Fullerene-Incorporated Nanocomposite Resist System for Nanolithograpy
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NANOCOMPOSITE
FULLERENE-INCORPORATED NANOLITHOGRAPY
SYSTEM
FOR
T. Ishii*, H. Nozawa** , E. Kuramochi, * and T. Tamamura* *NTT Basic Research Laboratories, Atsugi, Kanagawa, Japan, [email protected] * *NTT Photonics Laboratories, Atsugi, Kanagawa, Japan ABSTRACT A nanocomposite resist system that incorporates sub-nm fullerene molecules ( C6o and/or C70) into a conventional resist material is proposed for nanolithograpy. Fullerene has physically and chemically resistant characteristics, and its incorporation reinforces the original resist film, leading to substantial improvements in resist performance: etching resistance, pattern contrast, mechanical strength and thermal resistance. We have prepared a system composed of a positivetype electron beam resist, ZEP520, and C60 or a C60/C70 mixture and through the fabrication of high electron mobility transistors (HEMTs), X-ray masks, and groove-grating mirrors for lasers with nanometer dimensions confirmed improved resist performance, particularly resolution improvements due to enhanced etching resistance. By making use of a characteristic unique to the nanocomposite, which is that sensitivity readily changes with the fullerene content due to a dissolution inhibiting effect of fullerene, we have constructed a fullerene-incorporated bilayer resist system for a lift-off process and have successfully fabricated a highly-ordered array of self-organized boxlike nanostructures and a mold for nanoprinting. Further, solubility enhancement by fullerene derivatives has been examined for a higher degree of fullerene incorporation and better sensitivity characteristics in future nanocomposite resist systems. INTRODUCTION Electron beam lithography (EBL) is widely employed for nanometer device fabrication. For higher resolution in EBL, the general trend has been to use a higher acceleration voltage to increase beam resolution as
well as to minimize scattering effects. Several
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acceleration voltage of 100 kV are already used on a practical basis.
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However, it has become increasingly ultrasmall difficult to fabricate patterns due to the poor resistant qualities of conventional resist (3)Substrate Defects etching generally Resolution materials. increases with decreasing resist film thickness, so an extremely thin film is (b) Thick film process (a) Thin film process used for ultrasmall pattern fabrication Figure 1. Problems in conventional resist processes. [1]. The poor etching resistance of such thin film often results in contrast degradation or rounding of the upper corners of the patterns during development and in the formation of defects during etching [Fig. 1(a)]. Another problem is pattern collapse [Fig. 1(b)]. When a thicker resist film is used for deep substrate etching, the aspect ratio of the resultant patterns, defined as the ratio of pattern height and pattern width, becomes larger. Such thin and
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