Feasibility study on reactive ion etching occurrence in EUV-induced photoionized hydrogen plasmas based on electron temperature and electron density measurements

Abstract Temporal evolutions of electron temperature ( T e ) and electron density ( n e ) of photoionized hydrogen plasmas, which were induced by radiation from laser-produced Sn-plasma EUV sources, were measured using the laser Thomson scattering technique. Measured T e and n e ranged from 0.5–2.5 eV to 10 16 –10 18 m −3 , respectively, for hydrogen pressures of 50–400 Pa. The T e of this EUV-induced hydrogen plasma decayed with the thermal relaxation time between electrons and gases. The maximum value of T e in the time variation depended on hydrogen pressure. The lower the pressure, the higher the maximum T e , and it reached approximately 2 eV at 50 Pa. The sheath potential between the EUV-induced hydrogen plasma and the unbiased wall might be exceeded 6 eV at 50 Pa, which is sufficient to enhance the removal of Sn-debris from a Mo/Si multilayer mirror via reactive ion etching processes.