Atomic Layer Etching at the Tipping Point: An Overview

The ability to achieve near-atomic precision in etching different materials when transferring lithographically defined templates is a requirement of increasing importance for nanoscale structure fabrication in the semiconductor and related industries. The use of ultra-thin gate dielectrics, ultra thin channels, and sub-20 nm film thicknesses in field effect transistors and other devices requires near-atomic scale etching control and selectivity. There is an emerging consensus that as critical dimensions approach the sub-10 nm scale, the need for an etching method corresponding to Atomic Layer Deposition (ALD), i.e. Atomic Layer Etching (ALE), has become essential, and that the more than 30-year quest to complement/replace continuous directional plasma etching (PE) methods for critical applications by a sequence of individual, self-limited surface reaction steps has reached a crucial stage. A key advantage of this approach relative to continuous PE is that it enables optimization of the individual steps with regard to reactant adsorption, self-limited etching, selectivity relative to other materials, and damage of critical surface layers. In this overview we present basic approaches to ALE of materials, discuss similarities/crucial differences relative to thermal and plasma-enhanced ALD, and then review selected results on ALE of materials aimed at pattern transfer. Furthermore, the overview concludes with a discussion of opportunities and challenges ahead.