Manufacture Of The Micro/Nano Structures

The primary task in this project is to fabricate the nano-patterning on silicon dioxide and to optimize the fabrication techniques, which make the preparation for selective-area growth of nanowire solar cells. Nano-scale structures on silicon dioxide can be formed by using either nanoimprint lithography technique or electron-beam lithography technique. For micro-scale structures on silicon dioxide, photolithography technique is used, the fabricated silicon dioxide micro-patterning can be used for selective-area growth test of cubic silicon carbide.Nanoimprint lithography is used to fabricate the silicon dioxide nano-patterning by comparing the different patterning methods for silicon dioxide in the nano- and micro-scale structures, holes with diameters of 50-60 nm are defined in a 30 nm-thick silicon dioxide layer on a silicon substrate. The wafer will be used as a patterned substrate for gallium arsenide phosphide nanowire growth using molecular beam epitaxy. In the fabrication, a silicon stamp consisted of nanopillar arrays with a structure diameter of 50-60 nm was initially fabricated using electron-beam lithography followed by deep reactive-ion etching. Thereafter, the stamp was employed in the nanoimprint process using a hot-embossing imprinter. A wafer with a layer of silicon dioxide on top and coated with nanoimprint resist was prepared. During nanoimprint, the nano-pattern was transferred to the nanoimprint resist layer. Finally, by applying reactive-ion etching and wet etching on silicon dioxide, the nano-pattern was transferred to the silicon dioxide layer with desired hole diameters of 50-60 nm. During the electron-beam lithography process, the parameters such as exposure method, writing current and exposure dose were optimized. In nanoimprint lithography, different imprinters were tired and compared in order to obtain the expected hole sizes with good quality on the silicon dioxide layer.The nano-patterned silicon dioxide layer can also be produced using the electron-beam lithography. In this case, electron-beam exposure using different doses was performed on a positive electron-sensitive resist to create different sizes of nanohole arrays. After development, holes with diameters ranging from 35 to 50 nm were successfully fabricated in the resist. Further optimization of exposure conditions and etch processes of silicon dioxide are being carried out.For silicon dioxide micro-patterning, micro-structures with sizes ranging from 1 μm to 10 μm were fabricated using photolithography followed by reactive-ion etching. The wafers will be used for cubic silicon carbide selective-area growth. The purpose is to investigate the growth quality of cubic silicon carbide for various silicon dioxide structures.