Prospects for the development of optical systems for nanolithography

This paper discusses the principles under which high-resolution projection photolithographic objectives are created and the requirements on the optical materials used for them. It is shown that fluorite is one of the most promising materials for creating objectives for photolithography at wavelengths 248 and 193nm. A discussion is given of the prospects for developing lens-based projection objectives with high numerical aperture, the modern state of the production technology, and also methods for certifying the main optical parameters of photolithographic-quality fluorite. Fluorite crystals up to 300mm in diameter and 50mm thick have been fabricated and certified. The crystals grown using this technology have high transmittance (99.92–99.96% at λ=193nm), good optical homogeneity [Δn=(1–4)×10−6], and low birefringence (δ=0.5–2.0nm∕cm). The crystals have virtually no luminescence. Proposals are given for the development of photolithographic optics.

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