Novel low-temperature and high-flux hydrogen plasma source for extreme-ultraviolet lithography applications

Abstract

Inside extreme-ultraviolet (EUV) lithography machines, a hydrogen plasma is generated by ionization of the background gas by EUV photons. This plasma is essential for preventing carbon build-up on the optics, but it might affect functional performance and the lifetime of other elements inside the machine. The interaction of scanner materials and components with hydrogen plasma is investigated in controlled experiments using laboratory (off-line) setups, where the properties of EUV-generated plasmas are mimicked. Here, we present a novel experimental setup at TNO, where a low-temperature hydrogen plasma is generated by means of electron-impact ionization using a high-current, high-pressure electron beam (e-beam) gun. We show that the produced ion flux, peak ion energies, and radical-to-ion ratio are similar to that of the EUV-generated plasma. Since the e-gun has the option of operating the e-gun in the pulsed mode, it is possible to reproduce the time-dependent behavior of the scanner plasma as well. Moreover, as shown by Luo et al. [RSC Adv. 10, 8385 (2020)], electrons that impinge on surfaces mimic EUV photons in the generation of secondary electrons, which often drive radiation-induced processes (e.g., surface oxidation, reduction, and growth of carbon). We conclude that e-beam generated hydrogen plasma is a very promising technology for cost-effective lifetime testing of materials and optics, as compared to setups with EUV sources.