Principles and implications of shadow effect in EUV lithography

Extreme Ultraviolet (EUV) lithography has emerged as a crucial technology for the large-scale production of high-precision integrated circuits. Nonetheless, certain inherent challenges, such as the shadow effect, continue to impact the effectiveness of this technology. Shadow effect, caused by oblique incident angles and the thickness of the absorber, significantly degrades image quality. This paper first provides a detailed analysis of the principles, influencing factors and consequences of the shadow effect, then explores the interrelated factors relating to shadow effect including critical dimension, numerical aperture, chief-ray angle, reduction ratio and EUV mask fabrication process. Furthermore, four practical strategies are proposed to mitigate the shadow effect, offering valuable insights for engineers in their future research.