O₃-Annealing Effect on the Etching Resilience of a TiO₂/Al₂O₃ filter Prepared by Atomic Layer Deposition

Abstract

This research investigates the improvements of ozone (O 3 ) annealing on the optical and etching characteristics of TiO 2 /Al 2 O 3 multilayer band-pass filters designed for potential optoelectronic applications. The band-pass filters were fabricated using atomic layer deposition (ALD), and their performance was systematically analyzed after the addition of O 3 annealing at moderate temperatures (up to 300 °C). Results reveal that O 3 annealing improves the optical transmittance of the multilayers by approximately 40% without significant spectral changes (∼6 nm). The observed enhancement in the transmittance is attributed to the improved stoichiometry of TiO 2 . By filling in the oxygen vacancies created during the fabrication process, it reduces its extinction coefficient. Furthermore, the O 3 annealing enhances the stability of TiO 2 against wet etching, improving the uniformity of etched surfaces. Etching on the ozoneannealed multilayer was up to 8 times more homogeneous, as observed in the roughness. The relatively short duration of the O 3 annealing process, approximately 1.6 h, makes it a cost-effective alternative compared to using ozone in the ALD process, which can last several hours for thick optical coatings.