Exploring multilayer mirror designs for future EUV lithography

As the process nodes in EUV lithography continue to advance, pattern dimensions shrink, and the incident angles of EUV light used for exposure change accordingly. To accommodate these changes, mask structures must be adapted. While the MLM design has remained relatively unchanged over time, the need for new configurations is now being actively considered. Future MLM designs involve exploring various combinations of materials and layer thicknesses. However, experimental results for the reflectivity characteristics of deposited multilayers often deviate from simulation predictions due to factors such as interfacial mixing during fabrication. These challenges highlight the need for careful consideration of optical performance, manufacturability, and practical constraints when designing next-generation MLMs. In this study, we evaluate the performance of potential next-generation MLMs that were actually fabricated, based on the proposed evaluation metrics. Furthermore, we discuss the considerations that will be necessary in the future, including perspectives from lithography.