Time dependent collisional radiative model of an extreme ultraviolet driven plasma

Abstract

The ever increasing demand for smaller and faster computer chips requires an ever decreasing size of semiconductor structures. ASML, one of the world's leading providers of lithography systems for the manufacturing of chips, aims at using EUV (Extreme UltraViolet) radiation at 13.5 nm wavelength for its next generation of products. Due to high attenuation at this wavelength, the whole optics system must be in vacuum and mirrors have to be used instead of lenses. The pulsed EUV source photoionizes the low pressure ( 1 Pa) background argon gas which causes a weakly ionized plasma. In the plasma sheath region at the mirror surface ions will be accelerated towards the surface and can cause undesired sputtering of the multilayer mirror surface. In a previous Particle In Cell (PIC) model by Van der Velden et al. predictions were made of the plasma parameters. In this research a time-dependent Collisional Radiative Model (CRM) is made based on the corona plasma regime. Using non- Maxwellian electron distribution functions (EEDF) provided by the PIC model the CRM model calculates the argon excited state densities and the spontaneous photon emission rate. The results are compared to Optical Emission Spectroscopy measurements. The experiments show that the timescales on which the electrons in the EUV induced plasma lose their energy, are much shorter than predicted by the model. However, the general trends are predicted correctly. Furthermore, the 4p lines of ArI and ArII prove to be the best indicators of this process.

Date of Award	31 Oct 2009
Original language	English
Supervisor	J.J.A.M. van der Mullen (Supervisor 1), M.H.L. van der Velden (Supervisor 2) & M. van Kampen (Supervisor 2)