Next generation lithography to fabricate smaller and faster chips will use extreme ultraviolet ͑EUV͒ light sources with emission at 13.5 nm. A challenging problem in the development of this technology is the lifetime of collector optics. Mirror surfaces are subjected to harsh debris fluxes of plasma in the form of ions, neutrals, and other radiation, which can damage the surface and degrade reflectivity. This manuscript presents the measurement of debris ion fluxes and energies in absolute units from Xe and Sn EUV sources using a spherical sector ion energy analyzer. Experimentally measured erosion on Xe exposed samples is in good agreement with predicted erosion. This result allows prediction of erosion using measured ion fluxes in experiment. Collector optic lifetime is then calculated for Xe and Sn sources without debris mitigation. Lifetime is predicted as 6 h for Xe EUV sources and 34 h for Sn EUV sources. This result allows calculation of expected collector optic lifetimes, which can be an important tool in optimizing source operation for high volume manufacturing.

Extreme ultraviolet ͑EUV͒ light sources with efficient emission at 13.5 nm are needed for next-generation lithography. A critical consideration in the development of such a source is the lifetime of collector optics. These experiments expose optics to a large flux of energetic particles coming from the expansion of the pulsed-plasma EUV source to investigate mirror damage due to erosion, layer mixing, and ion implantation. The debris ion spectra are analyzed using a spherical sector energy analyzer ͑ESA͒ showing ion energies of 2 to 13 keV, including

Using the hydrodynamic model, we have derived a self-consistent model describing the dynamics of a collisional rf sheath driven by a sinusoidal current source. Numerical results have been obtained for the dependence of ion density, ion kinetic energy, sheath thickness, and sheath electric field, on the collision parameter and the current source parameter.

A critical issue for EUV lithography ͑EUVL͒ is the minimization of collector degradation from intense plasma erosion, debris deposition, and hydrocarbon/oxide contamination. Collector optics reflectivity and lifetime heavily depend on surface chemistry and interactions between fuels and various mirror materials, such as silicon, in addition to highenergy ion and neutral particle erosion effects. As a continuation of our prior investigations of discharge-produced plasma ͑DPP͒ and laserproduced plasma ͑LPP͒ Xe plasma interactions with collector optics surfaces, the University of Illinois at Urbana-Champaign ͑UIUC͒ has analyzed collector samples before and after exposure in a Sn-upgraded Xtreme Technologies EUV source. Sn DPP postexposure characterization includes multiple samples, Si/ Mo multilayer film with normal incidence, 200-nm-thick Ru film with grazing incidence, as well as a Gibbsian segregated ͑GS͒ Mo-Au alloy developed on silicon using a dc dualmagnetron cosputtering system at UIUC for enhanced surface roughness properties, erosion resistance, and self-healing characteristics to maintain reflectivity over a longer period of mirror lifetime. Surface analysis draws heavily on the expertise of the Center for Microanalysis of Materials at UIUC, and investigates mirror degradation mechanisms by measuring changes in surface roughness and film thickness as well as analysis of deposition of energetic Sn ions, Sn diffusion, and mixing of multilayer. Results from atomic force microscopy ͑AFM͒ and auger electron spectroscopy ͑AES͒ measurements show exposure effects on surface roughness and contamination. The best estimates of thickness and the resultant erosion measurements are obtained from scanning electron microscopy ͑SEM͒. Deposition, diffusion, and mixing effects are analyzed with depth profiles by AES. Material characterization on samples removed after varying exposure times in the XTS source can identify the onset of different degradation mechanisms within each sample. These samples are the first fully characterized materials to be exposed to a Sn-based DPP EUV source. Several valuable lessons are learned. First, hot mirrors exposed to SnCl 4 gas will cause decomposition of the gas and build up a contamination layer on the surface. Second, erosion is mitigated to some extent by the simultaneous deposition of material. Third, and most important, Gibbsian segregation works and a thin Au layer is maintained during exposure, even though overall erosion is taking place. This phenomenon could be very useful in the design of a collector optics surface. In addition, we present Sn DPP collector erosion mechanisms and contamination and provide insight into plasma-facing optics lifetime as high-volume manufacturing ͑HVM͒ tool conditions are approached.

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