Wavelength dependence of carbon contamination on mirrors with different capping layers

Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. In addition to the desired wavelength near 13.5 nm (EUV), plasma sources used in EUV exposure tools emit a wide range of out-of-band (OOB) wavelengths extending as far as the visible region. We present experimental results of contamination rates of EUV and OOB light using a Xe plasma source and filters. Employing heated carbon tape as a source of hydrocarbons, we have measured the wavelength dependence of carbon contamination on a Ru-capped mirror. These results are compared to contamination rates on TiO 2 and ZrO 2 capping layers.