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SU-8 is an epoxy-based negative-tone photoresist for microelectromechanical systems (MEMS).


SU-8 was developed from IBM Research [1]. SU-8 is prepared by dissolving an EPON SU-8 resin in an organic solvent. There are two different solvents available, gamma butyrolacton (GBL) and cyclopentanone. The SU-8 dissolved with the latter solvent is called SU-8 2000. The ratio of solvent to EPON determines the viscosity which influences the thickness of the resist layer when spun on a substrate.

SU-8 is a near-UV epoxy-based photoresist. The polymerization of SU-8 is based on chemical amplification, initiated upon UV-exposure, starting a cascade of subsequent chemical reactions. An acid is generated which catalysts the crosslinking formed among the epoxy groups. The monomers with eight epoxy sites yield a dense stable polymer.

The resist is structured by placing a mask between the resist and the light source during exposure, thereby making the parts hit by light insoluble and the parts protected by the mask pattern soluble in the developer, typically PGMEA (propylene glycol methyl ether acetate). Cured SU-8 has a high chemical resistance and excellent thermal stability. SU-8 structures with very high aspect ratios (20:1) and tall thicknesses (millimeter thick) can be fabricated using standard UV contact lithography. The photoresist is well suited for MEMS/Micromachining, UV-LIGA, and other thick and ultra thick (>50 μm) applications.

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  1. LaBianca N., Gelorme J.D., High-aspect-ratio resist for thick-film applications, Advances in Resist Technology and Processing XII (Ed. R. D. Allen), Processing SPIE, Vol. 2438, p. 846-852, 1995.