Research On Theory And Experiment Of UV-Lithography On SU-8 Photoresist

With the rapid development of MEMS, UV-LIGA technology based on SU-8 photoresist has been applied extensively. Theoretical and experimental study on UV-lithography on SU-8 photoresist was carried out in this paper, and the dimension precision and tolerance of SU-8 photoresist microstructure were studied quantitatively.Three processes of fabricating mold were introduced. They were silicon-mold process, back plate growing method and no back plate growing method. Compare with the three methods, no back plate growing method was more suitable for fabricating hot embossing metal mold for microfluidic chip. No back plate growing method is to electroform metal microstructure on the metal substrate directly by low-cost UV-LIGA technology based on SU-8 photoresist. UV-lithography on SU-8 photoresist was the pre-procedure of micro-electroforming, so its processing parameters and dimension precision determine the quality of micro-electroforming mold directly. In this paper, various influencing factors of processing parameters were investigated at first, and then experimental and simulated analysis was put up to get the optimum results of all the processing parameters. Lastly, standard process of UV-lithography of SU-8 photoresist was established. Base on the standard process, we have fabricated micro hot embossing metal mold and micro injection metal mold successfully by micro-electroforming.Based on Fresnel diffraction theory, an UV-exposure model and a dimensional tolerance model were established. The dimension and tolerance of SU-8 photoresist microstructure were simulated by MATLAB. Comparing the simulated results with experimental results, a good agreement between them was acquired. Based on the two models, dimension and tolerance of SU-8 photoresist microstructures can be predicted. Based on the UV-exposure model, development model was established by swelling theory. In addition, the swelling trend of SU-8 photoresist in development was analyzed. At last, we summarize the instruction effect of the UV-exposure model and the development model on experiments.The instruction effect of the UV-exposure model on experiments is as follows:(1) Simulated results demonstrated that feature width on the top of microchannel is smaller than feature width of mask. So the feature of mask should be wider than the final microchannel while designing.(2) Exposure dose should be changed with the thickness of SU-8 photoresist.(3) The size of gap in the UV-lithography largely influences the width change. Therefore the surface of SU-8 photoresist in the process should be kept as flat as possible to decrease the size of gap.(4) The cross section of microchannel can be predicted, so optimum processing...