Exposure characteristics and three-dimensional profiling of SU8C resist using electron beam lithography

The properties of a new type of chemically amplified resist, SU8C, are eval uated for electron beam lithography. This resist is a modification of the u ltraviolet sensitive negative epoxy SU8. Experimental results show that the sensitivity of SU8C is one of the highest among the different kinds of com mercially available resists. At 50 keV energy exposure, the saturation dosa ge of SU8C is similar to3.8 muC/cm(2) while that of PMMA is similar to 500 muC/cm(2). This implies that SU8C resist is suitable for large area exposur e. The contrast gamma can also be adjusted To near unity by adjusting the p ostannealing time, and this is essential for multilevel profiling. 16 level steps have been exposed in one electron beam exposure by changing the cloc k-frequency in sequence, and a vertical profile resolution of 20 nm has bee n achieved. Lines as narrow as 100 nm have been produced, showing that the resist has high resolution-down,to the nanoscale. Hardness measurements hav e also been carried out, and SU8C is an order of magnitude harder than epox y and PMMA. SU8C resist has high refractive index, high resolution, high se nsitivity, and large hardness, making it suitable for microscale binary opt ics fabrication. To demonstrate,:the suitability of SU8C resist in microsca le optical device fabrication, an array of Fresnel-lenses has been-designed and demonstrated. (C) 2001 American Vacuum Society.