Electron irradiation-enhanced water and hydrocarbon adsorption in EUV lithography devices

The accumulation of water and hydrocarbons molecules on pure Au smooth surfaces were monitored during 100 eV electron bombardment at various beam current levels. Our studies showed that these low energy electrons could accelerate the physical adsorption processes of the gaseous contaminant molecules on the mirror surface. The 100 eV electron beam was used to provide a rough simulation of the secondary electrons generated during the interaction between the EUV beam at 13.5 nm wavelength and the mirror surface in an EUVL device. The adsorption enhancement phenomenon was explained in accordance with Langmuir's Adsorption model by the increase of the sticking coefficient of adsorbed molecules onto the mirror surface. We have also shown that a positive biasing of the top of mirror surface can be used for preventing the secondary electron emission from the mirror surface.