Characterization of SU-8 as a photoresist for electron-beam lithography

Electron beam lithography (EBL) is widely used for patterning of sub-micron and nano-scale patterns. Patterns in the order of tens of nano meters have been successfully realized using EBL. There are increasing needs in high aspect ratio structures in sub-micron and nano scales for microelectronics and other applications. Traditionally, high aspect ratio structures in sub-micron and nano scales have been realized by precision lithography techniques and subsequent dry etch techniques. In this work, we present commercially available SU-8 as a potential resist that can be used for direct resist patterning of high aspect ratio structures in sub-micron and nano scales. Such resist pattern can be used as a polymeric mold to create high aspect ratio metallic sub-micron and nano scales structures using electroplating technology. Compared to the most commonly used EBL resist, PMMA (poly methylmethacrylate), SU-8 requires a factor of 100~150 less exposure doses for equal thickness. It results in a significant reduction of EBL processing time. In this paper, characterization results on the patterning of up to 4:1 aspect ratio SU-8 structures with minimum feature size of 500 nm is reported. In addition, preliminary results on high aspect ratio metallic sub-micron structures using electroplating technology are also reported.