PREPARATION OF 157NM TRANSMITTING BARIUM FLUORIDE CRYSTALS WITH PERMEABLE GRAPHITE

• Main Authors: MEYER-FREDHOLM, MICHELE, M., L, PELL, MICHAEL, A
• Format: Patent
• Language: English; French
• Published: 10.10.2002
• Edition: 7
• Subjects: AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUSPOLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR; BASIC ELECTRIC ELEMENTS; CHEMISTRY; COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM,CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THERARE-EARTH METALS; CRYSTAL GROWTH; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; INORGANIC CHEMISTRY; METALLURGY; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITHDEFINED STRUCTURE; REFINING BY ZONE-MELTING OF MATERIAL; SEMICONDUCTOR DEVICES; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITHDEFINED STRUCTURE; SINGLE-CRYSTAL-GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL ORUNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL

The object of the present invention is a process of preparing an optical fluoride crystal containing barium fluoride, which comprises loading a crucible with a barium fluorine starting material crystal feedstock which contains at least one oxide as impurity, and an effective and non-excess amount of at least one fluorinating agent which is solid at ambient temperature, melting said mixture within said crucible, growing the crystal, by controlled cooling of the molten mixture, controlled cooling of said crystal to ambient temperature, recovering said crystal; and which is characterised in that the oxide(s) resulting from the reaction between said fluorinating agent(s) and said oxide(s), the impurity or impurities, can be discharged from said crucible, in view of the intrinsic permeability of the material constituting it. Said process is particularly adapted for preparing 157 nm transmitting lithography excimer laser optical fluoride crystals in graphite crucibles. The object of the present invention is a process of preparing an optical fluoride crystal containing barium fluoride , which comprises : loading a crucible with a barium fluoride starting material crystal feedstock which contains at least one oxide as impurity, and an effective and non-excess amount of at least one fluorinating agent which is solid at ambient temperature, melting said mixture within said crucible, growing the crystal, by controlled cooling of the molten mixture, controlled cooling of said crystal to ambient temperature, recovering said crystal; and which is characterised in that the oxide(s) resulting from the reaction between said fluorinating agent(s) and said oxide(s), the impurity or impurities, can be discharged from said crucible, in view of the intrinsic permeability of the material constituting it. Said process is particularly adapted for preparing 157nm transmitting lithography excimer laser optical fluoride crystals in graphite crucibles. L'invention concerne un procédé d'élaboration de cristal optique au fluorure, à base de fluorure de baryum, qui comprend les étapes suivantes: chargement d'un creuset avec une charge de cristal au fluorure de baryum tenant lieu de matériau de départ, renfermant au moins un oxyde en tant qu'impureté, et une quantité efficace et non excédentaire d'au moins un agent de fluoration solide à température ambiante; fusion du mélange dans ce creuset; croissance du cristal, par refroidissement contrôlé du mélange fondu; refroidissement contrôlé du cristal à température ambiante; récupération du cristal. Le ou les oxydes résultant de la réaction entre le ou les agents de fluoration et le ou les oxydes ainsi que l'impureté ou les impuretés peuvent être évacués du creuset, compte tenu de la perméabilité intrinsèque du matériau constitutif du creuset. Le procédé décrit se prête particulièrement bien à l'élaboration, dans des creusets en graphite, de cristaux de système optique au fluorure pour laser excimère en lithographie à transmission de longueur d'onde de 157 nm.