Volatile Etch Species Produced During Thermal Al2O3 Atomic Layer Etching

The thermal atomic layer etching (ALE) of Al2O3 can be achieved using sequential fluorination and ligand-exchange reactions. Although previous investigations have characterized the etch rates and surface chemistry, no reports have identified the volatile etch products. This study explored the volatile etch species during thermal Al2O3 ALE at 300 °C using quadrupole mass spectrometry (QMS). HF was the fluorination reactant, Al(CH3)3 (trimethylaluminum (TMA)) and AlCl(CH3)2 (dimethylaluminum chloride, (DMAC)) were the metal precursors for ligand-exchange. When TMA was used as the metal precursor after the fluorination of Al2O3 powder, the QMS measurements revealed that the main ion species were consistent with dimers of AlF(CH3)2 (dimethylaluminum fluoride (DMAF)) with itself (DMAF+DMAF) or with TMA (DMAF+TMA). These ion species were observed after loss of a methyl group as Al2F2(CH3)3+ at m/z= 137 and Al2F(CH3)4+ at m/z= 133, respectively. In addition, an ion species consistent with a trimer was also obser...