Dr. Akira Kojima Profile

Dr. Akira Kojima

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Publications (5)

Proceedings Article | 27 June 2019 Paper

Development of massive parallel electron beam write system

Masayoshi Esashi, Hiroshi Miyaguchi, Akira Kojima, Naokatsu Ikegami, Nobuyoshi Koshida, Masanori Sugata, Hideyuki Ohyi

Proceedings Volume 11178, 111780B (2019) https://doi.org/10.1117/12.2532971

KEYWORDS: Electron beams, Prototyping, Photomasks, Electron beam lithography, Lithography, Optical systems, Optical fabrication, Display drivers, Silicon, Electrodes

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Proceedings Article | 21 March 2017 Presentation + Paper

Simulation analysis of a miniaturized electron optics of the massively parallel electron-beam direct-write (MPEBDW) for multi-column system

Akira Kojima, Naokatsu Ikegami, Hiroshi Miyaguchi, Takashi Yoshida, Ryutaro Suda, Shinya Yoshida, Masanori Muroyama, Kentaro Totsu, Masayoshi Esashi, Nobuyoshi Koshida

Proceedings Volume 10144, 101440L (2017) https://doi.org/10.1117/12.2257967

KEYWORDS: Electron beams, Objectives, Monochromatic aberrations, Finite element methods, Optical simulations, Silicon, Electrodes, Optical design, Prototyping, Geometrical optics, Lens design, Aberration correction, Distortion

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In this study, a simulation analysis of a miniaturized electron optics for the Multi-Column Massively Parallel Electron Beam Writing system is demonstrated. Analytical evaluation of space charge effect with prototype Massively Parallel Electron Beam Writing (MPEBW) system showed 2.86 nm blur in radius occurs on each beam with a convergence half angle of 3 mrad. The angle of each beam was increased to 10 mrad to reduce the space charge effect, the coulomb blur amount can be kept to less than 1 nm in radius. However, there was limitation to increasing the angle due to a spherical aberration. Since the beam current density from the electron emitter array in the prototype MPEBW system was 100 μA/cm²and the total beam current was 1μA with 100×100 array of 10μm square emitter, the influence of coulomb blur was small. By contrast, considerably increasing the number of beams and the beam current are planned in near future in MPEBW. The coulomb blur and other aberrations will not be controlled by merely adjusting the beam convergence angle. In order to increase total beam current, miniaturized electron optics have been designed for Multi-beam+Multi-column system. Reduction lens in the designed miniaturized electron optics with crossover free to reduce the influence of coulomb repulsion with narrow convergence half angle. Unlike conventional methods, the electron beams as principal rays do not intersect at one point, so even if the beam becomes extremely narrow, the coulomb repulsion effect does not increase at the crossover area. The reduction of the entire size of parallel beams in the designed electron optics was confirmed by simulation software. The simulation results showed that least confusion disk of 6.5 nm size was obtained at the beam convergence half angles of 3 mrad corresponding to the incident beam of ±0.1 mrad divergence angle. It showed that the miniaturized electron optics was suitable for 10 nm order EB writing. The crossover free electron optics of the miniaturized electron optics is possible due to dispersing the intersection points of the principal rays by a combination of a concentric electron optics and a tapered lens electrode of the reduction lens.

Proceedings Article | 22 March 2016 Paper

Development of a MEMS electrostatic condenser lens array for nc-Si surface electron emitters of the Massive Parallel Electron Beam Direct-Write system

A. Kojima, N. Ikegami, T. Yoshida, H. Miyaguchi, M. Muroyama, S. Yoshida, K. Totsu, N. Koshida, M. Esashi

Proceedings Volume 9777, 977712 (2016) https://doi.org/10.1117/12.2219338

KEYWORDS: Electron beams, Microelectromechanical systems, Electron beam lithography, Lithography, Silicon, Finite element methods, Optical simulations, Nanolithography, Prototyping, Optical systems, Electrodes, Objectives, Semiconducting wafers

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SPIE Journal Paper | 11 September 2015

Development of ballistic hot electron emitter and its applications to parallel processing: active-matrix massive direct-write lithography in vacuum and thin-film deposition in solutions

Nobuyoshi Koshida, Akira Kojima, Naokatsu Ikegami, Ryutaro Suda, Mamiko Yagi, Junichi Shirakashi, Hiroshi Miyaguchi, Masanori Muroyama, Shinya Yoshida, Kentaro Totsu, Masayoshi Esashi

JM3, Vol. 14, Issue 03, 031215, (September 2015) https://doi.org/10.1117/12.10.1117/1.JMM.14.3.031215

KEYWORDS: Silicon, Electrodes, Thin film deposition, Thin films, Lithography, Germanium, Metals, Printing, Semiconducting wafers, Copper

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Proceedings Article | 19 March 2015 Paper

Development of ballistic hot electron emitter and its applications to parallel processing: active-matrix massive direct-write lithography in vacuum and thin films deposition in solutions

N. Koshida, A. Kojima, N. Ikegami, R. Suda, M. Yagi, J. Shirakashi, T. Yoshida, Hiroshi Miyaguchi, Masanori Muroyama, H. Nishino, S. Yoshida, M. Sugata, Kentaro Totsu, M. Esashi

Proceedings Volume 9423, 942313 (2015) https://doi.org/10.1117/12.2085782

KEYWORDS: Silicon, Thin film deposition, Electrodes, Thin films, Lithography, Metals, Germanium, Semiconductors, Parallel processing, Ions

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Making the best use of the characteristic features in nanocrystalline Si (nc-Si) ballistic hot electron source, the alternative lithographic technology is presented based on the two approaches: physical excitation in vacuum and chemical reduction in solutions. The nc-Si cold cathode is a kind of metal-insulator-semiconductor (MIS) diode, composed of a thin metal film, an nc-Si layer, an n⁺-Si substrate, and an ohmic back contact. Under a biased condition, energetic electrons are uniformly and directionally emitted through the thin surface electrodes. In vacuum, this emitter is available for active-matrix drive massive parallel lithography. Arrayed 100×100 emitters (each size: 10×10 μm², pitch: 100 μm) are fabricated on silicon substrate by conventional planar process, and then every emitter is bonded with integrated complementary metal-oxide-semiconductor (CMOS) driver using through-silicon-via (TSV) interconnect technology. Electron multi-beams emitted from selected devices are focused by a micro-electro-mechanical system (MEMS) condenser lens array and introduced into an accelerating system with a demagnification factor of 100. The electron accelerating voltage is 5 kV. The designed size of each beam landing on the target is 10×10 nm² in square. Here we discuss the fabrication process of the emitter array with TSV holes, implementation of integrated ctive-matrix driver circuit, the bonding of these components, the construction of electron optics, and the overall operation in the exposure system including the correction of possible aberrations. The experimental results of this mask-less parallel pattern transfer are shown in terms of simple 1:1 projection and parallel lithography under an active-matrix drive scheme.

Another application is the use of this emitter as an active electrode supplying highly reducing electrons into solutions. A very small amount of metal-salt solutions is dripped onto the nc-Si emitter surface, and the emitter is driven without using any counter electrodes. After the emitter operation, thin metal (Cu, Ni, Co, and so on) and elemental semiconductors (Si and Ge) films are uniformly deposited on the emitting surface. Spectroscopic surface and compositional analyses indicate that there are no significant contaminations in deposited thin films. The implication is that ballistic hot electrons injected into solutions with appropriate kinetic energies induce preferential reduction of positive ions in solutions with no by-products followed by atom migration, nuclei formation, and the subsequent thin film growth. The availability of this technique for depositing thin SiGe films is also demonstrated by using a mixture solution. When patterned fine emission windows are formed on the emitter surface, metal and semiconductor wires array are directly deposited in parallel.

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