ALD Metal Fluorides for Ultraviolet Filter and Reflective Coating Applications

We report on the development of atomic layer deposition (ALD) processes for metal fluoride thin films with applications at ultraviolet wavelengths. The use of anhydrous hydrogen fluoride (HF) as a reactant in these ALD processes has allowed for the demonstration of thin films of magnesium, aluminum, and lithium fluoride at deposition temperatures as low as 100 degrees C. These films are used for anti-reflection coatings, optical filters, and solar-rejection filters integrated directly onto Si sensors, and as protective coatings for reflective aluminum optics in the UV. The low deposition temperature enables deposition directly on Si sensors without impacting device performance, as well as the coating of polymeric diffraction gratings. The use of HF-based chemistry is shown to yield new atomic layer etching (ALE) procedures that can be used for the same device developments. Applications related to terrestrial and space astronomy, astrophysics missions, and particle physics experiments are discussed.