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In lithography, the micromirror array (MMA) is utilized in the generation of customized source shapes optimized by source and mask optimization (SMO) technology. With irradiated laser ejecting from the surface of micromirror, the facula is positioned at the designated position. Through the progressive torsion of cantilevers, the electrostatic actuated micromirror realizes high-precision rotation corresponding to different driving voltages. Irradiated by 193nm UV laser, the heat sink accumulated on MMA leads to thermal expansion of structures. Thus, the voltage-angle (V-θ) curve serves deviation from the theoretical value, resulting in the distortion of illumination modes further. In order to estimate and eliminate the unfavorable effects on the rotation of MMA induced by heat sink, a biaxial electrostatic driven micromirror is initially designed and a multi-physical field model is established. Through equating the laser to a 2D surface source, in the thermal equilibrium state, the mirror surface temperature rises to 395.92K, with an introduced angular error of 3.313mrad when the driving voltage is 70V. The additional angle would exceed the design requirements of MMA and result in modes distortion. In order to eliminate the deformation of illumination mode in the pupil, a forced nitrogen cooling system is applied to suppress the accumulation of heat. Ultimately, the MMA without structural deformation could be adopted in the freeform pupil illumination modes generation in lithography.
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