An XTREME Technologies XTS 13-35 extreme ultraviolet (EUV) light source creates a xenon z pinch that generates 13.5nm light. Due to the near x-ray nature of light at this wavelength, extremely smooth metal mirrors for photon collection must be employed. These are exposed to the source debris. Dissolution of the z-pinch gas column results in high-energy ion and neutral release throughout the chamber that can have adverse effects on mirror surfaces. The XTREME commercial EUV emission diagnostic chamber was designed to maximize diagnostic access to the light and particulate emissions from the z pinch. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z pinch is followed by ejection of multiply charged ions and fast neutral particles that make up an erosive flux to chamber surfaces. Attenuation of this erosive flux to optical surfaces is attempted by inclusion of a debris mitigation tool consisting of foil traps and neutral buffer gas flow. Characterization of the z-pinch ejecta is performed with a spherical sector energy analyzer (ESA) that diagnoses fast ion species by energy-to-charge ratio using ion time-of-flight (ITOF) analysis. This is used to evaluate the debris tool’s ability to divert direct fast ions from impact on optic surfaces. The ITOF-ESA is used to characterize both the energy and angular distribution of the direct fast ions. Xe+ up to Xe+4 ions have been characterized along with Ar+ (the buffer gas used), W+, Mo+, Si+, Fe+, and Ni+. Energy spectra for these species from 0.5 up to 13keV are defined at 20° and 30° from the pinch centerline in the chamber. Results show a drop in ion flux with angular increase. The dominant species is Xe+ which peaks around 8keV. Ion flux measured against buffer gas flow rate suggests that the direct fast ion population is significantly attenuated through increases in buffer gas flow rate. This does not address momentum transfer from scattered ions or fast neutral particles. These results are discussed in the context of other investigations on the effects of total particle flux to normal incidence mirror samples exposed for 1×107 pulses. The samples (Si∕Mo multilayer with Ru capping layer, Au, C, Mo, Pd, Ru, and Si) were exposed to the source plasma with 75% argon flow rate in the debris mitigation tool and surface metrology was performed using x-ray photoelectron spectroscopy, atomic force microscopy, x-ray reflectivity, and scanning electron microscopy to analyze erosion effects on mirrors. These results are compared to the measured direct ion debris field.
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.
The XCEED chamber was designed to allow diagnostic access to the conditions experienced by collecting optics for a discharge produced plasma (DPP) source. The chamber provides access for EUV photodiodes, sample exposure tests, Faraday cup measurements, and characterization of the ion debris field by a spherical sector energy analyzer (ESA). The Extreme Ultraviolet (EUV) light source creates a xenon z-pinch for the generation of 13.5 nm light. Typical EUV emission is characterized though a control photodiode. The chamber also allows characterization of optic samples at varying exposure times for normal and grazing incidence reflection angles during tests lasting up to 40 million pulses. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z-pinch is followed by ejection of multiply-charged ions which can significantly damage nearby mirror surfaces. Characterization of the ejecta is performed with an ESA that diagnoses fast ion species by energy-tocharge ratio using ion time of flight (ITOF) analysis. The ITOF-ESA is used to characterize both the energy and angular distribution of the debris field. In the current paper, the ESA is applied only to the ion debris emitted from the source. The effects of total particle flux on mirror samples are investigated through exposure testing. Samples are exposed to the source plasma and surface metrology is performed to analyze erosion and deposition effects on mirrors within the source chamber.
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