A two-step exposure method to effectively reduce the proximity effect in fabricating nanometer-spaced nanopillars is presented.In this method,nanopillar patterns on poly-methylmethacrylate (PMMA) were partly crosslinked in the first-step exposure.After development,PMMA between nanopillar patterns was removed,and hence the proximity effect would not take place there in the subsequent exposure.In the second-step exposure,PMMA masks were completely cross-linked to achieve good resistance in inductively coupled plasma etching.Accurate pattern transfer of rows of nanopillars with spacing down to 40 nm was realized on a silicon-on-insulator substrate.
A novel simple dose-compensation method is developed for proximity effect correction in electron-beam lithography.The sizes of exposed patterns depend on dose factors while other exposure parameters(including accelerate voltage,resist thickness,exposing step size,substrate material,and so on) remain constant.This method is based on two reasonable assumptions in the evaluation of the compensated dose factor:one is that the relation between dose factors and circle-diameters is linear in the range under consideration;the other is that the compensated dose factor is only affected by the nearest neighbors for simplicity.Four-layer-hexagon photonic crystal structures were fabricated as test patterns to demonstrate this method.Compared to the uncorrected structures,the homogeneity of the corrected hole-size in photonic crystal structures was clearly improved.
