Extreme Ultraviolet - EUV Damage

EUV Damage

Like other forms of ionizing radiation, EUV and electrons released directly or indirectly by the EUV radiation are a likely source of device damage. Damage may result from oxide desorption or trapped charge following ionization. Damage may also occur through indefinite positive charging by the Malter effect. If free electrons cannot return to neutralize the net positive charge, positive ion desorption is the only way to restore neutrality. However, desorption essentially means the surface is degraded during exposure, and furthermore, the desorbed atoms contaminate any exposed optics. EUV damage has already been documented in the CCD radiation aging of the Extreme UV Imaging Telescope (EIT).

Radiation damage is a well-known issue that has been studied in the process of plasma processing damage. A recent study at the University of Wisconsin Synchrotron indicated that wavelengths below 200 nm are capable of measurable surface charging. EUV radiation showed positive charging centimeters beyond the borders of exposure while VUV (Vacuum Ultraviolet) radiation showed positive charging within the borders of exposure.

Studies using EUV femtosecond pulses at the Free Electron Laser in Hamburg (FLASH) indicated thermal melting-induced damage thresholds below 100 mJ/cm2.

An earlier study showed that electrons produced by the 'soft' ionizing radiation could still penetrate ~100 nm below the surface, resulting in heating.