Investigation on the thickness uniformity of TiO2 and Al2O3 coatings on meter-scale surfaces prepared by atomic layer deposition.

The feasibility of the atomic layer deposition (ALD) technique for the preparation of optical films on meter-scale full-aperture optical surfaces is demonstrated with a home-built ALD apparatus. Single-layer TiO₂ and Al₂O₃ films are prepared with the apparatus. Influences of precursor dosages and substrate temperature on thickness profiles of the single-layer films are investigated. Based on the study, an area of diameter approximately 700 mm is determined experimentally on the meter-scale substrate, where both the TiO₂ and Al₂O₃ films yield typical ALD characteristics. A two-layer coating with antireflective performance at 633 nm is prepared utilizing TiO₂ and Al₂O₃ as high and low refractive index sublayers, respectively. The nonuniformity in transmittance is 0.5%, as determined from four positions from the center to the rim of the ALD region. This work develops insight into ALD thickness profiles of optical films and, therefore, is helpful for practical applications of ALD on the fabrication of optical interference coatings on large-aperture optical surfaces.