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  Collector with fastening devices for fastening mirror shellsThe Patent Description & Claims data below is from USPTO Patent Application 20080042079. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to a collector for a projection exposure apparatus which is operated in a scanning mode along a scanning direction with a wavelength .ltoreq.193 nm, preferably .ltoreq.126 nm, more preferably with wavelengths in the extreme UV (EUV)-region. Said collector receives light from a light source and illuminates an area in a plane to be illuminated. The collector comprises a plurality of rotational symmetric mirror shells which are arranged within each other about a common rotational axis. [0003] The invention further also provides an illumination system with such a collector, a projection exposure apparatus with an illumination system in accordance with the invention as well as a method for the exposure of microstructures. [0004] 2. Description of the Related Art [0005] Nested collectors for wavelengths .ltoreq.193 nm, especially wavelengths in the region of X-rays, have become known from a plurality of documents. [0006] U.S. Pat. No. 5,768,339 shows a collimator for X-rays, with the collimator comprising several paraboloidal reflectors. The collimator according to U.S. Pat. No. 5,768,339 is used to form into a parallel beam a isotropically radiated ray beam of an X-ray source. [0007] A nested collector for X-rays has become known from U.S. Pat. No. 1,865,441 which is used--as in the case of U.S. Pat. No. 5,768,339--to collimate isotropic X-rays into a parallel beam of rays. [0008] U.S. Pat. No. 5,763,930 shows a nested collector for a pinch plasma light source which is used to collect the radiation emitted by a light source and to focus the same in a waveguide. [0009] U.S. Pat. No. 5,745,547 shows several arrangements of multi-channel optics which are used for concentrating the radiation of a source, especially X-rays, in a point. In order to achieve a high transmission efficiency, the invention according to U.S. Pat. No. 5,745,547 proposes elliptically shaped reflectors. [0010] An arrangement has been disclosed in DE 30 01 059 C2 for the use in X-ray lithography systems which comprises parabolic mirrors arranged in a nested way between X-ray source and mask. These mirrors are arranged in such a way that the diverging X-rays are shaped into a parallel beam leaving the arrangement. [0011] The arrangement according to DE 30 01 059 is merely used for achieving a favorable collimation for X-ray lithography. [0012] The arrangement of nested reflectors as known from WO 99/27542 is used in an X-ray proximity lithography system in such a way that light of a light source is refocused so that a virtual light source is formed. The nested shells can have an ellipsoidal shape. [0013] A nested reflector for high-energy photon sources is known from U.S. Pat. No. 6,064,072 which is used to shape the diverging X-rays into a parallel beam bundle. [0014] WO 00/63922 shows a nested collector which is used to collimate a neutron beam. [0015] A nested collector for X-rays is known from WO 01/08162 which is characterized by a surface roughness of the inner reflective surface, the individual mirror shells of less than 12 .ANG. rms. The collectors shown in WO 01/08162 also comprise systems with multiple reflections, especially also Wolter systems, and are characterized by a high resolution, as is also demanded in X-ray lithography for example. [0016] In addition to resolution, high requirements are also needed regarding evenness, uniformity and telecentricity with respect to illumination lens systems for EUV lithography, such as in DE 199 03 907 or WO 99/57732. SUMMARY OF THE INVENTION [0017] It is an object of the invention to provide a collector for an illumination system for microlithography with wavelengths .ltoreq.193 nm, preferably .ltoreq.126 nm, more preferably for wavelengths in the EUV range, which collector has a sufficient mechanical stability and a high light efficiency. Especially any negative effect with respect to uniformity of the illumination in the field plane by the collector should be avoided. [0018] Various effects influence the uniformity of the illumination in the field plane. A first effect comes from the collector, especially the shadows from the holding devices of the collector shells and the shadows from the collector shells of finite thickness influence the uniformity, although an optical integrator may follow in the light path of the illumination system subsequent to the collector optics. [0019] In operation the nested collector is heated up. By heating up the mirror shells the optical properties of the collector are influenced and thus the uniformity in the field plane. The change of optical properties may be in first order a focal drift. Further spherical aberration and astigmatism, and higher order aberrations. [0020] To improve the uniformity in the field plane according to one aspect of the invention a nested collector which illuminates a plane on the image side and comprises a plurality of mirror shells which are rotational symmetric about a rotational axis and the individual mirror shells are held by fastening devices, the fastening devices are comprising support spokes extending in a radial direction. [0021] The support spokes are arranged in such a way that when they are projected into the plane to be illuminated on the image side they are inclined relative to the y-direction of the local system of coordinates in this plane on the image side. That is, the projections of the spokes in the plane have either a positive slope or a negative slope relative to the y-direction, and so, are non-parallel to the y-direction. In this application the y-direction is the direction of the local system of coordinates which is parallel to the scanning direction of a projection exposure apparatus which is operated in a scanning mode and the x-direction is the direction of the local system of coordinates which is perpendicular to the scanning direction. [0022] It generally applies that the mechanical stability is improved the more support spokes are used. In order to keep the loss of light by vignetting as low as possible by the support spokes extending in the radial direction, it is advantageous when the spokes are as narrow as possible. Especially preferably the support spokes have a shape which tapers in the radial direction towards the rotational axis. This leads to the advantage that a high stability is achieved and the loss of light by shading effects is limited because the percentage rate of shadowed area relative to the circumference of a shell is always approximately the same. This will be achieved when the width of the support spoke increases proportionally to the distance from the common rotational axis. Continue reading... Full patent description for Collector with fastening devices for fastening mirror shells Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Collector with fastening devices for fastening mirror shells patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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