Generation and characterization of Ho: YLF solid-state laser-driven tin plasma for EUV lithography

Solid-state lasers operating at near- or mid-infrared wavelengths have great potential to become the future drive source of laser-produced plasma (LPP) light source for extreme ultraviolet (EUV) lithography. Here, we demonstrate the first comprehensive multi-diagnostic characterization and efficient 13.5-nm in-band EUV generation from a tin plasma driven by a self-developed 2 μm Ho: YLF solid-state laser. Furthermore, we systematically compare the plasma and EUV radiation for 1 μm and 2 μm driving lasers, showing enhanced EUV emissivity and reduced optical depth as well as markedly more isotropic angular distributions for the 2 μm case. It is worth noting that the EUV wall-plug conversion efficiency, defined as the electrical-to-EUV efficiency, reaches approximately 3‰ for the single-pulse 2 μm driver demonstrated in this work. This value is about 1.5 times higher than the approximately 2‰ estimated for commercial multi-pulse CO 2 -driven LPP-EUV lithography sources. These results establish Ho-doped 2 μm solid-state lasers as a promising driver for LPP-EUV sources. Moreover, this work provides a quantitative framework for further optimizing optical depth and laser-to-EUV conversion efficiency, with great potential for the next generation of EUV lithography.