EUV-induced hydrogen plasma and particle release

Extreme UV (EUV) lithography is the most advanced lithography technology for creating the patterns for state-of-the-art Integrated Circuits (IC), with critical dimensions down to 10 nm. This resolution is achieved by using a wavelength of 13.5 nm, imaging a reflective reticle onto a wafer via a mirror-based projection system. The system uses a low-pressure hydrogen background gas, which is excited into a low-density hydrogen plasma by the energetic EUV radiation. In the vicinity of the projection mirrors and reticle, this creates an aggressive environment that must be understood and managed to minimize molecular and particle contamination of the critical optical surfaces. In the past 25 years, main focus has been on the interaction between the EUV-induced plasma and the mirror surfaces. To secure best yield, however, focus should also be on the construction and functional surfaces close to the EUV beam. This paper will present details of energies and fluxes of the pulsed EUV-induced plasma, and its interactions with materials and particles.