Research and development of the EUV-FEL light source for lithography

Research and development of a high-power EUV light source are very important in EUV lithography to overcome the stochastic effects for a higher throughput and finer patterning in future. We have designed and studied a high-power EUV free-electron laser (FEL) based on energy-recovery linac (ERL) for future lithography. The EUV-FEL light source has many advantages such as extremely high EUV power without tin debris, narrow spectral bandwidth, upgradability to a Beyond EUV (BEUV) FEL, polarization controllability for high-NA lithography, low power consumption and low construction and running costs per scanner, as compared to the laser-produced plasma (LPP) source used for the present EUV lithography exposure tool. Demonstration of proof of concept (PoC) of the EUV-FEL has made progress using the IR-FEL in the Compact ERL (cERL) at High Energy Accelerator Research Organization (KEK). We also show future plans of remaining R&D items such as a main-linac cavity system with lower power consumption, improvements of the electron gun system for stable operation of 10-mA beam current and a compact variably-polarizing undulator with a lower cost to realize the EUV-FEL light source. After these R&Ds, we can start to build a prototype EUV-FEL smoothly and quickly.