Optical element fabrication method, optical element, exposure apparatus, device fabrication method

Abstract

There is to provide an optical element fabrication method including the steps of forming a thin film onto a substrate, and eliminating a color center produced in the forming step by giving energy to the substrate.

Description

[0001] The present invention generally relates to optical element fabrication methods, and more particularly to a fabrication method for a transmission type optical element including a thin film. The present invention is suitably applicable for fabricating fluoride crystal materials such as calcium fluoride, magnesium fluoride, etc. suitable for various kinds of optical elements, lenses, window materials, prisms, etc. employed in a wide wavelength range, e.g., from the vacuum ultraviolet region to the far-infrared region.[0002] Fluoride crystal has distinguished characteristics, which other optical materials do not have, such as less dispersion for white light, high transmittance for light having a wavelength shorter than the ultraviolet region, etc., thus having been so far used for a telescope lens with high resolution and low aberration. Recently, applications to a lens in an illumination optical system and a projection optical system in an exposure apparatus have been reviewed w...

AI Technical Summary

Benefits of technology

0007] Accordingly, it is an exemplified object of the present invention to provide an optical element fabrication method, exposure apparatus, device fabrication method, and devices, the fabrication method that can reduce an optical absorption produced when a thin film is fabricated on a substrate and can fabricate an optical element having excellent optical characteristics. The present invention is especially effective when the substrate includes fluoride crystal(s).

Problems solved by technology

However, the shorter the wavelength becomes, the larger light's absorption, diffusion, and interference become, and thus, along with a shorter wavelength of light from a light source, the reflection of light on the surface of an optical element such as a lens and a mirror cannot be neglected.

However, if a thin film is formed onto a substrate by using the sputtering and CVD methods that use plasma, and by the vacuum evaporation method that uses an electron gun, an electric potential difference is produced among ion, electron and the substrate, and the ion and electron breaks into the substrate, thus damaging the substrate and the thin film formed on the substrate.

This damage would change a compositional ratio of chemical compounds, and impair crystallization, thereby deteriorating optical characteristics of an optical element.

This damage includes generation of optical absorption (the so-called color center that absorbs light).

Then, although it is electrically stable, it is hard for light to transmit it, thus reducing its transmittance.

In particular, optical absorption is noticeably observed in a light wavelength range equal to or shorter than 300 nm, thus presenting the problem that a transmission type optical element reduces its transmittance, being unable to obtain expected optical characteristics.

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