Competition between AlO atomic layer etching and AlF atomic layer deposition using sequential exposures of trimethylaluminum and hydrogen fluoride.

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.