Reflective optical element, optical system and EUV lithography device

Abstract

In order to obtain optimal reflectivity on optical elements for the EUV and the soft X-ray range, multilayers constructed of a number of layers are used. Contamination or degradation of the surface leads to imaging defects and transmission losses. In the prior art, it has been attempted to counter a negative change in the surface by providing a cover layer system on the surface of the reflective optical element that should protect the surface. The invention renders the influence of the surface degradation manageable by a targeted selection of the distribution of thickness of the cover layer system, whereby at least one layer of the cover layer system has a gradient that is not equal to zero.

Description

CROSS REFERENCE [0001] This application is a continuation-in-part application of International Application No. PCT / EP2004 / 004368, filed Apr. 26, 2004 and published as WO 2004 / 097467 on Nov. 11, 2004, which claims the priority to German Application No. 103 19 005.8, filed Apr. 25, 2003.FIELD OF THE INVENTION [0002] The invention concerns a reflective optical element for the external ultraviolet and / or soft x-ray wavelength region with a cover layer system having at least one layer, whose spatial structure can be described in a Cartesian system of coordinates (x, y, z) with z=z(x, y). Other systems of coordinates are possible for describing the spatial structure. [0003] Moreover, the invention concerns an optical system or an EUV lithography device with at least two reflective optical elements for the extreme ultraviolet and / or soft x-ray wavelength region with at least one cover layer system. BACKGROUND OF THE INVENTION [0004] Multilayers composed of a plurality of layers are used to...

AI Technical Summary

Benefits of technology

[0012] The present invention is based on the principle of using not merely the selection of materials, but also the geometry of the cover layer system to render the general degradation and especially the contamination by carbon-containing substances as low as possible, or to make their influence manageable. By specific choice of the thickness distribution d(x, y) of the cover layer system as a function of its spatial coordinates, wherein at least one layer of the cover layer system should have a gradient not equal to zero, one can control how much contamination occurs at which places of the surface. In this way, the contamination can be calculated and factored in when operating or designing of reflective optical elements, optical systems, and EUV lithography appliances.

[0034] Semiconductor components produced with the help of the invented reflective optical elements or optical systems or EUV lithography appliances have the advantage of being produced with lower reject rates and lower cost. For on the one hand, the imaging quality is better since the degradation is manageable, and on the other hand longer lifetimes can be achieved for the devices.

Problems solved by technology

This generally leads to a degradation or contamination, e.g., by oxidation, carbon deposits, interdiffusion, material ablation, etc., of the multilayer surface.

These effects lead to imaging errors and transmission losses.

In the worst case, the desired imaging is totally impossible.

Thus, regeneration cycles must be provided during operation of the EUV lithography machine, which not only significantly increase the operating costs, but also in the extreme case lead to an irreversible damaging and, thus, may entail a replacement of the affected reflective optical elements.

While the protective layers of U.S. Pat. No. 5,958,605 and U.S. Pat. No. 6,228,512 provide a protection against degradation by the influence of oxygen, there still occurs a contamination from carbon-containing substances.

These lead to uncontrolled losses of reflectivity and changes in the wave front.

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