Fabrication of soft nanoimprint stamps and polymer subwavelength gratings by spin coating techniques

Abstract

We report on a fabrication technique of both soft nanoimprint stamps and sub-wavelength gratings (SWGs) by spin coating of a polymer solution on a silicon mold. One and two-dimensional grating structures of periods 200nm were first obtained by high-resolution electron beam lithography and reactive ion etching of a silicon wafer. Then, a solution of polymethyl methacrylate (PMMA) was spun coated on the etched silicon molds. After baking, a thin layer of polydimethylsiloxane (PDMS) was assembled with PMMA sheet and mounted on a glass carrier. Scanning electron microscopy images of the replicated samples show high quality features reproduced from the silicon mold. Since PMMA is transparent for visible and near-infrared wavelengths, the replicated subwavelength gratings are applicable for many kinds of optical devices. In addition, the fabricated structure can be used as soft nanoimprint stamps which provides clear advantages of large surface patterning. The optical properties of both two and one-dimensional SWGs have been studied theoretically based on rigorous coupled-wave analysis (RCWA). The measured transmittance of the replicated antireflection SWG agreed well with the theoretical calculations.