Fabrication of Two-Dimensional Micropattern Structures through Active Wavefront Control in Laser Interference Lithography

Laser interference lithography (LIL) is an established technique for fabricating precise and periodic microstructures. The non-orthogonal Lloyd’s mirror interferometer, a type of wavefront division interferometer with a simple structure and short non-common optical paths, offers excellent stability even in ordinary laboratory environments. Additional advantages include facile adjustment of the pitch of the interference fringe without a photomask, and the generation of large-area microstructures in a single step. However, the achievable geometries of the interference pattern are fundamentally limited by the design of the interference field, and the optical configurations or optical parameters must be redesigned to generate different patterns. To address this issue, a novel non-orthogonal two-axis Lloyd’s mirror interferometer employing active wavefront control using a spatial light modulator is proposed herein. The fringe position of the two-axis interference fringe pattern (dot array fringes) is controlled by independently applying dynamic phase modulation to the exposure sub-beams, enabling arbitrary translation of the fringe patterns during exposure. By shifting the positions of the dot array fringes, various micropattern geometries can be fabricated without modifying the optical configuration or optical parameters, while maintaining the advantages of LIL. Numerical calculations demonstrated that the dot array fringes can be translated independently in the X - and Y -directions via phase modulation, where an exposure-dose pattern with non-elliptical arbitrary patterns was generated by controlling the fringe trajectory. Using a constructed prototype optical system, various microstructures were fabricated by controlling the fringe trajectory and were quantitatively evaluated using scanning electron microscopy and atomic force microscopy. The fabricated geometrical parameters showed fair agreement with the corresponding simulated results, confirming the feasibility of the proposed method.