Fabrication of large area periodic nanostructures using Nanosphere Photolithography

Large area periodic nanostructures exhibit unique optical and electronic properties and have found many applications, such as photonic band-gap materials [1], high dense data storage [2], and photonic devices [3]. To fabricate these periodic nanostructures, conventional photolithography methods cannot easily reach the resolution required. High-resolution methods such as e-beam lithography and focal ion beam milling are too slow to reach a large area because of their inherent serial property. Nano-imprint methods are fast to be applied, but it needs to use the mold, which requires the same resolutions as the patterns. So, it also benefits from the development of fast, economic and high throughput fabrication methods with a high resolution. We have developed a maskless photolithography method—Nanosphere Photolithography (NSP)—to produce a large area of periodic nanopatterns in photoresist utilizing the silica micro-spheres to focus UV light [4][5]. Here we will extend the idea to fabricate large areas of periodic metallic nanostructures using the NSP method. We produced a large area periodic uniform nanohole array perforated in different metallic films, such as gold and aluminum. The diameters of these nanoholes are much smaller than the wavelength of UV light used and they are very uniformly distributed. The method introduced here inherently has both the advantages of photolithography and self-assembled methods. Besides, it also generates very uniform repetitive nanopatterns because the focused beam waist is almost unchanged with different sphere sizes.