New Amorphous Fluoropolymers of Tetrafluoroethylene with Fluorinated and Non-Fluorinated Tricyclononenes. Semiconductor Photoresists for Imaging at 157 and 193 nm Andrew E. Feiring,* Michael K. Crawford, William B. Farnham, Jerald Feldman, Roger H. French, Christopher P. Junk, Kenneth W. Leffew, Viacheslav A. Petrov, Weiming Qiu, Frank L. Schadt III, Hoang V. Tran, and Fredrick C. Zumsteg DuPont Central Research & DeVelopment, Experimental Station, P.O. Box 80328, Wilmington, Delaware 19880-0328 ReceiVed January 11, 2006; ReVised Manuscript ReceiVed March 3, 2006 ABSTRACT: Twenty-two tricyclo[4.2.1.0 2,5 ]non-7-ene (TCN) or 3-oxatricyclononene monomers, having fluorinated or nonfluorinated substituents on the four-membered rings, were prepared by cycloaddition reactions of functionalized olefins with norbornadiene or quadricyclane. Radical polymerizations with tetrafluoroethylene (TFE) and/or TFE and acrylates provided amorphous polymers with high solubility in standard organic solvents. The TFE/TCN dipolymers typically have glass transition temperatures of over 200 °C, substantially higher than TFE copolymers with norbornene. Perfluoroalkyl sulfonyl fluoride groups can be incorporated in the side chains of the TCN monomers giving soluble copolymers. Polymers which also incorporated acrylate monomers were prepared using a semibatch process to control composition. Selected polymers incorporating tertiary alkyl ester groups from the TCN monomer or acrylates have shown good image formation when compounded with a photoacid generator, imaged with 157 or 193 nm light, and developed using aqueous base. Introduction Fluorinated polymers continue to be of intense commercial and scientific interest because of their unique combination of properties, including high thermal and chemical stability and low surface energy, dielectric constant, refractive index, and flammability. 1 On the other hand, the traditional highly fluori- nated polymers, such as poly(tetrafluoroethylene), are difficult to process, are practically insoluble, and have high crystallinity, which limits optical applications. Adding enough acyclic comonomer to eliminate crystallinity tends to give polymers with low glass transition temperatures. 2 Amorphous, high T g perfluoropolymers (TeflonAF and Cytop) have been developed using cyclic or cyclizable monomers but they are soluble only in expensive, highly fluorinated solvents. 3,4 Several years ago, we began investigating amorphous co- polymers of tetrafluoroethylene (TFE) and polycyclic olefins, such as norbornene, as the binder polymer for photoresists for semiconductor manufacture at 157 nm. 5 This was based on our discovery that the TFE/norbornene copolymer has high transpar- ency at this very high energy irradiation wavelength and is resistant to the ion etching used in the manufacturing process, both critical features for this application which was then expected to be commercial in the middle of this decade. Our fully functional 157 nm photoresist (Figure 1) incorporated tert- butyl acrylate as the acid-labile solubility switch for imaging and the pendant fluoro alcohol groups as highly transparent aids for dissolution in aqueous base. 6-8 Other groups have also reported the utility of hexafluoro-2-propanol groups in 157 nm photoresists as highly transparent components with phenol-like acidity to aid dissolution in aqueous base. 9,10 We have recently described copolymers of TFE and a norbornene substituted by two hexafluoro-2-propanol substituents which show exceptional transparency. 11 Photolithography at 157 nm has now largely disappeared from the semiconductor road map due to the development of 193 immersion lithography as a less expensive alternative for generating features at the 65 nm and smaller nodes. We, therefore, retooled our effort toward development of fluorinated photoresists for 193 imaging. Although fluorine is not required for transparency at 193 nm, our results suggested that the TFE/ polycyclic olefin/acrylate polymers may have performance advantages. Typical photoresist binders for 193 nm imaging are based on norbornene/maleic anhydride/tert-alkyl acrylate 12 or poly(meth)acrylates with polycyclic and acid-labile groups in side chains. 13-23 The TFE/polycyclic olefin/acrylate copolymers eliminate the hydrolytically sensitive maleic anhydride moiety of the former class while adding an etch-resistant polycyclic group to the backbone relative to the latter class. We have also described improved line edge roughness in the fluoropolymers relative to the incumbent acrylate or methacrylate polymers. 24 During this work, we wished to explore polymers with greater functionality within the polycyclic olefin component. It quickly became apparent, however, that adding additional substituents to the 5 and 6 positions of the norbornene ring tended to inhibit copolymerizations with tetrafluoroethylene, presumably due to steric effects. We turned our attention to the tricyclo[4.2.1.0 2,5 ]- non-7-ene (TCN) system because substituents at the 3 and 4 positions (Figure 2) are more remote from the double bond and because a variety of substituted TCN derivatives with exo- orientation of the four-membered ring could be prepared. Several Figure 1. TFE/NB-F-OH/tert-butyl acrylate terpolymer for 157 nm imaging. Figure 2. Polycyclic olefin structures. 3252 Macromolecules 2006, 39, 3252-3261 10.1021/ma060070b CCC: $33.50 © 2006 American Chemical Society Published on Web 03/28/2006