LiF by atomic layer deposition—Made easy

Abstract

Lithium fluoride (LiF) is an integral part of UV optics. Recently, it has also gained attention for its role in the solid-electrolyte interphase on the anode of lithium-ion batteries. Atomic layer deposition (ALD) is the preferred tool for synthesizing conformal and pin-hole free LiF thin films, especially on high aspect ratio structures. Present routes to deposit LiF by ALD are based on HF or HF-pyridine as the fluorine source, requiring strict safety precautions. Other routes involve TiF4 or WF6, resulting in inclusions of Ti or W impurities in the resulting films. Herein, we present a new route to deposit LiF by ALD, using lithium tert-butoxide (LiOtBu) and NH4F as precursors. The process yields uniform films over a broad temperature range (150–300 °C), with a growth per cycle of 50.9 pm/cycle (225 °C). The films are free from any nitrogen contamination from the NH4F precursor. This process provides a facile route for high purity LiF thin films with the use of less harmful precursor chemistry.