Material properties of ion beam deposited oxides for the optoelectronic industry

Abstract

High quality, dense films of SiO2, Al2O3, Ta2O5, and TiO2 were deposited with an ion beam deposition system (IBD). IBD has significant advantages over other techniques in terms of directionality, stress control, repeatability, thermal stability, and film uniformity [J. J. Cuomo, J. M. E. Harper, C. R. Guarnieri, D. S. Yee, L. J. Atanasio, J. Angilello, C. T. Wu, and R. H. Hammond, J. Vac. Sci. Technol. 20, 349 (1982)]. To decrease the surface damage induced by ion bombardment, a multi-energy process was developed. This is especially important for laser facet coatings. The oxide films were optimized for the desired refractive index and zero absorption. Stress values of −0.2 to −0.5 GPa (compressive) and extremely good uniformity (<0.2%) of film thickness and refractive index were obtained. The impact of the IBD deposition angle on film stress was also investigated. These films showed excellent thermal stability with virtually no degradation of optical properties after three 1 h anneals at 350 °C (Δn<0.0124). With the exception of TiO2, all films remained in compressive stress after annealing. TiO2 turned tensile. With the variety of oxide materials developed, designing an anti-reflective or highly reflective stack, which satisfies requirements of stress, uniformity, deposition rate, and reflectance, becomes a matter of choosing the appropriate material set.