Extreme-ultraviolet spectra of xenon ions have been recorded in the 4.5 to 20 nm wavelength region using an electron beam ion trap and a flat field spectrometer. The electron beam energy was varied from 180 eV to 8 keV and radiation from charge states Xe 6+ to Xe 43+ was observed. Our measured wavelengths were compared to atomic structure calculations using the Cowan suite of codes. We have measured seventeen previously unreported features corresponding to transitions in Xe 35+ through to Xe 41+ with estimated wavelength uncertainties of ±0.003 nm. It was found that for the case of continuous injection of neutral xenon gas a wide range of charge states were always present in the trap but this charge state distribution was greatly narrowed, towards higher charge states, if a sufficiently low gas injection pressure was employed. The energy dependence of spectral lines arising from Xe 42+ and Xe 43+ revealed enhancement of the total ionization cross sections, due to excitation-autoionization of n = 2 electrons to n = 3 levels, in the Xe 41+ and Xe 42+ charge states.

A custom, flat field, extreme ultraviolet EUV spectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal to noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a novel procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar and Ne ions recorded with this spectrometer.2

Abstract:Spectra from xenon ions have been recorded at the NIST EBIT and the emission into a 2% bandwidth at 13.5 nm arising from 4d_5p transitions compared with that from 4d_4f and 4p_4d transitions in Xe XI and also with that obtained from the unresolved transition array (UTA) observed to peak just below 11 nm. It was found that an improvement of a factor of five could be gained in photon yield using the UTA rather than the 4d_5p emission. The results are compared with atomic structure calculations and imply that a significant gain in efficiency should be obtained using tin, in which the emission at 13.5 nm comes from a similar UTA, rather than xenon as an EUVL source material. BACKGROUND:The search for the optimum radiation source at 13.5 nm is one of the main challenges in EUV physics today. Currently the quest is to find a source with a conversion efficiency (CE) of 3% into 2% bandwidth as defined by the needs of the microelectronic industry [1]. The earliest work was performed with laser produced plasmas generated on solid targets. Kauffman et al. [2] attained a CE close to 1% into 3% bandwidth using 7.5 ns, 300 mJ frequency doubled Nd:YAG pulses focussed to a power density of 2×10 . In their work they performed an extensive survey of the emission from a large range of elements and found that the emission at the required wavelength peaked near tin. At higher power densities they noted that the intensity decreased. Shevelko et al. [4] also undertook an extensive study of the spectra of a large number of elements from laser produced plasmas with a KrF excimer laser focussed to a power density of 10 12 Wcm -2 onto planar targets including tin and found that the maximum intensity was in fact obtained for Ge and Re under these conditions. So early work already pointed to the sensitivity of the emission of specific elements to laser power density.In order to avoid the debris problems associated with solid targets other target materials were sought with strong emission in the 13-14 nm region. Jin and Richardson [5] used mass limited water ice targets, where the emission is from the O VI lines near 2 13 nm, to limit the debris. However, all of their early work with mass-limited targets produced significant levels of debris both in the form of ions and particulates of various sizes. The need to reduce particulate emission led to the choice of xenon. There is a line group between 13-14 nm in the spectrum of Xe which has been shown by a number of researchers to arise from 4d 8 _ 4d 7 5p transitions in Xe XI [6]. These lines have recently been identified by Churilov et al. [7] by comparison of new very high resolution data with atomic structure calculations using the suite of codes developed by Cowan [8]. Considerable work has 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 [9]. The highest conversion efficiencies (1.2% into 2% bandwidth) have been achieved using solid xenon by Shields et al. [1...

The time-independent ion distributions of variable composition laser-produced Sn plasmas are studied for a wide range of electron temperatures and atomic number densities, the purpose of which is to elucidate the effect that varying the number density of Sn within a mixed species plasma has upon the steady state populations of Sn and its ions. Particular emphasis will be placed on binary mixtures of Sn with Li, C, O or Sm and more specifically the charge states Sn8+ to Sn13+ within these mixed plasmas, where it will be assumed that the plasma is optically thin. It is found that using these composites has relatively little effect upon the Sn ion population distributions for plasma atomic number densities of less than approximately 1019.5 cm−3. However, for greater values of number densities the Sn ion populations can be shifted by as much as 10–15 eV for Li mixtures. These results are of particular relevance to current research being carried out on extreme ultraviolet lithographic technologies for the optimization of XUV sources in the 13.5 nm wavelength region, which include composite target investigations.

We have observed EUV spectra of xenon ions from the large helical device (LHD) at the National Institute for Fusion Science in Toki in the wavelength range of 10-17 nm using a high resolution SOXMOS spectrometer. A small quantity of xenon gas was injected into the large helical device. In some cases, the plasma evolution was stable and a steady discharge was obtained for several seconds, but sometimes the plasma underwent radiation collapse and rapid cooling and in this situation the EUV yield was significantly increased. Investigation of the spectra showed that during the heating phase and in a stable plasma, the emission was dominated by ions with open 4s and 4p subshells, while during radiation collapse, the spectra were dominated by lines from species with open 4d subshells. From a comparison of these spectra with theoretical data from atomic structure calculations and also with charge state specific data generated at Tokyo Metropolitan University, it was possible to make tentative assignments of the strongest lines arising from 4d-4f and 4p-4d transitions in Xe XVII and XVIII.