Fabrication and characterization of gold plated edges on thin substrates for measurement of e-beam diameter

Gold plated edges were fabricated on various substrates and were used as targets for precise electron beam diameter measurement and for system calibration in a commercial Cambridge Instruments e-beam lithography machine. Use of 4 μm square gold plated marker (0.85 μm thick), fabricated on 2 μm thick silicon nitride membrane, was found to enhance significantly the marker-to-substrate signal ratio, in comparison to commonly used lifted-off marker, and thus has improved the reliability of beam diameter measurement accuracy at low beam current for a 40 kV beam voltage. In a statistical sampling of about 2000 measurements, an accuracy of 5 nm (1 sigma value) has been obtained for 38 nm beam diameter by using this gold plated edge on silicon nitride membrane. Further, a Monte Carlo program, which models the effects of electron scattering taking place in target and substrate was used to increase the understanding of the experimental results. Simulated contrast behaviour was found to agree well with the experimental data for all three types of marker used in this study. Finally, the influence of the geometrical shape of the marker edge on beam diameter measurement was studied. By using an appropriate analytical function it was possible to take into account the effect of not perfectly vertical edge on small beam diameter measurements.