Fundamentals and limits for the EUV emission of pinch plasma sources for EUV lithography

Abstract

Future extreme ultraviolet (EUV) lithography will require high radiation intensities at a wavelength around 13.5 nm. The limits of emission in this spectral range from discharge based plasmas are discussed theoretically. The discussion is based on a simple MHD approach for a xenon plasma discharge and atomic data from the ADAS software package for radiative transitions, excitation and ionization of different ionization levels. Discharge parameters are chosen for the Philips' hollow cathode triggered pinch plasma. The calculations show that the 13.5 nm emission originates only from of Xe10+ ions and is optically thin. Ideally, the conversion efficiency is expected to scale linearly with the electron density in this case. The MHD calculations, however, show a lower increase with density. The loss channels leading to this behaviour, like leakage currents, will be discussed in detail. The identification of these losses allow, on the other hand, for a systematic improvement of the electrode system and the electrical circuit. In addition, theoretical emission spectra of xenon and tin as the most promising emitters around 13.5 nm will be compared with respect to the possible optimization potential of spectral emission characteristics.

Fusion-Related Ionization and Recombination Data for Tungsten Ions in Low to Moderately High Charge States

“…The effort to improve data and modeling tools is strongly continuing. Applications are mainly in fusion (see e.g., [9]) but also in the lighting industry (see e.g., [10]) and in astrophysics [11]. It is essential for a project like ADAS to implement reliable knowledge about processes and structures of the atoms and ions of the chemical elements that occur in the plasma to be investigated.…”

Heights integrated model as instrument for simulation of hydrodynamic, radiation transport, and heat conduction phenomena of laser-produced plasma in EUV applications.

“…An ideal variant of light source for EUV lithography is a small spherical object with enough density and an optimal temperature for the given material for EUV output. This approach is used in recent investigations [67,68] for improving EUV output efficiency, that is, the first part of this problem: possible target materials for effective radiation at the 13.5 nm area on the background of the total spectrum. However, the second part of the problem consists in the formation and efficient confinement of the EUV plasma in these optimal conditions (temperature plus enough density).…”

Theoretical and Experimental Investigations of the Suitability of Low‐Current Z‐Pinch Plasma as an Absorption Medium for Laser Radiation

“…The resulting plasma is a cylindrical column with a diameter of up to 3 mm and a length of approximately 2 mm. The discharge has a duration of approximately 200 ns (typically 100-500 ns; [10]). A typical emission spectrum obtained in the EUV spectral region is shown in Figure 2.…”