An Experimental Investigation into the Relationship Between Plasma Spot Sizes and Wavelengths in Laser-Produced Plasma-Based EUV

Xenon is a potential light source for extreme ultraviolet (EUV) lithography due to its engineering simplicity and advanced wavelength of 11.2 nm. The characterization of its emission spectra has been thoroughly studied.^1,2 In addition to the spectral research, the optical imaging investigations regarding the plasma spot images in the visible light range, deep ultraviolet (DUV) range, and EUV range were useful information for understanding its expansion dynamics. The presented work was examined using Nd: YAG laser-driven cryogenic Xenon target. This imaging study was conducted by varying the focal positions of the pulsed laser and the applied bandpass filters. In the experiments, the plasma spot sizes were measured and interpreted as dimensions in x- and y-directions with Gaussian curve fitting applied. The minimum spot sizes at the focal position were obtained for the visible, DUV, and EUV ranges. Interestingly, an engineering formula was derived for evaluating spot size across different wavelengths after we integrated our previous research on Xenon plasma within the 1-6 nm wavelength range. The analysis revealed a general trend of decreasing spot sizes logarithmically with shorter wavelengths. These findings provide a valuable reference for simulations and experimental studies related to plasma formation.

¹              V. P. Belik, S. G. Kalmykov, A. M. Mozharov, M. V. Petrenko, and M. E. Sasin,  Technical Physics Letters 43 (11), 1001 (2017).

²              S. C. Bott-Suzuki, A. Bykanov, O. Khodykin, M. Tillack, S. Cordaro, and C. McGuffey,  Journal of Applied Physics 126 (11) (2019).