Spectra of high energy ions as debris in laser-produced plasma EUV source

We evaluated the charge-separated spectra of highly charged suprathermal gadolinium (Gd) ions from a 1064-nm, nanosecond laser-produced plasma (LPP) extreme ultraviolet (EUV) source developed for beyond EUV (BEUV) lithography. The charge distribution of these suprathermal ions emitted from a solid planar Gd target was measured by an electrostatic energy analyzer (ESA). The maximum ionic charge state was observed to be Z = 16 and to possess a maximum energy of about 15 keV at the optimum laser intensity of 2 x 10¹² W/cm2 to produce the efficient 6.7-nm EUV emission. This evaluation provides important information essential for the development of debris mitigation schemes in the BEUV source for next generation lithography.