Sub-wavelength optical diffraction and photoacoustic metrologies forthe characterisation of nanoimprinted structures

摘要

We report on the use of two original techniques for the quality evaluation of nanoimprint lithography with 50nm feature size: sub-wavelength blazed diffraction gratings and photoacoustic metrology. Sub-wavelength diffractionhas been used to characterise nanoscale structures by studying the diffraction patterns of visible wavelengths of lightfrom gratings which are made up of features below the diffraction limit. Diffraction efficiencies of the diffracted ordersare related to the nanoscale line-widths, heights and defects of the gratings. A stamp of a sub-wavelength blazed gratingwas fabricated by electron beam lithography and reactive ion etching in silicon and imprinted by NIL with differenttools. Measured diffraction efficiencies agree with those from finite difference time domain simulations and wedemonstrated the possibility to distinguish diffraction patterns from successfully imprinted gratings and those with adefect. The photoacoustic method has been used for the first time to study nanoimprint polymers. Signals were obtainedfrom the top and bottom interfaces of polymer layers with aluminium and silicon, respectively, and thicknessescalculated from the time of flight of the acoustic wave and modelling physical parameters of the polymers, agree wellwith those measured by profilometry.