ABSTRACT
Three-dimensional nano structures with sloped sidewalls, nano gratings in curved surfaces or taped nano structures are key components in the optical system for use primarily in displays such as LCDs, energy fields such as solar cells. The semiconductor manufacturing process can meet nano fabrication demands, and the nano fabrication processs such as X-ray lithography process, electron beam lithography technique (Laddha 2001), and focus ion beam micromachining technology (Utke 2008) were developed. In 2007, high aspect ratio polymer structures fabrication technique is developed and high aspect ratio optical gratings have been created (Kato et al. 2007). The authors have developed high aspect ratio PMMA gratings with line as narrow as 150 nm using X-ray lithography. Based on the optical theoretical calculation, the sub-wavelengthstructured (SWS) arrays has a low reflectivity over a wide spectral bandwidth. And sub-wavelength structured (SWS) surfaces can use as antireflection coating on in the solar cell devices (Zhao & Avrutsky 1999). Dr. Kanamori of Tohoku University has fabricated polymethyl methacrylate (PMMA) SWS grating by using a silicon mold technique (Kanamori et al. 2002). SWS surfaces typically behave as layers of single material with designable principal indices of refraction. It allows for the design of broadband wide field-of-view matching layers and artificial moth eyes for optical application. Ueno in Ritsumeikan University of Japan developed a high aspect ration X-ray lithography method called deep X-ray lithography for nano-structures fabrication. It is a form of non-contact
lithography having the capability of fabricating high aspect ratio nano structures (Ueno 2001). In order to fabricate the anti-reflection film with moth eye structure, or use diffraction optical element (DOE) to adjust the wavelength of resonance reflection, the submicron structures are required. By using X-ray exposure, fabrication of the structure that its size is under less than the wavelength of the visible light is possible. A number of fabrication methods of diffractive optical elements have been reported so far, including electron beam lithography, FIB (focused ion beam) etching, and laser ablation. However, the resulting height of those structures is not sufficient. A fabrication technique for sub-wavelength two-dimensional arrays using X-ray lithography is introduced in the paper. The subwavelength gratings were fabricated by synchrotron radiation (SR) lithography by using SR source with the source wavelength range is from 0.1 nm to 1.0 nm, and metal Ta is used as X-ray absorber.
