Atomic Layer Etching of AlF3 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and Hydrogen Fluoride
2015
Lee, YoungHee | DuMont, Jaime W. | George, Steven M.
The atomic layer etching (ALE) of AlF₃ was demonstrated using sequential thermal reactions with Sn(acac)₂ and hydrogen fluoride (HF) as the reactants. AlF₃ ALE is the first example of the thermal ALE of a metal fluoride. AlF₃ ALE was investigated using in situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) measurements at temperatures from 150 to 250 °C. The QCM studies observed that AlF₃ was etched linearly with atomic level precision versus number of sequential reactant cycles. QCM investigations also revealed that the sequential Sn(acac)₂ and HF reactions were self-limiting versus reactant exposure. The FTIR spectroscopic analysis observed AlF₃ etching by monitoring the loss of absorbance of Al–F stretching vibrations in the AlF₃ film. The FTIR studies also suggested that the Sn(acac)₂ reaction is self-limiting because of the buildup of acac-containing species on the AlF₃ surface. The QCM measurements determined that the mass change per cycle (MCPC) increased with temperature from −2.0 ng/(cm² cycle) at 150 °C to −18.2 ng/(cm² cycle) at 250 °C. These MCPC values are equivalent to etch rates from 0.069 Å/cycle at 150 °C to 0.63 Å/cycle at 250 °C. In the proposed reaction mechanism for AlF₃ ALE, the Sn(acac)₂ reactant accepts fluorine from AlF₃ and donates acac to the surface. This reaction is believed to yield SnF(acac) and AlF(acac)₂ as volatile reaction products. The QCM and FTIR results suggest that the HF reaction converts AlF₂(acac)* surface intermediates to AlF₃* and volatile acacH reaction products. The ALE of other metal fluorides using Sn(acac)₂ and HF should be possible by a similar mechanism.
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