Scum-free patterning of SU-8 resist for electroforming applications

A simple approach is developed to obtain scum-free pattern transfer in SU-8 resist by UV-lithography for electroforming applications. SU-8 is an epoxy-based negative resist used in the fabrication of high-aspect ratio microstructures. SU-8 resist poses considerable processing difficulties and tends to leave organic residues of undeveloped resist on the surface of the exposed metallic seed layer. Scum-free pattern transfer in SU-8 resist is important for the subsequent electroplating process used to fabricate the high-aspect ratio metallic microstructures. Dry plasma etching processes are commonly used to remove the SU-8 residue prior to electroplating. However, these processes are complex and not cost-effective. In this work, it is shown that scum-free SU-8 patterns could be achieved by proper selection of process parameters such as soft-bake temperature, exposure time, post-exposure-bake temperature, developing time and rinsing in solvents. The success of this particular process is due to controlled rinsing of the patterned sample in acetone to remove the resist scum. The results of our method for patterning the SU-8 resist to fabricate nickel microstructures using this mold are reported.