Isotropic plasma atomic layer etching of Al2O3 using a fluorine containing plasma and Al(CH3)3

Nanofabrication techniques with atomic level precision are needed for advancement to smaller technology nodes in the semiconductor industry. Thermal atomic layer etching (ALE) is currently being developed to isotropically etch material for future applications. In this Letter, an alternative plasma-based ALE process for isotropic etching of Al2O3 is introduced involving SF6 plasma and trimethylaluminium [TMA, Al(CH3)3] pulses, providing higher etch rates and lower processing temperatures than conventional thermal ALE. This process illustrates that a fluorine-containing plasma can serve as a viable reactant for ALE and that plasmas—besides their conventional use in anisotropic ALE—can be employed for isotropic ALE. In situ spectroscopic ellipsometry measurements confirmed saturation of both SF6 plasma and TMA half-cycles, which results in an etch per cycle (EPC) of 3.1 ± 0.1 Å at 260 °C. The isotropic nature of the plasma ALE process was demonstrated by transmission electron microscopy analysis of Al2O3-coated 3D trench structures after performing ALE cycles. A mechanism of fluorination by F radicals and ligand exchange reactions involving TMA is proposed for this plasma ALE process based on observations from infrared spectroscopy, which are supported by reactant synergy analysis. This work establishes the benefits that a plasma can deliver for isotropic ALE.