Reflective optical element and EUV lithography appliance

Abstract

The invention relates to a reflective optical element and an EUV lithography appliance containing one such element, said appliance displaying a low propensity to contamination. According to the invention, the reflective optical element has a protective layer system consisting of at least one layer. The optical characteristics of the protective layer system are between those of a spacer and an absorber or correspond to those of a spacer. The selection of a material with the smallest possible imaginary part and a real part which is as close to 1 as possible in terms of the refractive index leads to a plateau-type reflectivity course according to the thickness of the protective layer system between two thicknesses d1 and d2. The thickness of the protective layer system is selected in such a way that it is less than d₂.

Description

CROSS REFERENCE [0001] This application is a continuation-in-part application of International Application No. PCT / EP2004 / 002014, filed Mar. 1, 2004 and published as WO 2004 / 079753 on Sep. 16, 2004, which claims the priority to German Application No. 103 09 084.3, filed Mar. 3, 2003.FIELD OF THE INVENTION [0002] The invention concerns a reflective optical element for the EUV and soft X-ray wavelength region, having a multilayer system and a protective layer system, wherein the side of the multilayer system facing the protective layer system terminates in an absorber layer. Furthermore, the invention concerns an EUV lithography appliance with a reflective optical element of this kind. BACKGROUND OF THE INVENTION [0003] Multilayers are composed of periodic repetitions, and in the most simple case a period consists of two layers. The one layer material should consist of a so-called spacer material, while the other layer material should consist of a so-called absorber material. Spacer m...

AI Technical Summary

Benefits of technology

[0023] In another preferred embodiment, the protective layer system ends toward the vacuum with a layer of a material that is inert to energy injection, that is, to bombardment with EUV protons or to external electric fields. This decreases the probability of spontaneous electron emission, which in turn might split apart the residual gases into reactive cleavage products. Hence, the deposition of contamination on the protective layer system is further reduced. One can influence the inertia to external electromagnetic fields, for example, by giving the surface the lowest possible relief and / or using materials that have a large gap between the valency band and the conduction band. Especially preferred for this are the materials Nb, BN, B4C, Y, amorphous carbon, Si3N4, SiC, as well as silicon dioxide in various stoichiometric relations. The silicon dioxide can be in the amorphous or polycrystalline, or possibly even the crystalline state.

Problems solved by technology

Although EUV lithography appliances have a vacuum or a residual gas atmosphere in their interior, it is not entirely possible to prevent hydrocarbons and / or other carbon compounds from being inside the appliance.

These carbon compounds are split apart by the extreme ultraviolet radiation or by secondary electrons, resulting in the depositing of a carbon-containing contamination film on the optical elements.

This contamination with carbon compounds leads to substantial reflection losses of the functional optical surfaces, which can have a considerable influence on the economic effectiveness of the EUV lithography process.

The contamination leads not only to reflectivity losses, but also to imaging errors, which in the worst case make an imaging impossible.

These significantly increase the operating costs.

But the cleaning cycles not only increase the down time, but also entail the risk of worsening of the homogeneity of the layer thickness of the reflective optical elements and the risk of increasing the surface relief, which leads to further reflectivity losses.

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