Sn-fueled High-brightness Compact EUV Light Source

A compact high-brightness EUV source is needed for high-throughput actinic mask inspection in EUV lithography. Ushio is developing a light source utilizing LDP technology where rotating Sn-covered electrodes, trigger lasers and pulsed electrical discharge are employed to create an EUV-emitting plasma at as high repetition rate as 10 kHz. A unique mechanical debris-mitigation system was found to be able to stop neutral particles and reduce fast-ion flux. Clean-photon EUV radiance, of which wavelength is 13.5 nm and band width is 2 %, obtained after the debris-mitigation system was 145 W/mm2/sr. Sputter rate of Ru mirror sample was 2~5 nm/Gpulse whereas Sn deposition was found not to grow with time. Up to 5 days of non-interrupted operation was successfully demonstrated.