Magnesium fluoride (MgF<sub>2</sub>) single crystal is expected as the alternative of Quartz for polarizing materials in high
power lithography system. MgF<sub>2</sub> is anisotropic crystal and its physical properties are different along each crystal axes.
Therefore it is difficult to make large diameter single crystal by using Bridgman method which is mainly used for growth
of fluoride crystals.
We have been studying on making large diameter and high quality single crystal by using Czochralski (CZ) method
[1,2]. Previously we reported the stable growth of it with 150mm diameter. This time we succeeded to grow the crystal
with over 200mm diameter.
Additionally, by improving the purification process and growth process, we succeeded to reduce 75 percent of the
amount of color center induced by irradiation of ArF laser.
In the semiconductor lithography technology, the polarized illumination system is applied to make the resolution more
microscopic, therefore the polarizer material with excellent durability against the high power ArF laser has been
required. Magnesium fluoride (MgF<sub>2</sub>) is one of a suitable material because of its laser durability and high transparency
in VUV region. Previously we reported MgF<sub>2</sub> single crystal with diameter of 100mm by using the Czochralski (CZ)
method. By optimizing the crystal growth conditions, MgF<sub>2</sub> single crystals with over 150mm in diameter have been
stably grown. Also these crystals show good optical properties and crystallinity.