Extreme ultraviolet sources for lithography applications

The source is a critical factor for the success of Extreme Ultraviolet Lithography (EUVL). This paper presents an update of the EUV source requirements. A comparison of the currently measured source performance with the specification is presented. For the source choice, it is also essential to understand the limits of the source and the way the source or the total source/lithography system could be improved to meet the lithography tool requirements in time. Although none of the currently known plans is compliant with requirements for an EUVL production tool, significant further improvement of their performance in the future seems feasible. Detailed analysis of the source requirements and the way to meet production tool specification, including increase in repetition rate fbr all the sources, are presented. Increase in energy per pulse, determined by dose reproducibility limit, for some of the sources is also discussed. Additional attention is paid to optimization of the tool wavelength and heat load within the source chamber and of the optical components due to of-band source radiation.