Testing low-temperature atomic layer deposition of aluminum oxide in a 36” chamber

A new atomic layer deposition (ALD) tool, named the meter-scale ALD system (MSAS), has been designed, constructed, and tested to apply uniform protective coatings over a substrate 36" in diameter. The novel chamber design utilizes a large substrate to be coated as a wall of the chamber. We discuss conceptual design and implementation of this new tool with potential applications to large astronomical optics, specifically protective coatings for silver telescope mirrors, and other large structures. In this work, trimethylaluminum and water was used to deposit aluminum oxide at a low reaction temperature of 60°C. Growth rates, dependent on precursor pulse times and chamber purge times, show that the two half-reactions occur in a saturated regime, which demonstrates typical characteristics of ideal ALD behavior. Thickness uniformity across a 36" substrate is within 2.5% of the average film thickness. MSAS aluminum oxide deposition process parameters are compared with those of a conventional 4" wafer-scale ALD tool. The results show promising application of transparent robust dielectric films as uniform barriers across large optical components.