| Abstract
| - The realization of next-generation extreme ultraviolet (EUV) lithography depends on the application of Ru-capped multilayer mirrors. Under EUV irradiation, carbon deposition due to the presence of hydrocarbons inthe vacuum environment rapidly degrades mirror reflectivity, thus preventing implementation of this technology.We show that in the presence of low-energy electron irradiation, which corresponds to the photoelectronenergy distribution encountered in practice, very low pressures (∼10-5 mbar) of NO or O2 are effective foroxidative removal of carbon from contaminated ruthenium surfaces at ambient temperature. This procedureleads to the net accumulation of oxygen on and beneath the metal surface. Subsequent exposure of the resultingRu surface to CO under electron irradiation leads to efficient removal of this oxygen, again at ambienttemperature. Carbon removal rates on the order of ∼4.5 × 10-5 nm s-1 are achievable, showing that sequential(or simultaneous) application of electron-induced oxidation and reduction reactions provides a viable strategyfor remediation (or mitigation) of EUV mirror contamination under operating conditions.
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