SU-8• is a polymer• EPON SU-8 - a negative epoxy based

photoresist containing 8-epoxy groups.

- a single molecule contains 8 epoxy groups in a bisphenol- A novalac glycidyl ether.

- dissolved in a organic solvent along with photoacid generator.

- is photosensitive(300- 400nm) - promotes cross-linking reaction

<http://www.zurich.ibm.com/st/mems/su8.html>

SU-8 Processing• A typical SU-8 process consists of

- Spin-coating

- Soft Bake

- Exposure

- Post Exposure bake(PEB)-to cross link exposed regions

of the film

- Development

- Rinse & dry

- Hard Bake (or curing-optional)

- Imaged material

- Remove (optional)

Features of SU-8• Why should we use SU-8?• Good adhesion • Optical absorption in the UV spectrum is

very low allowing patterning of thick coatings.

• Broad range of thickness can be obtained from one spin with a conventional spin coater (750 nm to 500 m)

• High aspect ratios ( ~15 for lines and 10 for trenches)- high degree of cross-linking.

• Optical transparency is > 98% at wave lengths of 500 to 850 nm.

<http://www.ee.ucla.edu/~jjudy/classes/ee250a/lectures/EE250A_Lecture_09_

Thick-Film_Lithography_SU-8_files/frame.htm>

Features of SU-8• High thermal resistance due to

• High chemical resistance cross-

linking

• SU-8 is compatible with standard silicon micro-electronic processing.

• SU-8 is used to create reverse patterns of channels, reservoirs, interconnects

• Non-conductive- can be used as dielectric during electroplating.

• Tg(glass transition temperature) is > 200 degrees centigrade and

• Td(decomposition temperature) is ~ 380 degree centigrade for fully cured SU-8.

• Modulus of elasticity is 4.02 GPa for tensile testing

Silicon

• Silicon(Si) is a semi-conductor

• Used as a Substrate.

• It is cheap and convenient for micro-electronic process like lithography.

• Adhesive to SU-8.

References• IBM Research -Zurich Research Laboratary. “ Epon SU-8 Photoresist”. <http://www.zurich.ibm.com/st/mems/su8.html>

• Judy, Jack. “Thick film Lithography & SU-8”. 2003.

<http://www.ee.ucla.edu/~jjudy/classes/ee250a/lectures/EE250A_Lecture_09_Thick-Film_Lithography_SU-8_files/frame.htm>

• Ruhmen,R, Pfeiffer,K. et.al. “ SU-8: a high performance material for Mems appilcation. Polymer in Mems. http://www.microchem.com/resources/tok_ebeam_resist.pdf

• Feng,Ru. Farris,R. “ Influence of Processing conditions on the thermal and mechanical properties of SU-8 negative Photoresist Coatings”. Journal of micromechanics and microengineering. Dec4 .2002.

<http://ej.iop.org/links/q61/JY4hey4mG8dIMzUo0E8OJA/jm3112.pdf>