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). This talk will discuss the gas-phase thermal ALE of metal oxides and metal nitrides using sequential fluorination and ligand-exchange reactions. HF and SF4 are the reactants for fluorination. Sn(acac)2, Al(CH3)3, AlCl(CH3)2 and SiCl4 are the metal precursors for ligand-exchange. The fluorination reaction converts the metal oxide or metal nitride to the metal fluoride. The metal precursor then accepts fluorine from the metal fluoride and donates one of its ligands to the substrate to produce volatile reaction products. Thermal ALE has been demonstrated for Al2O3, HfO2, ZrO2 and AlN. The etching rates are temperature dependent and are typically in the ~0.2-1.0 Angstrom/cycle range. The etching by thermal ALE is isotropic and surface roughness is observed to be lowered versus number of ALE cycles. In addition to other metal oxides and metal nitrides, thermal ALE should also be applicable to other materials such as metal phosphides, metal arsenides and elemental metals. One important application for thermal ALE is selective ALE. The ligands on the metal precursor for ligand-exchange can determine whether the metal in the metal fluoride can produce volatile reaction products. This talk will highlight Al2O3 ALE using HF and Al(CH3)3 and AlN ALE using HF and Sn(acac)2 as the reactants. Selective ALE will also be demonstrated for Al2O3, HfO2, ZrO2, SiO2, Si3N4 and TiN using Sn(acac)2, Al(CH3)3, AlCl(CH3)2 and SiCl4 as the metal precursors. Depending on time, results for ZnO ALE using HF and Al(CH3)3 will be presented that illustrate the new concept of “conversion-etch” where ZnO is first converted to Al2O3 prior to etching. The “conversion-etch” mechanism will enable the thermal ALE of a wider range of materials.

Atomic Layer Etching (ALE) using sequential thermal reactions: Atomic Layer Deposition (ALD) in reverse

253rd National Meeting (2017)

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