Application of in situ and ex situ Characterization of Atomic Layer Deposition Processes for Gallium Phosphide and Sodium Fluoride

Atomic layer deposition (ALD) is a vapor deposition technique for synthesizing thin films with nanometer thickness control. ALD films are deposited on a substrate surface in a cyclic layer-by-layer fashion utilizing alternating doses of highly reactive chemical precursors. Precursors are selected to undergo self-limiting chemical reactions with the surface, and desired film thickness is achieved by varying the number of ALD cycles accordingly. Optimization of ALD process parameters and precursor chemistry enables conformal coating of arbitrary substrate geometries, including high aspect ratio features such as trenches. In the decades since its introduction, ALD has been used for applications across many industries, including semiconductor device manufacturing, emerging battery technologies, and optoelectronics. In this work, I present investigation of two previously reported chemistries for ALD of gallium phosphide (GaP), as well as improvements made to a custom ALD reactor to facilitate better process control and characterization. I also present a new process for thermal ALD of sodium fluoride (NaF), with potential applications in electrode coatings for sodium-ion batteries. To my knowledge, this is the first report of NaF ALD. Finally, I summarize obstacles which may be addressed in future studies that build upon this work.