Ionic debris measurement of three extreme ultraviolet sources

Abstract

Generation of debris in extreme ultraviolet (EUV) light sources is an inherent and real threat to the lifetime of collection optics. Debris measurement of these sources is useful to enable source suppliers to estimate collector lifetime. At the Center for Plasma Material Interactions (CPMI) at the University of Illinois, an Illinois calibrated spherical sector electrostatic energy analyzer (ICE) was built to measure the ion debris flux in absolute units. In addition to ion flux, the detector is also capable of identifying different ion species present in the plasma utilizing energy-to-charge ratio discrimination. The lifetime of the collector optics is calculated using the measured ion flux. In the current investigation we compare the measurement of ion debris production in three different EUV sources: the Energetiq EQ-10M, the AIXUV-100, and the XTREME XTS 13-35. In the EQ-10M source, three angular measurements are coupled with three variations in operating pressure to measure consequent effects on debris production. These measurements reveal four predominant ion species in the energetic debris analysis: C+, Si+, Xe+, and Xe2+. The amount of debris is reduced as pressure is increased. Various debris mitigation methods are implemented in the AIXUV-100 source and results reveal that four ion species are observed (Ar+, Xe+, Xe2+, and W+), though there does not seem to be a dominant species. The first mitigation technique, backstreaming argon toward the source, reduces the amount of Ar+, Xe2+, and W+, yet increases the amount of Xe+ The increase in Xe+ flux is explained based on charge exchange phenomena. The ICE machine was then attached 1.92 m away from the pinch of XTS 13-35 source, and placed at 25° away from the normal line. The comparison of results reveals that the XTS 13-35 and the EQ-10M sources produced comparable amounts of energetic ion flux per watt of EUV light produced. The AIXUV-100 source generated more ion debris flux per watt of EUV light than the other two sources, though it should be noted that the AIXUV-100 source was capable of producing more than ten times the amount of EUV light power compared to any of the other sources.