Reduction of ion energies from a multicomponent Z-pinch plasma

This paper studies the expanding plasma dynamics of ions produced from a 5J Z-pinch xenon light source used for extreme ultraviolet (EUV) lithography. Fast ion debris produced in such plasmas cause damage to the collector mirror surface. Because of the great degree of erosion and the change in surface roughness properties, the reflectivity of EUV light at 13.5 nm drops drastically. Reducing ion energies and stopping the ion flux are a potential solution toward the success of EUV lithography. Ion energies are measured in kiloelectronvolt range using a spherical sector electrostatic energy analyzer. Preliminary computational work indicates that the observed high energies of ions are probably resulting from coulomb explosion initiated by pinch instability. Mixed fuel experiments are performed using a mixture of Xe, N₂, and H₂. The average energy of the expelled Xe ions is significantly decreased if the mobile lighter gas species are present in the main fuel. The magnitude of the Xe ion signal is reduced as well. This reduction in the quantity of heavy ions and their energy could greatly extend the lifetime of the collector optics used in EUV lithography.