Mitsubishi Heavy Industries Limited

Noriko Yamazaki

Satoshi Sakai

Minoru Danno

Hideo Yamakoshi

Shigenori Tsuruga

Hiroshi Futami

Shizuma Kuribayashi

An optical system includes a fluoride compound and has surfaces facing and exposed to plasma installed in an optical equipment which has an inner zone where the plasma exists. A 2 nm-20 nm protective film of a highly plasma-resistant material is formed on the surface of the fluoride compound that is exposed to the plasma.

Optical properties restoration apparatus, the restoration method, and an optical system used in the apparatus

An optical system has fluoride compounds provided in an environment exposed by vacuum ultraviolet light or plasma light, which has higher photon energy than an absorption wavelength of a base stock of the optical system. 1-layer of a protective film of SiOor metal oxides having a film thickness of 2-20 nm is formed at least on the light irradiation side (inner side) of the optical system to prevent the stripping of the fluorine atoms from the surface of the optical system. In addition, the protective film is a 1-layer film selected from one of SiO, MgO, TiO, or ZrO.

The objectives of the present invention are to prevent or inhibit the deterioration effects such as light transmission, diffraction, reflection, spectrum generation, and interference, and these combinations, and by so doing, decrease the frequency of maintenance operations such as window replacement and to reduce the costs for such operations. This invention is characterized by steps of creating a near vacuum zone with a presence of active energy to excite an oxidation reaction of carbon wherein the near vacuum zone faces the lighting surfaces of the optical system; generating negative ions or radicals in the near vacuum zone such as unstable chemical seeds containing oxygen atoms, such as OH radicals, OH ions, ozone, Oions, O-radicals; and removing or reducing the accumulated carbon which deposits on the lighting surface, by reacting the deposited carbon with the negative ions or radicals. More specifically, the method according to this invention is characterized by the step of supplying active energy while supplying a flow of gases containing oxygen atoms such as water gas or oxidizing gas (for example, water vapor, oxygen, hydrogen peroxide, ozone or mixtures of said gases with inactive gases (including air)) into the near vacuum zone, thereby removing or reducing the accumulated carbon which deposits on the lighting surface by exciting the oxidation reaction of the accumulated carbon with the supplied active energy.

Optical properties apparatus, the restoration method, and an optical system used in the apparatus

An optical properties restoration apparatus improves reliability and longevity of optical properties of an optical system, lying upon a vacuum boundary, by preventing, suppressing, or improving degradation of optical properties. The apparatus includes creating the near vacuum zone to excite an oxidation reaction of carbon, generating a flow of an oxygen atom-containing gas such as water gas or oxide gas in the near vacuum zone, and supplying active energy in the near vacuum zone to cause a carbon oxidation reaction between the oxygen atom-containing gas and the carbon. The near vacuum zone faces the lighting surfaces of the optical system and a lower limit value for a partial pressure of the gases containing oxygen atoms that is supplied to the near vacuum zone is set to a level over a speed of the carbon buildup that deposits on the lighting surfaces of the optical system.

The objectives of the present invention are to prevent or inhibit the deterioration of optical systems that determine the longevity of an optical apparatus which delivers effects such as light transmission, diffraction, reflection, spectrum generation, and interference, and these combinations, and by so doing, decrease the frequency of maintenance operations such as window replacement and to reduce the costs for such operations. This invention is characterized by steps of creating a near vacuum zone with a presence of active energy to excite an oxidation reaction of carbon wherein the near vacuum zone faces the lighting surfaces of the optical system; generating negative ions or radicals in the near vacuum zone such as unstable chemical seeds containing oxygen atoms, such as OH radicals, OHions, ozone, Oions, O-radicals; and removing or reducing the accumulated carbon which deposits on the lighting surface, by reacting the deposited carbon with the negative ions or radicals. More specifically, the method according to this invention is characterized by the step of supplying active energy while supplying a flow of gases containing oxygen atoms such as water gas or oxidizing gas (for example, water vapor, oxygen, hydrogen peroxide, ozone or mixtures of said gases with inactive gases (including air)) into the near vacuum zone, thereby removing or reducing the accumulated carbon which deposits on the lighting surface by exciting the oxidation reaction of the accumulated carbon with the supplied active energy.

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Yokohama, Japan

Noriko Yamazaki