Active and passive spectroscopy on EUV-producing discharge plasmas

Short-lived discharge plasmas are currently investigated as candidate sources of extreme ultraviolet (EUV) radiation for application in semiconductor lithography. They are operated in elements such as xenon and (more recently) tin, because of their favorable emission at 13.5 nm. A common property of these plasmas is the current-induced 'pinch' effect, that causes the plasma to collapse to an elongated, needle-like shape on the discharge axis. The typical plasma lifetime is in the tens to hundreds of ns.Various spectroscopic techniques can be applied for characterization of these plasmas. These include time-resolved EUV spectrometry and Stark broadening measurements at visible light wavelengths. Collective Thomson scattering of laser light can provide direct time and space resolved measurements of electron temperatures and densities.Specific experimental difficulties and the ranges of applicability of the different methods for measurements on pinch plasmas are discussed. Results of these measurements on a hollow cathode discharge in xenon and a vacuum-arc discharge in tin vapor are presented