Laser Shock Removal of Nanoparticles from Si Capping Layer of Extreme Ultraviolet Lithography Masks

Abstract

A new dry laser shock wave generated by a Nd:YAG laser was applied to remove nanosized polystyrene latex (PSL) particles on the silicon capping layer of an extreme ultraviolet lithography (EUVL) mask. UV laser was irradiated on the surface before irradiation with laser shock waves to increase the removal efficiency of the organic PSL particles. Owing to the expected damage to the surfaces, the energy of the UV laser was reduced to 8 mJ and the gap distance between the laser shock wave and the surface was increased to 10.5 mm. UV irradiation alone resulted in the removal of 50% of the particles. Exposure to the UV laser three times increased the removal efficiency to 70%. Over 95% particle removal efficiency was found when a laser shock wave was combined with the UV laser. However, the removal efficiency of the particles was below 25% by laser shock wave cleaning alone. Enhanced removal efficiency by UV laser irradiation may be attributed to the photothermal and chemical effects of UV light on the organic PSL particles.