Fast Proximity Corrections for Electron-Beam-Fabricated High Resolution and High-Aspect-Ratio Fresnel Zone Plate

Abstract

Fast proximity corrections for electron beam (e-beam) patterning with circular symmetry are implemented. Calculations are applied particularly to the Fresnel zone plate (FZP). Considerable reduction of numerical data is obtained by exploiting the symmetry of the FZP; the typical calculation time for a FZP with 300 zones is of the order of 30 min. Two accelerating voltages, 40 keV and 50 keV, were used to test the reliability of proximity corrections. It was demonstrated that in both cases, proximity corrections are necessary; at 40 keV, FZPs with 0.1 µ m resolution and high aspect ratio of 5 were fabricated, whereas at 50 keV, a resolution of 70 nm and high aspect ratio greater than 7 was attained. Comparison between experimental and theoretical evaluations of parameters related to the optical efficiency of the FZP, such as, zone line-width accuracy and line/space ratio, reveal them to be very close to their ideal values. According to an accurate metrological study by means of a scanning electron microscope (SEM), the zone line-width errors are within the SEM measurement accuracy where that for the outermost zones (line-widths between 70 nm and 100 nm) is better than 10 nm.