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.