Influence of environments on the footprint of particle contamination on EUV mask

Even if particles are removed still a residue or "footprint" is left behind. Such a footprint may in itself be large enough to become a printable defect. Footprint of silica and PSL particles with diameters of 100 nm which were deposited on Si surface and were stored at different environments was measured by atomic force microscope. Their particle removal forces also were measured. Footprint of silica and PSL particles and their particle removal forces represented that silica particles as an inorganic type particle were very sensitive humidity and it needs high removal force when the silica particle aged at higher humidity level and longer storage time. On the other hand, PSL particles as an organic type particle were not sensitive humidity, but footprints were observed even at low humidity condition and short storage time. This study could help to improve the understanding of particle adhesion on EUV mask and might help to improve mask life time longer.