Ultraviolet transmittance of SU-8 photoresist and importance in multi-wavelength photolithography

The transmission properties of SU-8 photoresist in the ultraviolet (UV) range are reported for resist thicknesses between 1 and 150 mu m in the soft-baked state prior to lithographic exposure. Multiple transmission wavelengths in the UV region between 200 and 400 nm are found to be suitable candidates for self-limiting exposure and thus polymerization depth. This enables a novel method to realize microarchitectures via standard photolithographic techniques. Examples of three dimensional hollow polymer microarchitectures are presented to demonstrate the advantages of this method. The coefficient of attenuation is calculated using Beer-Lambert's principle for different resist thicknesses. Published by the AVS.