Atomic layer etching (ALE) is the reverse of atomic layer deposition (ALD). ALE can be achieved using sequential, self-limiting thermal reactions. We have recently demonstrated Al2O3 ALE [1-3] and HfO2 ALE [4]. During the surface chemistry using HF and Sn(acac)2 as the reactants, the HF converts the metal oxide to metal fluoride. The Sn(acac)2 then accepts fluorine from the metal fluoride and concurrently donates an acac ligand to the metal in the metal fluoride to form a volatile reaction product.
These fluorination and ligand-exchange reactions lead to atomic layer controlled etching. This ALE approach is extendible to other materials besides metal oxides. Our current work has demonstrated the ALE of metal nitrides and elemental metals. The thermal ALE also displays selectivity depending on the stability and volatility of the metal reaction products. We are excited about the prospects for thermal ALE [5]. We believe ALE, together with ALD, will enable the fabrication of many advanced three-dimensional semiconductor structures.
1. Younghee Lee and Steven M. George, “Atomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF”, ACS Nano 9, 2061-2070 (2015).
2. Younghee Lee, Jaime W. DuMont and Steven M. George, “Mechanism of Thermal Al2O3 Atomic Layer Etching Using Sequential Reactions with Sn(acac)2 and HF” Chem. Mater. 27, 3648-3657 (2015).
3. Younghee Lee, Jaime W. DuMont and Steven M. George, “Trimethylaluminum as the Metal Precursor for the Atomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions”, Chem. Mater. 28, 2994-3003 (2016).
4. Younghee Lee, Jaime W. DuMont and Steven M. George, “Atomic Layer Etching of HfO2 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF”, ECS J. Solid State Sci. Technol. 4, N5013-N5022 (2015).
5. Steven M. George and Younghee Lee, “Prospects for Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reaction”, ACS Nano 10, 4889-4894 (2016).