13 March 2015 Debris monitoring and minimization system for EUV sources
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Abstract
In NXE laser-produced-plasma (LPP) light sources, extreme-ultra-violet (EUV) light is created by exciting small droplets of Sn with a pre-pulse and main pulse laser. The Sn droplet is converted into plasma, which emits the desired light wavelength. Under non-optimal conditions, tin debris fragments can be created that can contaminate the light source optics. The current presentation describes experiments with a novel metrology technique that can detect and quantify debris in the source. The results can be used to optimize source settings to significantly reduce contamination and increase lifetime and availability.

A novel optical technique uses a pulsed double cavity laser at 532 nm with beam-shaping optics that is fired at a synchronized time delay after the EUV burst. The light is converted to a thin light sheet that illuminates possible debris fragments in the direct region around the plasma.

Mie scattering theory is applied to convert the intensity of the incoming individual particles to an estimated diameter estimation and the two frames are correlated with advanced particle tracking algorithms to capture the velocity and direction of each individual particle. Because light intensity is used for particle sizing, small individual particles can be detected. The technique provides particle count, diameter, direction and velocity information.

This technique has successfully been applied on operating NXE test sources. It has proven to directly identify plasma conditions with significant debris reduction. Furthermore, it has potential to correlate the plasma settings to lifetime estimations and thus can be used for both source optimization and design.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Arjen de Jong, Arjen de Jong, René T. M. Jilisen, René T. M. Jilisen, Mark van de Kerkhof, Mark van de Kerkhof, Arnold van Putten, Arnold van Putten, } "Debris monitoring and minimization system for EUV sources", Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94221V (13 March 2015); doi: 10.1117/12.2176162; https://doi.org/10.1117/12.2176162
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