On the compatibility of free-electron lasers with EUV scanners

Abstract

The compatibility of Free-Electron Lasers (FELs) with Extreme Ultraviolet (EUV) scanners is a pivotal consideration as EUV lithography advances. Unlike plasma sources that emit incoherent light, FELs offer relatively coherent light with distinct characteristics including narrower bandwidth, higher repetition rates, and shorter pulse durations. This study elaborates on the integration process of FEL sources with existing scanner systems without necessitating modifications to the scanner's illumination or projection optics. We delve into the coherence and speckle considerations crucial for maintaining image quality and minimizing defects in photolithography. Our findings reveal that the spatio-temporal splitting of FEL pulses, facilitated by the scanner's illumination system, effectively mitigates coherence and speckle-related challenges. Moreover, the analysis of potential pulse damage reveals that despite the high peak power of FELs, the design of the scanner ensures that the risk of damage to optics is minimal. This research shows that it is practical and possible to use FEL sources in EUV scanners, enhancing their performance and efficiency in semiconductor manufacturing.