Shrinkage of SU-8 microstructures during carbonization

SU-8 is a negative photoresist that is widely used as a precursor to carbon in the fabrication of 3D carbon microstructures. These microstructures are used in applications including sensors, manipulators and batteries. The SU-8 structures are usually made using photolithography and heat treated to high temperatures in an inert atmosphere to achieve carbonization. The shrinkage that results during carbonization affects the design of devices where these structures are used. In this work we studied the shrinkage during carbonization. We emphasized the impact of 1) carbonization protocol and 2) geometry and shape of the SU-8 precursor. Using statistical analysis with ANOVA, we concluded that the geometry of the structure, pyrolysis temperature and pyrolysis atmosphere play a major role in determining the shrinkage of the SU-8 structures. We did not observe a statistically-valid impact from changes in dwell times and heating rate. Based on these results, we present a series of relations to help predict the shrinkage of SU-8 microstructures during carbonization, and facilitate the design of carbon 3D microstructures in different fields.