Atomic layer etching (ALE) is a subtractive counterpart to atomic layer deposition (ALD), both relying on sequential, self-limiting surface reactions to achieve atomic-scale precision. Where ALD builds material layer-by-layer through alternating precursor and reactant exposures, ALE removes material in a similarly controlled fashion. The two processes share fundamental principles of surface saturation and cyclic operation, making them complementary for advanced nanofabrication, particularly in high-aspect-ratio patterning and interface engineering.
The ALE process consists of two or more steps per cycle, typically including modification and removal phases. In the modification step, the surface is chemically altered using a reactive species, forming a volatile or weakly bonded layer. The subsequent removal step involves exposing the modified surface to energy (thermal, plasma, or ion bombardment) or a second reactant to desorb or etch the altered material. Each cycle removes a predictable, often sub-monolayer thickness, enabling atomic-level control over material removal. This self-limiting mechanism ensures uniformity and conformality, even in complex 3D structures, mirroring ALD’s strengths in deposition.
A key synergy between ALE and ALD lies in their combined use for precise pattern definition. For example, in gate-all-around transistor fabrication, ALD can deposit a conformal high-k dielectric, while ALE trims excess material or shapes critical dimensions without damaging underlying layers. The cyclic nature of both processes allows for fine-tuning thickness or etch depth by simply adjusting the number of cycles. This level of control is unattainable with conventional continuous etching or deposition techniques, which often suffer from non-uniformity or process drift.
Another advantage of pairing ALE with ALD is the ability to correct deposition imperfections. ALD-grown films may exhibit edge roughness or overhang in high-aspect-ratio features, which ALE can smooth or remove selectively. The complementary processes enable atomic-scale corrections, such as removing interfacial oxides before depositing a new layer or tuning sidewall angles in 3D NAND structures. This iterative deposition-and-etch approach is critical for next-generation devices requiring sub-nanometer accuracy.
Material selectivity is another area where ALE and ALD demonstrate synergy. By carefully choosing reactants and conditions, ALE can selectively remove one material while leaving others intact, just as ALD can deposit material selectively on specific surfaces. Combining these capabilities enables complex heterostructures, such as alternating semiconductor and dielectric layers in superlattices or precise interface engineering in magnetic tunnel junctions. The self-limiting reactions in both processes minimize unwanted side reactions that could degrade device performance.
Thermal and plasma-enhanced variants exist for both ALE and ALD, offering additional compatibility. Thermal ALE, like thermal ALD, relies on purely chemical reactions, avoiding plasma-induced damage—a critical advantage for sensitive materials. Plasma-assisted ALE and ALD provide higher reactivity at lower temperatures, useful for processing thermally fragile substrates. Matching the energy input (thermal or plasma) between deposition and etching steps reduces integration challenges in multi-step fabrication sequences.
The cyclic nature of ALE and ALD also facilitates in-situ process monitoring and control. Techniques such as quartz crystal microbalance or optical emission spectroscopy can track mass changes or reaction byproducts in real time for both processes. This shared metrology framework simplifies process optimization and fault detection when alternating between deposition and etching steps in the same tool or cluster system.
Challenges remain in aligning ALE and ALD for certain applications. While ALD has matured for a wide range of materials, ALE processes are still under development for many compounds. Achieving matching etch and deposition rates at the same temperature can be difficult, requiring careful tuning of chemistries. Additionally, the surface reactivity needed for ALE may differ from ALD, complicating sequential processing without intermediate treatments.
Despite these challenges, the combined use of ALE and ALD is becoming indispensable for advanced semiconductor nodes, quantum devices, and nanophotonic structures. As feature sizes shrink below 5 nm, the ability to add or subtract material with atomic precision will only grow in importance. The complementary nature of these techniques offers a pathway to overcome fabrication limits that single-process approaches cannot address.
Future developments will likely focus on expanding the library of ALE processes to match ALD’s material versatility, improving cycle times for high-throughput manufacturing, and integrating both techniques into clustered tools for seamless processing. Advances in precursor chemistry and reaction mechanisms will further enhance selectivity and reduce thermal budgets, enabling new applications in flexible electronics and bio-nanotechnology.
In summary, atomic layer etching and atomic layer deposition form a complementary pair of techniques that share self-limiting, cyclic reaction mechanisms. Their combined use enables unprecedented control in nanofabrication, from correcting deposition artifacts to enabling 3D architectures with atomic-scale precision. As both processes mature, their synergy will play a central role in overcoming the challenges of next-generation nanomanufacturing.