[en] Full text: The wavelength of choice for the next extreme UV lithography (EUVL) step, 13.5 nm, is based on the availability of MoSi multilayer mirrors with excellent reflectivity (Approx. 72%) at this wavelength with a reflectance bandwidth of approximately 0.5 nm. A wide variety of pulsed discharge sources using xenon or xenon/helium mixtures are being actively investigated and developed by a number of companies and laboratories. However all of the conversion efficiencies reported to date for these devices are close to 0.5%. Considerable work has also been expended on exploring the feasibility of using laser produced plasmas of xenon clusters produced by supersonic jets or gas puffs from nozzles or solid xenon targets. The highest conversion efficiencies (1.2% into 2% bandwidth) have been achieved using solid xenon. In xenon, the transitions responsible are 4d - 5p in Xe XI. Since this is an open shell species, plasma modeling puts the maximum population attainable at 45%. The required conversion efficiency figure has now been revised upwards to better than 3% conversion into a 2% bandwidth. We have proposed that tin should be potentially the brightest emitter at this wavelength. The transitions responsible in tin arise from n=4-n=4 lines from stages VIII through XIII that merge to form an unresolved transition array (UTA). If the tin concentration is reduced to 10%, the peak brightness increases due to enhanced radiation transport at lower density. Furthermore, if the remaining 90% of the constituents are low Z materials the radiation emitted is concentrated in a band 1-2-nm wide centred near 13.5 nm. The extreme brightness of these features is a direct result of the transfer of oscillator strength from the continuum 4d- ef resonance known to dominate the EUV absorption of the neutral and low ion stages to discrete 4d-4f transitions