CaF_2 Single Crystal for Semiconductor Lithography(<Special Issue>Crystal Growth Technology of Fluoride and Oxide Developed from the Viewpoint of Their Material and Functional Properties)

Abstract

Semiconductor lithography plays an important role in miniatur-izing electronic devices with high integration, and the material which constitutes the optical system of a stepper machine serves as a critical element in determining the quality and stability in mass production of integrated circuits. CaF_2 single crystals, which excel synthetic quartz in transmittance, are the preferred lens material in such stepper machines. In this review, we report our recent work on CaF_2 crystal growth and its quality improve-ment such as reduced stress birefringence, higher refractive index homogeneity and higher laser resistance.