Aluminum precursor interactions with alkali compounds in thermal atomic layer etching and deposition processes

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. In this work, 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 materials-selective thin film deposition at these reduced substrate temperatures. We discuss the possible mechanisms of the etching enhancement, along with prospects for extending this approach to other material systems.