Structure and optical property of large-size CaF<sub>2</sub> single crystals grown by the CZ method

I. Masada; T. Nawata; Y. Inui; T. Date; T. Mabuchi; E. Nishijima; T. Fukuda

doi:10.1117/12.657249

15 March 2006 Structure and optical property of large size CaF₂ single crystals grown by the CZ method

I. Masada, T. Nawata, Y. Inui, T. Date, T. Mabuchi, E. Nishijima, T. Fukuda

Proceedings Volume 6154, Optical Microlithography XIX; 61542P (2006) https://doi.org/10.1117/12.657249
Event: SPIE 31st International Symposium on Advanced Lithography, 2006, San Jose, California, United States

Abstract

CaF₂ single crystals are required for the most suitable lens materials for the ArF laser lithography stepper because of its excellent transparency and laser durability in the DUV region. We have succeeded in growing the large size and high quality CaF₂ single crystals with both <111> and <100> orientation, and the diameter of 300mm by means of the Czochralski (CZ) method. The refractive index homogeneity is one of the most important optical properties required for the lithography lens material. Particularly, the residual homogeneity which is a high-order refractive index distribution after subtraction of Zernike 36 coefficient is very important. The vein-like striations were observed in the residual homogeneity pattern of the CaF₂ single crystals. The structure of CaF₂ single crystal correlating with the residual homogeneity is characterized by using the reflection X-ray topography. It is observed that the structure of CaF₂ single crystal composed with sub-grains parted by the small-angle tilt boundaries. The sub-grains are grown along the growth direction. It is understood that the large angle tilt type sub-boundaries among the domains composed of small sub-grains correspond to the vein-like striations. In the growth of CaF₂ single crystal, the sub-grain structure of seed is introduced into grown crystal. While the bending of crystal lattice plane from the neck toward the shoulder lead to the large angle tilt type sub-boundaries. Use of high crystalline seed and control of crystal lattice plane in the shoulder are effective in the growth of high crystalline CaF₂ single crystal getting good residual homogeneity.

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I. Masada, T. Nawata, Y. Inui, T. Date, T. Mabuchi, E. Nishijima, and T. Fukuda "Structure and optical property of large size CaF₂ single crystals grown by the CZ method", Proc. SPIE 6154, Optical Microlithography XIX, 61542P (15 March 2006); https://doi.org/10.1117/12.657249

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KEYWORDS

Crystals

X-rays

Single crystal X-ray diffraction

Diffraction

Optical properties

Refractive index

Deep ultraviolet

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