Aluminum-based mirrors with an aluminum fluoride protective coating: A comparative study of small and large-scale atomic layer deposition systems

In this study, we introduce a novel approach in atomic layer deposition (ALD) for telescope mirror protection using a meter-scale ALD system (MSAS) designed for large substrates, addressing previous limitations in ALD applications for telescope mirrors. MSAS incorporates a unique reaction chamber design, allowing uniform protection coatings on 900 mm substrates. We extensively analyzed ALD of aluminum oxide (AlOx), comparing it with a wafer-scale ALD system (WSAS). Our findings reveal scalable ALD processes with optimized parameters, offering applications for silver-based telescope mirrors. For aluminum-based telescope mirrors (Al-mirrors) operating in the far UV spectral range, we explored the use of aluminum fluoride (AlFx) as a transparent protection coating. Unlike traditional ALD of AlOx, ALD of AlFx is uncommon, posing challenges in achieving a 2 nm uniform coating. Furthermore, susceptibility of Al-mirrors to oxidation complicates the coating process. Through the study and modifications in MSAS, we gained critical insights into scaling ALD processes for AlF3 protection coatings, offering unique solutions for improving Al-mirrors’ performance and durability.