A negative resist for high aspect ratio features (useful for Replica molding).

SU-8 is an epoxy-based negative photoresist developed by IBM for the semiconductor industry. SU-8 can be used for thicknesses ranging from below 1μm to 2mm and give very high aspect ratio structures (> 20 : 1 ) using standard contact photolithography. It shows great chemical and thermal stability in addition to being biocompatible.

SU-8: the epoxy oligomer Bisphenol A Novolak is the basis of SU-8 formulations. The monomer has eight epoxy groups that form a strong cross-linking network upon exposure and give the resist its excellent thermal and mechanical properties.

SU-8 is most sensitive to light at 365 nm which coincides with the I-line of mercury lamps found in most contact aligners. The light is absorbed by photoactive triarylsulfonium hexafluorantimonium salts in the resist. The onium salts release a proton each which acts as a Lewis acid and induce cross-linking. Each molecule can catalyze numerous polymerization reactions. The process is further amplified by increased diffusion during the post-exposure bake. Chemically amplified photoresists like SU-8 are therefore very sensitive to light and require fewer photons for full exposure.

• SU-8 2
• SU-8 5
• SU-8 2100

    Leave in solution @ 70°C. 
    Remover PG will swell and lift off minimally cross-linked SU-8 2000.

    RIE 200W
    80 sccm O2
    8 sccm CF4
    100mTorr
    10°C