Lithography Study Of UV-LIGA Technology

MEMS technology is a hot topic of science and industry in the 21th century, and microfabrication technologies are the key to the MEMS development. LIGA ( Lithographie,Galvanoformung, Abformung ) and UV-LIGA(Ultraviolet LIGA) technologies are veryimportant and useful technologies of micro fabrication. In the MEMS field, microstructure withhigh height and high aspect ratio is often used. LIGA and UV-LIGA technologies are the very wayto fabricate this microstructures. The process of UV-LIGA technology is almost the same as theprocess of LIGA technology except the exposal source. LIGA use the synchrotron radiation X-rayas an exposal source, however, UV-LIGA uses the common ultraviolet radiation as exposal source,therefore, UV-LIGA is much cheaper than LIGA in cost and can be more widely used. SU-8 photoresist is often used in UV-LIGA technology. It is a negative, epoxy type, nearUV photoresist based on EPON SU-8 epoxy resin. Because of its low absorption in UV band,the whole photoresist can be evenly exposed, therefore it is fit to fabricate the microstructureswith high height and high aspect ratio. Due to this advantage, it is often used in the UV-LIGAtechnology to fabricate high-height and high-aspect-ratio MEMS applications. In this thesis, the UV-LIGA lithography process is investigated, the effect of processparameters on SU-8 microstructures is also discussed. Then the transmission spectrum duringthe UV band of 280-350nm and 350-400nm has been analyzed and the penetration length ofdifferent wavelengths during the UV band has been calculated and the proper exposal waveband which is one of the key parameters for the uniform exposure has been obtained. Theinfluence on the SU-8 microstructrure for short penetration length which causes unevenexposure has been discussed by comparing with the SEM images exposed in the different UVband. Then, the proper exposal dosage can be found by comparing with the SEM imagegotten in different exposal dosage. Using this method, the proper exposal dosage to differentheight SU-8 photoresist can be obtained. Finally, using the mask designed and according tothe research of UV-LIGA process based on SU-8 photoresist, some SU-8 microstructures havebeen successfully accomplished. The SEM image shows that the microstructures have highaspect ratio sidewall and the line's width of microstructures is consistent to the line's width onthe mask,the highest height reach up to 400μm and the highest aspect ratio is 15.