Plasma Processes for Isotropic and Anisotropic Atomic Layer Etching

The development of nanoelectronics towards increasingly complex 3D nanostructured devices requires novel combinations of anisotropic and isotropic etching. Atomic layer etching (ALE) will play an important role in the fabrication of such nanodevices because of its Ångstrom-level control and ability to uniformly etch on complex structures. Previously reported ALE processes can be classified in two main categories: plasma processes for anisotropic etching and thermal chemistries for isotropic etching.<br/>In this contribution, results for both isotropic and anisotropic ALE will be discussed, focusing on the unique opportunities provided by plasmas. The relatively unexplored category of using plasmas for isotropic ALE allows for processing at lower temperatures and higher etch rates, as will be demonstrated for processes involving fluorination with a SF₆ plasma. Recent work also focuses on isotropic ALE based on etching by diketone dosing (e.g., hexafluoroacetylacetone) and plasma cleaning steps. Infrared spectroscopy and simulation studies revealed that the mechanism of etching with diketones involves a competition between etching and inhibition reactions.