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2 April 2010 Surface electron emission lithography system based on a planar type Si nanowire array ballistic electron source
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In this paper we report on the development of a Surface Electron Emission Lithography system (SEL) for high resolution and high throughput Electron Beam (EB) lithography. The Parallel EB lithography is performed on a 1:1 prototype electron stepper. A planar type silicon nanowire array ballistic electron emitter (PBE) is employed as a patterned electron emitting mask in this system. The PBE has a metal / silicon nanowire array / semiconductor structure. The nanowire is composed of interconnected silicon nanocrystallites. When a bias voltage is applied to the nanowire, the electrons injected from semiconductor substrate are accelerated via cascade tunneling between silicon nanocrystallites, and emitted from metal surface electrode. The PBE exhibits properties originated from the ballistic transport in nanosilicon layer. The electrons are emitted with uniform intensity in the surface. The emission current is fluctuation-free and low sensitivity against an environmental atomosphere. The PBE projects the pattern on the target wafer in the electron optics of parallel electric and magnetic fields. If all emitted electrons have same initial velocity, they are focused at the same distance. The pattern of the mask on the PBE is reproduced on the target wafer at the distance of the n (n=1, 2, ...) cycle of the spiral trajectory of the electron. Practical resolution is limited by the chromatic aberration in this system. We can improve the resolution by reducing the initial energy spread and emission angle dispersion of the emitted electrons because of the characteristics of the ballistic electron emission from PBE. In this study, we confirmed that the submicron patterns is reproduced all over the area of 2.8 mm square. This homogeneity of exposure in the extended area results from the uniformity of nanowire array produced by self-organized chemical reaction process. This technique will be available to produce next generation MEMS with lower cost than that of optical stepper.
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A. Kojima, T. Ohta, H. Ohyi, and N. Koshida "Surface electron emission lithography system based on a planar type Si nanowire array ballistic electron source", Proc. SPIE 7637, Alternative Lithographic Technologies II, 763712 (2 April 2010);

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