Hirokazu Aoyama

Thermal Stability and Electrochemical Properties of Fluorine Compounds as Nonflammable Solvents for Lithium-Ion Batteries

Differential scanning calorimetry study demonstrated that mixing of fluoro-ethers and fluoro-carbonates improved the thermal stability of 0.67 mol/L LiClO 4 ―ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 by volume). The oxidation currents were smaller in the fluorine compound-mixed electrolyte solutions than in 0.67 mol/L LiClO 4 ―EC/DEC/PC, which also shows a high stability of the fluorine compound-mixed electrolyte solutions against electrochemical oxidation. Electrochemical reduction of fluorine compounds took place at the higher potentials than EC, DEC, and PC, as suggested by the highest occupied molecular orbital and lowest unoccupied p-molecular orbital energies of the fluorine compounds. However, charge/discharge experiments using natural graphite (NG) electrodes showed that the fluorine compounds increased first coulombic efficiencies due to the quick formation of the solid electrolyte interphase on NG in PC-containing solvents.

Electrochemical Behavior of Nonflammable Organo-Fluorine Compounds for Lithium Ion Batteries

The electrochemical behavior of organo-fluorine compounds with antioxidation ability has been investigated. Oxidation currents of fluorine-compound-containing ethylene carbonate (EC)/diethyl carbonate (DEC) solutions were much smaller than those of EC/ DEC and EC/DEC/propylene carbonate (PC) at potentials higher than 6 V vs Li/Li + . Electrochemical reduction of fluorine compounds started at ca. 2 V vs Li/Li + , higher than those for EC, DEC, and PC. However the first coulombic efficiencies for natural graphite electrodes in fluorine-compound-containing EC/DEC mixtures were nearly the same as those in EC/DEC without an increase in irreversible capacities. Furthermore the first coulombic efficiencies in fluorine-compound-containing EC/DEC/PC mixtures were much larger than those in EC/DEC/PC itself. The results show that the fluorine compounds used in the present study can be used as nonflammable solvents for lithium ion batteries.

Novel main-chain-fluorinated polymers for 157-nm photoresists

Main-chain-fluorinated base-resins, including tetrafluoroethylene and norbornene derivatives, were synthesized and their fundamental properties, such as transparency at 157 nm and solubility in a standard alkaline developer, were characterized. A high transparency, i.e., absorbance of less then 0.5 μm-1, was achieved by optimizing the polymerization conditions with a variety of counter monomers. It was found that the polymerization conditions could also control the dissolution rates of the fluoropolymers and increased the dissolution rate of unprotected fluoropolymers by about three orders of magnitude, which was sufficient for the alkaline developability. Positive-working resists based on fluororesins were developed and showed good transparency of less than 1 μm-1 at 157 nm, and good solubility in a standard alkaline solution of 0.26-N tetramethylammonium (without any swelling behavior). And an acceptable etching rate as resistant as ArF resists was obtained and 65-nm dense lines could be delineated by the exposure at 157-nm wavelength.

Method of producing 1,1,1,3,3-pentafluoropropane, a method of producing 1,1,1,3,3-pentafluoro-2-halogeno-3-chloropropane, and a method of producing 1,1,1,2,3,3-hexachloropropene

There are provided production methods of 1,1,1,3,3-pentafluoropropane characterized in that 1,1,1,3,3-pentafluoro-2,3-dichloropropane is reacted with hydrogen fluoride in the presence of a noble metal catalyst; of 1,1,1,3,3-pentafluoro-2-halogeno-3-chloropropane characterized in that the halogenated propene indicated as general formula I is fluorinated in the presence of antimony trihalogenide and/or antimony pentahalogenide by hydrogen fluoride of mole ratio of or over five times the said antimony halogenide in a liquid phase; and of 1,1,1,2,3,3-hexachloropropene characterized in that 1,1,1,2,2,3,3-heptachloropropane is reacted with an aqueous solution of alkali metal hydroxide in the presence of a phase transfer catalyst. Therefore, an industrial manufacturing method which is possible to obtain the objective product easily at low cost and high yield can be provided.

Synthesis of novel fluorinated norbornene derivatives for 157-nm application

We have synthesized various main-chain fluorinated polymers and studied their transparency and solubility. The main-chain fluorinated polymers were synthesized by co- or ter-polmerization of tetrafluoeoethylene (TFE) with cyclic monomers, especially TFE with newly synthesized norbornene derivatives. Transparency of the main-chain fluorinated polymers tended to be higher with higher fluorine contents. But exact absorbance of the main-chain fluorinated polymers by modifying the STUPID calculation. Solubility of the main-chain fluorinated polymers functionalized by hydroxyfluoroalkyl groups was also studied. We have developed a model to predict pKa of hydroxyfluoroalkyl groups incorporated in the norbornene derivatives, and studied correlation between pKa(OH) and solubility of the co-polymers of the hydroxyfluoroalkyl-functionalized norbornene derivatives with TFE. pKa Of the hydroxyfluoroalkyl groups were lower with higher fluorine contents, and solubility of the co-polymers tended to be higher with lower pKa of the hydroxyalkyl groups.

The dissolution behavior of tetrafluoroethylene-based fluoropolymers for 157-nm resist materials

Main-chain-fluorinated base-resins, using the copolymer of tetrafluoroethylene and functional (hexafluoroisopropanol (HFA) group) norbornene, were synthesized. Partial protection of its hydroxyl group as ethoxymethyl group was achieved by two methods, by copolymerization (Method A) or by polymer reaction (Method B). The partial protection by copolymerization was conducted by copolymerizing TFE with the mixture of protected and unprotected monomers (Method A, copolymerization). The partial protection was also carried out by reacting hydroxyl group of the polymer, which is composed of TFE and unprotected monomers with ethoxymethyl chloride in the presence of an amine (Method B). In the polymer reaction, only exo position of the norbornene unit was protected. Their fundamental properties, such as transparency at 157 nm and solubility in a standard alkaline developer, were characterized and studied. A high transparency, i.e., absorbance of less than 0.4 μm-1, was achieved in both methods. However, the polymer prepared by the polymer reaction (Method B) was deprotected more quickly. And this polymer had a higher dissolution rate and development contrast than the polymer prepared by copolymerization (Method A). The Positive-working resists based on this fluororesins were developed and 55 nm dense lines could be delineated by the exposure at 157 nm wavelength with alternating phase shift mask on a 0.9 NA 157 nm exposure tool.

Characterization of TFE/norbornene-based fluoropolymer resist for 157-nm lithography

Fluoropolymers are key materials in the single-layer resists used in 157-nm lithography. We have been studying fluoropolymers to determine their potential use as base resins. These polymers are main-chain fluorinated polymers synthesized by co-polymerizing tetrafluoroethylene (TFE) and functional norbornene. We developed a new polymer that is highly transparent and has high dry-etching resistance by attaching a PG-F protecting group, which has high dry-etching resistance, to a TFE/norbornene-based fluorinated polymer. The dry-etching rate for the 15 % blocked polymer was 1.50 times that of a KrF resist and its absorption coefficient at a 157-nm-exposure wavelength was 1.06 /μm. We introduced various photoacid generators (PAGs) to the polymer, and compared lithographic performance. As a result, we found polymer with a triphenylsulfonium-salts-based PAG had a good pattern profile, and polymer with a high-acidity PAG resolved a fine pattern. In particular, polymer with a triphenylsulfonium perfluorooctane sulfonate PAG was able to resolve a 60-nm line and space pattern. We then added various quenchers to the polymer and the PAG, and compared pattern profiles. We found that the use of a high-basicity quencher improved the resolution of the resist and line edge roughness. Consequently, that the polymer with the triphenylsulfonium perfluorooctane sulfonate PAG and tributylamine quencher could resolve a 55-nm line and space pattern. These results provided guidelines for choosing the PAG and quencher for this polymer.

Synthesis of fluorinated materials for 193-nm immersion lithography and 157-nm lithography

Various fluorinated polymers were synthesized for application in 193-nm immersion lithography with the goal of improving 157-nm photoresist performance. Their fundamental properties were characterized, such as transparency at 193-nm and 157-nm (wavelength) and solubility in water and a standard alkaline developer. High transparency, i.e., absorbance better than 0.3 μm-1 at 193-nm wavelength, was achieved. The dissolution behaviors of them were studied by using the Quartz Crystal Microbalance (QCM) method. We find that the dissolution rate of Poly(norbornene-2-fluoro-2-hexafluoroalchol) (PNB1FVIP) in 0.065N tetramethylammonium hydroxide (TMAH) was >200 times (nm/s) faster than that of the copolymer of tetrafluoroethylene (TFE) and norbornene-2-fluoro-2-hexafluoroalchol (TFE/NB1FVIP). A resist based on TFE/NB1FVIP was able to delineate 75 nm dense lines by exposure at 193-nm (wavelength) with an alternating phase shift mask using a 0.75 NA ArF scanner. The dissolution rates of the fluoropolymers in water and a 0.262N and 0.065 TMAH can be controlled by optimizing counter monomers containing hexafluoroisopropanol (HFA) unit, carboxylic acid unit and so on. In addition, we have collect water contact angle data. This data shows that fluoropolymers can be used as resist cover materials for 193-nm immersion lithography.

Development and characterization of new 157-nm photoresists based on advanced fluorinated polymers

Fluorinated polymers show a good transparency at the 157-nm exposure wavelength for single-layer resists. We have developed fluorinated resist polymers for 157-nm lithography. These polymers are main-chain fluorinated polymers synthesized by the co-polymerization of tetrafluoroethylene (TFE) and polymers such as poly(TFE/norbornene/α-fluoroolefin) fluoropolymers (FP1). In this paper, a number of polymerization initiators were evaluated in the polymerization of PF1-type polymers in order to investigate the effect of polymer end groups on optical and dissolution properties. We found that the polymer end group greatly affects the dissolution properties of these polymers when using a standard 0.26N tetramethylammonium hydroxide (TMAH) aqueous developer solution. These end groups also affect the polymer transparencies at 157-nm, and the resulting lithographic performance. The fluorocarbon initiator named “F2” induced the lowered absorbance (~0.4μm-1) and an increase in the dissolution rate (~300 nm/sec) without noticeable amounts of swelling. These polymer-based resists can achieve a resolution of less than 60-nm using a 157-nm laser microstepper (NA=0.85) with a Levenson-type strong phase shifting mask.

Synthesis of novel α-fluoroacrylates and related polymers for immersion lithography

Immersion lithography is being actively developed toward mass production for 55nm node devices and beyond. Advances are being made toward large depths of focus and higher resolution, but the underlying problem of machine and material cost increases remains. Our work over the past few years has shown that the main-chain fluorinated base resins realized by the co-polymerization of tetrafluoroethylene (TFE) and norbornene derivatives offer high dissolution rates and moderate surface properties. However, it is difficult to synthesis these materials and their high cost is disadvantageous. Recently, we switched our attention to &agr;-fluoroacrylate and have synthesized various monomers and polymers for immersion lithography. &agr;-fluoroacrylate has a polymerization rate faster than acrylate and methacrylate, and its polymers are superior to theirs. In this paper, we will report these synthesis methods and immersion specific properties such as the dissolution rate in standard alkaline solution and water contact angle. Furthermore, we consider with relationship between dissolution rate and polymer structure by infrared method.