SU-8 photoresist

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Su-8 and SU-8 redirect here. For the Soviet ground attack aircraft, see Sukhoi Su-8; for the Soviet self-propelled artillery project, see T-28#Experimental models
SU-8 molecule

SU-8 is a commonly used epoxy-based negative photoresist. It is a very viscous polymer that can be spun or spread over a thickness ranging from below 1 micrometer up to above 300 micrometers and still be processed with standard contact lithography.[1] It can be used to pattern high aspect ratio (> 20) structures.[2] Its maximum absorption is for ultraviolet light with a wavelength of 365 nm (it is not practical to expose SU-8 with g-line ultraviolet light). When exposed, SU-8's long molecular chains cross-link causing the solidification of the material. SU-8 series photoresists use gamma butyrolactone as the primary solvent.

SU-8 was originally developed as a photoresist for the microelectronics industry, to provide a high-resolution mask for fabrication of semiconductor devices. It is now mainly used in the fabrication of microfluidics (mainly via soft lithography, but also with other imprinting techniques such as nanoimprint lithography[3]) and microelectromechanical systems parts. It is also one of the most biocompatible materials known [4] and is often used in bio-MEMS.

SU-8 is highly transparent in the ultraviolet region, allowing fabrication of relatively thick (hundreds of micrometers) structures with nearly vertical side walls. After exposition and developing, its highly cross-linked structure gives it high stability to chemicals and radiation damage. Cured cross-linked SU-8 shows very low levels of outgassing in a vacuum.[5] However it is very difficult to remove, and tends to outgas in an unexposed state.[6]

The main developer for SU-8 is 1-methoxy-2-propanol acetate.[7]

Newer formulations[edit]

SU-8 2000 series resists use cyclopentanone for the primary solvent and can be used to create films between 0.5 and 100 µm in thickness. This formulation may offer improved adhesion on some substrates versus the original formulation.[8]

SU-8 3000 series resists also use cyclopentanone for the primary solvent and are designed to be spun into thicker films ranging from 2 to 75 µm in a single coat.[8]

Its polymerization process proceeds upon photoactivation of a photoacid generator (triarylsulfonium salts) and subsequent post exposure baking. The polymerization process it a cationic chain growth, which takes place by ring opening polymerization of the epoxide groups.

External links[edit]


  1. ^ "SU-8 Resists: FAQs". MicroChem. Archived from the original on May 17, 2009. Retrieved 21 July 2011. 
  2. ^ Liu, J.; Cai, B.; Zhu, J.; Ding, G.; Zhao, X.; Yang, C.; Chen, D. "Process research of high aspect ratio microstructure using SU-8 resist" Microsystem Technologies 2004, V10, (4), 265.
  3. ^ Jesse Greener, Wei Li, Judy Ren, Dan Voicu, Viktoriya Pakharenko, Tian Tang and Eugenia Kumacheva "Rapid, cost-efficient fabrication of microfluidic reactors in thermoplastic polymers by combining photolithography and hot embossing" Lab Chip, 2010, doi: 10.1039/b918834g.
  4. ^ Nemani, Krishnamurthy V.; Moodie, Karen L.; Brennick, Jeoffry B.; Su, Alison; Gimi, Barjor (October 2013). "In vitro and in vivo evaluation of SU-8 biocompatibility". Materials Science and Engineering: C 33 (7): 4453–4459. doi:10.1016/j.msec.2013.07.001. 
  5. ^ SU-8 photosensitive epoxy
  6. ^ SU-8 Photoresist Processing
  7. ^
  8. ^ a b