Surface fluorination and volatilization using hydrogen fluoride and trimethyaluminum (TMA) is a useful approach to the thermal atomic layer etching of Al2O3. We have previously shown that significant enhancement of the TMA etching effect occurs when performed in the presence of lithium fluoride chamber-conditioning films. Now, we extend this enhanced approach to other alkali halide compounds including NaCl, KBr, and CsI. These materials are shown to have varying capacities for the efficient removal of AlF3 and ultimately lead to larger effective Al2O3 etch rates at a given substrate temperature. The most effective compounds allow for continuous etching of Al2O3 at substrate temperatures lower than 150 °C, which can be a valuable route for processing temperature-sensitive substrates and for improving the selectivity of the etch over other materials. The strong interaction between TMA and alkali halide materials also results in material-selective thin-film deposition at these reduced substrate temperatures. We discuss possible mechanisms of this etching enhancement and prospects for extending this approach to other material systems. The consequences of using TMA as an ALD and ALE precursor are discussed in the context of interface engineering for alkali-containing substrates such as lithium battery materials.
Keywords: alkali halide; atomic layer etching; hydrogen fluoride; lithium fluoride; trimethylaluminum.