Laser Superdiffraction Optical Needle Direct Writing Lithography Method for Single-Exposure Fabrication of High-Aspect-Ratio Microstructures

In this paper, a laser superdiffraction optical needle direct writing lithography method for single-exposure fabrication of high-aspect-ratio microstructures (HARMs) is proposed. The principles of 3/4 circular image focusing and lithography exposure are theoretically analyzed, and the experimental setup is built. Experiments show that the linear interval and focusing accuracy of this method can reach 60 and 0.1 mu m, respectively. Compared with the circular image focusing method, this method can determine the direction of defocus through the opening direction of the 3/4 circular spot. In addition, an optical needle with a resolution of 0.308 mu m, a depth of focus of 1.836 mu m, and an aspect ratio of 5.9538 is achieved by tightly focusing a radially polarized beam modulated by an annular amplitude type modulator with an annular factor of 0.7. Using this optical needle as the direct writing head, the HARM with a line width of 0.22 mu m, a depth of 1.76 mu m, and an aspect ratio of 8 is obtained experimentally by adjusting the photolithographic process parameters in combination with the focus detection curve. This method has the advantages of high fabrication efficiency, super diffraction resolution and high-aspectratio, which provides a new research idea for the fabrication of HARMs.