High-Resolution Patterning of Various Large-Area, Highly Ordered Structural Motifs by Directional Photofluidization Lithography: Sub-30-nm Line, Ellipsoid, Rectangle, and Circle Arrays

Abstract

A major challenge in nanolithography is to overcome the resolution limit of conventional patterning methods. Herein, we demonstrate a simple and convenient approach to generate sub-30-nm various structural motifs with precisely controlled sizes, shapes, and orientations. The proposed method, the directional photofluidization of an azopolymer, follows the same philosophy as a path-changing approach, for example, thermal-reflow of polymer arrays, in that post-treatment simultaneously leads to a reduction of the feature sizes and line-edge roughness (LER) of nanostructures. However, in contrast to thermal-induced isotropic reflow, directional photofluidization provides unprecedented flexibility to control the structural features, because the direction of photofluidization can be arbitrary controlled according to the light polarization. Furthermore, this approach offers good control of the final features due to a gradual reduction in the rate of photofluidization during light irradiation. More importantly, the photofluidic behavior of the azopolymer significantly reduces the LER, and thus it can improve the quality of nanostructures. Finally, the far-field process of directional photofluidization enables hierarchical nanofabrication, in contrast to mechanical contact fabrication, because the patterned light can reconfigure the polymer arrays selectively. Our approach is potentially advantageous for the fabrication of various structural motifs with well-controlled dimensions on the nanoscale and with minimized LER.