Ultraviolet optical properties of aluminum fluoride thin films deposited by atomic layer deposition

Abstract

Aluminum fluoride (AlF3) is a low refractive index material with promising optical applications for ultraviolet (UV) wavelengths. An atomic layer deposition process using trimethylaluminum and anhydrous hydrogen fluoride has been developed for the deposition of AlF3 at substrate temperatures between 100 and 200 °C. This low temperature process has resulted in thin films with UV-optical properties that have been characterized by ellipsometric and reflection/transmission measurements at wavelengths down to 200 nm. The optical loss for 93 nm thick films deposited at 100 °C was measured to be less than 0.2% from visible wavelengths down to 200 nm, and additional microstructural characterization demonstrates that the films are amorphous with moderate tensile stress of 42–105 MPa as deposited on silicon substrates. X-ray photoelectron spectroscopy analysis shows no signature of residual aluminum oxide components making these films good candidates for a variety of applications at even shorter UV wavelengths.

Metal Fluorides as Lithium-Ion Battery Materials: An Atomic Layer Deposition Perspective

“…In addition, as already mentioned, AlF 3 is a potential artificial SEI-layer for protecting both cathodes and anodes [47,143,145,[165][166][167]. Thus, AlF 3 has become a much studied ALD material in the past few years [143,145,147,149,156]. Magnesium fluoride showed growth rates of 0.6 to 0.3 Å/cycle in the deposition temperature range of 100 to 250 • C (Figure 12a) [148].…”

“…Magnesium fluoride showed growth rates of 0.6 to 0.3 Å/cycle in the deposition temperature range of 100 to 250 • C (Figure 12a) [148]. AlF 3 showed a similar decrease in growth rate, being 1.2 Å/cycle at 100 • C and 0.5 Å/cycle at 200 • C (Figure 12c) [149]. MgF 2 films were crystalline and showed small amounts of carbon and oxygen impurities and a slight fluorine deficiency in XPS measurements (Figure 12d) [148].…”

“…The work on fluoride deposition using HF has been continued by many groups, including Hennessy et al, who have deposited magnesium and aluminum fluoride films using anhydrous HF with bis(ethylcyclopentadienyl)magnesium and TMA as metal precursors [148,149]. Magnesium fluoride is an interesting material due to its large band gap and low refractive index [142,153].…”

“…Magnesium fluoride is an interesting material due to its large band gap and low refractive index [142,153]. Aluminum fluoride is a material with a similar variety of possible optical applications [149,[162][163][164]. In addition, as already mentioned, AlF 3 is a potential artificial SEI-layer for protecting both cathodes and anodes [47,143,145,[165][166][167].…”

Materials and process development for the fabrication of far ultraviolet device-integrated filters for visible-blind Si sensors

“…Recent research at JPL has led to the development of several ALD processes for metal fluorides using anhydrous HF as the fluorine-containing precursor. 17,18 The simplicity of this ALD chemistry has enabled the demonstration of the metal fluoride ALD processes indicated in Table 1 at temperature as low as 100 °C, and with reduced impurity concentration and superior UV optical properties. These developments have been employed at JPL in the fabrication of protected aluminum mirrors with coatings of ALD MgF 2 , AlF 3 , and LiF films.…”