Evaluation of the dry resist octavinylsilsesquioxan and its application to three-dimensional electron-beam lithography

Structurization of three-dimensional surfaces has become more and more important for micro-mechanics, micro-electronics, and micro-optics. It is widely accepted that resist processes present fewer hazards to personel and environment than conventional wet resist processes. Octavinylsilsesquioxan is investigated as a dry negative tone resist. It is employed to structure 250 mu m deep steep surface steps, to modify fabricated three-dimensional structures with dot gratings for metrology applications, and to generate optical microlenses of 6 mu m to 150 mu m diameter on wafers and on the end of monomode fibers. The negative tone dry 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 degrees C. The resist is characterized using layers with a thickness in the range from 50 nm to 1 mu m. Electrons with an energy ranging from 5 keV to 50 keV are used. The sensitivity of V-T8 films is 40 mu C/cm(2) at 20 keV, which is orders of magnitude higher than that of other dry resist systems. The resist exhibits high dry etch resistivity. Its contrast is increased from 0.7 to 2.1 using plasma etching in CF4 as a post-development step.