Single layer etching
 | This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages)
|
| Process type | Material removal process |
|---|---|
| Inventor | Various researchers |
Single layer etching is a chemical processing technique that removes material one atomic or molecular layer at a time. Manufacturers apply the technique in semiconductor fabrication for precise control over device features as sizes shrink below 10 nm. Atomic layer etching (ALE) targets individual atomic layers. Molecular layer etching (MLE) focuses on molecular layers, often in organic or hybrid inorganic-organic films. These self-limiting methods provide nanoscale precision and smooth surfaces.
Single layer etching removes material one layer at a time at the atomic or molecular scale. Manufacturers use the technique in semiconductor fabrication for precise control over device features. Atomic layer etching (ALE) targets atomic layers. Molecular layer etching (MLE) focuses on molecular layers, often in organic or hybrid films.
Process
[edit]ALE employs sequential, self-limiting reactions. The cycle consists of surface modification followed by removal. Modification exposes the surface to chemicals or plasma that react with the top atomic layer to form a reactive species. Removal uses low-energy ions or other agents to desorb the modified layer. The process repeats, with etch depth determined by cycle count. For silicon, chlorine gas or plasma chlorinates the surface to form a silicon chloride layer roughly 0.5 nm thick. Argon ions at ~50 eV then sputter the modified layer. Plasma assistance accelerates reactions and supports low-temperature processing. Etch depth per cycle typically reaches 0.7 nm, maintaining smooth, uniform surfaces.[1][2][3]
Self-limitation arises from saturation: modification halts after covering the top layer, and removal affects only the modified portion. Synergy between steps prevents etching during isolated exposures. Directional ALE uses ions for anisotropic control in high-aspect-ratio features. Isotropic ALE etches uniformly in all directions.[4][5][6]
MLE adapts the approach to molecular layers in films grown by molecular layer deposition (MLD), such as alucone (an aluminum-based metalcone, i.e., a hybrid organic-inorganic thin film material).[7] Sequential exposures to lithium organic salt and trimethylaluminum etch these hybrid materials. The lithium salt cleaves aluminum-oxygen bonds, and trimethylaluminum methylates the surface to yield volatile products. Etch rates show temperature dependence: ~0.4 nm per cycle at 160 °C and ~3.6 nm per cycle at 266 °C.[8] Halogen-free chemistries suit organic-inorganic hybrids.
Both ALE and MLE decouple reactions to reduce variability, roughness, and damage relative to conventional reactive ion etching. Reactive ion etching encounters transport limitations and mixed damage layers. Single layer methods avoid these through controlled, sequential steps.
History
[edit]Researchers explored ALE concepts starting in the late 1980s. Work in 1988 addressed diamond etching. In 1989, studies demonstrated bilayer etching of gallium arsenide. The 1990s focused on directional ALE for silicon and III-V compounds as alternatives to reactive ion etching, e.g., using carbon tetrafluoride.
The 2000s shifted emphasis to oxides and group III-V materials. Interest surged around 2010 to meet sub-10 nm device requirements. Lam Research demonstrated plasma-assisted silicon ALE on commercial reactors in 2013. Fabrication plant evaluations began in 2014. Sematech initiated ALE workshops that year.[1] Atomic layer deposition, the deposition counterpart, saw industrial adoption for high-k dielectrics starting in 2007.
MLE developed later. Studies on etching metalcone films appeared around 2020.[8] Related patents for molecular layer etching emerged thereafter.[9]
Applications
[edit]Single layer etching supports semiconductor manufacturing where atomic precision is required. ALE shapes features in 3D logic devices. It removes material in high-aspect-ratio structures with minimal damage. Silicon dioxide etches selectively over silicon nitride using fluorocarbon-based approaches. Group III-V materials such as gallium arsenide and indium phosphide preserve stoichiometry through chlorination or oxidation followed by removal.[1] Metals including copper undergo chlorination and hydrogen plasma removal. Two-dimensional materials such as graphene use oxygen plasma and neutral beams. The technique aids interconnects and emerging materials at sub-10 nm nodes.[1]
MLE controls geometries in nanoscale devices coated by MLD. It enables precise patterning of hybrid thin films for microscopic architectures.[8] Nanofabrication leverages both methods for efficient device fabrication.
Research
[edit]ALE reverses atomic layer deposition principles using thermal or plasma-enhanced reactions.[6] Plasma generates radicals and enables directional etching. Etch amounts per cycle reach angstrom scales. Thermal dry etching of cobalt uses sequential chlorine and diketone exposures.[10] Novel radical modules improve adsorption in advanced systems.
MLE research emphasizes self-limiting, halogen-free processes. Quartz crystal microbalance and infrared spectroscopy verify mechanisms.[8]
Reviews document ALE on more than 20 materials across over 100 studies.[1] Future efforts target higher throughput via faster cycles and improved hardware.
Advantages
[edit]Single layer etching delivers atomic-scale precision and reduces variability in small devices. Surfaces remain smooth with flat etch fronts. The method minimizes geometry-dependent loading effects. Selectivity improves for oxides over nitrides and other pairs. Low-energy ions avoid sputtering damage.
Challenges
[edit]Throughput remains a challenge in early setups with cycle times of 1–5 minutes, but commercial tools advance gas modulation and purge efficiency
Background etching during modification requires tight control. Removal energies must stay below damage thresholds to prevent nonideal behavior. Industry adoption demands standardized terminology and productivity gains for cost-effective scaling. MLE exhibits strong temperature dependence, requiring precise thermal control. Broader material selectivity needs further development.
See also
[edit]References
[edit]- ^ a b c d e Kanarik, K. J.; Lill, T.; Hudson, E.; Sriraman, S.; Tan, S.; Marks, J.; Vahedi, V.; Gottlieb, R. (2015). "Overview of atomic layer etching in the semiconductor industry". Journal of Vacuum Science & Technology A. 33 (2): 020802. doi:10.1116/1.4913379.
- ^ "Plasma Etching and ALE". Hiden Analytical. Retrieved 2026-01-24.
- ^ "Argonne molecular layer etching tool enables precise control of thin film materials". ASM International. 2020-02-20. Retrieved 2026-01-24.
- ^ "Atomic Layer Etching (ALE)". Oxford Instruments. Retrieved 2026-01-24.
- ^ "Atomic Layer Etching (ALE) | Steven M. George Research Group | University of Colorado Boulder". www.colorado.edu. Retrieved 2026-01-24.
- ^ a b Lill, T.; Kanarik, K. J.; Gottlieb, R.; Vahedi, V. (2018). "Atomic Layer Etching: Rethinking the Art of Etch". The Journal of Physical Chemistry Letters. 9 (10): 2635–2642. doi:10.1021/acs.jpclett.8b00997.
- ^ Young, Matthias J.; Choudhury, Devika; Letourneau, Steven; Mane, Anil; Yanguas-Gil, Angel; Elam, Jeffrey W. (2020-02-11). "Molecular Layer Etching of Metalcone Films Using Lithium Organic Salts and Trimethylaluminum". Chemistry of Materials. 32 (3): 992–1001. doi:10.1021/acs.chemmater.9b03627. ISSN 0897-4756.
- ^ a b c d Abdulagatov, A. Z.; George, S. M. (2020). "Molecular Layer Etching of Metalcone Films Using Lithium Organic Salts and Trimethylaluminum". Chemistry of Materials. 32 (3): 1021–1033. doi:10.1021/acs.chemmater.9b03627.
- ^ "Molecular layer etching (US11257682)". labpartnering.org. Retrieved 2026-01-24.
- ^ Konh, Mahsa; He, Chuan; Lin, Xi; Guo, Xiangyu; Pallem, Venkateswara; Opila, Robert L.; Teplyakov, Andrew V.; Wang, Zijian; Yuan, Bo (March 2019). "Molecular mechanisms of atomic layer etching of cobalt with sequential exposure to molecular chlorine and diketones". Journal of Vacuum Science & Technology. A, Vacuum, Surfaces, and Films: An Official Journal of the American Vacuum Society. 37 (2): 021004. doi:10.1116/1.5082187. ISSN 0734-2101. PMC 6396405. PMID 30940989.