2 June 2000 Measurement of excimer-laser-induced birefringence in fused silica and calcium fluoride
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Fused silica and calcium fluoride are the standard lens materials for the 193 nm (ArF excimer laser) generation step and scan systems. In this paper, the author reports measurements of induced birefringence in both fused silica and calcium fluoride samples exposed to ArF excimer laser irradiation. A new birefringence measurement instrument, known as the ExicorTM system, was used for mapping birefringent images. Different patterns of induced birefringence in fused silica samples were observed for samples irradiated with 'unpolarized' and polarized excimer lasers. Birefringence induced in fused silica with linearly polarized excimer laser irradiation contradicts the traditional compaction model. The measurement result of a CaF2 element confirms that 193 nm excimer laser irradiation induces no observable birefringence in CaF2.
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Baoliang Bob Wang, Baoliang Bob Wang, } "Measurement of excimer-laser-induced birefringence in fused silica and calcium fluoride", Proc. SPIE 3998, Metrology, Inspection, and Process Control for Microlithography XIV, (2 June 2000); doi: 10.1117/12.386523; https://doi.org/10.1117/12.386523

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