Competition between Al2O3 atomic layer etching and AlF3 atomic layer deposition using sequential exposures of trimethylaluminum and hydrogen fluoride

Abstract

The thermal atomic layer etching (ALE) of AlO can be performed using sequential and self-limiting reactions with trimethylaluminum (TMA) and hydrogen fluoride (HF) as the reactants. The atomic layer deposition (ALD) of AlF can also be accomplished using the same reactants. This paper examined the competition between AlO ALE and AlF ALD using in situ Fourier transform infrared (FTIR) vibrational spectroscopy measurements on AlO ALD-coated SiO nanoparticles. The FTIR spectra could observe an absorbance loss of the Al-O stretching vibrations during AlO ALE or an absorbance gain of the Al-F stretching vibrations during AlF ALD. The transition from AlF ALD to AlO ALE occurred versus reaction temperature and was also influenced by the N or He background gas pressure. Higher temperatures and lower background gas pressures led to AlO ALE. Lower temperatures and higher background gas pressures led to AlF ALD. The FTIR measurements also monitored AlCH* and HF species on the surface after the TMA and HF reactant exposures. The loss of AlCH* and HF species at higher temperatures is believed to play a vital role in the transition between AlF ALD at lower temperatures and AlO ALE at higher temperatures. The change between AlF ALD and AlO ALE was defined by the transition temperature. Higher transition temperatures were observed using larger N or He background gas pressures. This correlation was associated with variations in the N or He gas thermal conductivity versus pressure. The fluorination reaction during AlO ALE is very exothermic and leads to temperature rises in the SiO nanoparticles. These temperature transients influence the AlO etching. The higher N and He gas thermal conductivities are able to cool the SiO nanoparticles more efficiently and minimize the size of the temperature rises. The competition between AlO ALE and AlF ALD using TMA and HF illustrates the interplay between etching and growth and the importance of substrate temperature. Background gas pressure also plays a key role in determining the transition temperature for nanoparticle substrates.

Atomic layer deposition of aluminum fluoride using Al(CH3)3 and SF6 plasma

“…9,20 This trend is likely related to a reduced amount of HF adsorbed on the surface at higher temperatures, leading to decreased TMA adsorption in the precursor halfcycle, which is analogous to dehydroxylation for metal oxide ALD. 22 A transition from AlF 3 ALD to Al 2 O 3 atomic layer etching (ALE) at temperatures above 250 C, as found by Lee et al, was however not observed. This difference can be explained by the fact that our actual sample temperature is lower than the set table temperature due to reduced thermal contact in vacuum (see also the supplementary material).…”

“…20,21 Moreover, Dumont and George found that the temperature dependence of the growth per cycle (GPC) can be explained by the amount of HF adsorbed on AlF 3 , which decreases with temperature. 22 In this work, SF 6 plasma was explored as the co-reactant for ALD of metal fluorides. Using trimethylaluminum [TMA, Al(CH 3 ) 3 ] as precursor and SF 6 plasma as F-source, high-purity AlF 3 films were deposited in an Oxford Instruments FlexAL TM ALD reactor.…”

“…The temperature dependence of the HF surface density can thus explain the decrease of GPC with temperature. 22 Note that Eq. (1a) states that one methyl group is eliminated upon precursor adsorption, although removal of two or three methyl groups may also be possible.…”

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

“…The AlF 3 deposition from TMA and HF showed an interesting etching reaction: above 250 • C the precursor pulses etched the AlF 3 film [143,149]. This reaction has later been exploited in developing atomic layer etching processes [170][171][172]. The AlF 3 process has been successfully utilized in protecting freestanding LiCoO 2 /MWCNT (multi-walled carbon nanotube)/nanocellulose fibril electrodes, showing better protection at high potentials compared to the more common artificial SEI material Al 2 O 3 [173].…”

Characterisation of Defluorination Reaction and Solid Electrolyte Interphase in Fluoride-Shuttle Battery Anode MgF2

“…The most critical problem lies with the construction of the anode. This is because typical anode materials such as AlF 3 , CaF 2 , LaF 3 and MgF 2 have wide band gaps (E g) of ~10.8 eV 16 , ~11.8 eV 17,18 , ~10.5 eV 19 , and ~11.8 eV 20 , respectively.…”