A method involving multi-exposure with low-power is presented to fabricate an SU-8 mold based on a digital micromirror device (DMD) maskless lithography with an LED source at a wavelength of 405 nm. The SU-8 mold is used for the fabrication of a PDMS concentration gradient generator (CGG). During a one-time exposure, it is easy to over-expose at the top and under-expose at the bottom of a thick SU-8, which then forms a T-shaped structure. This is more obvious for high-absorption coefficients such as 365 nm. We found that by taking advantage of the partially absorbed and partially transmissive characteristics of the 405-nm wavelength, multi-exposure can form an effective photochemical reaction channel in SU-8 and can solve the problem mentioned above. However, excessive exposure will cause the linewidth to increase, therefore, it is necessary to find a tradeoff for the number of multi-exposure times. For a 55-µm thick SU-8, the tradeoff threshold is found to be 25. Three types of SU-8 CGG molds were fabricated at this threshold. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-shaped structures.

提出了一种涉及低功耗多次曝光的方法，以基于数字微镜器件（DMD）无掩模光刻技术的SU-8模具制造，该光源具有波长为405 nm的LED源。SU-8模具用于制造PDMS浓度梯度发生器（CGG）。在一次性曝光期间，很容易在厚厚的SU-8的顶部过度曝光而在底部曝光不足，然后形成T形结构。对于诸如365 nm的高吸收系数，这一点更加明显。我们发现，利用405 nm波长的部分吸收和部分透射特性，多重曝光可以在SU-8中形成有效的光化学反应通道，并可以解决上述问题。但是，过度曝光会导致线宽增加，因此，必须找到多重曝光次数的折衷方案。对于55 µm厚的SU-8，折衷阈值为25。在此阈值下制造了三种类型的SU-8 CGG模具。结果表明，SU-8模具的实际轮廓与设计轮廓非常吻合，没有任何T形结构。