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As lithographic techniques advance in their capabilities of shrinking microelectronics devices, the need for improved resist materials, especially for extreme ultraviolet (EUV), has become increasingly pressing. In this work, we study the molecular layer deposition (MLD) of an Al-based hybrid thin film resist, known as “alucone,” extending our previous research that tested the Hf-based hybrid thin film “hafnicone” as an EUV resist. Alucone is grown at 100 ºC using the metal precursor trimethylaluminum and the organic precursor ethylene glycol. Like hafnicone, alucone behaves as a negative tone resist that can resolve 50-nm line widths, though preliminary data suggest that alucone’s line patterns are more sharply defined than those of hafnicone. Whereas hafnicone’s sensitivity is 400 μC/cm2 using 3 M HCl as the developer, alucone’s sensitivity is not yet as good (4800 μC/cm2 using 0.125 M HCl). Our study of alucone offers new insight into structural features of an MLD film that can lead to desired EUV-responsive behavior. This insight may accelerate the development of vapor-deposited inorganic resists for use in electron-beam and EUV lithography. 

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. 

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.

 

In recent years, area‐selective atomic layer deposition (AS‐ALD) has attracted increasing interest for its applications in back‐end interconnect processes, and selective deposition of Al₂O₃is of particular interest because Al₂O₃can serve as an etch hard mask. However, Al₂O₃is one of the most difficult ALD systems to block. In this work, a strategy is presented to enhance the blocking ability of dodecanethiol (DDT) self‐assembled monolayers (SAMs) against Al₂O₃ALD. It is shown that by conducting DDT deposition on a slightly oxidized Cu surface, which is mainly composed of Cu₂O, rather than on a freshly acid‐etched Cu surface, which mainly consists of metallic Cu, the quality of the DDT SAM can be improved. It is further shown that the DDT SAMs formed on Cu₂O‐covered Cu substrates are about 3–4 times more effective in blocking Al₂O₃than that on acid‐etched Cu surfaces when ALD is performed under subsaturation condition. However, as the Cu oxidation process continues, CuO is formed and the blocking ability of DDT degrades. Finally, selective Al₂O₃deposition on DDT‐treated Cu/low‐kpatterns using the combined strategy of Cu oxidation and subsaturation conditions achieves selectivity of 0.99 after 4 nm of Al₂O₃ALD.

 

Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η⁴‐2,3‐dimethylbutadiene ruthenium⁽⁰⁾tricarbonyl (Ru(DMBD)(CO)₃), a zero‐valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. The authors study the growth mechanism of this precursor by in situ quartz‐crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO)₃produces high‐quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical chemical vapor deposition processes, with a strong dependence on both temperature and reaction timescale. The non‐self‐limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, it is suggested that the findings can be generalized to the broader class of zero‐oxidation state carbonyl‐based precursors used in thermal ALD, with insight into the design of effective saturation studies.