Simple technique for beam focusing in electron beam lithography on optically transparent substrates

A beam focusing technique is developed for electron beam lithography on transparent substrates wherein the substrate height is estimated as a plane calculated from height data measured from perimeter metal. The effectiveness of this method, which avoids problems associated with metal-on-resist coatings, is verified with pores and gratings in ZEP520A resist on 1×1in.2 indium tin oxide/quartz slides and on 4 in. quartz wafers. Using a Vistec EBPG-5000 electron beam lithography tool at 50 keV, we achieved consistent 18 nm diameter pores at 59 nm pitch across 41 μm of substrate tilt without direct height measurements at the writing sites.