The unique layer-by-layer growth mechanism of atomic layer deposition (ALD) enables exceptional uniformity, conformality, and accurate film thickness control for many thin films. To date, ALD has been limited to relatively small-sized substrates. In optical systems, these properties are of utmost importance as sustaining optical performance requires not only a high degree of uniformity (large size substrates) but also excellent conformality when it comes to complex micro-or macrostructures (Complex shape substrates). For the traditional physical vapor deposition, to reach a high level of uniformity and conformality on domes, need to design specialized motion structures. This comes with an extensive load of mechanical work and process optimization, ultimately leading to tight control of the process parameters, even it the results may not be ideal. In this work, A new ALD tool has been designed, constructed, and tested to apply uniform protective coatings in a deposition dome with over 0.2 m diameters. We have named it as conformal ALD system (CAS), which employs a unique chamber design, and our design approach is adapted to any size of hemispherical dome and dome with Von Karman curves. To demonstrate our idea, we have used a hemispherical dome holder (radius = 100 mm), deposited on the inner side by depositing Al2O3 films, and on the outer side by depositing Ta2O5 films. Measuring their thickness distribution at the typical position of the dome, we have been able to achieve a revolutionary change in the range of non-uniformity, that is, to achieve nonuniformities close to 1 % over the entire structure. Ultimately, our results demonstrate an exceptional method to realize high-quality optical coatings on the most challenging surfaces, paving the way for the mass production of critical optical components with complex shapes for a variety of applications ranging from the camera module to defense.

Optical coatings on complex surface using atomic layer deposition

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ACS Fall 2022

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