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

This research investigates the improvements of ozone (O3) annealing on the optical and etching characteristics of TiO2/Al2O3 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 O3 annealing at moderate temperatures (up to 300 °C). Results reveal that O3 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 TiO2. By filling in the oxygen vacancies created during the fabrication process, it reduces its extinction coefficient. Furthermore, the O3 annealing enhances the stability of TiO2 against wet etching, improving the uniformity of etched surfaces. Etching on the ozone-annealed multilayer was up to 8 times more homogeneous, as observed in the roughness. The relatively short duration of the O3 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.