Structural and optical study of RF-magnetron sputtering SnO₂ thin films: impact of post annealing temperature

Abstract

Tin oxide (SnO2) thin films are prepared using radio frequency magnetron sputtering (RF) method and then annealed at different temperatures in the range of 550–750 ∘C for 1 hour. The effects of annealing temperature on the structural and optical properties of the films are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectrophotometer. It is evident that the annealed films have flat surface with smooth morphology. Based on the XRD graph, as deposited films were amorphous and the annealed films had polycrystalline nature and contain the SnO2 tetragonal rutile phase. According to Raman spectra, the annealed films revealed three vibration modes Eg, A1g and B2g at the frequencies of Sn-O bond vibrations, which related to the SnO2 phase. The samples exhibit an average optical transmittance with more than 80 % between 400 - 700 nm. The refractive index values were in the range of 0.9-2.4 at visible wavelength. It is found that with increasing annealing temperature the films become more transparence while the refractive index and the extinction coefficient increased. The optical band gap energy decreases with increasing annealing temperature that means that the optical quality of annealed films is improved.