Research Of Fabrication Of SU-8 Mold And Microfluidic Chip Based On Maskless Digital Lithography

The increasing demand for high aspect ratio microstructures in micro-nano machining field.Because of its excellent chemical,mechanical,physical and other performance advantages,SU-8 photoresist has become an ideal material for making microstructures with high aspect ratio.The most successful technique for preparing high aspect ratio microstructures is photolithography.How to achieve high-efficiency and low-power micro-nano processing under the condition of high precision is an urgent problem to be solved.The maskless digital lithography technology has been widely developed and applied due to the advantages of real-time,efficient and low-cost graphics transfer.This paper is to study the mold fabricating method of SU-8 photoresist based on the maskless digital lithography technology.These include the components of a maskless digital lithography system based on DMD(digital micromirror device),the principle of DMD tilt scanning exposure,the modeling of repeated exposure,and the processing and preparation method of microfluidic chip based on SU-8 mold.The advantage of maskless digital lithography is demonstrated by analyzing the experimental data.The main research work of this paper is as follows:Firstly,it introduces the technological process of mask lithography,maskless lithography and nano-imprint lithography,as well as the advantages and disadvantages of making SU-8 molds.The system structure of maskless digital lithography used in this experiment is mainly introduced,including the core device DMD,illumination optical system,projection imaging optical system,and control platform system based on X-Y-Z three-axis positioning.Secondly,we study the fabrication of micro-sized SU-8 molds based on maskless digital lithography.The exposure of SU-8 photoresist is usually focused on feature size of50?m and above,and does not involve the fabrication of micro-sized SU-8.In this paper,according to the photochemical reaction mechanism of SU-8 photoresist and Beer-Lambert's law of light intensity attenuation,a DMD tilt scanning repeated exposure method is proposed.The photoresist characteristics and technological process suitable for fabricate SU-8 mold fabricating are introduced.We also analyzed and discussed SU-8molds with different feature sizes.The results show that lines with a minimum characteristic size of 5?m can be fabricated within the allowable error range,and when the feature size is10?m,the line width error is only 0.32%.This shows that the proposed method can not only show the characteristics of low power consumption,low error,high efficiency and high precision when fabricating micro-sized SU-8 molds,but also can be extended to other types of thick photoresist exposure.Finally,based on fabrication of micro-sized SU-8 mold,the material matrix and corresponding curing agent used in microfluidic chip are mixed in a certain proportion,poured on the SU-8 mould that has been fabricated.After the hot treatment,the soft mold for imprinting lithography and the drug development can be obtained by stripping the mold.The fabrication process of microfluidic chip are introduced,and two kinds of microfluidic chip with different microchannel structure are tested,analyzed and discussed.The results show that based on fabrication of micro-sized SU-8 mold,microchannels with high aspect ratio,high accuracy,and smooth edges can be fabricated.It is demonstrated that the combination of two methods of DMD tilt scanning repeated exposure and microfluidic chip casting in maskless digital lithography can effectively process microfluidic chips.