Yoshihiko Nakano

Targeting improved DMFC performance

Improved DMFC performance through reduction in the extent of methanol crossover in the polymer electrolyte membrane is described. Introduction of a thin barrier layer of polybenzimidazole (PBI) at the Nafion®117 surface by screen printing is shown to reduce methanol permeability whilst maintaining proton conductivity at a level comparable to that of the parent material. Experimental trials using these Nafion®117/PBI composite films show improved DMFC performance; an increased working current density range of 42% combined with an increase in maximum power output of 46% over that of the parent material.

Novel antireflective layer using polysilane for deep ultraviolet lithography

A bottom antireflective layer (ARL) is essential for deep ultraviolet (UV) lithography. We have just developed a polysilane antireflective layer (PSARL) process. PSARL can act as an antireflective layer due to the Si–Si bond which has absorption in the deep UV region, and it can be etched with high selectivity to resist under etch conditions that use a chlorine plasma which is a suitable inorganic silicon etchant. Similar to the conventional organic ARL process, PSARL can be simply spin coated onto the substrate, and removed with an asher using an O2/CF4 gas mixture. The partially cross-linked diphenylsilane copolymer was evaluated with a view to its application as an ARL material and the results obtained are presented in this article.

Novel latent initiator for cationic polymerization of epoxides

A novel latent initiator for cationic polymerization of epoxides, a composite catalyst containing aluminum complexes and phenol derivatives protected with tert-butoxycarbonyl groups (tBOC), is reported. At a certain temperature, protected phenols generate the parent phenols which are coinitiators with aluminum complexes. The deprotection temperature of the tBOC group depends on the structure of the phenol moieties. Bis(p-t-butoxycarbonyloxyphenyl)sulfone (Ph1) generates (p-dihydroxyphenyl)sulfone (PhH1) at around 150°C, the temperature at which the curing of epoxides is conventionally carried out. The thermally generated PhH1 and aluminum complexes initiate the curing of epoxides. Epoxy resin compositions containing these composite catalysts have a long shelf life at room temperature and are cured at around 150°C, showing that the composite catalyst has excellent latent properties.

Polysilane spherulites and their high photoluminescence quantum yields

Large polysilane spherulites have been observed. The spherulites were prepared by controlling the removal rate of solvents from poly(n-butyl-n-pentylsilane) under a xylene atmosphere. The diameter of the spherulites was greater than 0.1 mm. The structure of the spherulites was compared with that of the polysilane powder by polarized microscopy, SEM, DSC, and x-ray diffractometry. A high photoluminescence quantum yield of 0.3 was obtained for the spherulites.

Investigation of the organic solar cell characteristics for indoor LED light applications

We report an experimental study on the current–voltage characteristics of organic solar cells (OSCs) under indoor light illumination. A daylight color light-emitting diode (LED) was used as the indoor light source. We investigated the short circuit current density, open circuit voltage, and fill factor of the OSC under LED irradiation and compared them with those for a crystal silicon solar cell (c-Si-SC), which occupy a large part of the solar cell market. We found that compared with the c-Si-SC, the OSC had higher power conversion efficiency (PCE). We also derived the maximum feasible PCE of an OSC for indoor applications and calculated that a PCE value of 21.3% could be obtained under daylight color LED illumination at approximately 200 lx. From the results of the calculation, it became apparent that the open circuit voltage plays an important role in achieving a high PCE from OSCs, indicating they are promising as electrical energy harvesting module for indoor applications.

Application of polysilanes for deep-UV antireflective coating

Application of polysilanes for a deep UV (DUV) bottom anti- reflective coating (BARC), in order to resolve the problem posed by the insufficient anti-reflection with thin conventional organic BARC applied on transparent dielectric film, is described. The newly developed polysilane anti- reflective coating has the real part of refractive index, n equals 2.00, and the imaginary part, k equals 0.23 at 248 nm. The polysilane coating is immiscible with a chemically amplified photoresist, and is not removable during normal wet development of photoresist. Etching rate of the polysilane is 2 times faster than that of DUV resist during BARC etching, and lower than that of DUV resist during dielectric film etching. The polysilane layer is easily removed by ashing using O2 gas process. Using thick polysilane coating, it can realize both the suppression of the interface reflection between the resist and BARC and good critical dimension control on dielectric film.

Poly(phenylhydrosilane): Base‐developable polysilane resist

Poly(phenylhydrosilane) becomes soluble in a 2.38% tetramethylammoniumhydroxide aqueous solution after exposure to UV light. This is the first report that the polysilanes not bearing acidic groups can be developed with dilute basic aqueous solutions. Addition of 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone increases the resist sensitivity. The reaction mechanism is as follows: PS1 photodecomposes to form silyl compounds having SiOH groups, which become soluble in an aqueous base solution, because these silane compounds bearing SiOHs are acidic.

Optimization of polysilane structure as fast-etching bottom antireflective coating for deep ultraviolet lithography

A bottom antireflective coating (BARC) is essential for deep ultraviolet lithography. We have already reported the BARC composed of polysilanes which can be spin coated and etched faster than resists. In this study, polysilane structures are optimized in order to set the etch selectivity against resists to a higher level than that previously reported without losing the antireflection performance. The results indicate that the networked polysilanes structure is the most suitable. Poly(methylhydrosilane) whose Si–H is partially cross-linked and has the highest silicon content of 64.8 wt% yields the optimal results. The resist profile is achieved on it without footing and residue. The refractive index at the wavelength of KrF excimer (248 nm) is n=1.93, k=0.32, and the polymer reduces multi-reflection in both resists and in transparent substrates. The etch selectivities are 4.8 under Cl2 plasma and 6.6 under HBr plasma, which are much higher than that of an organic BARC, namely, about 1.

Spun-on carbon antireflective layer with etch resistance for deep and vacuum ultraviolet lithography processes

Dry etch resistance and antireflective performance were studied for a film containing a high amount of carbon (83.4 wt %), which was named the spun-on carbon film. The film was formed by using a carbon cluster precursor synthesized by reductive coupling of a mixture of carbon tetrabromide and phenylbromide. The refractive indices of the spun-on carbon film at the exposure wavelengths of excimer lasers are n=1.72, k=0.35 (KrF), n=1.46, k=0.67 (ArF), and n=1.37, k=0.14 (F2). A bilayer bottom antireflective coating system composed of upper spun-on glass (SOG) and lower spun-on carbon was evaluated. By optimizing the SOG thickness, the reflectivity is reduced to 0.2% (KrF), 3.3% (ArF), and 0.5% (F2). Remarkable improvement is observed at the KrF and F2 wavelengths. Resist profiles are obtained without any footing, residue, or standing wave using the KrF and ArF scanning steppers. The etch resistance of the spun-on carbon film is 1.34 times greater than that of the thermally oxidized novolak film (i.e., a conv...

Application of organic silicon cluster to patter transfer process for deep UV lithography

In this paper, organic silicon cluster is investigated as bottom anti-reflective coating (BARC) material compatible with the RIE mask for the substrate(oxide) etch in a thin resist process for deep UV lithography. It can be simply spin-coated and suppress reflection by single layer BARC process. Excellent etch properties closer to a-Si, namely high etch selectivity of resist:BARC during BARC etch and great etch resistance without deformation during oxide etch, are achieved.