The 3D structural shape-control using Synchrotron Radiation (SR) lithography for the configurations of less than a micron-size has been realized. The fabrication process will be described in details. Moreover, the structure with aspect ratio as high as 4 was achieved. The briefly introduced fabrication process is to deposit a PMMA (polymethylmethacrylate) layer to a silicon substrate by spin coating. The layer is used as the X-ray resist. Subsequently, to expose SR onto the resist through an X-ray mask, then to develop the exposed resist. The principal shape-control is accomplished by optimizing each parameter influencing the resist formation, the exposed SR dosage, and development time. All mentioned above are the parameters determined from the fabrication of an arbitrary shape which is the main purpose in this paper. The targeted evaluation of the fabricated structures is to provide the line and space of 1μm pitch, 1.9μm line-height, and aspect ratio of 4. The technique for optimization of the experimental condition and each parameter for the fabrication process will be explained in the paper. This research is expected to be useful for other related work on manufactures of sub-micron structure. The suggested applications are; a variety of optical elements such as the polarized light beam splitters, diffraction optical elements, and a number of applications in device or system which requires nanoscale structures will find this work employable. The fabrication technique of higher aspect ratio and narrower line-width will be investigated in the future research.
In this paper, influences of Fresnel diffraction for the advance accuracy in sub-micron resolution of the PCT (Planepattern to Cross-section Transfer) technique are discussed. Some analytical simulations were performed for a prediction of X-ray intensity distribution. The X-ray mask pattern employed in this work was a set of right triangles placed in double rows facing each other which was designed by the fact that when mask slit becomes narrower while approaching the corner, the influence of the diffraction gradually becomes more significant. In X-ray lithography, especially for optical applications, it has been realized that the Fresnel diffraction is most effective factor for designing the shape of slits in submicron. The group of triangle mask patterns has 1.48 μm-pitch and 20 μm-height with 0.5 μm-thick Ta absorber. The submicron structure was successfully fabricated by PCT with a proximity gap of 300 μm. The fabricated structure exposed by 1.84kJ/cm3 X-ray dose has 190 nm in height. The analysis was summarized by comparing the PCT simulations and the data from experimental results.
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