A Calibration Method for the Resolution of 2D TPP Laser Direct Writing

To improve the fabrication efficiency of the two-photon polymerization (TPP) laser direct writing, the TPP exposure process was set to complete by a single-line scan, which was named 2D TPP. The voxel of the 2D TPP should be large enough to cross the photoresist and the underlayer. To explore the resolution limit of the 2D TPP considering the thickness of the photoresist, a new method named the 45° scanning method was proposed. Meanwhile, a two-photon micro-nano fabrication platform was developed. A group of experiments based on the orthogonal decomposition method was carried out to analyze the width and length of the voxel on the S1805 photoresist under different laser power and processing speed. To confirm whether the resolution of the micro-nano structures fabricated by 2D TPP is consistent with the width of the voxel, aluminum wire grids were fabricated through the 2D TPP and the metal lift-off process. A second-order regression equation of the machining resolution and input parameters of the 2D TPP is deduced. The correlation coefficient between the width of the voxel and the aluminum wire grids is 0.961, which means a significant positive correlation between them. Finally, the second-order regression model derived from the fabrication resolution of the 2D TPP was validated by experiments. Full 2D grids were fabricated using 2D TPP and mental lift-off process. This paper provides a convenient, low-cost, and high-efficiency method for calibrating the fabrication resolution of 2D TPP on various photoresists.