Investigation of laser produced high-Z plasma soft X-ray sources

Over the past 10 years Extreme Ultraviolet Lithography (EUVL) sources based on 13.5nm emission from Sn plasmas have been investigated. Sn plasmas produce strong resonant emission due to 4d-4f, 4p-4d and 4d-5p transitions around 13.5 nm, which overlap in adjacent ion stages to yield an intense unresolved transition array (UTA). The UTA consists of hundreds of thousands of near-degenerate resonance lines, therefore high intense emission can be obtained from Sn plasmas at around 13.5 nm. A high power EUV source is an important requirement for EUVL. Shorter wavelength sources can not only be used for EUVL, but also material science, and biological imaging near the water window. According to a previous work, it was shown that the UTA peak wavelength depends on atomic number and will therefore extend down towards the water window region¹. This may be of great interest if a high power source can be achieved using UTA emission.