Fluoride crystal, optical article, and production method

A fluoride crystal containing at least one kind of atoms selected from the group consisting of Zn, Cd, Pb, Li, i and Na with a content of 10 ppm or less, and containing oxygen with a content of 50 ppm or less.

A method of producing a fluoride crystal comprising conducting a refining step of adding a scavenger to a raw material of calcium fluoride and refining the raw material at least once, and a crystal growth step of further adding the scavenger to the refined raw material and growing a crystal by using a crucible lowering method, wherein an amount of the scavenger to be added in a first refining step is 0.04 to 0.1 mol % based on the raw material, and wherein a total amount of the scavenger to be added in the subsequent refining steps and the crystal growth step is 10% to 50% based on the amount of the scavenger to be added in the first refining step.

A method of producing a fluoride crystal comprising conducting a refining step of adding a scavenger to a raw material of fluoride and refining the raw material at least once, and a crystal growth step of further adding the scavenger to the refined raw material and growing a crystal, wherein an amount of the scavenger to be added in a first refining step is 0.04 to 0.1 mol % based on the raw material, and wherein a total amount of the scavenger to be added in the subsequent refining steps and the crystal growth step is 10% to 50% based on the amount of the scavenger to be added in the first refining step.

A method of producing a fluoride crystal comprising conducting a refining step of adding a scavenger to a raw material of fluoride and refining the raw material, and a crystal growth step of further adding the scavenger to the refined raw material and growing a crystal, wherein an amount of the scavenger to be added in the refining step is 0.04 to 0.1 mol % based on to the raw material, and wherein an amount of the scavenger to be added in the crystal growth step is 10% to 50% based on the amount of the scavenger to be added in the refining step.

A method of producing a fluoride crystal comprising conducting a refining step of adding a scavenger to a raw material of fluoride and refining the raw material at least twice, and a crystal growth step of further adding the scavenger to the refined raw material and growing a crystal, wherein an amount of the scavenger to be added in a first refining step is 0.04 to 1 mol % based on the raw material, and wherein a total amount of the scavenger to be added in the subsequent refining steps and the crystal growth step is 10% to 50% based on the amount of the scavenger to be added in the first refining step.

An exposing apparatus comprising an illuminating light source, a stage for mounting an object to be exposed, and a plurality of optical articles provided in at least one of an optical illuminating system and an optical projection system, wherein at least one of the optical articles comprises a fluoride crystal having an internal transmittance of 70% or more with respect to a 135 nm wavelength light, and containing at least one kind of atoms selected from the group consisting of Zn, Cd, Pb, Li, Bi and Na with a content of 10 ppm or less.