Research Disclosure

摘要

To reduce the transmission loss of extreme ultraviolet (HUV) radiation in an EUV lithographic apparatus, an optical column of the EU V lithographic apparatus is commonly located within a near-vacuum vessel. The near-vacuum vessel usually comprises a small amount of hydrogen gas at low pressure (e.g. a few Pa) which, during operation, is photo-ionized by the EUV radiation to form a hydrogen plasma. The hydrogen plasma limits deterioration of the reflectivity of mirrors in the optical column due to hydrocarbon impurities, and also limits surface oxidation through water and/or oxygen impurities adsorbing to the EUV irradiated surface. The hydrogen plasma may, however, produce volatile hydrides, radicals and ions which may deposit on surfaces in the HUV lithographic apparatus, and particularly unfavourably on mirrors, pellicles and/or reticles. Such deposition of volatile particles may create extra adsorption losses in the HUV lithographic apparatus, in particular if the deposits are partially or fully oxidized.