microstructure. The resistivity increased whereas the electron mean free path decreased with an increase in nitrogen content or a decrease in grain size.