Optical constants and properties of dual-ion-beam sputtering Ta₂O₅/SiO₂ thin film by spectroscopy

Single Ta₂O₅ and double layer Ta₂O₅/SiO₂ films are deposited on Si and fused silica substrates by dual-ion-beam sputtering. With the Cauchy dispersion model, the optical constants of Ta₂O₅ and SiO₂ thin films are obtained by fitting the transmission spectra of single Ta₂O₅ and double layer Ta₂O₅/SiO₂ films using the combination of simplex and genetic algorithm (GA) optimization method. It shows that the results calculated by fitting the whole optical spectra are well consistent with the measuring values. The refractive index error and thickness error of single layer Ta₂O₅ film are less than 0.001 nm and 1 nm, respectively. In the case of double layer Ta₂O₅/SiO₂ films, the maximum refractive index error and thickness error are in the range of 0.004 nm and 2.5 nm, respectively. In addition, the deposited double layer Ta₂O₅/SiO₂ thin films are treated at 400°C in air. The changes of microstructure, surface morphology and optical properties of the Ta₂O₅/SiO₂ films are investigated.