Extreme ultraviolet light sources and soft x-ray laser based on discharge produced plasma

Abstract

Due to the demand to realize shorter wavelength light sources, extreme ultraviolet (EUV) sources and soft x-ray laser (SXRL) are under development. The development of EUV sources at the wavelength of 13.5 nm started to realize light sources to be used for next generation lithography. Xenon was used at the beginning of development, however, to attain higher conversion efficiency, tin is now used as fuel. As a coherent light source, capillary discharge SXRL is under development. After the demonstration of Ne-like Ar SXRL by using electron collisional excitation scheme, the effort to shorten the wavelength has been made by adopting recombination scheme such as H-like N. Though the challenge has not yet been successful, the source has potential to be used as a SXR source in the water window wavelength region. Current status of EUV and SXR sources based on discharge produced plasma will be given. EUV source, SXR laser, Capillary discharge, Z-pinch, Discharge produced plasma 1. INTRODUCTION To meet the requirement for the next generation lithography, the research and development of 13.5 nm extreme ultraviolet (EUV) light sources based on discharge produced plasma (DPP) has been energetically pushed forward for the last decade. Although the research started from a xenon (Xe) capillary DPP EUV source, to reduce the interaction between plasma and the capillary inner wall, a Xe gas jet EUV source without a capillary was developed and the formation of EUV emission plasma with a small diameter at discharge current of 10 kA was successfully realized. The obtained EUV conversion efficiency of Xe plasma is less than 1%. In order to increase the conversion efficiency, which leads to the reduction of thermal load on the discharge head, a laser assisted DPP tin (Sn) EUV source has been also studied. It was demonstrated