Abstract:
There is provided a grating apparatus for filtering wavelengths ≦100 nm. The grating apparatus includes multiple individual grating elements having grating lines. The individual grating elements are positioned one behind another on a curved support surface in relation to a plane spanned by the grating apparatus in a direction of beans of a light bundle that is incident on the grating apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of International Application No. PCT/EP03/02419, filed Mar. 10, 2003, which claims priority of German Patent Application No. 102 12 691.7, filed Mar. 21, 2002. The content of these applications is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a grating element for filtering wavelengths ≦100 nm, having multiple individual grating elements, the individual grating elements having grating lines resulting in a grating periodicity.  
         [0004]     2. Description of the Related Art  
         [0005]     In order to be able to reduce the structure widths for electronic components even further, particularly in the submicron range, it is necessary to reduce the wavelength of the light used for microlithography. The use of light having wavelengths less than 100 nm, e. g., lithography using soft x-rays, i.e., EUV lithography, for example, is conceivable.  
         [0006]     EUV lithography is one of the most promising future lithography technologies. Currently, wavelengths in the range of 11-14 nm, particularly 13.5 nm, are under discussion as the wavelengths for EUV lithography for a numeric aperture of 0.2-0.3. The image quality in EUV lithography is determined by the projection objective and by the illumination system. The illumination system is to provide the most uniform possible illumination of the field plane in which the structure-bearing mask, the reticle, is positioned. The projection objective images the field plane in an image plane, i.e., the wafer plane, in which a light-sensitive object is positioned. Projection exposure systems for EUV lithography are implemented using reflective optical elements. The shape of the field of an EUV projection exposure system is typically that of an annular field having a high aspect ratio of 2 mm (width)×22-26 mm (curve length). The projection systems are typically operated in scanning mode. Reference is made to the following publications in regard to EUV projection exposure systems: 
        W. Ulrich, S. Beiersdörfer, H. J. Mann, “Trends in Optical Design of Projection Lenses for UV and EUV lithography” in Soft X-ray and EUV Imaging Systems, W. M. Kaiser, R. H. Stulen (Editors), Proceedings of SPIE, Volume 4146 (2000), pp. 13-24, and     M. Antoni, W. Singer, J. Schultz, J. Wangler, I. Escudero-Sanz, B. Kruizinga, “Illumination Optics Design for EUV Lithography” in Soft X-ray and EUV Imaging Systems, W. M. Kaiser, R. H. Stulen (Editors), Proceedings of SPIE, Volume 4146 (2000), pp. 25-34.        
 
         [0009]     The content of each of these publications is included in its entirety in the present application.  
         [0010]     In illumination systems for wavelengths ≦100 nm, the problem exists that the light sources of illumination systems of this type emit radiation which may lead to undesired exposure of the light-sensitive object in the wafer plane of the projection exposure system and, in addition, optical components of the exposure systems, such as the multilayer mirror, are heated in this way.  
         [0011]     To filter out the undesired radiation, transmission filters, made of zircon, for example, are used in illumination systems for wavelengths ≦100 nm. Filters of this type have the disadvantage of high light losses. Furthermore, they may be destroyed very easily through thermal stress.  
         [0012]     As an alternative to this, it is possible to perform the filtering using grating elements, which have multiple individual gratings having a grating period assigned to the individual gratings, for example. In a method of this type, use is made of the circumstance that light of the 0 th  order of diffraction in particular, which corresponds to a significant component of radiation having wavelengths which are not of the used wavelengths, in the range of 7 to 25 nm, for example, may be filtered out with the help of a diaphragm down stream of the grating element in the beam path.  
         [0013]     Grating elements, such as reflection gratings, particularly echelette gratings having a total efficiency near 60%, have been known for sometime from monochromator construction for synchrotron radiation sources. Good results are obtained using gratings in a monochromator construction even when the monochromator is illuminated by a synchrotron radiation source having a high energy flux.  
         [0014]     The behavior at diffraction gratings is described by the grating equation 
 
 n (λ/ p )=sin α−sin β
 
 using the grating period p, the order of diffraction n, the angle of incidence in relation to the surface normal α, the angle of diffraction in relation to the surface normal β, and the wavelength λ. 
 
         [0015]     If one observes convergent or divergent radiation, the optical effect of the grating must be considered.  
         [0016]     Reference is made to the following publications, the content of whose disclosure is included in its entirety in the present application, in regard to the use of diffraction gratings in monochromators: 
        H. Petersen, C. Jung, C. Hellwig, W. B. Peatman, W. Gudat: “Review of plane grating focusing for soft x-ray monochromators”, Rev. Sci. Instrum. 66 (1), January 1995     M. V. R. K. Murty: “Use of convergent and divergent illumination with plane gratings”, Journal of the Optical Society of America, Volume 52, No. 7, July 1962, pp. 768-773     T. Oshio, E. Ishiguro, R. Iwanaga: “A theory of new astigmatism- and coma-free spectrometer”, Nuclear Instruments and Methods 208 (1993) 297-301        
 
         [0020]     A grating element may be used for spectral filtering in an illumination system for wavelengths ≦100 nm if the individual orders of diffraction and the wavelengths are clearly separated from one another.  
         [0021]     This is simplest in a focused beam. In this case, a focus or light source image having a defined diameter exists in the focal point. However, a certain aperture must be selected for the focused beam so that overall lengths which are too long do not result. For beam bundles at higher aperture, however, the grating design is more difficult, or greater aberrations are obtained.  
         [0022]     If the requirement of separating the individual orders of diffraction is fulfilled, complicatedly constructed grating elements result, having a continuously changing grating constant or an arrangement on a curved surface, for example. Gratings of this type may only be manufactured with a very large effort.  
         [0023]     Alternatively, the grating element may also be constructed from multiple individual gratings having continuously changing grating constants.  
         [0024]     The individual gratings are preferably designed as blaze gratings, which are optimized for maximum efficiency in one order of diffraction. Blaze gratings are known, for example, from Lexikon der Optik [Lexicon of Optics], edited by Heinz Hagerborn, pp. 48-49. They are distinguished by an approximately triangular groove profile.  
         [0025]     A grating element which is constructed from multiple individual gratings has the disadvantage that if the same blaze angle is used for the different individual gratings in the convergent beam path, because of the angular divergence of the incident beams, a strongly varying diffraction efficiency results in the 1st order, for example; i.e., η (1), depending on the point of incidence. If the gratings are implemented with different blaze depths depending on the position, the blaze depth differences of the different individual gratings are very large, which requires very complex manufacturing.  
       SUMMARY OF THE INVENTION  
       [0026]     The object of the present invention is thus to overcome the disadvantages of the related art, in particular to specify a grating apparatus that is easy to manufacture, separates the 0 th  and 1 st  orders of diffraction, and provides a grating apparatus, even in the convergent beam path, that has a largely uniform diffraction efficiency independently of the angle of incidence of the beams of the beam bundle, so that if a grating apparatus of this type is used in an illumination system, a largely homogeneous intensity distribution is implemented behind a diaphragm plane.  
         [0027]     The above-mentioned object is achieved in that the individual grating elements are positioned one behind another, in the direction of the beams of the beam bundle which is incident on the grating apparatus, on a curved surface in relation to the plane spanned by the grating apparatus. The curved surface is generally a surface having continuous curvature, the curvature of the surface not being spherical, but rather increasing with a decreasing angle of incidence.  
         [0028]     In a preferred embodiment, the curved support surface is a curved surface approximated by a continuous polygonal progression. This has the advantage that flat individual gratings may be used, which are easier to manufacture.  
         [0029]     The individual gratings positioned one behind another on a curved surface preferably each have variable grating periods. In this way, even better separation of the 0th and 1st orders of diffraction is achieved. If an average line density G of the individual grating elements is defined, the line density on the individual gratings varies by Δg and Δg is in the range 40 lines/mm≦Δg≦200 lines/mm.  
         [0030]     It is preferable if the individual grating elements, as described previously, for individual grating elements positioned on a continuous polygonal progression, each have a flat grating surface comprising the grating lines.  
         [0031]     As an alternative to this, the individual grating elements may each have an aspheric grating surface, comprising the grating lines, by which the required variation of the line density may be reduced.  
         [0032]     In order to prevent astigmatic fading of the intermediate image, which is generally caused by the diffraction of the convergent beam bundle on planar gratings, the grating lines of an individual grating element may be curved.  
         [0033]     The curvature of the support surface on which the individual grating elements are positioned is preferably selected so that the blaze angle of the individual grating elements implemented as blaze gratings varies so little that the diffraction efficiency deviates only slightly from the maximum blaze efficiency.  
         [0034]     In addition to the grating apparatus according to the present invention, the present invention also provides an illumination system having such a grating apparatus. The illumination system comprises an object plane and a field plane, at least one grating apparatus according to the present invention, and at least one physical diaphragm in a diaphragm plane, which is positioned downstream from the grating apparatus in the beam path from the object plane to the field plane.  
         [0035]     In an illumination system having two faceted optical elements, as is disclosed, for example, in U.S. Pat. No. 6,198,793 or U.S. Pat. No. 6,438,199, the content of whose disclosure is included in its entirety in the present application, a largely homogeneous intensity distribution, i.e., homogeneous illumination, is achieved particularly in the plane in which the mirror with field facets is positioned downstream of the physical diaphragm in the beam path.  
         [0036]     The at least one physical diaphragm in the illumination system is used for the purpose of avoiding stray light of other than the desired order of diffraction, particularly the 0 th  order of diffraction, having wavelengths well above 100 nm, reaching the illumination system. The at least one physical diaphragm preferably blocks the light of the 0 th  order of diffraction and the further orders of diffraction except for the desired order of diffraction, which is preferably the 1 st  order of diffraction. It is especially preferable if the beams have wavelengths in the range from 7 to 25 nm after the physical diaphragm due to the combination of grating and physical diaphragm.  
         [0037]     To generate a convergent light bundle, the illumination system may comprise a collector unit. The collector unit provides for the convergent light bundle, and when the convergent light bundle impinges onto the grating apparatus, the convergent light bundle is deflected.  
         [0038]     The focus of the light bundle for an n th  order of diffraction of the grating apparatus especially preferably comes to lie at the location of the physical diaphragm or in proximity to the physical diaphragm, wherein |n|=1.  
         [0039]     In order to avoid too large of a thermal load on the physical diaphragm in the diaphragm plane or on following optical elements, a part of the undesired radiation may be filtered out through further diaphragms in the illumination system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]     The present invention will be described in the following for exemplary purposes on the basis of the drawings:  
         [0041]      FIG. 1  shows an arrangement of a grating apparatus having individual gratings positioned one behind another in the beam path from the collector unit of an illumination system to a diaphragm  
         [0042]      FIG. 2  shows an exemplary embodiment of the present invention having 18 individual grating elements  
         [0043]      FIG. 3  shows a schematic sketch for deriving the characteristic values of the exemplary embodiment according to  FIG. 2   
         [0044]      FIGS. 4   a  and  4   b  show an illustration of a blaze grating for deriving the blaze depths and/or the blaze angle  
         [0045]      FIG. 5  shows the diffraction efficiency for grating elements, implemented as blazed gratings, which are made of different materials  
         [0046]      FIG. 6  shows an EUV projection exposure system having an illumination system according to the present invention. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0047]      FIG. 1  shows a grating apparatus  1  having multiple individual gratings  9 . 1 ,  9 . 2 ,  9 . 3  in the beam path of an illumination system. The individual gratings  9 . 1 ,  9 . 2 ,  9 . 3  are positioned one behind another in the beam direction. The light of a light source  3  is collected by a collector unit, e.g., collector  5 . In this example, the collector  5  is an ellipsoidal mirror which generates an image of the light source  3 . The collimated light bundle having an aperture of approximately NA=0.1 downstream of the collector  5  is deflected via the grating apparatus  1  in grazing incidence in such a way that the intermediate image of the light source generated by the grating through diffraction in the +1 st  order of diffraction comes to lie at a focus  16  in or near the diaphragm plane of a physical diaphragm  7 . 3 .  
         [0048]     Undesired radiation may already be filtered out by multiple partial diaphragms  7 . 1 ,  7 . 2  positioned in front of the physical diaphragm  7 . 3 , in order to reduce the thermal load on the physical diaphragm  7 . 3  having the circular opening, which is located in the focal plane of the desired order of diffraction, in this case the +1 st  order  16 . The partial diaphragms  7 . 1 ,  7 . 2  may additionally be cooled, which is not shown. The grating apparatus  1  may also be cooled, through a rear cooler, for example a rear cooling device  8 . The rear cooling device  8  is preferably a liquid cooling device having inlet and outlet  10 . 1 ,  10 . 2 . Through the grating apparatus  1  and the physical screen  7 . 3 , it is possible to completely block the 0 th  order, which comprises all wavelengths of the light source, in an illumination system that comprises an optical element according to the present invention and a diaphragm  7 . 3  positioned downstream therefrom. In addition, all higher orders except the +1 st  order are blocked.  
         [0049]     In the following, an exemplary embodiment of a grating apparatus according to the present invention having multiple individual gratings which are positioned on a curved support surface is to be specified. Identical components as in  FIG. 1  are provided with a reference number increased by 100. A collimated light bundle  100  is shown, which originates from the light source (not shown in  FIG. 2 ) and impinges onto the entire grating apparatus according to the present invention. The two edge beams  102 ,  104  and the center beam  106  are shown. Furthermore, the virtual intermediate image focus Z of the light source (not shown in  FIG. 2 ), which is generated by the collector (also not shown), is shown. The origin of a rectangular coordinate system in the x, y, and z directions is defined in the intermediate image focus Z. This coordinate system is shown in  FIG. 2 . All values specified in the following Table 1 are based thereon. Overall, the exemplary embodiment shown in  FIG. 2  comprises 18 individual grating elements. Exemplary embodiments having fewer than 18 individual gratings are also possible, having 10, 7, or 5 individual gratings, for example, without deviating from the idea of the present invention. The position of the individual grating elements, of which the individual grating elements  109 . 1 ,  109 . 2 ,  109 . 17 ,  109 . 18  are shown in  FIG. 2 , are specified in the following Table 1 in the intermediate image focus Z in the 0 th  order of diffraction in the x and y directions in relation to the coordinate system.  
         [0050]     The center beam  106  of the light bundle  100  is coincident with the coordinate axis in the x direction for y=0 of the coordinate system in the intermediate image focus Z. Furthermore, a normal  111  is shown in  FIG. 2 , and the angles α, φ, and ω for the first individual grating element  109 . 1 , which are shown again in greater detail in  FIG. 3 , are also indicated in  FIG. 2 . Identical components as in  FIG. 2  have the same reference numbers. Each individual grating element absorbs a partial light bundle  100 . 1  of the total light bundle  100  originating from the light source. Each partial light bundle comprises a lower edge beam  104 . 1  and an upper edge beam  102 . 1  and a center beam  106 . 1 . α identifies the angle of incidence of a beam, in this case the center beam  106 . 1  of the incident partial light bundle  100 . 1  in relation to the normal  111 . 1  of the individual grating elements  109 . 1 , which is perpendicular to the grating surface, β identifies the angle of emergence in the order of diffraction, in this case the +1 st  order of diffraction, of a diffracted beam, in this case the diffracted center beam  106 . 1  of the partial light bundle  100 . 1  in relation to the normal  111 . 1 . An intermediate image of the light bundle diffracted in the +1 st  order of diffraction comes to lie at a focus  113  in a plane of a physical diaphragm  107 . 3 . The origin of the x, y, z coordinate system is defined as described in  FIG. 2  by the virtual intermediate image focus Z.  
         [0051]     The angle φ identifies the angle of an incident beam, such as the center beam  106 . 1  of the partial light bundle in relation to the coordinate axis in the x direction at y=0. The angle ω identifies the angle of inclination of the individual grating element, in this case the individual grating element  109 . 1 , in relation to the x coordinate axis at y=0. The angle χ identifies the angle of emergence of a diffracted beam of the partial light bundle, in this case the center beam  106 . 1 . The following interrelationships apply: 
 
α=90°−ω−φ and 
 
β=90°−χ+ω
 
         [0052]     The angles α, φ, and ω thus defined are specified for all individual grating elements of the entire grating apparatus composed thereof in Table 1. The angles α and φ are each specified for the lower and upper edge beams and the center beam of a partial light bundle incident on the particular individual grating element, and the angle ω identifies the angle of inclination of the particular individual grating in relation to the x-axis of the coordinate system specified by the virtual intermediate image focus.  
         [0053]     The individual gratings, as may be seen from  FIG. 3 , are positioned on a continuous polygonal progression, i.e., the edges of neighboring individual gratings directly adjoin one another, so that with grazing incidence of the light bundle  100 , mutual shadowing of the partial light bundles is not possible. The abutment of the edges of neighboring individual gratings is shown for the individual gratings  109 . 1  and  109 . 2 . Besides the position coordinates x and y and the angle coordinates φ, α, and ω, the blaze angle ε and the grating line density G and line/mm are specified for the exemplary embodiment in Table 1 having 18 individual gratings.  
         [0054]     The blaze angle is defined in  FIGS. 4   a  and  4   b.    
         [0055]     Furthermore, the physical diaphragm  107 . 3  downstream from the individual grating element  109 . 1  is shown in  FIG. 3 . The focus  113  of the light source (not shown in  FIG. 3 ) generated by the +1 st  order of diffraction of the individual grating elements  109 . 1 ,  109 . 2 ,  109 . 17 ,  109 . 18  lies in the plane of the physical diaphragm  107 . 3 .  
         [0056]     The width of the 18 individual gratings positioned on a support  115  is reduced with falling angle of incidence a from 51.25 mm for the 1 st  individual grating  109 . 1  to 18.03 mm for the 18 th  individual grating  109 . 18 . The support  115  may be cooled. The support  115  spans a plane E which is tilted at an angle ω Center  in relation to the x coordinate axis. The individual grating elements are positioned on a curved surface K of the support  115  in relation to this plane E. The individual grating elements are tilted by an angle ω′=ω Center −ω in relation to the plane E. The curved support surface is a continuous polygonal progression without restriction in this case. For the exemplary embodiment shown in  FIG. 3 , the position coordinates x, y and the angles φ, α, the blaze angle ε, and the grating constant G are specified in Table 1 in the respective columns. Furthermore, the angle of inclination ω of the particular individual grating element is specified. Since the individual grating elements are planar in the exemplary embodiment shown, it is only necessary to specify an angle of inclination ω to characterize the position of the individual grating element on the curved support surface. The position coordinates x, y and the angles φ, α, the blaze angle ε, and the grating constant G are specified for three points of an individual grating in each case, specifically the two edge points of the individual grating in the x direction and the central position of the particular individual grating in the x direction. The edge points correspond to the points of incidence of the edge beams of the particular partial light bundle and the center position corresponds to the point of incidence of the center beam of the particular light bundle. The position of the intermediate image in the −1 st  order of diffraction is at x=54.604 mm and at y=208.885 mm in the y direction.  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     TABLE 1                           Grating element having individual gratings positioned on a       continuous polygonal progression                X   Y   φ   α   ε               [mm]   [mm]   [°]   [°]   [°]   G [L/mm]                        Individual grating 1 ψ  = 12.70033°                834.9   −93.01   −6.70   84.00   1.38   459.13           809.9   −92.38   −6.51   83.81   1.42   488.34           784.9   −86.74   −6.31   83.61   1.47   520.39            Individual grating 2 ψ  = 12.81684°                784.9   −86.74   −6.31   83.49   1.35   479.20           762.84   −81.72   −6.11   83.30   1.39   507.72           740.79   −76.71   −5.91   83.09   1.43   538.83            Individual grating 3 ψ  = 12.92932°                740.79   −76.71   −5.91   82.98   1.32   496.65           719.48   −71.82   −5.70   82.77   1.36   526.91           698.18   −66.92   −5.48   82.55   1.41   556.00            Individual grating 4 ψ  = 13.03754°                698.18   −66.92   −5.48   82.44   1.30   516.91           677.69   −62.17   −5.24   82.20   1.34   549.08           657.19   −57.43   −4.99   81.96   1.38   584.30            Individual grating 5 ψ  = 13.14127°                657.19   −57.43   −4.99   81.85   1.28   540.40           637.54   −52.85   −4.74   81.60   1.32   574.63           617.90   −48.26   −4.47   81.32   1.36   612.17            Individual grating 6 ψ  = 13.24027°                617.90   −48.26   −4.47   81.23   1.26   567.58           599.15   −43.85   −4.19   80.95   1.30   604.04           580.40   −39.44   −3.89   80.65   1.34   644.07            Individual grating 7 ψ  = 13.33437°                580.40   −39.44   −3.89   80.55   1.25   598.93           562.58   −35.21   −3.58   80.25   1.29   637.79           544.75   −30.99   −3.26   79.92   1.33   680.49            Individual grating 8 ψ  = 13.42343°                544.75   −30.99   −3.26   79.83   1.24   634.94           527.89   −26.96   −2.92   79.50   1.28   676.38           511.02   −22.94   −2.57   79.15   1.32   721.91            Individual grating 9 ψ  = 13.50738°                511.02   −22.94   −2.57   79.06   1.24   676.13           495.12   −19.12   −2.21   78.70   1.28   720.31           479.22   −15.30   −1.83   78.32   1.32   768.83            Individual grating 10 ψ  = 13.58621°                479.22   −15.30   −1.83   78.24   1.24   722.99           464.29   −11.69   −1.44   77.86   1.28   770.04           449.36   −8.08   −1.03   77.44   1.32   821.70            Individual grating 11 ψ  = 13.65996°                449.36   −8.08   −1.03   77.37   1.25   775.96           435.39   −4.69   −.62   76.96   1.29   826.02           421.42   −1.29   −.18   76.52   1.33   880.91            Individual grating 12 ψ  = 13.72876°                421.42   −1.29   −.18   76.44   1.26   835.43           408.39   1.89   .27   76.01   1.30   888.61           395.36   5.08   .74   75.54   1.34   946.81            Individual grating 13 ψ  = 13.79277°                395.36   5.08   .74   75.47   1.28   901.74           383.24   8.05   1.20   75.00   1.32   958.11           371.11   11.03   1.70   74.51   1.36   1019.67            Individual grating 14 ψ  = 13.85221°                371.11   11.03   1.70   74.45   1.30   975.12           359.88   13.80   2.20   73.95   1.34   1034.71           348.60   16.58   2.72   73.42   1.38   1099.62            Individual grating 15 ψ  = 13.90732°                348.60   16.58   2.72   73.37   1.32   1055.70           338.16   19.16   3.24   72.85   1.36   1118.51           327.72   21.75   3.80   72.30   1.40   1186.72            Individual grating 16 ψ  = 13.9584°                327.72   21.75   3.80   72.24   1.35   1143.51           318.05   24.15   4.34   71.70   1.39   1209.48           308.38   26.56   4.92   71.12   1.43   1280.9            Individual grating 17 ψ  = 14.00571°                308.38   26.56   4.92   71.07   1.38   1238.46           299.42   28.79   5.49   70.50   1.42   1307.50           290.46   31.03   6.097   69.90   1.45   1381.97            Individual grating 18 ψ  = 14.04956°                290.46   31.03   6.10   69.85   1.41   1340.32           282.15   33.11   6.69   69.26   1.45   1412.31           273.85   35.18   7.32   68.63   1.48   1489.64                      
 
         [0057]     In a second exemplary embodiment, a grating apparatus according to the present invention comprises a total of 8 individual gratings.  
         [0058]     The grating apparatus having 8 individual gratings extends over a total of 521.5 mm in the X direction. The 8 individual gratings are flat individual grating elements which are positioned next to one another on a continuous polygonal progression.  
         [0059]     The angle of inclination ω of the flat grating surfaces to the X-axis increases continuously and nearly linearly from 12.4° for the first element up to 13.6° for the eighth element.  
         [0060]     The angle of incidence a falls from 83.8° for the first element to 69.4° for the eighth element. The average blaze angle ε of each of the individual elements is constant at 1.21° and has a minimum variation of ±0.2% and a maximum variation of ±7.9% over the surface of the individual elements.  
         [0061]     The average groove density of the individual elements rises continuously from 374 L/mm for the first element to 1160 L/mm for the eighth element, the largely linear variation of the groove density dG/dX over the surface increasing continuously from 1.1 mm −1  for the first element up to 7.1 mm −1 .  
         [0062]     Using a grating apparatus of this type having a total of 8 individual gratings, in combination with the collector mirror element, a punctual, spectrally decomposed image of the light source is generated in the screen surface at the wavelength λ=13.5 nm. The minimum distances of the images of the source generated in the 0th and 2nd orders of diffraction from the focal point of the 1st order of diffraction on the screen surface are &gt;14 mm and &gt;12 mm, respectively.  
         [0063]     The individual grating elements are coated, for example, with a ruthenium reflection coating, which has the highest reflectivity of all known metal coatings for λ=13.5 nm. The blaze efficiency in the 1st order of diffraction calculated for this reflection coating rises continuously from 65.7% for the first element to 68.1% for the fourth element and then falls to 56.8% for the eighth element.  
         [0064]     The special advantage of this grating apparatus having a total of 8 individual gratings is that only a small number of 8 individual grating elements is necessary, the average blaze angle on all individual elements is constant, and therefore the grating grooves of all individual elements may be produced using the same technological method (e.g., mechanical grating graduation or holographic exposure with subsequent ion beam etching), all individual elements are used in a blaze arrangement, so that the diffraction efficiency is an average of 64.9%, and the efficiency only varies by +3.2/−8.1%, so that a largely homogeneous intensity distribution is achieved over the cross-section of the light bundle passing the diaphragm, and the radiation passing the diaphragm having an opening diameter of 2 mm, for example, and used in the further illumination system, which has wavelengths between 13.0 and 14.0 nm, may be separated from the radiation emitted by the source having other wavelengths with an intensity ratio of &gt;1000/1.  
         [0065]     In order to obtain a grating apparatus  101  having optimal diffraction efficiency η (+1) in the +1st order, each individual grating of the grating apparatus  101  is implemented as a blaze grating.  
         [0066]     In  FIG. 4   a,  a blaze grating having an approximately triangular groove profile is shown. An incident beam is incident on the individual grating designed as a blaze grating, such as the individual grating  209 . 1  having the grating period P;  202  identifies the beam diffracted at the grating in the 0th order and  204  identifies the beam diffracted in the +1 st order,  206  identifies the beam diffracted in the −1st order, and  208  identifies the beam diffracted in the +2nd order. The following equation results for the blaze angle as a function of the values cited above: 
 
ε=arctan( B/P ) 
 
         [0067]     In this case, B identifies the blaze depth and P identifies the grating period. In  FIG. 4   b,  the condition is given by the diffraction geometry shown 
 
ε=(α−β)/2 
 
 that the incident beam  200  incident with the angle α in relation to the grating normal is diffracted with the blaze efficiency associated with blaze angle ε at the diffraction angle β in relation to a grating normal  211  into the beam in the direction toward the focus  113  in  FIG. 3 . Under this blaze condition, the grating equation assumes the form: 
 
 n·λ/p =sin(α)−sin(α−2ε)=sin(θ/2+ε)−sin(θ/2−ε) 
 
 in which 
 
θ=α+β
 
 identifies the deflection angle between incident beam  200  and beam  204 . 
 
         [0068]     As  FIG. 5  shows, the diffraction efficiency in the +1st order η (+1) is a function of the position X on the grating apparatus and on the materials used in the grating surface and/or the reflection coating applied to the grating. The x-dependence of the diffraction efficiency is determined by the x-dependence of the angle of incidence α and the blaze angle ε.  
         [0069]     In  FIG. 5 , reference number  1000  identifies the diffraction efficiency η (−1) at a wavelength of λ=13.5 nm for ruthenium, reference number  1002  for palladium, reference number  1004  for rhodium, and reference number  1006  for gold.  
         [0070]     As may be seen from  FIG. 5 , the highest efficiency is to be achieved with ruthenium, at 0.7. However, a coating made of palladium or rhodium, which have better long-term properties, has an efficiency η (−1) of 0.67, which is only worse by 3%. Gold is typically used in synchrotron gratings, but has significantly worse efficiency than the above-mentioned materials at λ=13.5, as may be seen from the curve  1006 .  
         [0071]     An EUV projection exposure system having a grating apparatus according to the present invention is shown in  FIG. 6 . All components which are identical to components in the preceding figures have a reference number increased by 2000. The EUV projection exposure facility comprises a light source  2003 , and a collecting optical component, e.g., a collector  2005 , which is implemented as a nested collector in accordance with German Patent Application DE-A-10102934, filed on Jan. 23, 2001 with the German Patent Office (counterpart of U.S. patent application Publication No. 2003-0043455 A1), the content of which is included in its entirety in the present application. The collector  2005  images the light source  2003  lying in the object plane of the illumination system in an image of the light source or a secondary light source  2004  at a focus  2016  in or near a plane of a physical diaphragm  2007 . 3 .  
         [0072]     In the present case, the light source  2003 , which may be a laser plasma source or a plasma discharge source, for example, is positioned in the object plane of the illumination system; the image of the primary light source, which is also referred to as the secondary light source, comes to lie in the image plane of the illumination system.  
         [0073]     Additional diaphragms  2007 . 1 ,  2007 . 2  are positioned between grating apparatus  2001  and the physical diaphragm  2007 . 3 , in order to block the light of undesired wavelengths, particularly wavelengths greater than 30 nm. According to the present invention, the focus of the −1 st  order comes to lie in the plane in which physical diaphragm  2007 . 3  is situated, i.e., the light source  2003  is imaged nearly stigmatically in the plane of the physical diaphragm  2007 . 3  by the collector and grating spectral filter in the −1 st  order of diffraction. The imaging in all other orders of diffraction is not stigmatic.  
         [0074]     Furthermore, the illumination system of the projection system comprises an optical system  2020  for shaping and illuminating the field plane  2022  with an annular field. As a mixing unit for homogeneous illumination of the field, the optical system comprises two faceted mirrors  2029 . 1 ,  2029 . 2 , as well as two imaging mirrors  2030 . 1 ,  2030 . 2  and a field-forming grazing-incidence mirror  2032 . Additional diaphragms  2007 . 4 ,  2007 . 5 ,  2007 . 6 ,  2007 . 7  for suppressing stray light are positioned in the optical system  2020 .  
         [0075]     The first faceted mirror  2029 . 1 , the field faceted mirror, generates multiple secondary light sources in or near the plane of the second faceted mirror  2029 . 2 , the pupil faceted mirror. Since, using the grating apparatus according to the present invention, the intensity distribution in and downstream of the diaphragm plane of the physical diaphragm  2007 . 3  is homogenized, a largely homogeneous intensity distribution, i.e., homogeneous illumination, is achieved on the facetted mirror  2029 . 1  (i.e., mirror having field facets). The following imaging optic images the facetted mirror  2029 . 2  (i.e., mirror having pupil facets) in the exit pupil  2034  of the illumination system, which comes to lie in the entrance pupil of a projection objective  2026 . The angles of inclination of the individual facets of the first and second faceted mirrors  2029 . 1 ,  2029 . 2  are laid out in this case so that the images of the individual field facets of the first faceted mirror  2029 . 1  overlap in the field plane  2022  of the illumination system and thus a largely homogenized illumination of the structure-bearing mask, which comes to lie in the field plane  2022 , is made possible. The segment of the annular field is implemented via a field-forming grazing-incidence mirror  2032  which is operated using grazing incidence.  
         [0076]     A double-faceted illumination system is disclosed, for example, in U.S. Pat. No. 6,198,793, and imaging and field-forming components are disclosed in PCT/EP/00/07258. The content of the disclosure of these publications is included in its entirety in the present application.  
         [0077]     The structure-bearing mask positioned in the field plane  2022 , which is also referred to as a reticle, is imaged in the image plane  2028  of the field plane  2022  with the help of the projection objective  2026 . The projection objective  2026  is a 6-mirror projection objective, as is disclosed, for example, in U.S. patent application Publication No. 2002-0056815, the content of which is included in its entirety in the present application. The object to be exposed, such as a wafer, is positioned in the image plane  2028 .  
         [0078]     The present invention specifies an optical element for the first time, with which it is possible to select undesired wavelengths directly after the primary light source, homogenization of the intensity distribution in and behind the diaphragm plane of the physical diaphragm in an illumination system being achieved through an arrangement of multiple individual gratings on a curved support surface, on a continuous polygonal progression, for example. In addition, the manufacturing of the grating apparatus is greatly simplified, since the blaze angle differences on the different gratings are minimized.  
       LIST OF REFERENCE NUMBERS  
       [0000]    
       
           1  grating apparatus  
           3  light source 5  collector  
           7 . 1 , 7 . 2  partial diaphragms  
           7 . 3  physical diaphragm  
           8  rear cooling device  
           9 . 1 , 9 . 2 , 9 . 3  individual gratings  
           10 . 1 , 10 . 2  inlet and outlet of the cooling device  
           16  focus  
           100 , 100 . 1  collimated light bundle and/or partial light bundle originating from the light source  
           101  grating element  
           102 , 102 . 1  upper edge beam of the light bundle and/or partial light bundle incident from the light source  
           104 , 104 . 1  lower edge beam of the light bundle and/or partial light bundle incident from light source  
           106 , 106 . 1  center beam of the light bundle and/or partial light bundle incident from the light source  
           107 . 3  physical diaphragm  
           109 . 1 , 109 . 2 ,  109 . 17 ,  109 . 18  individual gratings  
           111 , 111 . 1  normals  
           113  focus  
           115  support  
           200  incident beam  
           202  beam diffracted in the 0th order  
           204  beam diffracted in the 1st order  
           206  beam diffracted in the −1st order  
           208  beam diffracted in the +2nd order  
           211  grating normal  
           1000 , 1002 ,  1004 , 1006  diffraction efficiency η (−1) for different materials  
           2001  grating apparatus  
           2003  light source  
           2004  secondary light source  
           2005  collector  
           2007 . 1 ,  2007 . 2  diaphragms  
           2007 . 3  physical diaphragm  
           2007 . 4 ,  2007 . 5 ,  2007 . 6 ,  2007 . 7  diaphragms  
           2016  focus  
           2020  optical system  
           2022  field plane  
           2026  projection objective  
           2028  image plane  
           2029 . 1 ,  2029 . 2  faceted mirror  
           2030 . 1 ,  2030 . 2  imaging mirror  
           2032  field-forming grazing incidence mirror  
           2034  exit pupil of the illumination system  
          Z virtual intermediate image focus in the 0th order  
          α angle of incidence of a beam in relation to the grating normal  
          φ angle of a beam in relation to the x coordinate axis  
          ω angle of inclination of an individual grating