Characterization of collector optic material samples exposed to a discharge-produced plasma extreme ultraviolet light source

Abstract

Extreme ultraviolet (EUV) 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 (ESA) showing ion energies of 2 to 13 keV, including Xe+-Xe+4, Ar+, W+, Mo+, Fe+, Ni+, and Si+. Microanalysis is performed on samples exposed to 10 million pulses, including atomic force microscopy (AFM), showing increased roughness for most exposed samples. Notably, a Mo-Au Gibbsean segregated alloy showed surface smoothing over this time frame, suggesting that the segregation worked in situ. TRIM predictions for ion implantation are consistent with ion debris measurements from the ESA. Finally, time exposures of samples from 2, 20, and 40 million pulses show an initial roughening with smoothing of the exposed samples at longer time frames. Constant erosion is demonstrated with the SEM. These analyses give an experimental account of the effects of the ion debris field on optic samples exposed to the EUV source.