Maskless method
Schematic view: (a) spin-on deposition of photoresist on a substrate, (b) a monolayer of silica or polystyrene spheres formed on top of the photoresist, (c) UV light exposure of the photoresist covered by the monolayer of HCP microspheres - the two-dimensional intensity of the UV light in the photoresist plane, calculated using three-dimensional FDTD analysis, is shown on the right, (d) sub-wavelength patterns obtained after removing the sphere's photoresist development - an AFM image of a developed photoresist is shown on the right. (Image credit: Northwestern University, US)