Atomic Layer Deposition of LaF3 Thin Films using La(thd)3 and TiF4 as Precursors

Abstract

AbstractLanthanum fluoride is a vacuum ultraviolet (VUV) transparent material which is widely used in optical applications. An atomic layer deposition (ALD) process is developed for depositing lanthanum fluoride thin films for the first time. LaF3 films are grown at 225–350 °C using La(thd)3 and TiF4 as precursors. The crystallinity, morphology, composition, thicknesses, and refractive indices of the films are analyzed by X‐ray diffraction/reflection (XRD/XRR), atomic force microscopy (AFM), scanning electron microscopy (SEM), time‐of‐flight elastic recoil detection analysis (TOF‐ERDA), and UV‐vis spectrophotometry. Electrical properties, such as permittivity and leakage current density, are also studied. An exceptionally high growth rate of about 5 Å per cycle is achieved at 225–250 °C. The films are polycrystalline, the refractive indices vary between 1.57 and 1.61, and the permittivity is 12.3. The impurities detected in the LaF3 film are Ti, C, O, and H. The level of all of these tends to decrease with increase in the deposition temperature, and is only 3.5 at.‐% at 350 °C.