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Supplementary Explanation 1.Background and prehistory for the PBW technique A micro-machining technique with a resolution of nano-meter level using several tens keV energy electron beams (EB) has already been established for manufacturing nano-devices, such as micro-photonic, sensor, semiconductor devices and so on. However, in such nano-manufacturing using EB technology, there is a limitation in processing depth due to multiple scattering of several tens keV electrons in resist material. PBW, a fine machining technique using proton beams, on the other hand, enables us to manufacture fine structures with the high aspect ratio at a horizontal resolution of 100 nm level, which is still inferior to EB. The technique of PBW has been improved by Prof. Frank Watt in National University of Singapore since 1997 and been developed at limited numbers of research institutes mainly in Europe for these five years. In TIARA, a MeV-energy light-ion microbeam system was developed and the smallest beam size of within 250 nm in diameter has been achieved in this system. Since 2005, partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research, 2005, No.17310085, study of PBW technique has been started in collaboration of JAEA and SIT on the basis of this microbeam formation technique in TIARA. Our success in manufacturing � Arch of Triumph� shape structure showed that PBW technique should be promising tool for mold fabrications or flexible prototyping of advanced devices with high aspect ratio and/or 3D structures. With this achievement, the development of prototyping advanced optical micro-devices for evaluation could be boosted up so as to make PBW technique meet requirements from industrial applications. 2.Proton Beam Writing (PBW) Technique PBW technique is one of mask-less lithography techniques using MeV energy proton micro-nanobeam. PBW, therefore, enables us to reduce the cost and the period in manufacturing devices without mask processes. Fine flexible-patterned shapes can be written on resist material, polymer film by scanning the proton micro-nanobeam in PBW. After irradiation, concave or convex polymer structures appear after removing polymer of the exposed part (positive type of resist) or unexposed (negative one), respectively. PBW technique has an ability to create fine structure with the high-perpendicularity and high-aspect ratio, because the MeV energy proton beam introduces much higher density ionization effects to the materials along its almost straight penetration track compare to EB. PBW is a cost- and time-effective technique, because it is a direct write technique with no mask processes. In addition, one can control the machining depth by changing the proton beam energy. Then, 3D structures, such as �Arch of Triumph� shape structure, as shown in Fig. 1, can be made by overlapped direct write process using two different energy proton beams. The PBW technique had initially been developed by the group of Prof. Frank Watt in University of Singapore 10 years ago. They had succeeded to manufacture relief and 3D structures with tens of nano-meter scale using hydrogen molecular ion (H2+) beam with 2 MeV energy. This announcement shows that the first achievement of PBW for 3D structures with the special resolution of hundreds of nano-meter level in Japan has reached to the world level. Using 3 MeV proton micorobeam in TIARA, the maximum depth of the 3D structures reached until 50 µm, which was three times higher than that of 2 MeV H2+ beam at National University of Singapore. 3.Manufacturing 3D structures The 3D structures, as shown in Fig. 1, were demonstrated using a negative-type resist (SU-8). Figure 2 illustrates its exposure and development processes schematically. Firstly 3-MeV proton microbeams were irradiated so as to penetrate the resist layer for the structure of whole height, then 1.2 MeV beam to stop at specific depth in the negative resist for the structure of the upper part. After the irradiation, development, that is dissolving non-irradiation part of resist using the organic solution, was made so that the 3D structure appeared. (BACK) |
