Overlay deviation caused by mask heating during EUV exposure

초록

As the resolution of EUV lithography continues to improve, the allowable overlay tolerance has decreased to the sub-nanometer level, increasing the significance of mask thermal behavior on process stability. However, the measured overlay used for correction in actual processes includes the combined influence of mask heating, optical system aberrations, stage motion, and alignment errors, making it difficult to isolate the direct contribution of mask heating. To overcome this limitation, the thermo-mechanical response of the mask during exposure was modeled independently through simulation and translated into the corresponding wafer overlay. The temporal and spatial evolution of mask temperature and deformation during repeated exposures was analyzed, and the overlay magnitude and distribution were compared under various exposure conditions, including pattern type, dose, and numerical aperture (NA). Under the 0.55 NA condition, pronounced layer-to-layer errors were observed at in-die stitching regions where adjacent half-fields meet. These results indicate that mask heating is one of the dominant sources of overlay variation in high-resolution EUV lithography processes. © 2025 SPIE. All rights reserved.

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