Scan-speed trade-offs in the thermo-mechanical response of EUV pellicles under slit-scan exposure

Abstract EUV pellicles operate under intense slit-scanning exposure and are therefore susceptible to scan-induced thermal and mechanical instabilities. In this work, we numerically investigate the scan-speed-dependent thermo-mechanical response of EUV pellicles using a transient heat-transfer model coupled with two-dimensional thermoelastic analysis. Both the instantaneous peak temperature, which tracks the moving thermal hotspot, and the global peak temperature, defined as the maximum temperature reached over the entire exposure process, are identified to characterize thermal loading. Beyond peak temperature, we evaluate temperature gradients, in-plane stress, in-plane displacement, and accumulated thermal dose as complementary performance metrics. A thermal-exposure asymmetry metric is further introduced to quantify the spatial mismatch between the moving exposure slit and the delayed thermal response. The results reveal non-monotonic and competing dependencies of these metrics on scan speed. In particular, intermediate scan speeds maximize in-plane displacement despite reduced peak temperatures, while higher scan speeds suppress accumulated thermal dose and temperature gradients. These findings demonstrate that peak temperature alone, whether instantaneous or global, is insufficient to characterize pellicle behavior. Reliable EUV pellicle operation therefore requires a balanced, multi-metric optimization of scan conditions.