Antireflection sub-wavelength gratings fabricated by spin-coating replication

We fabricated an antireflection subwavelength grating (SWG) on a polymethyl methacrylate (PMMA) by a spin-coating replication technique. Silicon molds of a two-dimensional tapered grating of 200 nm period and 90 nm deep have been obtained using electron beam lithography and reactive ion etching. Replication has been done by direct spin-coating a 9.35 μm thick PMMA on the mold, followed by an appropriate mounting on a glass substrate. The transmittance in the wavelength region ranging from 500 to 800 nm was measured and compared with the calculation results on the basis of rigorous coupled-wave analysis. At these wavelengths, the transmittance of the SWG was increased in comparison with that of the flat PMMA sheet, in good agreement with the theoretical calculations.