Research Of SU-8 Resist Lithography Using Ultraviolet Laser

MEMS technology is a hot topic of science and industry in the 21st century, and micro-fabrication technologies are the key to the MEMS development. In the MEMS field, microstructure with high height and high aspect ratio is often used. LIGA(X-ray lithography,electroforming,micro-replication) technology are the very way to fabricate this microstructures. The exposal source of LIGA technology is expensive synchrotron radiation X-ray, so that constrains it's wide application. The Laser-LIGA technology provided by this research is the first technology to use ultraviolet laser as the exposal source for SU-8 photoresist lithography. It is a technology with lower cost and big potential to increase the aspect ratio as well as wider application.With the third harmonic 355nm Nd:YAG laser as the exposal source, the lithography of SU-8 photoresist is studied. The differences of the monochromaticity and the direction of ultraviolet laser and non-laser ultraviolet source are analyzed firstly. The advantage of ultraviolet laser in exposing SU-8 photoresist is discussed. The process of SU-8 photoresist lithography is researched, and the influence of steps like coating and soft-bake on the lithography is studied. And the dependences of the depth of exposal on exposal time as well as on laser power are studied. It is found that with fixed laser power and increasing exposal time, the increasing of the depth of exposal grows slower, the exponential increasement can be express by the equation: , the depth of exposal becomes satured with increasing exposal time; with fixed exposal time and increasing laser power, the depth of exposal increases linearly and can be express by the equation: y =40. 5x0.151y = 0 .238x+44.454. Finally, microstructures of SU-8 photoresist with difference thickness are manufactured according to previous experimental results. The SEM pictures show that the graphics feature good qualities and vertical sidewalls, the thickness of SU-8 photoresist is up to 250 microns and the aspect ratio can reach 10. Analyse to the experimental data shows that there is still much potential to increase the aspect ratio.