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.
We propose a concept of organic small molecule-based EUV resists that do not require sub-stoichiometric ingredients. Based on our previous results with highly fluorinated electron-beam (e-beam) resists, we designed amorphous small molecules equipped with perfluoroalkyl ether (PFAE) chains. The synthesis of the prototype was carried out successfully, and its physical properties, imaging mechanism, and performance were all evaluated under e-beam exposure conditions. Although the prototype showed slightly low sensitivity to EUV irradiation, we were able to mitigate the issue by appending other cross-linkable functional moieties. The modified version showed decent negative-tone patterning performance under e-beam exposure and could form images under EUV irradiation and the pattern development step using highly fluorinated solvents.
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