Atomic Layer Etching at the Tipping Point: An Overview

Abstract

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. The overview concludes with a discussion of opportunities and challenges ahead. A requirement of increasing importance for nanoscale device fabrication is the ability to achieve atomic scale etching control and materials selectivity during pattern transfer.1-8 An etching method corresponding to Atomic Layer Deposition (ALD), i.e. Atomic Layer Etching (ALE), is expected to satisfy these needs as critical dimensions continue to shrink below the 10 nm scale.Demonstrations of self-limited dry etching methods capable of near-atomic resolution have a long history in the dry etching community and a brief review will be presented below. Key challenges for these approaches have been specialized equipment, long process times and low throughput.9,10 However, a recent demonstration using a commercial plasma etch tool 10 and activities within the dry etching community 11 provide indications that the situation has changed, and that we may have reached for ALE the Tipping Point which Gladwell defined as the "the moment of critical mass, the threshold, the boiling point" when "ideas and products and messages and behaviors spread like viruses do".12 This is due to several factors, including unprecedented demands on dry etching technology introduced by the semiconductor device evolution according to Moore's law that can be satisfied by atomic layer etching, advanced capabilities in plasma etch, and the existence of a critical level of information on plasma etch and ALD methods as applied in the semiconductor fabrication space.In this article we will provide a review of background of these approaches, and focus on issues that have to be overcome for widespread implement...

The 2017 Plasma Roadmap: Low temperature plasma science and technology

“…Much attention is focused on atomic-scale (i.e. sub-nanometer-scale) control of surface reactions for materials processing [5,48,49]. As the dimensions of semiconductor devices continue to diminish, thin film deposition and etching techniques often demand control at atomistic length scales.…”

“…The technological requirements to maintain atomistic control in PMI and minimize the damage of materials while changing the material/structure in a desirable fashion have pushed plasma-based techniques increasingly towards fundamental limits [5]. For example, plasmas with a low ion energy have been used for plasma-assisted atomic layer deposition (ALD) [48] and atomic layer etching (ALE) [49]. Material surface processing for biomedical applications has also attracted much attention.…”

“…The industrial needs for plasma processing that enables materials modification, deposition,and etching in the sub-nanometer range have led to the development of plasma-based processes involving sequences of individual, self-limited surface reaction steps [48,49]. While these capabilities have been demonstrated for a range of plasma chemistry/materials systems, further progress in this area requires improved control of ion energy distributions, enhanced temporal control of power, molecular precursors, gas delivery and pumping [54].…”

“…The fundamentals of materialplasma interaction at the atomic scale, in particular during PEALD, are not well understood. Surface analytical techniques, such as those used for understanding plasmaenhanced Si deposition [64], thermal ALD deposition [58] and dielectric etch [49], can help in this regard. Quantum chemistry modeling can be used to clarify many neutralbased processes.…”

Atomic layer etching of gallium nitride (0001)

“…This can be a single atomic (or molecular, as in this work) layer etched in one etch cycle. [6][7][8] Historically, ALE was developed mostly using ion beam or neutral beam etching systems, 5 often custom built. Recently, it was suggested that conventional plasma etch tools can be used for ALE (Ref.…”