High aspect ratio grating fabrication by imprint lithography

A fine grating with high aspect rate pattern is one of the essential elements for advanced nano optical devices such as a quarter wave plate. To fabricate high aspect ratio pattern having sub wavelength feature size, nanoimprint lithography is applied. However, fatal defects caused by mechanical stress and friction between the mold and polymer are significant problems. To eliminate the defects, the process sequence, pressure and temperature conditions are optimized. Using Si based mold, sub wavelength grating having 200nm in width and over 1.7 micron in height is demonstrated using PMMA thin film on quartz substrate. This method is a promising technology for industrial production of advanced nano optical elements having high aspect ratio structure.