abstract |
A perfluoropolyether (PFPE) index matching medium (120). The medium (120) may be used with electromagnetic radiation (152) having a wavelength below 220nm. The medium (120) may be used between two optical surfaces (115 and 150) or between an optical surface (115) and an object (150). The medium (120) may be used as an immersion fluid in an immersion lithographic system (100). |