O-Annealing Effect on the Etching Resilience of a TiO/AlO filter Prepared by Atomic Layer Deposition.

This research investigates the improvements of ozone (O) annealing on the optical and etching characteristics of TiO/AlO 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 annealing at moderate temperatures (up to 300 °C). Results reveal that O 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. By filling in the oxygen vacancies created during the fabrication process, it reduces its extinction coefficient. Furthermore, the O annealing enhances the stability of TiO 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 O 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.