Debris-Free, Droplet Laser Plasma Sources In The Euv And Soft X-Ray Ranges

Previous work with a 100-kHz water droplet system generated 13-nm and 116-nm line emissions from a Li-like O2 plasma produced by 10-ns duration, 10-Hz Nd:YAG laser pulses at approximately 1012 W/cm2. A detailed quantitative study of this source was performed with a 100-Hz laser. The radiation efficiency and the long-term operation were characterized, and results show that the droplet laser plasma source comes close to satisfying all the near-term needs of extreme ultraviolet lithography (EUVL). In particular, an overall conversion efficiency of laser light to 13-nm emission within the required spectral bandwidth in excess of 0.6%, comparable to any other existing source at this wavelength