Effects of thermal annealing on ion beam sputtered SiO2 and TiO2 optical thin films

Ion beam sputtered SiO2 and TiO2 optical thin films are investigated. The optical properties absorption, light scattering and refractive index and the mechanical properties thickness, density and stress are studied directly after deposition and after posttreatment by isochronal annealing up to 300 degrees C. Absorption losses of SiO2 single layers decrease under annealing. The corresponding extinction is reduced below 1x10(-6) at 514 nm. The dynamics of this process is investigated. The density which is higher than bulk density decreases, while the thickness increases. TiO2 single layers show a more complex behavior under postannealing. At higher temperatures this behavior is dominated by crystallite growth in anatase and rutile modification. Compressive stress is reduced. The single layer results of both materials are compared with those of double layers and Fabry Perot multilayers. Differences in absorption are discussed. In double layer systems, lowest bulk extinction of TiO2 is estimated with 1.5x10(-5) at 514 nm. An irreversible peak shift of Fabry Perot filters after annealing comes from changes in thickness and refractive index. The overall performance of multilayer systems can be improved by an adapted annealing procedure.