SU8C resist for electron beam lithography

Electron beam lithography for the fabrication of direct write binary optical elements is a challenge issue. In order to fulfill such requirement, the selection of electron beam resist is very critical. In this paper, we introduce a new type of resist, SU8C with modified solvent, cyclopentanone, which satisfies the required criteria. The exposure characteristics of SU8C by electron beam lithography are discussed. Different parameters such as post exposure baking time, hardness, refractive index, vertical and lateral resolution were investigated. The exposure dosage of SU8C is one of the smallest among most commercially available electron beam resists. By varying the post exposure baking time, the contrast curve can also be altered. With near-unity contrast, multilevel profiles up to 16 levels were fabricated with variable widths. This was demonstrated by adjusting the clock frequency of the e-beam system, which in turn varies the absolute dosage exposure. With relative high refractive index and high resolution, SU8C is suitable for the fabrication of optical elements, including optical waveguides, lens arrays and grating structures. Binary optics element fabricated using SU8C was demonstrated, and the corresponding optical properties were measured.