Development of Free-Electron Laser Sources for XUV Projection Lithography

Abstract

Future rf-linac-driven free-electron lasers (FELs), operating in the extreme-ultraviolet (XUV) range from 4 nm to 100 nm, could be excellent exposure tools for extending the resolution limit of projection optical lithography to ≤0.1 µm and with adequate total depth of focus (1 to 2 µm). The capability of such FELs to produce relatively high-average power at a tunable wavelength with selectable spectral bandwidth will enable these lasers to offset the inherently low throughput of the XUV projection optics which will have about five reflections at ≤50% each. When operated at a moderate duty rate of ≥1%, one XUV FEL should be able to supply sufficient average power to support high-volume chip production for multiple lithographic steppers operating simultaneously. In this multiplexed arrangement, the FEL photon-source cost per wafer level Is projected to be lower than proposed alternatives. Recent progress in attaining a very bright electron beam, short-period magnetic undulator, and high-reflectance resonator mirrors are described which make feasible a near-term demonstration of FEL operation below 100 nm.