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Journal Articles

Application of natural linear polysaccharide to green resist polymers for electron beam and extreme-ultraviolet lithography

Takei, Satoshi*; Oshima, Akihiro*; Oyama, Tomoko; Ito, Kenta*; Sugahara, Kigen*; Kashiwakura, Miki*; Kozawa, Takahiro*; Tagawa, Seiichi*; Hanabata, Makoto*

Japanese Journal of Applied Physics, 53(11), p.116505_1 - 116505_7, 2014/11

 Times Cited Count:6 Percentile:66.66(Physics, Applied)

The application of natural linear polysaccharide to green resists was demonstrated for electron beam (EB) and extreme-ultraviolet (EUV) lithography. Because of the water solubility of natural polysaccharides, the water spin-coating and water-developable processes realize an environmentally friendly manufacturing process for next-generation electronic devices. The developed green resist with a weight-average molecular weight of 83,000 and 70 mol % hydroxyl groups was found to have acceptable properties such as spin-coat ability on 200 mm wafers, pillar patterns of 100-400 nm with a high EB sensitivity of 10 $$mu$$ C/cm$$^{2}$$, etch selectivity with a silicon-based middle layer in CF$$_{4}$$ plasma treatment, and high prediction sensitivity to EUV region.

Journal Articles

Fabrication of fine imaging devices using an external proton microbeam

Sakai, Takuro; Yasuda, Ryo; Iikura, Hiroshi; Nojima, Takehiro; Koka, Masashi; Sato, Takahiro; Ishii, Yasuyuki; Oshima, Akihiro*

Nuclear Instruments and Methods in Physics Research B, 332, p.238 - 241, 2014/08

 Times Cited Count:0 Percentile:100(Instruments & Instrumentation)

We have successfully fabricated novel microscopic imaging devices made from UV/EB curable resin using an external scanning proton microbeams. The devices are micro-structured fluorescent plates that consist of an array of micro-pillars that align periodically. The base material used in the pillars is UV/EB curable resin and each pillar contains phosphor grains. The pattern exposures were performed using a proton beam writing technique. The height of the pillars depends on the range of the proton beam. Optical microscopy and scanning electron microscopy have been used to characterize the samples. The results show that the fabricated fluorescent plates are expected to be high-spatial-resolution imaging devices.

Journal Articles

Organic solvent-free water-developable sugar resist material derived from biomass in green lithography

Takei, Satoshi*; Oshima, Akihiro*; Ichikawa, Takumi*; Sekiguchi, Atsushi*; Kashiwakura, Miki*; Kozawa, Takahiro*; Tagawa, Seiichi*; Oyama, Tomoko; Ito, Shoji*; Miyasaka, Hiroshi*

Microelectronic Engineering, 122, p.70 - 76, 2014/06

 Times Cited Count:21 Percentile:19.44(Engineering, Electrical & Electronic)

Biomass-derived branched sugar resist material was developed for environmentally-friendly electron beam lithography (EBL). The developed resist enables organic solvent-free water-developable process. The resist performance was evaluated using 75 keV EBL system. Lines of 50-200 nm were fabricated with high sensitivity of 7 $$mu$$C/cm$$^{2}$$. The resist is developable in pure water at 23 $$^{circ}$$C for 60 s, and it has acceptable CF$$_{4}$$ etch selectivity.

Journal Articles

Positive-negative dual-tone sensitivities of ZEP resist

Oyama, Tomoko; Nakamura, Hirotaka*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

Applied Physics Express, 7(3), p.036501_1 - 036501_3, 2014/03

 Times Cited Count:4 Percentile:77.17(Physics, Applied)

A chlorinated polymer ZEP is a main-chain scission type (positive-tone) high-sensitivity resist. However, we found that ZEP changes to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100 kV electron beam as a dual-tone are evaluated with various developers. Owing to different solvation strengths, the resist sensitivity varied with different developers in the positive-tone region. On the other hand, it was found that the threshold dose for the positive-negative inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, we found that the amount of chlorine atoms and terminal double bonds generated by chain scission determines the threshold of the P-N inversion. This result provides important information for possible ZEP applications such as a dual-tone resist.

Journal Articles

Pulse radiolysis study on a highly sensitive chlorinated resist ZEP520A

Hosaka, Yuji*; Oyama, Tomoko; Oshima, Akihiro*; Enomoto, Satoshi*; Washio, Masakazu*; Tagawa, Seiichi*

Journal of Photopolymer Science and Technology, 26(6), p.745 - 750, 2013/12

 Times Cited Count:10 Percentile:60.18(Polymer Science)

ZEP520A is one of the most popular positive electron beam (EB) resists used in research and photomask fabrication owing to its excellent properties. Herein, EB-induced initial reactions of ZEP520A were investigated via pulse radiolysis (EB energy: 28 MeV, time resolution: 10 ns). Dissociative electron attachment and formation of a charge transfer complex were definitive contributing factors to the efficient degradation of ZEP520A. Furthermore, products induced by direct ionization of ZEP520A were observed in a highly concentrated ZEP520A solution in tetrahydrofuran, suggesting that initial reactions in the ZEP520A solid film that are induced only by direct ionization could be simulated via pulse radiolysis in specific solutions.

Journal Articles

Micro/nanofabrication of poly($$_{L}$$-lactic acid) using focused ion beam direct etching

Oyama, Tomoko; Hinata, Toru*; Nagasawa, Naotsugu; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*; Taguchi, Mitsumasa

Applied Physics Letters, 103(16), p.163105_1 - 163105_4, 2013/10

 Times Cited Count:8 Percentile:59.29(Physics, Applied)

Micro/nanofabrication of biocompatible and biodegradable poly($$_{L}$$-lactic acid) (PLLA) was evaluated using focused Ga ion beam direct etching. The fabrication performance was determined with different ion fluences and fluxes. It was found that the etching speed and fabrication accuracy were affected by irradiation-induced heat because the resistance of PLLA to thermal deformation is decreased when above its glass transition temperature (approximately 60$$^{circ}$$C). By controlling the irradiation conditions, controlled micro/nanostructures of PLLA were fabricated, such as holes ($$phi$$80 nm) and alphabets (width: 100 nm). Moreover, focused ion beam (FIB)-irradiated surfaces were analyzed using micro-area X-ray photoelectron spectroscopy. Owing to reactions such as the physical sputtering of atoms and radiation-induced decomposition, PLLA was gradually carbonized with increasing C=C bonds expected to have good cell attachment properties.

Journal Articles

Method of predicting resist sensitivity for 6.x nm extreme ultraviolet lithography

Oyama, Tomoko; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

Journal of Vacuum Science and Technology B, 31(4), p.041604_1 - 041604_5, 2013/07

Journal Articles

Micro-/nanofabrication of cross-linked poly($$_{rm L}$$-lactic acid) using electron beam nanoimprint lithography

Okubo, Satoshi*; Nagasawa, Naotsugu; Kobayashi, Akinobu*; Oyama, Tomoko*; Taguchi, Mitsumasa; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*

Applied Physics Express, 5(2), p.027303_1 - 027303_3, 2012/02

 Times Cited Count:3 Percentile:84.07(Physics, Applied)

Electron beam nanoimprint lithography was proposed for fabricating the micro-/nanostructures of cross-linked poly($$_{rm L}$$-lactic acid) (RX-PLLA). PLLA with triallyl isocyanurate (TAIC) solutions were dropped on the Si-molds fabricated by the conventional EB lithography technique. PLLA/TAIC on Si-molds were imprinted and cross-linked with doses from 10 to 500 kGy at room temperature under vacuum. The micro-/nanostructures of RX-PLLA were successfully obtained with high accuracy. Hence, it was found that the imprinted structures of RX-PLLA (100 kGy irradiation) show low line edge roughness and high thermal durability at 120 $$^{circ}$$C.

Journal Articles

Development of function-graded proton exchange membrane for PEFC using heavy ion beam irradiation

Shiraki, Fumiya*; Yoshikawa, Taeko*; Oshima, Akihiro*; Oshima, Yuji*; Takasawa, Yuya*; Fukutake, Naoyuki*; Oyama, Tomoko*; Urakawa, Tatsuya*; Fujita, Hajime*; Takahashi, Tomohiro*; et al.

Nuclear Instruments and Methods in Physics Research B, 269(15), p.1777 - 1781, 2011/08

 Times Cited Count:7 Percentile:44.89(Instruments & Instrumentation)

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe$$^{54+}$$ ion beam with the energy of 6 MeV/u under a vacuum condition. Irradiated films were grafted with styrene monomer and then sulfonated. The membrane electrode assembly (MEA) fabricated by the function graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.

Journal Articles

Study on depth profile of heavy ion irradiation effects in poly(tetrafluoroethylene-co-ethylene)

Gowa, Tomoko*; Shiotsu, Tomoyuki*; Urakawa, Tatsuya*; Oka, Toshitaka; Murakami, Takeshi*; Oshima, Akihiro*; Hama, Yoshimasa*; Washio, Masakazu*

Radiation Physics and Chemistry, 80(2), p.264 - 267, 2011/02

 Times Cited Count:6 Percentile:50.15(Chemistry, Physical)

High linear energy transfer (LET) heavy ion beams were irradiated to poly(tetrafluoroethylene-co-ethylene) (ETFE) under vacuum and in air. The irradiation effects in ETFE as a function of the depth was precisely evaluated by analyzing each one of the films of the irradiation samples which were made of stacked ETFE films. It was indicated that conjugated double bonds would be generated by heavy ion beam irradiation, and their amounts should show the Bragg-curve-like distributions. Also, it was suggested that higher LET beams would induce radical formation in high density and longer conjugated C=C double bonds could be generated by the second-order reactions. Moreover, for irradiation samples in air, C=O was produced correlating to the yield of oxygen molecules diffusing from the sample surface.

Journal Articles

Changes to the chemical structure of isotactic-polypropylene induced by ion-beam irradiation

Oka, Toshitaka; Oshima, Akihiro*; Motohashi, Ryota*; Seto, Naoto*; Watanabe, Yuji*; Kobayashi, Ryoji*; Saito, Koki*; Kudo, Hisaaki*; Murakami, Takeshi*; Washio, Masakazu*; et al.

Radiation Physics and Chemistry, 80(2), p.278 - 280, 2011/02

 Times Cited Count:6 Percentile:50.15(Chemistry, Physical)

The chemical structures of various ion-beam irradiated isotactic-polypropylene samples were studied. Results of micro-Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy suggest not only the linear energy transfer, but also the fluence is effective in local transformation of the isotactic-polypropylene.

Journal Articles

Micro-fabrication of biodegradable polymers using focused ion beam

Okubo, Satoshi*; Takahashi, Tomohiro*; Takasawa, Yuya*; Gowa, Tomoko*; Sasaki, Takashi*; Nagasawa, Naotsugu; Tamada, Masao; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*

Journal of Photopolymer Science and Technology, 23(3), p.393 - 397, 2010/11

 Times Cited Count:4 Percentile:84.1(Polymer Science)

Microfabrication of biodegradable polymers such as poly(butylene succinate-${it co}$-adipate) (PBSA) and poly($$varepsilon$$-caprolactone) (PCL) were demonstrated using focused ion beam (FIB) with maskless direct etching. As the result, the micro structures of PBSA and PCL were obtained. The etching depth of both PBSA and PCL were increased with increasing FIB fluence, and the etching rates were estimated to be about 1.3 $$times$$ 10$$^{-18}$$ $$mu$$m/(ions cm$$^{-2}$$) and 1.2 $$times$$ 10$$^{-18}$$ $$mu$$m/(ions cm$$^{-2}$$), respectively. Moreover, very thin films of PBSA and PCL were made by spin-coating method. The thicknesses of the spin-coated samples were about 200 nm, and the surface roughness was less than 10 nm (RMS). The fine structures such as micro-gear of PBSA and PCL were obtained without solid debris. The line width of the fabricated structure was about 250 nm.

Journal Articles

Ion beam irradiation effects on resist materials

Gowa, Tomoko*; Takahashi, Tomohiro*; Oka, Toshitaka; Murakami, Takeshi*; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*

Journal of Photopolymer Science and Technology, 23(3), p.399 - 404, 2010/08

Journal Articles

Study of ion-beam-induced damage and luminescence properties in terbium-implanted AlGaN

Park, J.-H.*; Wakahara, Akihiro*; Okada, Hiroshi*; Furukawa, Yuzo*; Kim, Y.-T.*; Chang, H.-J.*; Song, J.*; Shin, S.*; Lee, J.-H.*; Sato, Shinichiro; et al.

Japanese Journal of Applied Physics, 49(3), p.032401_1 - 032401_5, 2010/03

 Times Cited Count:1 Percentile:93.74(Physics, Applied)

Journal Articles

Light emitting FET based-on spatially selective doping of Eu in AlGaN/GaN HEMT

Okada, Hiroshi*; Takemoto, Kazumasa*; Oikawa, Fumitake*; Furukawa, Yuzo*; Wakahara, Akihiro*; Sato, Shinichiro; Oshima, Takeshi

Physica Status Solidi (C), 6(Suppl.2), p.S631 - S634, 2009/05

Light emitting field effect transistor (FET) based-on AlGaN/GaN high electron mobility transistor (HEMT) structure with spatially selective doping of rare-earth ions (REIs) as a luminescence center in the channel is proposed and investigated. Fabricated device showed excellent I-V characteristics as a transistor with gate control. By applying a drain bias of 20 V, red emission suggesting a luminescence from Eu ion was clearly observed. Applying a negative bias to the Schottky gate decreased the luminescence intensity.

Journal Articles

Development of apparatus for electron irradiation and in-situ I-V characteristics measurements for space solar cells

Fumon, Takashi*; Kobayashi, Ippei*; Oshima, Takeshi; Sato, Shinichiro; Okuda, Shuichi*; Taniguchi, Ryoichi*; Iwase, Akihiro*

Proceedings of 8th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-8), p.203 - 206, 2008/12

We developed an apparatus for electron irradiation and in-situ current-voltage (I-V) characteristics measurements for space solar cells. The apparatus was interfaced to an electron linear accelerator at Radiation Research Center of Osaka Prefecture University. By using this apparatus, the electron irradiation with the energies from 6 MeV to 12 MeV can be performed at various temperatures from -196 $$^{circ}$$C to 100 $$^{circ}$$C. In-situ I-V characteristic measurements are also possible at the temperature from -196 $$^{circ}$$C to 100 $$^{circ}$$C. As a first demonstration using this apparatus, we performed two experiments. First, I-V characteristics of a Si solar cell were measured at room temperature and at low temperature. Secondly, the Si solar cell was irradiated with 10 MeV electrons and I-V characteristics were measured at room temperature. The experimental result was compared with those for 1 MeV electron irradiation and 10 MeV proton irradiation.

Journal Articles

Total dose effects on heavy-ion induced gate current in MOS structure

Takahashi, Yoshihiro*; Fugane, Masaru*; Imagawa, Ryo*; Owaki, Akihiro*; Hirao, Toshio; Onoda, Shinobu; Oshima, Takeshi

JAEA-Review 2008-055, JAEA Takasaki Annual Report 2007, P. 7, 2008/11

no abstracts in English

Journal Articles

380 keV proton irradiation effects on photoluminescence of Eu-doped GaN

Okada, Hiroshi*; Nakanishi, Yasuo*; Wakahara, Akihiro*; Yoshida, Akira*; Oshima, Takeshi

Nuclear Instruments and Methods in Physics Research B, 266(5), p.853 - 856, 2008/03

 Times Cited Count:7 Percentile:50.59(Instruments & Instrumentation)

To develop light emitting devices with radiation hardness, photoluminescence properties of non- and Eu-doped GaN after proton irradiation were investigated. The samples were irradiated with protons at 380 keV up to 1$$times$$10$$^{14}$$/cm$$^{2}$$ at room temperature RT. The photoluminescence properties for the samples were measured at RT. As a results, the luminescence properties for non-doped GaN much decrease due to irradiation at 1$$times$$10$$^{13}$$/cm$$^{2}$$. On the other hand, for Eu-doped GaN, the luminescence properties that correspond to the transition did not show any degradation after irradiation at 1$$times$$10$$^{14}$$/cm$$^{2}$$.

Journal Articles

The H-Invitational Database (H-InvDB); A Comprehensive annotation resource for human genes and transcripts

Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.

Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01

 Times Cited Count:50 Percentile:24.92(Biochemistry & Molecular Biology)

Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.

Journal Articles

Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Iguchi, Harukazu*; Hamada, Yasuji*; Nakano, Haruhisa*; Oshima, Shinsuke*; Ito, Kimitaka*; et al.

Nuclear Fusion, 47(10), p.S718 - S726, 2007/10

 Times Cited Count:86 Percentile:4.45(Physics, Fluids & Plasmas)

Present status of experiments on zonal flows is overviewed. Innovative use of modern diagnostics has revealed the existence of zonal flows, their spatio-temporal characteristics, their relationship with turbulence, and their effects on confinement. Particularly a number of observations have been accumulated on the oscillatory branch of the zonal flow, dubbed as geodesic acoustic modes suggesting necessity of theories to give their proper description. Several new methods have elucidated the zonal flow generation processes from the turbulence. Further investigation of relationship between the zonal flows and confinement is strongly encouraged as cross-device activity.

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