Corning Incorporated

Michele M L Meyer-Fredholm

Michael A Pell

The present invention is directed to a method of making large diameter metal fluoride sungle crystals that can be used in optical lithograpby systems, for example, excimer laser that operate below 200 nm. In addition, the invention is directed to metal fluoride single crystals suitable for use in such lithographic ststems, such fluoride crystals having a internal transmission of &#x2267;99.9% at 193 nm and &#x2267;99.0% at 157 nm.

Preparation of 157nm transmitting barium fluoride crystals with permeable graphite

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 characterized 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 a crystal, which comprises: loading a crucible with a mixture of the appropriate starting material 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 characterized 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 dimensions of said crucible and of the intrinsic permeability of the material constituting it. Said process is particularly adapted for preparing (mono)crystals of CaF in graphite crucibles.

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Avon, France

Michele M L Meyer-Fredholm