Three-dimensional electron-beam lithography using an all-dry resist process

Abstract

Micromechanics, microelectronics, and micro-optics favor structurization of three-dimensional surfaces. Dry resist processes present fewer hazards to personnel and environment than conventional wet resist processes. The negative tone dry resist octavinylsilsesquioxan is investigated in its applicability to three-dimensional structurization of surfaces having a high relief. This resist, also known as V-T8, enables coating of arbitrary substrates by evaporation in high vacuum. After exposure it is developed in high vacuum by a dry thermal treatment at 200 °C. The resist is characterized with electron exposures with an energy ranging from 5 to 50 keV. Its sensitivity is 40 μC/cm2 at 20 keV. The resist exhibits high dry etch resistivity. Its contrast is increased from 0.7 to 2.1 using plasma etching in CF4 as a postdevelopment step. The dry resist is employed to structure 250 μm deep steep surface steps and to modify fabricated three-dimensional structures with dot gratings for metrology applications.