Debris mitigation power of various buffer gases for CO₂ laser produced tin plasmas

Abstract

Debris mitigation using an ambient gas is the easiest way for laser-produced plasma extreme ultraviolet light source. The debris mitigation power of hydrogen, helium and argon buffer gases against CO2 laser produced tin plasma plumes was quantitatively estimated by means of the visualization imaging system as well as the optical emission spectroscopy technique. The debris mitigation power of hydrogen buffer gas was assessed under ambient pressure ranging from 30 to 104 Pa. The debris mitigation power of the hydrogen buffer gas was determined as 150 eV mm−1 for energetic particles of 400 eV under a pressure of 104 Pa, which remained as high as 40 eV mm−1 at a pressure of 100 Pa. The maximum stopping power and collision scattering cross section of argon were measured to be almost three times larger in comparison with hydrogen and one and a half times larger than helium atmosphere at a pressure of 2000 Pa. Time-resolved optical emission spectroscopy showed that thermalizing collisions were responsible for slowing down the fast energetic ions and atoms towards a thermal equilibrium.

Extreme ultraviolet emission and confinement of tin plasmas in the presence of a magnetic field

“…12 It is well known that the EUV LPP source emits debris in the form of energetic ions, atoms, and molten droplets. 13,14 The ablated Sn vapor and debris will be deposited on various components, including the surface of the ML mirror, which causes degradation in mirror reflectivity. Several schemes proposed for mitigating the ion and atom debris, however, none of them can completely mitigate the additional damage from neutrally charged debris.…”

“…Several schemes proposed for mitigating the ion and atom debris, however, none of them can completely mitigate the additional damage from neutrally charged debris. 12,13 Ionized and neutral particle flux causes the sputtering and implantation of the debris species into the ML mirror coating, lowering its reflectivity. 15 Several mitigation schemes have been proposed to improve the lifetime of the ML mirror, for example, using magnetic fields, 16 a gas curtain, 17 low energy prepulses, 18 and mass-limited targets.…”

Collimation of laser-produced plasmas using axial magnetic field

“…Apart from conversion efficiency of laser energy to EUV photons, the cleanness of the EUV LPP sources is also extremely important for their use in semiconductor lithography (Coons et al, 2010). The EUV LPP source emits debris in the form of energetic ions, atoms, and molten droplets (Wu et al, 2012). Several schemes are proposed for mitigating the ion and atom debris, which includes ambient gas, magnetic field, combination of both magnetic field and ambient gases, mass-limited targets, electrostatic repeller fields, etc.…”

Measurements of hydrogen gas stopping efficiency for tin ions from laser-produced plasma

“…20 The interaction of Sn plasma plume with background gases has been studied in various experimental conditions. [18][19][20][21][22] However, direct measurements of Sn ion stopping in the above-mentioned gases are still lacking. This paper reports on the experimental studies of Sn þ and Sn 2þ ion stopping by hydrogen for ion energies in the range of $0.1-10 keV.…”