Atomic layer deposition of magnesium fluoride via bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride

A new process has been developed to deposit magnesium fluoride (MgF2) thin films via atomic layer deposition (ALD) for use as optical coatings in the ultraviolet. MgF2 was deposited in a showerhead style ALD reactor using bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride (HF) as precursors at substrate temperatures from 100 to 250 degrees C. The use of HF was observed to result in improved morphology and reduced impurity content compared to other reported MgF2 ALD approaches that use metal fluoride precursors as the fluorine-containing chemistry. Characterization of these films has been performed using spectroscopic ellipsometry, atomic force microscopy, and x-ray photoelectron spectroscopy for material deposited on silicon substrates. Films at all substrate temperatures were transparent at wavelengths down to 190 nm and the low deposition temperature combined with low surface roughness makes these coatings good candidates for a variety of optical applications in the far ultraviolet. (C) 2014 American Vacuum Society.