In 2001, under the technical support by Prof. Fukuda from Tohoku University,
Tokuyama Corporation started to develop the large diameter Calcium Fluoride (CaF₂) single crystal by using Czochralski (CZ) method. The goal of this development is to get in operation of Fluoride Single Crystal Business. 'Large diameter', 'CZ method' and 'Fluoride materials' are 3 key words of our project. We have been established 4 core technologies, 'Large diameter single crystal growth', 'CZ method furnace', 'Mass production', 'Optical evaluation for Lithography', and also have been acquired 'processing' and 'annealing' technologies.
In 2004, we have become the first in the world to successfully grow ultra-large diameter (300mm) CaF₂ single crystals by the CZ technique. We made efforts to improve the crystal qualities in order to satisfy the requirements for optical material of next generation lithography.
A transmittance, a laser durability, a homogeneity of refractive index and a stress birefringence are the four major optical properties. Because of growth conditions have significant influence for the quality of single crystals, we have to carefully control the growth conditions such as temperature gradient, growth rate and melt convection. Also we need to optimize the annealing process to reduce the internal stress. As a consequence of our research, we find out the CZ method has some advantages and good properties in compare to another method. Last year, Tokuyama CaF₂ single crystals have been adopted by 193 nm lithography system. Now we have to establish mass production technology with a high productivity and stability. And also, we have been developed other fluoride materials such as MgF₂ and BaLiF₃. The mission of this development is not only to market entry but also to suggest Tokuyama Research & Development capability.

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