HF-Based Approaches for the Thermal Atomic Layer Modification of Ultraviolet Optical Coatings
(Room Room 104-A)
02 May 19
10:40 AM
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11:20 AM
Tracks:
Joint Session of Emerging Technologies and Plasma Processes Focused on Atomic Layer Processes (ALP)
In this work we describe the development of thermal ALD processes for metal fluoride materials such as MgF2, AlF3, and LiF using anhydrous hydrogen fluoride (HF) as the fluorine-containing precursor. The use of ALD is investigated as an alternative to more conventional PVD methods for these materials in order to explore potential improvements in uniformity, morphology, and film-thickness scaling for optical applications operating in the far ultraviolet (90-200 nm). These ALD fluoride materials are particularly useful in the far UV when combined with aluminum thin films to fabricate reflective mirror coatings and detector- integrated solar-blind filter coatings. However, combining ALD methods with high performance PVD Al layers has challenges associated with the formation of undesirable interfacial oxide. The use of thermal atomic layer etching (ALE) methods is shown to be an effective method for removing this oxide inside the ALD chamber prior to subsequent fluoride encapsulation. We describe modifications to an HF-based ALE chemistry that enables this process to operate at low substrate temperatures (<200 °C), while retaining the self-limiting characteristics of the process. The scalability of this overall approach for large-aperture mirror systems and the performance of solar-blind Si imaging sensors will be discussed in the context of possible future NASA astrophysics and planetary missions.