Atomic layer processing approaches for the fabrication of ultraviolet aluminum coatings

Aluminum thin films are often utilized for UV applications where other metals like gold and silver are ineffective, but the efficiency of Al in structures like mirror coatings and bandpass filters can be limited by the presence of native oxide. Previous work has investigated the development of thermal atomic layer etching (ALE) methods to remove this native oxide prior to subsequent encapsulation with fluoride dielectric materials deposited by atomic layer deposition (ALD). This ALE process has involved cyclic exposure to trimethylaluminum and HF in the presence of alkali materials which has been shown to enhance of the oxide removal efficacy at a given substrate temperature. In this current work we investigate ALE co-reaction with cesium fluoride which is shown to enable aluminum oxide etching at temperatures as low as 125 °C and reduce the amount of etch damage experienced by the Al layer. We report on the fabrication of broadband protected Al mirror coatings using this ALE/ALD approach and summarize ongoing and future NASA astrophysics missions that will benefit from this development.