Monitoring phase transitions in β -W thin films using ellipsometry

Abstract Understanding and monitoring phase transformations in tungsten thin films is crucial for advancing applications in spintronics, including MRAM technology. This study investigates spectroscopic ellipsometry as a non-destructive method for identifying and distinguishing between the tungsten phases beta-tungsten ( β -W) and alpha-tungsten (α-W) in thin films. In this study, β -W thin films of, ranging from 15 to 150 nm in thickness, were deposited on silicon substrates using DC magnetron sputtering. Phase transition to α-W was then induced in selected samples. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), grazing-incidence x-ray diffraction (GIXRD), x-ray reflectivity (XRR), and four-point probe resistivity. Optical properties were subsequently measured using a spectroscopic ellipsometer, and the data were used to build and fit B-Spline models in CompleteEASE 6 software. The optical parameter data from the tested samples were then fitted successfully for both tungsten phases. The data analysis has shown distinct refractive index patterns for the α -W and β -W phases in films with thicknesses of 15, 30, and 60 nm. This work demonstrates that spectroscopic ellipsometry can effectively be used as an additional in situ tool, complementing other characterization techniques, to detect and monitor phase transformations in tungsten thin films.