• 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

SU-8

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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 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.

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_Lect ure_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

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