<p>The damage to Ru-coated [Mo/Si] multilayer mirrors caused by Li- and Sn-based EUV light sources was investigated through SRIM/TRIM simulations. These results demonstrate that Li ions cause significantly less sputtering and defect generation in Ru[Mo/Si] mirrors compared to Sn ions. These results suggest that a Ru-capped mirror with Li-based EUV light source is more effective in mitigating mirror damage compared to Sn-based source. Additionally, the impact of Li ions on the Ru layer is minimal, indicating that Li-based sources can extend mirror lifespan. Furthermore, the Li–He EUV light source system enables He ions to selectively etch Li debris, offering an alternative to SnH₄ for chemical etching of Sn debris on the mirror. The simulation suggests that He provides better protection against ion damage than other gases and can be optimized by mixing with Ar. These findings highlight the potential of Li-based EUV sources to improve mirror longevity and performance.</p> Graphical abstract <p></p>