Study of a novel ALD process for depositing MgF2 thin films

Magnesium fluoride is an ultraviolet (UV) transparent material which is widely used in optical applications over a wide wavelength range. We have developed a novel atomic layer deposition (ALD) process for depositing magnesium fluoride thin films for the first time. MgF2 films were grown at 250-400 degrees C using Mg( thd)(2) and TiF4 as precursors. The crystallinity, morphology, composition, thicknesses and refractive indices of the films were analyzed by X-ray diffraction/ reflection ( XRD/XRR), transmission electron microscopy ( TEM), atomic force microscopy ( AFM), field emission scanning electron microscopy ( FESEM), time-of-flight elastic recoil detection analysis ( TOF-ERDA), and UV-vis spectrophotometry. Electrical properties were also measured. The growth rate was temperature dependent decreasing from 1.6 A cycle 21 at 250 degrees C to 0.7 angstrom cycle(-1) at 400 degrees C. The films were polycrystalline at 250 - 400 degrees C. The refractive indices were between 1.34 - 1.42 and the permittivity 4.9. The impurity levels were below 0.6 at.% in the films deposited at 350 - 400 degrees C.