Prediction of overlay deviation caused by reticle heating during EUV exposure

초록

Background: Overlay requirements are becoming increasingly stringent as process nodes shrink and high numerical aperture (NA) extreme ultraviolet (EUV) systems are introduced. Wafer overlay arises from multiple superimposed contributors, among which thermally induced effects during EUV exposure can become nonnegligible under tight overlay budgets. Aim: We aim to clarify, through simulation-based analysis, the role of reticle heating as an independent contributor to wafer overlay formation in EUV lithography. Approach: Reticle heating and the resulting thermo-mechanical deformation under EUV exposure are modeled through simulation based on the EUV optical path and exposure conditions. The calculated reticle deformation is converted into wafer overlay using the projection optics reduction factor, enabling direct analysis of overlay components induced by reticle heating. Results: Wafer overlay dominated by accumulated average reticle thermal deformation exhibits spatially different distributions depending on intra-field position and exposure history. Overlay behavior evolves across fields and wafers as the reticle thermal state changes under repeated exposures. Consequently, reticle heating becomes a systematic source of overlay variation across fields, wafers, layers, and exposure conditions. Conclusions: These findings provide a basis for understanding overlay behavior associated with reticle heating in future high-NA EUV processes and for developing improved overlay analysis and control strategies.

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