Short-wavelength out-of-band EUV emission from Sn laser-produced plasma. (25th January 2018)

• Record Type: Journal Article
• Authors: Torretti, F; Schupp, R; Kurilovich, D; Bayerle, A; Scheers, J; Ubachs, W; Hoekstra, R; Versolato, O O
• Is Part Of: Journal of physics. Volume 51:Number 4(2018:Feb. 15)
• Publication Date: 2018-01-25
• Subjects: EUV spectroscopy -- highly charged ions -- laser-produced plasma; 31.15.ae -- 32.30.Rj -- 52.50.Dg -- 52.70.La; Atoms -- Periodicals; Molecules -- Periodicals; Optics -- Periodicals; Nuclear physics -- Periodicals; 539.6
• DOI: 10.1088/1361-6455/aaa593
• Languages: English
• ISSNs: 0953-4075

Abstract

Abstract: We present the results of spectroscopic measurements in the extreme ultraviolet regime (7–17 nm) of molten tin microdroplets illuminated by a high-intensity 3 J, 60 ns Nd:YAG laser pulse. The strong 13.5 nm emission from this laser-produced plasma (LPP) is of relevance for next-generation nanolithography machines. Here, we focus on the shorter wavelength features between 7 and 12 nm which have so far remained poorly investigated despite their diagnostic relevance. Using flexible atomic code calculations and local thermodynamic equilibrium arguments, we show that the line features in this region of the spectrum can be explained by transitions from high-lying configurations within the Sn 8 + –Sn 15 + ions. The dominant transitions for all ions but Sn 8 + are found to be electric-dipole transitions towards the n = 4 ground state from the core-excited configuration in which a 4 p electron is promoted to the 5 s subshell. Our results resolve some long-standing spectroscopic issues and provide reliable charge state identification for Sn LPP, which could be employed as a useful tool for diagnostic purposes.