| 摘要 |
A projection exposure apparatus capable of projecting and exposing mask pattern images onto a substrate by means of a optical projection system, the apparatus includes an optical illumination system capable of illuminating a mask utilizing an excimer laser illuminating light source in a wavelength range of 230 nm or less, and an optical projection system including optical members that include a calcium fluoride crystal with a total alkaline earth metal impurity content of 1x1018 atom/cm3 or less, and which projects images of the mask pattern onto a substrate. The calcium fluoride crystal is manufactured by a method including the steps of adding a fluorinating agent to a powdered calcium fluoride forming a mixture, placing the mixture in a growing crucible inside a vacuum furnace, and evacuating the vacuum furnace. Once the vacuum furnace is evacuated, the temperature is elevated a first time inside the vacuum furnace to a temperature exceeding a melting point of the mixture and is maintained at a predetermined constant temperature inside the vacuum furnace until a polycrystalline material is formed. The polycrystalline material is then cooled and the temperature inside the vacuum furnace is elevated until the polycrystalline material is melted, wherein crystal growth of the polycrystalline material is promoted and a crystal ingot is formed.
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