As a critical resolution enhancement method, source and mask optimization (SMO) technology significantly improves imaging quality and process window performance by optimizing the source shape and mask pattern simultaneously through multiple iterations. The existing approaches for implementing optimized illumination modes with high degrees of freedom are typically based on two methods: the diffractive optical element (DOE) and the micromirror array (MMA). The limitations of the DOE-based method include the inflexibility of the illumination modes and partial energy loss. The MMA-based method can flexibly achieve arbitrary source shapes by modulating the tilt angles of the thousands of micromirrors. However, current MMA manufacturing faces challenges for the large-scale integration of micromirrors. Existing two-dimensional (2D) mirrors mainly rely on external movable frames and multiple electrodes, which complicate the manufacture of the MMA. In this study, we report a 2D micromirror mechanical structure with a single serpentine beam and two fixed electrodes. We also propose an optimized electrode structure to reduce the driving voltage. We believe that the designed micromirror array has great potential for application in illumination systems.

In this study, a 2D micromirror machine with a serpentine beam is designed. A movable plate is supported by the beam fixed to an anchor on the substrate. The micromirror surface is coated with the high reflective layer of a 193 nm laser to reduce the energy loss in the lithography system. Two symmetrically distributed electrode structures are placed below the movable plate. The micromirror employs a serpentine beam as the mechanical force driving part, which is actuated by the electrostatic force between the fixed electrodes and movable plate. The driving process of the micromirror is sequentially simulated and analyzed. Subsequently, a stepped electrode structure is designed to reduce the driving voltage. In addition, based on the established mechanical model of the micromirror, the voltage–displacement tilt curves of the initial and optimized electrode structures are obtained through multi-physical field coupling simulation analysis.

By using different electrode configurations, the designed micromirror can achieve three operating conditions (Table 5). Therefore, the micromirror can achieve a 2D tilt with only two fixed electrodes, which significantly simplifies the driving module of the micromirror array. Under Con. 3 condition, when the bias voltage applied to the driving electrodes reaches approximately 55 V, the maximum tilt angle reaches 26.2 mrad.Compared with the initial driving electrode structure with the maximum tilt angle of 17.8 mrad, the corresponding pull-down displacement of the moving plate is increased by 46.6% (Fig. 8), effectively reducing the driving voltage during micromirror operation. The stress distributions of the two different electrode structures are obtained through simulations (Fig. 9).

In this study, an effective micromirror composed of a movable plate, two fixed electrodes, and a serpentine beam is proposed. The designed micromirror eliminates the need for external movable frame configurations, effectively simplifying the mirror structure. In addition, a stepped electrode structure is proposed. When a voltage of 55 V is applied to both electrodes, the maximum tilt angle reaches 26.2 mrad.Compared with the initial driving electrode structure with the maximum tilt angle of 17.8 mrad, the corresponding pull-down displacement of the moving plate is increased by 46.6%. This micromirror structure, which simplifies the driving module and reduces the driving voltage, has great potential for applications in illumination systems.