Stability of hexafluoroacetylacetone molecules on metallic and oxidized nickel surfaces in atomic-layer-etching processes

Adsorption of enol hexafluoroacetylacetone (hfacH) on nickel oxide (NiO) fcc (100) and metallic Ni fcc (100) surfaces and the stability of the adsorbate was examined using first-principles quantum mechanical simulations. It was shown that an hfacH molecule can be unstable and dissociate on an Ni metal surface. On an NiO surface; however, an hfacH molecule can be deprotonated and form a hexafluoroacetylacetonate anion (hfac−) bonded stably with positively charged Ni atoms of the surface. The results are consistent with observations of the interaction of hfacH with NiO and Ni surfaces in earlier experiments. The results also explain the mechanisms of the adsorption steps in the thermal atomic layer etching of Ni based on the cyclic processes of surface oxidation and formation of volatile organo-nickel complexes.