Reduction of buried microstructure diffraction in fabricating curved microstructure by multiple exposure method

When fabricating curved microstructure with DMD-based digital lithography, the buried microstructure formed in photoresist will introduce a distinct diffraction effect, which hinders the improvement in the fabrication fidelity. In this paper, a multiple exposure method is demonstrated to reduce the effect of buried microstructure diffraction. In this method, a high-space-frequency curved microstructure is decomposed into multiple low-space-frequency sub-microstructures, whose corresponding digital masks are successively exposed at the same position of substrate. Lithography experiments are implemented by introducing the multiple exposure method within the DMD-based digital lithography system. The experimental results show that the effect superimposed on the lithography pattern caused by the buried microstructure diffraction can be effectively reduced. In addition, we discuss the influence factors of buried microstructure diffraction by using FDTD method. The experimental results suggest that this fabrication method is potentially suitable for deep microstructure, particularly curved microstructure.