Extreme Ultraviolet Light

Extreme ultraviolet (EUV) light at the desired wavelength, 13.5 nm, is created through very high energy releases of photons due to the de-excitation of heavily ionized tin, Sn¹⁴⁺. This degree of ionization is only possible in a strong plasma, which in industry is created by irradiating tin droplets with a high-power laser. A large problem associated with this type of EUV source is tin debris buildup on the mirror, leading to reduced EUV intensity over time as the mirror gets dirtier. Previously, work has been done at the Center for Plasma-Material Interactions (CPMI) to use a hydrogen plasma to etch the tin off the surface of the mirror, effectively cleaning it in-situ. Although effective for cleaning, debris can still damage the mirror due to high energies. A small scale EUV source has been created, allowing for less intensive experimentation on tin debris within the chamber. This source is called MK-III and is shown on the right. The laser is pulsed at various powers, creating varying intensities of EUV as plotted below. After laser pulses, the tin target is irradiated, creating EUV light and creating tin debris within the chamber. Hydrogen gas is flowed in the chamber at 100 sccm at various pressures, finding better debris removal at lower pressures as shown in the SEM images.