Damage Free Particle Removal from Extreme Ultraviolet Lithography Mask Layers by High Energy Laser Shock Wave Cleaning

Plasma shock waves induced by focusing a Q-switched Nd:YAG laser at a maximum energy of 1.8 J in air were characterized by a laser beam deflection method and were applied to 50 nm silica particle removal from a Al2O3/TaN/Ru/MoSi 40 pairs as the extreme ultraviolet lithography (EUVL) mask layers on silicon wafer. A high energy laser induced shock wave effectively removed 50 nm silica particles from the EUVL mask layers. The change of sample topography before and after laser shock cleaning was measured by an atomic force microscope. Surface damage was observed at a gap distance of 1.5 mm. The dimensions of the plasma plume were characterized as a function of the laser energy and focus-to-surface gap distance. The plasma plume was the main source for damaging the surface. A high energy laser induced shock wave with a gap distance of over 3 mm achieved damage-free sub-100 nm particle removal.

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