Uncrosslinked SU-8 as a sacrificial material

SU-8 has gained wide popularity as a surface micromachining material, mostly due to characteristics of the epoxy in the crosslinked state. However, uncrosslinked SU-8 also has interesting properties, particularly as a planar sacrificial layer in surface micromachined processes. Uncrosslinked SU-8 can maintain a flat, stable surface for subsequent surface micromachining; it is chemically resistant to subsequent surface micromachining; and uncrosslinked SU-8 can be removed selectively in the presence of a wide range of materials, including metals, semiconductors, oxides, ceramics and many polymers. The processing of uncrosslinked SU-8 as a sacrificial layer is mostly unchanged from the conventional method. However, care must be taken to not to expose the SU-8 to UV radiation when patterning and avoid significant movement of the uncrosslinked SU-8 when taken above the glass transition temperature (~65 °C). In this paper, uncrosslinked SU-8 as a sacrificial layer is demonstrated, the fabrication details are described, and an application is shown.