Limitations of proximity-effect corrections for electron-beam patterning of planar photonic crystals

Abstract

We investigate the patterning accuracy limits of electron-beam lithography with different proximity-effect correction (PEC) methods applied to the fabrication of planar photonic crystal structures (PPCS). Energy-intensity distribution simulations reveal that conventional energy-equalization PEC techniques present a lower limit of the best attainable hole-radius variation of 1% for a generic PPCS, while a method proposed by Watson (midpoint-equalization PEC) should inherently account for beam broadening and theoretically can reach perfect accuracy. Simulation results are verified experimentally. Additionally, we introduce a new method to determine the beam-broadening parameter . We compare energy-equalization PEC and midpoint-equalization PEC regarding the impact of geometrical key parameters of PPCS on achievable patterning accuracy, and show that proximity effects impose severe limitations on the patterning of structures with large fill ratios and/or small lattice constants. Furthermore, we perform a sensitivity analysis of both PEC methods on the proximity parameters and show that overestimation of the backscatter efficiency can actually improve the lithographic accuracy of the energy-equalization method and mimic the midpoint-equalization PEC method to a certain degree.