Atomic Layer Deposition of LiF Thin Films from Lithd, Mg(thd)2, and TiF4 Precursors

Lithium fluoride is an interesting material because of its low refractive index and large band gap. Previously LiF thin films have been deposited mostly by physical methods. In this study a new way of depositing thin films of LiF using atomic layer deposition (ALD) is presented. Mg(thd)(2), TiF4 and Lithd were used as precursors, and they produced crystalline LiF at a temperature range of 300-350 degrees C. The films were studied by UV-vis spectrometry, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM), time-of-flight elastic recoil detection analysis (ToF-ERDA), and energy dispersive X-ray spectroscopy (EDX). In addition, film adhesion was tested by a Scotch tape test. This method results in LiF films with a growth rate of approximately 1.4 angstrom per cycle. According to the ToF-ERDA measurements, the films are pure LiF with very small Mg and Ti impurities, the largest impurity being hydrogen with contents below 1 atom %.