Optical EngineeringExtreme ultraviolet free-electron laser-based projection lithography systems
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Free-electron laser (FEL) sources, driven by rf linear accelerators, have the potential to operate in the extreme ultraviolet (XUV) spectral range with more than sufficient average power for high-volume projection lithography. For XUV wavelengths from 100 to 4 nm, such sources will enable the resolution limit of optical projection lithography to be extended from 0.25 to 0.05 μm with an adequate total depth of focus (1 to 2 μpm). Recent developments of a photoinjector of very bright electron beams, high-precision magnetic undulators, and ring-resonator cavities raise our confidence that FEL operation below 100 nm is ready for prototype demonstration. We address the motivation for an XUV FEL source for commercial microcircuit production and its integration into a lithographic system, including reflecting reduction masks, reflecting XUV projection optics and alignment systems, and surface-imaging photoresists.