Atomic Layer Etching as a Scaling Enabler: From Isotropic Chemistry to Selective, Directional, and Geometry-Driven Patterning

Continued scaling in semiconductor manufacturing increasingly relies on atomic-scale control of etching for complex 3D material stacks, making patterning precision a growing industrial bottleneck. Atomic layer etching (ALE) has emerged as a key enabler, with plasma-driven anisotropy and surface-chemistry control allowing improved selectivity and profile fidelity for advanced logic and memory integration. Current approaches emphasize decoupling surface modification from material removal to enable low-temperature, highly controlled processes.

From an industry perspective, the focus is shifting toward systematic ALE process development frameworks that combine thermodynamic screening, tailored half-cycle chemistries, and experimental verification of etch rates and selectivity. These strategies are increasingly relevant as device architectures push beyond conventional materials and dimensions. At the same time, ALE is gaining attention for its potential to reduce process complexity, energy use, and chemical consumption, positioning it as both a scaling and sustainability enabler for future semiconductor manufacturing.

In a recent paper by Smith et al (reference below), Thermal ALE is described as a purely chemical, vapor- or gas-phase process in which both the surface modification and removal steps are self-limiting and thermally activated. Volatile products are typically formed through ligand-exchange reactions that generate metalorganics. Because no ions are involved, this mode of ALE is intrinsically isotropic, leading to uniform material removal in all directions. This makes thermal ALE attractive for conformal trimming, lateral recessing, and highly selective etches, but fundamentally limits its ability to produce vertical, profile-controlled features.

(a) Periodic table of the elements showing which metals, metal oxides, and metal nitrides have had ALE processes developed for them. In developing a new ALE process, determining the nature of the volatile etch product is critical, with some metals proving more favorable to etching via the formation of volatile metalorganics and others via volatile metal halides. Data compiled from the ALE Database [reference]. (b) An outline of the pathways by which reported ALE processes can proceed. Metals, metal oxides, and metal nitrides can be halogenated, with the modified layer removed by subsequent Ar⁺ sputtering or ligand exchange. Metals can be oxidized or nitrided, and the metal oxide or nitride subsequently etched. (c) Gibbs free energy minimization and volatility diagram analysis can be used to theoretically screen possible etch processes. (d) Various surfaces of Ni modified with (1) surface O, (2) mixed surface and subsurface O, and (3) subsurface O. The Gibbs free energy of reaction showed the importance of having an oxidized sublayer to achieve favorable thermodynamic etching. Adapted from ref [reference]. (e) Analysis of Gibbs free energy of reaction: nitridation of nickel could form metastable Ni3N, which can be etched through favorable reactions with formic acid, forming dimers of nickel formates. by Smith et al (reference below)

In contrast, plasma ALE introduces ions as an active control parameter, most commonly during the removal step. A plasma first forms a chemically modified surface layer, such as a halogenated or oxidized film, which is then selectively removed by directional ion bombardment within a narrow ALE energy window. The momentum of the ions provides anisotropy, enabling vertical etching with atomic-scale precision while suppressing continuous sputtering. This directionality comes at the cost of tighter process windows and increased sensitivity to ion-induced damage.

A hybrid plasma–thermal ALE approach is presented as a way to decouple anisotropy from volatilization chemistry. In this scheme, plasma exposure is used to directionally modify the surface or precisely control the thickness of the modified layer, while removal proceeds via isotropic, thermally driven ligand-exchange reactions. This allows anisotropy to be engineered through selective surface modification rather than sputtering alone. Overall, the key conclusion is that isotropic versus directional behavior in ALE is determined by how and where ions are used, not simply by whether the process is labeled thermal or plasma.

Comment on Geometry

From an industrial standpoint, atomic layer etching is emerging as a core patterning technology as device scaling shifts toward complex 3D architectures and heterogeneous material stacks where conventional plasma etching reaches its limits. Smith et al. highlight that future adoption will be driven by selective ALE, enabled by surface-chemistry engineering, controlled anisotropy, and precise balance between etching and deposition rather than brute-force sputtering. In this landscape, AlixLabs’ use of geometrical selectivity extends the ALE paradigm by exploiting feature pitch and local geometry as an additional selectivity axis, enabling pattern multiplication and critical dimension scaling without added lithography complexity. The convergence of chemical, directional, and geometrical selectivity positions ALE not as a niche technique, but as a scalable, cost- and sustainability-aligned solution for next-generation semiconductor manufacturing.

The relevance of these advances is underscored by their recent and upcoming exposure at major industry forums. Results demonstrating sub-10 nm, high-aspect-ratio patterning with APS™ were presented at the 248th Electrochemical Society (ECS) Meeting in October 2025, marking an important milestone in validating the technology on bulk silicon using mature lithography. This momentum continues at SPIE Advanced Lithography + Patterning 2026, where AlixLabs will present new APS™ results spanning nanoimprint lithography and simplified self-aligned quadruple patterning, including joint work with UMC. Together, these events signal APS™ and geometrically selective ALE moving from concept and lab validation toward broader industrial evaluation and integration.

AlixLabs announced that Dr. Dmitry Suyatin, CIPO and Co-Founder, presented new APS™ (Atomic Layer Etching Pitch Splitting) results at the 248th ECS Meeting in Chicago (October 12–16, 2025), demonstrating high-aspect-ratio, narrow-fin patterning on bulk silicon with critical dimensions below 10 nm using standard 193-nm immersion lithography. The results reinforce APS™ as a viable path to advanced logic patterning without next-generation scanners, enabling reduced process complexity and cost. Supported by recent patent milestones and progress toward a beta tool planned for operation in fall 2026, APS™ is positioned to move from lab-scale validation toward production-grade refinement, aligning with AlixLabs’ goal of making advanced semiconductor manufacturing more accessible and sustainable.

AlixLabs announced its participation at SPIE Advanced Lithography + Patterning in San Jose, where two abstracts by Reza Jafari Jam et al and Robin Athlé et al have been accepted for oral presentation, including one in collaboration with United Microelectronics Corporation (UMC). The presentations will showcase recent progress in APS™ (Atomic Layer Etching Pitch Splitting), demonstrating sub-13 nm half-pitch patterning on silicon and a simplified alternative to self-aligned quadruple patterning that delivers a 4× density increase using a streamlined three-step process. Together, the talks highlight APS™ as a precise, cost-effective, and more sustainable approach to advanced nano-patterning that reduces complexity compared with conventional multi-patterning schemes.

Reference:

AlixLabs – News

Adapted from Smith, T. G. and Chang, J. P., Atomic Layer Etching in Patterning Materials: Anisotropy, Selectivity, Specificity and Sustainability, Plasma Chemistry and Plasma Processing, 46:9 (2026), © The Author(s) 2026. Published by Springer Nature and licensed under CC BY 4.0.

Smith, T. G., Chang, J. P., Atomic Layer Etching in Patterning Materials: Anisotropy, Selectivity, Specificity and Sustainability, Plasma Chemistry and Plasma Processing, 2026, 46:9.

Atomic Layer Etching in Patterning Materials: Anisotropy, Selectivity, Specificity and Sustainability | Plasma Chemistry and Plasma Processing