Effect of annealing on composition, structure and optical properties of SrHfON thin films

SrHfON thin films were deposited on Si substrate by radio frequency (RF) magnetron reactive sputtering. Composition, structure and optical properties of the SrHfON films in relation to rapid thermal annealing (RTA) temperatures were analyzed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). The XPS analysis indicates that the peaks of Sr 3d, Hf 4f, O 1s, and N 1s shift toward higher binding energy after the RTA treatment. The XRD results show that the SrHfON films remain amorphous after RTA treatment at 900 °C. Optical constants of the as-deposited and annealed SrHfON films are extracted based on a parameterized Tauc–Lorentz (TL) model. With the increase of annealing temperatures, the refractive index increases while the extinction coefficient decreases. The annealed SrHfON films have higher ɛ1 and lower ɛ2 than the as-deposited SrHfON films. Moreover, the extracted indirect bandgap values are 4.98, 5.06, and 5.18¦eV for the as-deposited and annealed SrHfON thin films at 600 and 900 °C, respectively.