Image twist and placement error during EUV exposure

초록

In extreme ultra-violet (EUV) lithography, the local critical dimension uniformity (LCDU) and placement error are major contributors to edge placement error (EPE) budgets, thereby exerting a significant influence on product yield. During exposure, transient thermal deformation of the resist and underlying layers induces time-varying image blur, which deteriorates aerial image contrast and shifts the effective image centroid. Consequently, local PE accumulates across the exposure field, degrading global overlay accuracy. In this study, the coupled thermal–mechanical response of the resist on top of the wafer during scanning exposure is simulated under ASML NXE:3400B scanner conditions to quantitatively evaluate the relationship between deformation-induced image twist and pattern placement deviation. The proposed simulation framework enables correlation of local image degradation with field-scale overlay behavior. The results reveal that the transient in-plane deformation occurring during exposure induces orientation-dependent image twist along both the x- and y-scan directions, whose magnitude varies with pattern type. Furthermore, a strong correlation is observed between the placement error and the temporal trend of deformation, highlighting how local dynamic distortion can propagate to global overlay deviations in high-NA lithography. (2025) Published by SPIE. Downloading of the abstract is permitted for personal use only.

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