Influence of the electrode wear on the EUV generation of a discharge based extreme ultraviolet light source

Reliability and a long maintenance interval are major requirements for the industrial use of an extreme ultraviolet (EUV) source. In this paper we present results on the influence of the electrode erosion on the EUV generation and its lifetime limiting characteristics. The geometry of the electrodes and their influence on the gas pressure distribution within the electrode system have been found to be the key variables to characterize the regime of operation. This better understanding allows for an optimization of device parameters (e.g. gas flow or pulse energy) to counteract the erosion process, in order to increase the maintenance interval and EUV output. The EUV source under investigation is based on a hollow cathode triggered pinch plasma. A new trigger concept is introduced that enables free adjustment of the gas pressure during operation, thus enabling the operation with a high conversion efficiency of up to >0.7 %/2πsr at 13.5 nm and 2% bandwidth. The efficiency for the peak brilliance is up to ~2.6 W kW−1 mm−2sr−1 while the maximum electrical input power of the system is 15 kW.