Andrew E. Feiring

Aromatic monomers with pendant fluoroalkylsulfonate and sulfonimide groups

Abstract Novel styrene and dimethylisophthalate monomers with pendant lithium fluoroalkylsulfonate or sulfonimide functional groups have been prepared from the corresponding phenolic intermediates. One route involves several steps and uses 1,2-dibromotetrafluoroethane as the key fluorinated intermediate. A second route with fewer steps utilizes a perfluoroalkylsulfonyl-substituted vinyl ether as the source of the fluorinated substituents but affords a product with significantly higher equivalent weight.

Fluorocarbon‐ended polymers: Metal catalyzed radical and living radical polymerizations initiated by perfluoroalkylsulfonyl halides

Perfluoroalkylsulfonyl chlorides and bromides initiate metal catalyzed free radical polymerization of both hydrocarbon and fluorocarbon monomers affording polymers with perfluoroalkyl end groups. In the case of styrene (S) and methyl methacrylate (MMA) with Cu-based catalysts the process affords polymers with a relatively narrow molecular weight distribution and linear dependence of molecular weight on conversion, suggesting that a living radical polymerization mechanism occurs. The orders of reaction in monomer, initiator and catalyst for these polymerizations were determined. In the case of PMMA, the detailed structure of a perfluorobutane chain-end was determined by NMR analysis. Perfluoroalkylsulfonyl chlorides are stable in neutral aqueous media. This permits their use as initators for fluoroolefin polymerizations in H 2 O. Poly(tetrafluoroethylene-co-hexafluoropropylene) was obtained in good yield with few ionic end groups. The aqueous fluoroolefin polymerization appears to be catalyzed by metal zero species from the reactor walls.

Perfluoroalkylation of thiols. Evidence for a radical chain process

Abstract Perfluoroalkyl sulfides are formed from primary or secondary perfluoroalkyl iodides and aromatic or aliphatic thiolates without UV irradiation. Perfluoroalkyl radicals are intermediates as demonstrated by inhibition and trapping studies.

Design of very transparent fluoropolymer resists for semiconductor manufacture at 157 nm

Photolithography at 157 nm requires development of new photoresists that are highly transparent at this wavelength. Transparent fluoropolymer platforms have been identified which also possess other materials properties required for chemically amplified imaging and aqueous development. Polymers of tetrafluoroethylene (TFE), a fluoroalcohol-substituted norbornene and an acid-labile acrylate ester show the best combination of properties. A solution, semibatch, free-radical polymerization process was developed allowing synthesis of the terpolymers on a multikilogram scale. Further property enhancements may arise from replacing the norbornene with functionalized tricyclononenes. Formulated resists have been imaged in a 157 nm microstepper.

Chemistry in hydrogen fluoride V. Catalysts for reaction of HF with halogenated olefins

Abstract Tantalum pentafluoride, niobium pentafluoride, titanium tetrachloride, and molybdenum pentachloride catalyze the addition of hydrogen fluoride to tetra - and tri chloroethene and related compounds. Hydrogenation of tetrachloroethene to 1,1,2,2-tetrachloroethane was observed using hydrogen, methylcyclopentane, and TaF5 in HF.

Synthesis of partially fluorinated monomers and polymers for ion-exchange resins

Novel hydrofluorovinyl ethers CF2CFOCH2CF2CF2SR (R=methyl (2a) and tert-butyl (2b)) were prepared using tetrafluoroethylene as the only fluorinated starting material. Another monomer, CF2CFOCH2CF2CF2SO2C(CH3)3 (2c), was obtained by oxidation of an intermediate with the HOF reagent produced from fluorine and water in acetonitrile. The vinyl ethers 2a–c homopolymerize under typical free radical conditions to give low to moderate molecular weight amorphous polymers. These monomers readily copolymerize with tetrafluoroethylene to give higher molecular weight copolymers which can be melt fabricated into films. Copolymer compositions are essentially identical to monomer feed compositions. The S-tert-butyl pendant groups are converted cleanly to sulfonyl chlorides in one step using chlorine and aqueous trifluoroacetic acid. Chlorination (Cl2) of the S-methyl or S-tert-butyl substituted polymers affords the corresponding sulfenyl chlorides which can be oxidized to sulfonyl chlorides by chlorine and aqueous acid or aqueous sodium hypochlorite. Alternatively, the S-tert-butyl groups can be oxidized to sulfones using the HOF reagent. Reaction of the tert-butylsulfones with chlorine or bromine trifluoride provides sulfonyl chlorides or fluorides, respectively.

Fluoropolymers for 157-nm lithography: optical properties from VUV absorbance and ellipsometry measurements

With the introduction of 157 nm as the next optical lithography wavelength, the need for new pellicle and photoresist materials optimized for this wavelength has produced much activity in optical characterization of thin film materials. Here we focus on ultra transparent fluoropolymers for 157 nm pellicle applications where absorbances below 0.01/micrometers are necessary to achieve transmissions above 98 percent. Transmission-based absorbance/micrometers measurements performed using VUV spectroscopy are characterized by rapid turn-around time, and are essential during the materials design and screening phase of a new materials development program. Once suitable candidate materials families have been identified for development into 157 nm pellicles, VUV ellipsometry becomes essential to model the film structure, characterize the complex index of refraction, and to tune the pellicles etalon design. Comparison of VUV absorbance measurements of fluoropolymer thin films on CaF2 substrates with VUV ellipsometry measurements of the same polymers on silicon substrates demonstrates some of the artifacts in, and helps define the accuracy of transmission based absorbance measurements. Fresnel interference fringes can produce transmission oscillations that can lead to underestimation, or even negative values, of the film absorbance. Film thickness nonuniformity can serve to reduce the Fresnel interference fringes, leading to reduce variation in the apparent 157 nm absorbance for micrometers thick films. VUV ellipsometry coupled with Fresnel analysis of the thin film/substrate system formally takes into consideration all of these optical artifacts, while at the same time determining the complex index of refraction of the materials. Using VUV ellipsometry and Fresnel analysis, the absorbance values do not show the large apparent oscillations, the film thickness is directly determined in the measurement, and film microstructure is also modeled. We have identified ultra transparent fluoropolymers which have 157 nm absorbances below 0.01/micrometers . These materials have the appropriate optical properties for use as 157 nm pellicles with greater than 98 percent transmission. This is an important for the development of 157 nm lithography, since the lack of a 157nm pellicle has been identified as a critical path issue.

Synthesis of arylperfluoroalkyl ethers by direct fluorination

Abstract Arylperfluoroalkyl ethers ArOCF 2 CF 2 X (X = F, OC 3 F 7 ) were prepared from vinyl ethers ArOCF = CFX by reaction with elemental fluorine at low temperatures. The best solvent for fluorination was a mixture of chloroform and fluorotrichloromethane. Yields were improved by adding ethanol to the solvent mixture. The starting olefins were prepared by decarboxylation of the acid salts ArOCF 2 CF 2 CO 2 Na (X = F) or by reaction of areneoxides with perfluoropropylvinyl ether (X = OC 3 F 7 ).

Oxidative fluorination of aromatic compounds in liquid hydrogen fluoride

Abstract Toluene derivatives bearing electronegative substituents are cleanly fluorinated on the methyl group by reaction with lead dioxide or nickel dioxide in liquid HF. For example, 4-nitrotoluene gives in high yield a mixture of 4-nitrobenzyl fluoride and 4-nitrobenzal fluoride. Aromatic cation radicals are proposed as intermediates.

Semifluorinated polymers: 1. Synthesis and characterization of side chain liquid crystalline polymers containing semifluorinated oligooxyethylene based flexible spacers

Abstract The synthesis and characterization of polymethacrylates, polyacrylates and polysiloxanes containing 4-methoxy-4′-hydroxybiphenyl (4-BP), 4-methoxy-4′-hydroxy-α-methylstilbene (4-MS) and 4-hydroxy-4′-methoxy-α-methylstilbene (4′-MS) mesogenic groups and a semifluorinated triad based on tetrafluorooxetane, hexafluoropropylene oxide and trifluoroethylene oxide is described. All polymers display a SA mesophase and side chain crystallization. In the case of polymers based on 4-MS and 4′-MS the highest degree of decoupling seems to be displayed by the polymethacrylates. This result is in contrast to the behaviour of the corresponding polymers containing aliphatic spacers. The polymethacrylate based on 4-BP displays an unusual ‘inverse’ monotropic SA·mesophase which to our knowledge was not previously encountered in any liquid crystal systems. The synthesis and characterization of copolymethacrylates and copolysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers is also described.