Jun Irisawa

Intermolecular interaction between the pendant chain of perfluorinated ionomer and water

The intermolecular interaction energies between a water molecule and four models of pendant chains for perfluorinated ionomers, such as CF3OCF2CF2SO3H, CF3OCF2CF2SO3−, CF3CF2CF2COOH, CF3CF2CF2COO−, were analyzed by using a molecular orbital calculation. In order to investigate a variety of configurations, five hundred random configurations that water and monomer contact at their van der Waals surfaces were generated for each system. We employed an empirical correction method for dispersion energy defined by the equation Edisp = −fd(R)C6R−6, so as to reduce the computational costs. The C6 coefficients of this equation were optimized to reproduce the energies obtained at the MP2/aug-cc-pVDZ level of calculations, and then overall intermolecular interaction energies (Eint = EHF + Edisp) were evaluated as a summation of Edisp and intermolecular interaction energy at the HF/aug-cc-pVDZ level (EHF). From these analyses, we obtained the following conclusions. (1) The ether oxygen in the pendant chain cannot bind with water strongly due to fluorination. (2) De-protonations of sulfonic and carboxylic acids extend the region where water molecules sufficiently bind with pendant chains, and this effect would cause rich water absorption when these pendant chains form membranes. Therefore, the degree of proton disassociation would be one of the key factors for the water sorption ratio and membrane morphology. (3) The binding energy of the optimized configuration for CF3CF2CF2COO− + H2O is about 2.5 kcal mol−1 larger than that for the CF3OCF2CF2SO3− + H2O system because of the larger electron negativities of the oxygen atoms on deprotonated carboxylic acid compared with those on the sulfonic acid.

Ab initio 13C and 19F NMR chemical shifts calculations for halogenated propanes

Abstract Ab initio GIAO calculations were carried out on halogenated propanes, CClF2–CF2–CXYZ (X, Y, Z; H, Cl or F) and CF3–CXY–CHCl2 (X, Y; H, Cl or F), to estimate their 19F and 13C NMR chemical shifts values, considering all their rotamers. Although, the calculated values tend to be larger for the 19F NMR chemical shifts and smaller for the 13C NMR chemical shifts than the observed values, the calculated values show fairly good linear relationships with the observed values. The Hartree–Fock 6-31G(d) level of theory is of sufficient accuracy for application of assignment and prediction of 13C and 19F NMR chemical shifts of halogenated propanes.

Synthesis and properties of (E)-1,2-difluoroethylene derivatives: improvement of the ultraviolet light stability

The synthesis and properties of (E)-α,β-difluorostilbene derivatives were studied. In particular, we investigated three suppression methods of (E)–(Z) isomerisation by shortening the molecular conjugation length, which included the introduction of a fluorine atom into the ortho or para position of the benzene ring or the replacement of the benzene ring with a cyclohexane ring. The relationship between the molecular structure of liquid crystals and the level of isomerisation by ultraviolet (UV) light was discussed.

Dry-etching resistance of fluoropolymers for 157-nm single-layer resists

Novel fluoropolymers having partially fluorinated monocyclic (5-membered and 6-membered ring) structure have been synthesized with radical cyclo-polymerization, which have C-F bond in the polymer main chain and also possess fluorocontaining acidic alcohol group. These polymers have excellent transparency lower than 1.0 μm-1 at 157nm wavelength, a small amount of outgassing, high sensitivity and good adhesion to the wafer. However, this fluoropolymer have lower etching resistance (half of conventional KrF resists) and it must be improved for applying to the single-layer resist. In this paper, we show the new model of the estimation of the dry-etching resistance for designing polymer compositions. It is well known that the model using carbon-atom-density as a parameter is useful for estimating dry-etching resistance. However, these models did not agree with the results of our fluoropolymers. Our new model was focused on the surface area and the volume of the polymer. We succeeded to explain the relationship between the dry-etching resistance and the composition of the fluoropolymer. According to this model, the compositions of fluoropolymer such as protective groups, protective ration and co-polymer units were optimized to improve their etching resistance.

The modeling of immersion liquid by using quantum chemical calculation

For realizing next generation 193nm immersion lithography, developing suitable high refractive index liquid is an very important issue. To overcome the trade off relationship between high refractive index (optimally more than 1.6 ) and low absorbance (similar degree with H2O 0.0036cm-1), the molecular modeling based on quantum chemical ab-initio calculation was performed. We have successfully developed the predictive method of frequency-dependent refractive index for liquid and its absorbance. Then, we tried to estimate these properties to search for optimal candidates. In this paper, we report on the estimated results of the refractive index n and the absorbance at 193nm for some candidate compounds. We believe we could demonstrate the usefulness of the predictive method by using the quantum chemical calculation for developing new liquids, even if there were some degree of errors in the absolute values. We have found the -SO2- (like sulfone, sulfonate, sulfate) containing five- and six-membered ring compounds such as sulfolane and sultone etc. would achieve both high refractive index around 1.6 and relatively low absorbance. XeF4O and Bi(CF3)3 ,unfortunately, had absorption at 193nm due to the weak binding outer valence electrons. In the case of alkyl Si and Ge, Si(CH2CH3)4 might have a good balance of refractive index 1.59 and relatively low absorbance. Si(CH3)3CH2CH2OH and Ge(CH2CH3)4 were estimated to have refractive index of over 1.6, but have been estimated these might have sightly stronger absorption.

Fluoropolymers for 157-nm single-layer resists developed using a new etching rate estimation model (KI-Model)

For 157-nm single-layer resists, dry etching resistance is an important issue because of the difficulty of striking a balance between 157-nm transparency and an acceptable level of dry etching resistance. To achieve an acceptable trade-off, the fluorine atom can be introduced into the resist polymer structure to obtain higher transparency, despite the fluorine atom’s high reactivity in the plasma etching process. We recently proposed a model for estimating dry-etching-resistance (the KI-model) and have shown that it can be effectively applied to the design of new fluoropolymer structures. Through simulation based on the KI-model, we were able to develop a new fluoropolymer with good dry etching resistance and high transparency. We found that a new protective group, 2-cyclohexylcyclohexanoxymethyl (CCOM), improved the characteristics of our novel fluoropolymer, compared with use of a MOM group, when used in the base resin of the resist. In this paper, we report on the usefulness of the KI-model for developing new fluorinated protective groups and new base polymers. Moreover, we have developed a new base fluoropolymer which has higher transparency and a similar degree of dry etching resistance as a monocyclic fluoropolymer with a CCOM protective group.