RESIST HEATING EFFECTS IN 25 AND 50 KV E-BEAM LITHOGRAPHY ON GLASS MASKS

Electron sensitive resists have been exposed on optical masks in a variably shaped spot electron beam lithography system, EL3, at 25 and 50 kV and beam current densities up to 50 A/cm2 to evaluate the effects of resist heating during electron exposure. Resist heating effects are primarily observed in dense patterns at high electron exposure dose. For the purpose of comparison resist heating effects are quantified in terms of the development rate change that is caused by the temperature rise in the resist during electron beam exposure. From an energy density point of view the maximum temperature rise in the resist during exposure is very similar for both 25 and 50 kV exposures. The area on the mask over which the temperature rise in the resist can change resist properties is significantly larger at 50 kV: up to 20-mu-m at 50 kV compared to approximately 5-mu-m at 25 kV. Using sensitive electron beam resists requiring 1-5-mu-C/cm2 exposure dose no resist heating effects are observed at beam current densities up to 50 A/cm2.