UTA versus line emission for EUVL: studies on xenon emission at the NIST EBIT

Spectra from xenon ions have been recorded at the NIST electron beam ion trap (EBIT) and the emission into a 2% bandwidth at 13.5 nm arising from 4d --> 5p transitions compared with those 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 I I nm. It was found that an improvement of a factor of 5 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.