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 mm) 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>