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 mu m 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 mn 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. (c) 2005 Elsevier B.V. All rights reserved.