Effects of anion size on ionic conductivity were studied for a series of solid polymer electrolytes prepared from lithium polyanionic salts based on a series of lithium bis͓͑perfluoromethyl͒sulfonyl͔imide ͑LiTFSI͒ units connected together by perfluoroalkane linkers to form oligomeric anionic chains of variable length. Solid polymer electrolytes were prepared from the salts using polyethylene oxide as the host and characterized using X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy. Ionic conductivities were measured over a temperature range between 120°C and ambient for electrolytes with ethylene oxide ͑EO͒/Li ratios of 30:1 and 10:1. Solid polymer electrolytes prepared from the lithium polyanionic salts exhibited ionic conductivities that were consistently lower ͑by factors of between 2 and 10͒ relative to those of monomeric LiTFSI-based electrolytes over the entire temperature and salt concentration ranges. This finding probably reflects a diminished contribution of anions to the overall conductivity for salts with large, polymeric anions. Trends in ionic conductivity with respect to anion chain length and EO/Li ratio were studied. The existence of an optimal anion chain length that is different for solid polymer electrolytes of differing EO/Li ratio was noted and is rationalized in terms of the cumulative effects of anion mobility, ion-pairing, variations in host chain dynamics in the vicinity of ions as a function of anion structure, and salt-phase segregation on the conductivity.

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Fluorocarbon polymers and siloxane-based polymers have been identified as promising resist candidates for 157 nm material design because of their relatively high transparency at this wavelength. 1 This paper reports our recent progress toward developing 157 nm resist materials based on the first of these two polymer systems. In addition to the 2hydroxyhexafluoropropyl group, α-trifluoromethyl carboxylic acids have been identified as surprisingly transparent acidic functional groups. Polymers based on these groups have been prepared and preliminary imaging studies at 157 nm are described. 2-(Trifluoromethyl)bicyclo[2,2,1]heptane-2-carboxylic acid methyl ester derived from methyl 2-(trifluoromethyl)acrylate was also prepared and gas-phase VUV measurements showed substantially improved transparency over norbornane. This appears to be a general characteristic of norbornane-bearing geminal electron-withdrawing substituents on the 2 carbon bridge. Unfortunately, neither the Ni II nor Pd II catalysts polymerize these transparent norbornene monomers by vinyl addition. However, several new approaches to incorporating these transparent monomers into functional polymers have been investigated. The first involved the synthesis of tricyclononene (TCN) monomers that move the bulky electron-withdrawing groups further away from the site of addition. The hydrogenated geminally substituted TCN monomer still has far better transparency at 157 nm than norbornane. The second approach involved copolymerizing the norbornene monomers with carbon monoxide. The third approach involved free-radical polymerization of norbornene monomers with tetrafluoroethylene and/or other electron-deficient comonomers. All these approaches provided new materials with encouraging absorbance at 157 nm. The lithographic performance of some of these polymers is discussed.

The synthesis and characterization of several new fluoropolymers designed for use in the formulation of photoresists for exposure at 157 nm will be described. The design of these platforms has in some cases been inspired by ab initio quantum mechanical calculations of excited state transition energies and by interpretation of gas phase VUV spectrophotometric data. We have explored anionic polymerizations, free radical polymerizations, metal-catalyzed addition polymerizations and metal-catalyzed copolymerizations with carbon monoxide in these studies. The polymers and resist formulations were characterized by VUV spectrometry and variable angle spectroscopic ellipsometry ͑VASE͒. Resist formulations based on these polymers were exposed at the 157 nm wavelength to produce high-resolution images that will be presented.

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