(Invited) Atomic Layer Etching Using Thermal Reactions: Atomic Layer Deposition in Reverse

Abstract

Atomic layer etching (ALE) can remove thin films with atomic layer control based on sequential, self-limiting surface reactions. ALE can be viewed as atomic layer deposition (ALD) in reverse. This paper reviews Al2O3 ALE using sequential, self-limiting thermal reactions. In the proposed mechanism for thermal Al2O3 ALE, fluorination reagents, such as HF, fluorinate the Al2O3 substrate to form an AlF3 surface layer and volatile H2O. A metal precursor, such as Sn(acac)2, subsequently accepts fluorine from the AlF3 surface layer and donates an acac ligand to the aluminum in the AlF3 surface layer to form volatile Al(acac)3 or AlF(acac)2 reaction products. These fluorination and ligand-exchange reactions with HF and Sn(acac)2 lead to temperature-dependent etching rates of Al2O3 from 0.14 Å/cycle at 150°C to 0.61 Å/cycle at 250°C. This reaction mechanism can be extended to a variety of other materials including metal nitrides, metal phosphides, metal arsenides and elemental metals.