Area‐selective atomic layer deposition (AS‐ALD) techniques are an emerging class of bottom‐up nanofabrication techniques that selectively deposit patterned ALD films without the need for conventional top‐down lithography. To achieve this patterning, most reported AS‐ALD techniques use a chemical inhibitor layer to proactively block ALD surface reactions in selected areas. Herein, an AS‐ALD process is demonstrated that uses a focused electron beam (e‐beam) to dissociate ambient water vapor and “write” highly resolved hydroxylated patterns on the surface of highly oriented pyrolytic graphite (HOPG). The patterned hydroxylated regions then support subsequent ALD deposition. The e‐beam functionalization technique facilitates precise pattern placement through control of beam position, dwell time, and current. Spatial resolution of the technique exceeded 42 nm, with a surface selectivity of between 69.9% and 99.7%, depending on selection of background nucleation regions. This work provides a fabrication route for AS‐ALD on graphitic substrates suitable for fabrication of graphene‐based nanoelectronics.
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Intrinsic and atomic layer etching enhanced area-selective atomic layer deposition of molybdenum disulfide thin films
For continual scaling in microelectronics, new processes for precise high volume fabrication are required. Area-selective atomic layer deposition (ASALD) can provide an avenue for self-aligned material patterning and offers an approach to correct edge placement errors commonly found in top-down patterning processes. Two-dimensional transition metal dichalcogenides also offer great potential in scaled microelectronic devices due to their high mobilities and few-atom thickness. In this work, we report ASALD of MoS2 thin films by deposition with MoF6 and H2S precursor reactants. The inherent selectivity of the MoS2 atomic layer deposition (ALD) process is demonstrated by growth on common dielectric materials in contrast to thermal oxide/ nitride substrates. The selective deposition produced few layer MoS2 films on patterned growth regions as measured by Raman spectroscopy and time-of-flight secondary ion mass spectrometry. We additionally demonstrate that the selectivity can be enhanced by implementing atomic layer etching (ALE) steps at regular intervals during MoS2 growth. This area-selective ALD process provides an approach for integrating 2D films into next-generation devices by leveraging the inherent differences in surface chemistries and providing insight into the effectiveness of a supercycle ALD and ALE process.
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- NSF-PAR ID:
- 10496133
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology A
- Volume:
- 41
- Issue:
- 5
- ISSN:
- 0734-2101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Modern-day chip manufacturing requires precision in placing chip materials on complex and patterned structures. Area-selective atomic layer deposition (AS-ALD) is a self-aligned manufacturing technique with high precision and control, which offers cost effectiveness compared to the traditional patterning techniques. Self-assembled monolayers (SAMs) have been explored as an avenue for realizing AS-ALD, wherein surface-active sites are modified in a specific pattern via SAMs that are inert to metal deposition, enabling ALD nucleation on the substrate selectively. However, key limitations have limited the potential of AS-ALD as a patterning method. The choice of molecules for ALD blocking SAMs is sparse; furthermore, deficiency in the proper understanding of the SAM chemistry and its changes upon metal layer deposition further adds to the challenges. In this work, we have addressed the above challenges by using nanoscale infrared spectroscopy to investigate the potential of stearic acid (SA) as an ALD inhibiting SAM. We show that SA monolayers on Co and Cu substrates can inhibit ZnO ALD growth on par with other commonly used SAMs, which demonstrates its viability towards AS-ALD. We complement these measurements with AFM-IR, which is a surface-sensitive spatially resolved technique, to obtain spectral insights into the ALD-treated SAMs. The significant insight obtained from AFM-IR is that SA SAMs do not desorb or degrade with ALD, but rather undergo a change in substrate coordination modes, which can affect ALD growth on substrates.
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Abstract Although there have been several demonstrations of area‐selective atomic layer deposition (AS‐ALD) of dielectric on dielectric in metal/dielectric patterns, the reverse process of selective dielectric on metal (DoM) is not as well developed due to the challenge of inhibiting only the dielectrics. Unavoidable native oxide formation on metals tends to lead to similar surface chemical properties between metal and dielectric substrates, decreasing the selectivity in inhibitor adsorption. Hence, to achieve DoM, preventing unwanted inhibitor adsorption on metals is critical. This study demonstrates a two‐step strategy of first applying a dodecanethiol (DDT) self‐assembled monolayer (SAM) on a Cu/SiO2pattern to protect the Cu surfaces from subsequent deposition of an octadecyltrimethoxysilane (OTMS) inhibitor, which then selectively forms an OTMS SAM on SiO2. It is further shown that by removing the DDT protector with thermal treatment before AS‐ALD, subsequent ALD growth on Cu is not affected while ALD remains blocked on the OTMS‐covered SiO2regions. Using this strategy, DoM is demonstrated with selectivity above 0.9 after 5.6 nm of ZnO and 1.5 nm of Al2O3ALD. This work presents a new approach to expand the material systems available to AS‐ALD which may help enable more applications in microelectronics, optoelectronics, and energy.
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Abstract Bending and folding techniques such as origami and kirigami enable the scale‐invariant design of 3D structures, metamaterials, and robots from 2D starting materials. These design principles are especially valuable for small systems because most micro‐ and nanofabrication involves lithographic patterning of planar materials. Ultrathin films of inorganic materials serve as an ideal substrate for the fabrication of flexible microsystems because they possess high intrinsic strength, are not susceptible to plasticity, and are easily integrated into microfabrication processes. Here, atomic layer deposition (ALD) is employed to synthesize films down to 2 nm thickness to create membranes, metamaterials, and machines with micrometer‐scale dimensions. Two materials are studied as model systems: ultrathin SiO2and Pt. In this thickness limit, ALD films of these materials behave elastically and can be fabricated with fJ‐scale bending stiffnesses. Further, ALD membranes are utilized to design micrometer‐scale mechanical metamaterials and magnetically actuated 3D devices. These results establish thin ALD films as a scalable basis for micrometer‐scale actuators and robotics.
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Atomic layer deposition (ALD) is a technologically important method to grow thin films with high conformality and excellent thickness control from vapor phase precursors. The development of new thermal ALD processes can be limited by precursor reactivity and stability: reaction temperature and precursor design are among the few variables available to achieve higher reactivity, unlike in solution synthesis where the use of solvent and/or a catalyst can promote a desired reaction. To bridge this synthesis gap between vapor and solution, we demonstrate the use of an ultrathin coating layer of a vapor-phase compatible solvent—an ionic liquid (IL)— onto our growth substrate to perform ALD of SnO. Successful SnO deposition is achieved using tin acetylacetonate and water, a process that otherwise would require a stronger counter-reactant such as ozone. The layer of IL allows a solvent-mediated reaction mechanism to take place on the growth substrate. We report a growth per cycle of 0.67 Å/cycle at a deposition temperature of 100 °C in an IL comprised of 1-ethyl-3-methylimidazolium hydrogen sulfate. Characterization of the ALD films confirms the SnO film composition, and 1H and 13C NMR are used to probe the solvent-mediated ALD reaction, suggesting a solvent-mediated addition-elimination type mechanism forming acetone and acetate. Density functional theory calculations show that the ionic liquid solvent is beneficial to the proposed solvent-mediated mechanism by lowering the C-C bond cleavage energetics of acetylacetonate compared to the vapor phase. A general class of ligand-modification reactions for thermal ALD is thus introduced in this work.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1116/6.0002811
