Grey scale structures formation in SU-8 with e-beam and UV

An experimental study of the possibility to fabricate grey scale optical elements and 3D structures in SU-8 resist was carried out. It was found that the negative CAR SU-8 has a contrast smaller than 1 for PEB at a temperature of 20-45 °C and a sensitivity of the order of 1 µC/cm2 to 20-keV e-beam and 100 mJ/cm2 to 365-nm UV radiation. Continuous surface relief 3D structures formation in SU-8 by UV exposure was demonstrated both with true grey scale photomasks made with a high-energy beam sensitive glass and binary coded grey scale photomasks. A new technology for 3D self-supporting structure formation in thick SU-8 resist layer was suggested for applications in microfluidics and bioscience. This technique includes anchor elements exposure with UV for the whole resist thickness and a subsequent exposure of the self-supporting fine structures in the upper resist layer only with a low-energy electron beam.