A Scalable 5 kW Microwave Discharge Plasma (MDPP) Source for Next-Generation EUV Lithography: Design, Thermal Management, and Spectral Purity Analysis

The semiconductor industry's reliance on Extreme Ultraviolet (EUV) lithography is currently bottlenecked by the Laser-Produced Plasma (LPP) source, which suffers from low conversion efficiency (CE~5%), tin debris, and massive power consumption (>1 MW). In this paper, we propose a scaled-up Microwave Discharge Plasma (MDPP) source as a possible alternative. By scaling a laboratory microwave-discharge approach to a 5 kW microwave input, we outline a design that delivers between about 5 W and 110 W of in-band EUV power, depending on a conversion efficiency (0.5% to 10%) that is not yet verified for xenon. We address the main engineering bottlenecks of MDPP through three solutions: (1) a water-cooled aluminium nitride (AlN) capillary, transparent to microwaves, to manage a 4,500 W thermal load, (2) magnetic confinement and a magnetic nozzle to shrink the emitting column and reach a geometric etendue of about 1.0 mm²·sr, and (3) a Zr filter and two Mo/Si mirrors that reach a spectral purity above 99.99% under stated assumptions. A source-to-machine analysis shows that, for a 20 W target at the intermediate focus, a 5 kW source needs a conversion efficiency of at least about 3.6% with hemispherical collection, and about 81% with the closed end-on capillary, so the source geometry must be chosen from the optics requirement. Our calculations also expose open problems: the plasma density needed for efficient 13.5 nm emission is far above what a 100 mTorr, 2.45 GHz discharge is known to reach, and the Zr filter and the collection geometry limit the usable power. The design is therefore a concept for further modeling and experiment, not a demonstrated source.