In this study, we present a method to enhance the sensitivity of fluorinated EUV resists by leveraging the rapid coupling reaction between electrophilic carbon radicals and electron-rich alkenes. To validate the impact of the vinyl groups, DVS-HNF was synthesized by introducing fluorinated alkyl chains and silyl vinyl functional groups into the model compound. Additionally, TMS-HNF and EDMS-HNF, which do not contain a vinyl moiety, were synthesized for comparison. To evaluate the patterning properties of the three materials, e-beam lithography experiments were conducted, resulting in the formation of negative-tone patterns for all three materials. Comparing sensitivities, DVS-HNF with two vinyl moieties exhibited the most excellent sensitivity, confirming the effective collaboration between fluorinated alkyl radicals and vinyl groups. After performing an EUV lithography experiment on DVS-HNF, it was confirmed that a 30 nm negative-tone pattern was successfully formed with excellent sensitivity. These results substantiate the potential of the single-component molecular resist for high performance EUV lithography.
High numerical aperture (NA) EUV lithography is considered as the most-promising candidate for next generation lithography protocol that will play a crucial role in meeting the demand on the enhanced semiconductor performance and productivity. While this technology enables the fabrication of sub-10 nm patterns, the increased NA has posed challenges, such as reduced depth of focus and narrower process margins. To overcome these hurdles, it is essential to apply thinner resist films while ensuring that the resulting small patterns maintain sufficient physical and chemical durability. Moreover, considering that thinner films absorb fewer photons, the resist molecular structure should be designed to compensate sensitivity burdens. Here, an approach has been proposed to enhance sensitivity by accelerating the solubility change of a well-known tinbased nanocluster resist. To accomplish this goal, it is important to increase not only the number of secondary electrons but also reaction sites and promote radical-based chemical reactions. We aimed at experimentally validating this concept by utilizing elements with high EUV absorbance and highly reactive functional groups with tin radicals. As a model resist, we chose a tin-oxo cage material consisting of a divalent cation containing 12 tin atoms and two counter anions. Our findings indicate that the introduction of unsaturated groups capable of building bridging bonds with radicals leads to fast solubility change at a lower exposure dose, thus enhancing sensitivity. This research offers a promising direction for the development of resists tailored for High NA EUV lithography.
Extreme UV (EUV) lithography is entering full-scale production of high-end IC chips. This transition gives researchers in academia and industry ample motivation to propose new chemistries that will contribute to alleviating the resolution-line edge roughness-sensitivity trade-off dilemma of EUV lithography. We also have a great interest in the radical chemistry of carbon-fluorine bonds working under EUV and have explored its applicability as a platform for implementing novel EUV resists. While it was checked that the chemical concept is viable by using fluorinated small molecules and polymers, it needed to be upgraded in terms of patterning resolution and sensitivity. Recently, we extended successfully the radical-based strategy to the tin-oxo nano cluster resist concept. Soluble fluorinated tin-oxo clusters could be prepared, and they were cast into thin films from a fluorous solution. When the thin film was exposed to EUV radiation, it lost solubility, resulting in the formation of negative-tone images. Under an EUV lithographic condition, the thin film could be tailored down to 10 nm or smaller sized features. In addition, their unique solubility in chemically orthogonal solvents also enabled the build-up of a bilayer structure composed of a non-fluorinated reactive polymer underlayer without curing. The stacked film structure was found to be helpful for the sensitivity improvement. These results propose another interesting EUV resist candidate possessing unique capabilities in thin film processing.
We propose a method for easily determining the extent of solubility change of chemically amplified resist (CAR) films with different types of extreme UV (EUV)-absorbing elements. The concentration of acid molecules depends on the production yield of secondary electrons, and it affects the deprotection reaction rate in the resist and ultimately the residual resist film thickness. Materials capable of increasing EUV absorption were prepared by incorporating tin, iodine, or hydrogen in a model fluoroalkylated copolymer. A CAR film containing a proton exchange component was spin-coated on a substrate, and a thin film composed of one of the fluoroalkylated copolymers containing elements and a photoacid generator was cast thereon. Under EUV irradiation, the iodine containing copolymer increased the decomposition rate of the CAR film, unlike the case of the tin- or hydrogen containing copolymer. For practical use, we prepared an iodinated sensitizer based on a CT contrast agent, iohexol, for utilizing it as an EUV sensitizer in an EUV lithography (EUVL) experiment, and it was found that the iohexol-based iodinated sensitizer could simultaneously act as a sensitizer and a base quencher. These results show that iodinated compounds can help enhance the patterning performance of CARs in EUVL.
In this study, a molecular resist capable of high-resolution patterning with excellent sensitivity was pursued by introducing a metal atom into a small molecular fluorinated core. After selecting the phthalocyanine (Pc) unit as a molecular framework, exhibiting excellent chemical stability and etch resistance, fluorinated alkyl and aryl moieties and zinc atoms were incorporated into the framework to complete the synthesis of Pc-based EUV resists. Analyses of the recovered compounds were performed by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT IR), and ultraviolet–visible (UV-vis) spectroscopy to confirm that the structures of the desired materials were secured properly. Through the electron-beam lithographic experiments, it was verified that all the thin films composed of the three Pc materials lost their solubility by interacting with high-energy electrons to form negative-tone images. When EUV lithography was carried out on ZnPc-A, which has linear perfluoroalkyl moieties, 40 nm-sized patterns were formed at the relatively small energy of 34 mJ/cm2. From the synthesis and lithographic characterization results, it can be assumed that fluorinated metallophthalocyanine materials can be considered EUV resist candidates. However, for highresolution patterning, it is necessary to maintain an appropriate film thickness and adjust the processing parameters, including the adhesion to the substrate.
In this presentation, we show our efforts toward the discovery of extreme UV (EUV) resists based on the radical reactions that highly fluorinated molecular units undergo. Recently, we reported that small molecules equipped with perfluoroalkyl ether (PFAE) chains or fluoroarene units show solubility change under high-energy electron beam (e-beam) or EUV light via intermolecular chemical network formation. Although this non-chemical amplification-type imaging mechanism worked without the help of any catalytic species, its low sensitivity characteristics had to be improved for practical use. A solution was sought in polymeric resist platforms, particularly those possessing a uniform composition and high enough glass transition temperature (Tg). A perfluoroalkyl moiety was introduced to maleimide (Mi) to give RFMi, which could then be copolymerized in an alternating manner with styrene (P1) and a styrenic derivative containing a Sn atom (P2) or acid-labile protective group (P3). By using a reversible deactivation radical polymerization method, the copolymers could have narrow molecular weight distributions (polydispersity index (PDI) < 1.5) along with their uniform monomer compositions. Thanks to the rigid backbone structure enabled by the maleimide units, the perfluoroalkylated copolymers could be characterized by high Tgs over 100‡C. When lithographic patterning tests were performed under EUV exposure conditions, the thin films of all the alternating copolymers could be tailored down to the 30-nm size, and in particular, the one with Sn atoms (P2) made patterns with 22 mJ/cm2. These results demonstrate the useful nature of the imaging chemistry that highly fluorinated molecular units enable under high energy radiation.
In this presentation, we will show our efforts for the discovery of high-performance imaging reactions based on fluorine and radical chemistry working under high-energy radiation. Prior to this study, we have reported molecular resists equipped with rather flexible perfluorinated alkyl ether (PFAE) chains and their imaging behavior as negative-tone resists under electron beam irradiation. In this study, we turned our attention to another fluorinated unit, fluorinated aromatic compounds, possessing structural rigidity that we believe contributes to achieving improved patterning capabilities. Successful coupling reactions between a phenolic resist core and fluorinated arenes provided fluorinated molecular resists, which we evaluated in terms of imaging behavior under e-beam and EUV lithographic conditions. The solubility of their thin films was decreased by the high-energy radiation; thus, negative-tone patterns down to 30 nm half-pitch could be obtained after development in fluorous solvents.
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