Abstract
ABSTRACT Optical lithography continues its transition to shorter wavelengths to support the semiconductor industrys production of faster microchips to meet evolving market demands. The next step for optical lithography is likely to use the F 2 excimer laser at 157.63 nm (157 nm, according to the industrys naming convention). At 157 nm, among the limited number of fluoride crystals with acceptable optical properties calcium fluoride is the only practical lens material for step and scan systems due to its readiness for mass production. Since the discovery of intrinsic birefringence in CaF 2 at deep ultraviolet (DUV) wavelengths, the optical lithography industry has developed a critical interest in measuring birefringence at 157 nm. In response to this need, we have developed a DUV birefringen ce measurement system. In this article, we describe the working principle, system construction, technical performance and selected applications for measuring lithography gr ade calcium fluoride lens bl anks at DUV wavelengths.
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