Modern computer chips as well as the entire semiconductor industry rely on Extreme Ultraviolet Lithography (EUVL) at 13.5 nm ± 1% to create finer resolution features. In the industrial settings, the 13.5 nm photons are generated by a plasma following the interaction of 20-30 μm diameter molten tin droplets with focused CO2 pulsed laser beams running at kHz repetition rates. Although the 13.5 nm light generation process has already been comprehensively studied numerically, only a handful of experimental studies report simultaneous measurements of the plasma parameters relevant to the production of the highly charged ions Sn8+‒Sn14+ responsible for the EUV light. Time-resolved collective Thomson scattering measurements, probing simultaneously the electron and ion features would provide a complete picture of the physics at play. To prepare experimental data analysis, a MATLAB-based fitting tool was developed for real-time inference of the electron density, electron temperature and average charge state from Thomson scattering experimental spectra. Least-squares fitting using lsqcurvefit from MATLAB is deployed in conjunction with the analytical expression of the Thomson scattering spectral density function to perform a non-linear regression model for the fitting of the experimental data.
This work was made possible by funding from the Department of Energy for the Summer Undergraduate Laboratory Internship (SULI) program. This work is supported by the US DOE Contract No. DE-AC02-09CH11466.
Rauschenberger, Alyssa K.
"Spectral Fitting Approach for Collective Thomson Scattering Experiments on an Extreme Ultraviolet Plasma Light Source,"
Macalester Journal of Physics and Astronomy: Vol. 10:
1, Article 9.
Available at: https://digitalcommons.macalester.edu/mjpa/vol10/iss1/9