Thermal atomic layer etching (ALE) is a thin film removal technique based on sequential, self-limiting surface reactions. ALE is the reverse of atomic layer deposition (ALD). Thermal ALE is important for nanofabrication because thermal ALE provides for atomic layer controlled and isotropic etching. This talk will discuss the surface chemistry of thermal ALE procedures that have been developed recently for the thermal ALE of metal oxides, metal nitrides and elemental metals. (1) Thermal Al2O3 ALE will be discussed first using HF and Al(CH3)3 as the reactants. This surface chemistry employs sequential fluorination and ligand-exchange reactions. HF fluorinates Al2O3 to produce a surface AlF3 layer. The ligand-exchange reactions then produce volatile etching products such as AlF(CH3)2. (2) Some metal nitrides do not have stable fluorides and can not be etched using fluorination and ligand-exchange reactions. However, many of these materials can be etched using surface chemistry based on oxidation and fluorination to a volatile fluoride. TiN ALE using O3 and HF as the reactants will be presented as an example of this new approach. O3 oxidizes TiN to produce a surface TiO2 layer before the spontaneous etching of TiO2 by HF. (3) In addition, many elemental metals react vigorously with fluorine and form very thick fluoride layers or volatile fluorides that are incompatible with an ALE process. These elemental metals can first be oxidized to the metal oxide and then etched using fluorination followed by ligand-exchange reactions or alternative reaction pathways. The surface chemistry of W ALE will be discussed using oxidation, conversion to a different metal oxide, and then fluorination to a volatile fluoride. W ALE employs O3, BCl3 and HF as the reactants. O3 oxidizes W to produce a surface WO3 layer. BCl3 converts WO3 to a surface B2O3 layer and then B2O3 is spontaneously etched using HF.

Surface chemistry of thermal atomic layer etching

255th National Meeting (2018)

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