Model of neutralization of highly ionized Xe generated by laser-produced plasma

Abstract

Condenser erosion caused by high-energy ions is a current issue in EUV sources. Measurements of the charge and energy distributions of Xe ions by EUVA revealed that energetic, kiloelectronvolt-order ions were formed in Xe-laser-produced plasma (LPP). The charge distribution shows a peak for doubly charged ions, and the number of ions with n charges monotonically decreases as n increases. Since highly charged ions around Xe10+ are probably formed in optimized EUV plasma, the observed charge distribution strongly suggests that charge transfer reactions occur in the LPP chamber. If that is true, the reactions will produce high-energy neutrals. In this study, the rate equations for charge transfer reactions were solved numerically; and the change in charge state distribution over time was calculated. The initial charge distribution was assumed to have a peak for Xe10+, based on the plasma model. The dependence of charge transfer cross section was taken to be nb, where n is the number of charges and b was set near unity, based on the model. The calculated charge distribution agreed well with the experimental data. The calculations predict that charge transfer reactions produce fast neutrals, the number of which is of the same order or larger than that of charged ions.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.