Atomic Layer Etching (ALE)

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, 鈥淎tomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF鈥, ACS Nano9, 2061-2070 (2015).

2.  Younghee Lee, Jaime W. DuMont and Steven M. George, 鈥淢echanism of Thermal Al2O3 Atomic Layer Etching Using Sequential Reactions with Sn(acac)2 and HF鈥 Chem. Mater.27, 3648-3657 (2015).

3.  Younghee Lee, Jaime W. DuMont and Steven M. George, 鈥淭rimethylaluminum as the Metal Precursor for the Atomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions鈥, Chem. Mater. 28, 2994-3003 (2016).

4.  Younghee Lee, Jaime W. DuMont and Steven M. George, 鈥淎tomic Layer Etching of HfO2 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF鈥, ECS J. Solid State Sci. Technol. 4, N5013-N5022 (2015).

5.  Steven M. George and Younghee Lee, 鈥淧rospects for Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reaction鈥, ACS Nano10, 4889-4894 (2016).