Abstract:
Illumination optics that can be used, for example, for EUV projection microlithography are disclosed. Also disclosed are illumination systems provided with such illumination optics, projection exposure apparatuses provided with such illumination systems, related methods of manufacturing microstructured elements, and microstructured elements obtained by these methods.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to German patent application serial number 10 2006 056 035.3, filed Nov. 28, 2006, which is hereby incorporated by reference. 
     FIELD 
     The disclosure relates to illumination optics that can be used, for example, for EUV projection microlithography. The disclosure also relates to illumination systems provided with such illumination optics, projection exposure apparatuses provided with such illumination systems, related methods of manufacturing microstructured elements, and microstructured elements obtained by these methods. 
     BACKGROUND 
     Projection exposure apparatuses are known and are disclosed, for example, in U.S. Pat. No. 6,658,084. 
     SUMMARY 
     In one aspect, the disclosure features illumination optics configured to illuminate an illumination field in a reticle plane with radiation. The illumination optics include a facet mirror and a changing device. The facet mirror includes a plurality of facets configured to generate a defined illumination setting in the illumination field. Each facet is configured to be allocated to a partial beam of the radiation, and the facet mirror has subunits which themselves are comprised of facet groups having at least one facet each. The changing device is configured to interchange at least one of the sub-units of the facet mirror with at least one interchangeable subunit. The illumination optics are configured to be used in EUV microlithography. 
     In another aspect, the disclosure provides an illumination system that includes illumination optics as described in the preceding paragraph and an EUV light source. 
     In a further aspect, the disclosure provides a projection exposure apparatus that includes an illumination system as described in the preceding paragraph and projection optics configured to image the illumination field in an image field of an image plane. 
     In an additional aspect, the disclosure features a method that includes using a projection exposure apparatus as described in the preceding paragraph to make a microstructured element. 
     In some embodiments, the disclosure provides illumination optics which offer the possibility of changing between several illumination settings with less technical effort. 
     In certain embodiments, the disclosure provides illumination optics having a facet mirror divided into subunits which themselves are composed of facet groups having at least one facet each. A changing device is provided for interchanging at least one of the subunits of the facet mirror with at least one interchangeable subunit. 
     To provide several illumination settings, it is possible to interchange individual subunits of the facet mirror with other subunits leading to different illumination conditions. In practice, the illumination conditions can be altered by changing the illumination of the illumination field, i.e. the distribution of the illumination angles (illumination setting) by which field points are illuminated. Illumination of the illumination field, i.e. its illuminated surface area, often remains unchanged in practice. Interchanging subunits of the facet mirror on a block-by-block basis can provide a mechanical solution for changing the illumination settings which requires much less technical effort than tilting individual facets. Cooling of the facet mirror, which often is often desirable, can also be ensured while maintaining interchangeability of the subunits. The illumination settings can be changed via just a few actuators of the changing device. Groups of facets, such as groups of facets possessing a larger number of individual facets, can remain mechanically connected, thus helping to ensure an efficient cooling of the facets. Depending on the desirable properties in terms of, for example, throughput or structural resolution of a projection exposure apparatus, the illumination optics can provide the right illumination setting for each of these properties. 
     In some embodiments, the disclosure provides an illumination optics where at least one facet mirror is configured as a field facet mirror having a plurality of field facets to generate secondary light sources. A pupil facet mirror is provided in the vicinity of at least some of the secondary light sources generated by the field facet mirror. The pupil facet mirror has a plurality of pupil facets which are impinged by EUV radiation via their corresponding field facets. The pupil facet mirror is a part of an optical equipment required to image the field facet mirror in the reticle plane. Illumination of the pupil facet mirror can be altered by interchanging individual subunits of the field facet mirror with other subunits, thus resulting in a different illumination setting. The facet mirror, which is provided with interchangeable subunits, is configured as the field facet mirror. It is not necessary for the pupil facet mirror to be disposed at the exact same location of the secondary light source which is generated. Optionally, the pupil facets of the pupil facet mirror are arranged at a specific distance to the location of the secondary light source, as described in, for example, U.S. Pat. No. 6,611,574. 
     The illumination optics can optionally be designed in a way as to generate the secondary light sources sagittally and tangentially in planes which are located at a distance to one another. Such an arrangement is known, for example, from U.S. Pat. No. 6,507,440. 
     In some embodiments, the illumination optics is provided with a single facet mirror having interchangeable subunits. At the same time, the single facet mirror provides for a defined illumination of the illumination field. A corresponding facet mirror is described in, for example, EP 1 024 408 A2. 
     In certain embodiments, the disclosure provides a field facet arrangement, where the field facets of the field facet mirror are oriented in a way as to enable a subunit of the field facet mirror to illuminate pupil facets which are arranged in a relatively small area of the pupil facet mirror when compared with the entire aperture of the pupil facet mirror. It is possible to change between principal settings, e.g. changing between a conventional and an annular setting, by interchanging subunits of the field facet mirror. Changing between principal settings may not be possible if pupil facets, which are distributed over the entire aperture of the pupil facet mirror, were illuminated by each subunit of the field facet mirror. 
     In some embodiments, the disclosure provides a changing device with an interchanging drive for interchanging displacement of a subunit carrier in a way as to change between two subunits of the field facet mirror and being provided with a positioning drive for positioning displacement of a base body of one of the subunits of the changing device between a mirror position, where the subunit is situated in a fixed position in the field facet mirror, and a neutral position for interchanging displacement of the subunit carrier, can be realized via a simple drive technology. 
     In certain embodiments, the disclosure provides a swivel drive that enables the subunit carrier to be rotated about a swivel axis and being part of the interchanging drive provides for the implementation of several interchangeable subunits, with the changing device requiring a tiny amount of space. 
     In some embodiments, the disclosure provides an arrangement of the swivel axis, wherein the swivel axis coincides with a central axis of the field facet mirror, allows for a compact arrangement of the changing device in the vicinity of, and particularly downstream of the field facet mirror. 
     In certain embodiments, the disclosure provides a cooling arrangement of the changing device that has a delivery line system for a cooling medium for cooling the interchangeable subunits, in which a line section extends along the swivel axis avoids problems with the cooling line arrangement when the changing device is displaced. The cooling system can be designed in a closed-loop manner. 
     Optionally, at least one line section of the delivery line system may be configured as a flexible line section. In that case, the base body of the interchangeable subunits is displaceable between the mirror position and the neutral position with minimal technical effort. 
     In some embodiments, the disclosure provides a positioning drive with a lever arm a free end of which is attached to a base body and is rotatable about a swivel joint via a motor, thus providing for a change of its position. This can, for example, be realized in a structurally simple manner. 
     In certain embodiments, the disclosure provides changing device arrangements including at least one stop for defining the mirror position and/or comprising at least one snap-in locking unit for fixing the mirror position, which can enable the subunit to be positioned in the mirror position in an exact position and an exact angle. 
     In some embodiments, at least one of one area of the pupil facet mirror and the illumination field may be illuminated by stationary, i.e. non-interchangeable, subunits of the facet mirror. Such subunits can illuminate areas of the pupil facet mirror which must be illuminated at any given illumination setting, and/or illuminate the illumination field in always the same way. This can result in a simpler structural design of the illumination optics. 
     In certain embodiments, the disclosure provides local area illumination by the interchangeable subunits, wherein an interchangeable subunit illuminates a central area of the pupil facet mirror or a first annular area surrounding a central area of the pupil facet mirror or an external annular area of the pupil facet mirror or an adjacent annular area of the pupil facet mirror. The adjacent annular area adjoins an external annular area or two opposite external boundary areas of the pupil facet mirror. The boundary areas have the shape of a pitch circle or a segment or two opposite adjacent boundary areas of the pupil facet mirror. The adjacent boundary areas have the shape of a pitch circle or a segment. Adjoining the external boundary areas of the pupil facet mirror or opposite areas adjoining the central area, have proved particularly suitable when different illumination settings are to be provided. Corresponding local area illumination settings can also be implemented in embodiments of the illumination optics in which secondary light sources are generated sagittally and tangentially in planes that are located at a distance to one another, or which are provided with a single facet mirror comprising interchangeable subunits. In the latter case, corresponding areas of the illumination field are illuminated to different extents when the subunits are interchanged. 
     In some embodiments, the disclosure provides illumination systems with the illumination optics, projection exposure apparatuses with the illumination systems, methods of manufacturing microstructured elements using the projection exposure apparatuses, and microstructured elements obtained by the methods. 
     In certain embodiments, the disclosure provides an illumination system having illumination optics and an EUV light source. In some embodiments, the disclosure provides a projection exposure apparatus having such an illumination system and projection optics configured to image the illumination field in an image field of an image plane. In certain embodiments, the disclosure provides a method of manufacturing a microstructured element via a process that includes: providing a projection exposure apparatus as aforesaid, providing a substrate to at least part of which a layer of a light-sensitive material is applied, providing a mask or a reticle provided with structures to be imaged, projecting of at least a part of the reticle to an area of the light-sensitive layer via the projection exposure apparatus or via: implementing the facet mirror of the illumination optics of the projection exposure apparatus in a first configuration of subunits during a first projection step, interchanging one of the subunits of the facet mirror by an interchangeable subunit so as to create a second configuration of subunits of the facet mirror, projecting at least a part of the reticle to an area of the light-sensitive layer via the projection exposure apparatus or by the aforesaid method where at least two subunits of the facet mirror are interchanged with interchangeable subunits for creating the second configuration. In some embodiments, the disclosure provides a microstructured element. 
     In the following, exemplified embodiments will be described in detail in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional, in particular meridional, view of a projection exposure apparatus for EUV projection microlithography, 
         FIG. 2  is a plan view of an exemplified embodiment of a field facet mirror which is divided into a stationary subunit provided with groups of field facets and an interchangeable subunit provided with groups of field facets, 
         FIG. 3  is a schematic plan view of a pupil facet mirror where the pupil facets illuminated by a group of field facets of the interchangeable subunit of the field facet mirror according to  FIG. 2  are shown hatched, 
         FIG. 4  is a schematic view of pupil facets of the pupil facet mirror which are illuminated by the stationary subunit and the interchangeable subunit of the field facet mirror according to  FIG. 2 , 
         FIG. 5  is a schematic view of pupil facets of the pupil facet mirror according to  FIG. 4 , which are illuminated by the field facet mirror according to  FIG. 2 , after interchanging the interchangeable sub-unit with another interchangeable subunit, 
         FIG. 6  is a schematic plan view of another field facet mirror provided with one stationary subunit and two interchangeable subunits, 
         FIG. 7  is a plan view of a changing device for interchanging at least one of the two interchangeable subunits of the field facet mirror according to  FIG. 6  with other interchangeable subunits, the changing device being provided with a total of four interchangeable subunits, 
         FIG. 8  is a schematic section of the changing device according to  FIG. 7  which is provided with a positioning drive for positioning displacement of a base body of one of the interchangeable subunits between a mirror position and a neutral position, 
         FIG. 9  is a schematic view of the base body of an interchangeable sub-unit before it is moved into the mirror position of the field facet mirror, 
         FIG. 10  shows a pupil facet mirror provided with differently marked areas which are illuminable via the subunits of the field facet mirror according to  FIG. 6 , and are provided with a plurality of pupil facets, 
         FIG. 11  shows, in a similar representation as in  FIG. 6 , another embodiment of a field facet mirror provided with one stationary subunit as well as two interchangeable subunits, 
         FIG. 12  shows, in a similar representation as in  FIG. 7 , a changing device which is provided with four interchangeable subunits for the field facet mirror according to  FIG. 11 , 
         FIG. 13  shows the schematic illumination of a pupil facet mirror via the field facet mirror according to  FIG. 11 , the latter being represented in a first configuration comprising a stationary subunit and two interchangeable subunits, 
         FIG. 14  shows the schematic illumination of a pupil facet mirror via the field facet mirror according to  FIG. 11 , the latter being represented in another configuration comprising a stationary subunit and two interchangeable subunits, 
         FIG. 15  shows another embodiment of a field facet mirror provided with one stationary subunit and two interchangeable subunits, and 
         FIG. 16  shows, in a similar representation as in  FIG. 7 , a changing device for the interchangeable subunits of the field facet mirror according to  FIG. 15 , the changing device comprising four interchangeable subunits. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic representation of a projection exposure apparatus  1  for EUV projection microlithography. The projection exposure apparatus  1  serves to image a structure, which is situated in a reticle plane on a reticle  2 , onto a light-sensitive layer of a wafer  4  in a wafer plane  5 . 
     An illumination optics, the entirety of which is designated by the reference number  6 , serves to illuminate an illumination field in the reticle plane  3 . Together with an EUV light source  7 , the illumination optics  6  is configured as an illumination system of the projection exposure apparatus  1 . 
     EUV radiation  8  emitted by the EUV light source  7  is initially collected by a collector  9  which is schematically represented in  FIG. 1 . Subsequently, the collimated EUV beam hits a field facet mirror  10  provided with a plurality of schematically indicated field facets  11 . The field facets  11  serve to generate secondary light sources. The field facets  11  are allocated to particular partial beams  12  of the EUV radiation  8 . 
     A pupil facet mirror  13  is disposed at the location of the secondary light sources generated by the field facet mirror  10 . The pupil facet mirror  13  is provided with a plurality of pupil facets  14  which are schematically indicated in  FIG. 1  and are impinged by the EUV partial beams  12  via their respective field facets  11 . 
     The pupil facet mirror  13  is part of an optical equipment  15  that serves to image the field facet mirror in the reticle plane  3 . The optical equipment  15  is further provided with two imaging mirrors  16 ,  17 . 
     The structure of the illumination system is schematically represented in  FIG. 1  and serves to demonstrate the functions of the field facet mirror  10  and the pupil facet mirror  13 . The collector  9  as well as the optical equipment  15  can also be configured in a different arrangement and composed of differently-shaped components as well as different numbers of components. 
     EUV radiation  8  reflected by the reticle  2  is imaged in an image field in the wafer plane  5  via a schematically indicated projection optics  18 . 
       FIG. 2  shows a plan view of the field facet mirror  10 . The individual field-facets  11  have the shape of an arc. It is also possible to provide straight, i.e. rectangular field facets. The field facets  11  are arranged in groups  19  of ten field facets  11  each. The groups  19  of field facets are again arranged in five columns of field facets which are numbered from the left to the right as  20 ,  21 ,  22 ,  23 , and  24  in  FIG. 2 . The columns  20  and  24  comprise three groups of field facets of ten field facets  11  each and a residual group  25  of three field facets  11  each. The columns  21  and  23  comprise five groups  19  of field facets as well as a residual group  26  of five field facets  11 . The central column  22  comprises six groups  19  of field facets. The columns of field facets  20  to  24  are arranged symmetrically in such a way as to fill a boundary circle  27 , in which the columns  22  to  24  are inscribed, to the greatest possible extent. The groups of the field facet mirror  10  can also be arranged in a different way. The field facets can in particular be divided into a different number of columns. Moreover, it is possible to arrange less or more than ten field facets per group. 
     The field facet mirror  10  is divided into a stationary subunit  28  and an interchangeable subunit  29 . A boundary between the subunits  28 ,  29  is shown dashed in  FIG. 2 . The interchangeable subunit  29  comprises the two bottom groups  19 ,  26  of the columns  21  and  23  as well as the two bottom groups  19  of the central column  22 . 
       FIG. 3  shows a schematic plan view of the pupil facet mirror  13 . The pupil facets  14  are circular in shape and form hexagonal close packed units inscribed in a boundary circle  30 . Other close packed configurations of the pupil facet mirror are also possible. The chosen configuration depends on the optical design and also on the shape of the individual pupil facets. Also,  FIG. 3  indicates schematically the illumination of several groups of the pupil facets  14  via the field facets  11  of one of the groups  19  of field facets of the interchangeable subunit  29 , e.g. the upper of the two groups  19  of field facets of the central column  22  of the interchangeable subunit  29  in  FIG. 2 . The ten field facets  11  of this group  19  illuminate ten pupil facets  14   a  which are arranged in a central area of the pupil facet mirror  13  and are shown diagonally hatched in  FIG. 3 . This central area is a tiny fracture of the entire aperture of the pupil facet mirror  13 . In-between the field facets  14   a  thus illuminated, there are non-illuminated field facets  14  in this group  19  which are illuminated by other field facets of the interchangeable sub-unit  29 . All in all, the field facets  11  of the interchangeable subunit  29  completely illuminate a central area  31  of the pupil facet mirror  13 , as indicated in  FIG. 4 . The field facets  11  of the stationary subunit  28  of the field facet mirror  10  according to  FIG. 2  illuminate a first annular area  32  surrounding the central area  31 . 
     The boundary between the stationary subunit  28  and the interchangeable subunit  29  of the field facet mirror  10  is also indicated by dashed lines in  FIG. 1 . Here, the interchangeable subunit  29  is shown in a mirror position complementary to the stationary subunit  28 , thus forming a complete field facet mirror  10 . In the mirror position, the respective interchangeable sub-unit is situated in an exact position and an exact angle. A base body  33  of the interchangeable subunit  29  is attached to a free end of a lever arm  34 , as shown in greater detail but still schematically in  FIG. 8 . The lever arm  34  is rotatable about a swivel joint  35  via a motor, thus allowing for a displacement of the interchangeable subunit  29  between the mirror position and a lower neutral position shown hatched in  FIG. 8 , thus ensuring a positioning displacement of the interchangeable subunit  29 . A gear motor serves as a positioning drive  36 . A pinion gear  37  driven by the gear motor engages with a rack  38  whose free end bears against the underside of the lever arm  34  at a distance to the swivel joint  35 . 
     As shown schematically in  FIG. 9 , the base body  33  of the interchangeable subunit  29  is provided with oblique lateral guide surfaces  40  which are formed complementary to guide surfaces  41  of a base body  42  of the stationary subunit  28  of the field facet mirror  10 . The mirror position of the interchangeable subunit  29  is moreover exactly determined by stops  43  bearing against the underside of the base body  42  from below when situated in the mirror position. Additionally, the mirror position is fixable via a snap-in locking unit which is not described here. 
     The positioning drive  36  is part of a changing device  44  for interchanging the interchangeable subunit  29  of the field facet mirror  10  with at least one further interchangeable subunit. The subunit which may serve as a replacement for the interchangeable subunit  29  is hereinafter referred to as  29 ′. The changing device  44  will be described in greater detail together with further embodiments of the field facet mirror. The changing device  44  is connected a central control device  46  of the projection exposure apparatus  1  via a signal which is sent along a signal line  45 . 
     An interchanging drive  44   a  enables the changing device  44  to be rotated about a central swivel axis  44   b  which extends vertically downwards in  FIG. 1 . The interchangeable subunit  29  is thus interchangeable with the second interchangeable subunit  29 ′, which is attached to another lever arm  34 , once the interchangeable subunit  29  has been lowered to a neutral position. Since the swivel axis  44   b  is arranged eccentrically to the field facet mirror  10 , the interchangeable subunits  29 ,  29 ′ are oriented tangentially to the stationary part of the field facet mirror. The changing device  44  is therefore also referred to as a tangential changing device. 
     The second interchangeable subunit  29 ′, which replaces the interchangeable subunit  29  of the field facet mirror  10  according to  FIG. 2 , is not additionally shown in the drawing. According to  FIG. 2 , the second interchangeable subunit has the same structure and the same shape as the interchangeable subunit  29 . The two interchangeable subunits are distinguished by the field facets  11  which are tilted to different extents. The field facets  11  of the second interchangeable subunit are tilted in a way as to not illuminate a central area of the pupil facet mirror  13  but an external annular area  47  surrounding the first annular area  32 . Illumination of the pupil facet mirror  13  via the second interchangeable subunit  29 ′, which replaces the interchangeable subunit  29 , is shown in  FIG. 5 . The central area  31  is no longer illuminated. Instead, the two annular areas  32  and  47  are illuminated. A conventional illumination setting is thus interchangeable with an annular illumination setting by interchanging the interchangeable subunit  29  with the second interchangeable subunit  29 ′. 
       FIG. 6  shows another example of a field facet mirror  48 . Elements which correspond to those described previously with reference to  FIGS. 1 to 5  as well as  8  and  9  are designated by the same reference numbers, and are not described again. 
     Along with a stationary subunit  49 , the field facet mirror  48  is provided with two interchangeable subunits  50 ,  51 . Both interchangeable subunits  50 ,  51  are shown in the mirror position in  FIG. 6 . The subunits  49  to  51  are cooled via a cooling liquid. The latter enters the base body  42  of the field facet mirror  48  through an inlet line  52  and leaves the base body  42  through a discharge line  53 . 
     The interchangeable subunit  50  shown at the top of  FIG. 6  illuminates the central area  31  of the pupil facet mirror  13 , as shown in  FIG. 10 . The interchangeable subunit  51  shown at the bottom of  FIG. 6  illuminates a first annular area  54  surrounding the central area  31 . The stationary subunit  49  illuminates another annular area  55  surrounding the first annular area  54 . The areas  31 ,  54  and  55  have a total of 155 pupil facets  14 . The central area  31  and the annular area  66  have 49 pupil facets  14  each. The annular area  54  and the external annular area  65  have 54 pupil facets  14  each. The pupil facet mirror  13  is thus provided with a total of 257 pupil facets  14 . 
     A changing device  56  schematically shown in  FIG. 7  is arranged at the side facing away from the EUV radiation  8 , i.e. below the drawing plane and below the base body  42  in  FIG. 6 , by which the interchangeable subunits  50 ,  51  is interchanged with further interchangeable subunits  57 ,  58 . The interchangeable subunits  50 ,  51 ,  57 ,  58  are shown in the lowered neutral position in  FIG. 7 . Details of the positioning drive, whose structure in the changing device  56  corresponds to that shown in  FIG. 8  and  FIG. 9 , are omitted in  FIG. 7 . 
     An interchanging drive  59  schematically indicated in  FIG. 7  enables the changing device  56  to be in particular infinitely rotated about a central swivel axis  60  by 90°, the swivel axis being perpendicular to the drawing plane in  FIG. 7 . The interchangeable subunits  50 ,  51 ,  57 ,  58  are disposed on an annular subunit carrier surrounding the interchanging drive  59 . The swivel axis  60  coincides with a central axis  60   a  of the field facet mirror  48 . Corresponding to the changing devices described hereinafter, the changing device  56  is thus also referred to as a circular changing device. 
     The changing device  56  is provided with a delivery line system  61  in order to cool the subunits  50 ,  51 ,  57 ,  58  via a cooling liquid. A line section  62  of the delivery line system  60  is arranged along the swivel axis  60 . Inlet lines  63  and discharge lines  64  are connected to the line section  62 , thus ensuring the transport of cooling liquid to and from the bodies  33  of the interchangeable subunits  50 ,  51 ,  57 ,  58 . As indicated in  FIG. 8  and  FIG. 9 , the lines  63 ,  64  are flexible, thus allowing a problem-free displacement of the subunits  29  or, alternatively,  50 ,  51 ,  57 ,  58 . 
     When the interchangeable subunits  50 ,  51  are to be interchanged with the interchangeable subunits  57 ,  58 , the interchangeable subunits  50 ,  51  are initially lowered from the mirror position to the neutral position via their positioning drives  36 . The interchanging drive  59  is then rotated about the swivel axis  60  by 90° in the clockwise direction, i.e. away from the position shown in  FIG. 7 . Subsequently, the interchangeable subunits  57 ,  58  are lifted from the neutral position to the mirror position via their positioning drives  36  until the guide surfaces  40 ,  41  bear against each other, and the stops  43  bear against the underside of the base body  42  of the stationary subunit  49 . The interchangeable subunits  57 ,  58  can additionally be locked via the snap-in locking unit (not shown) so as to fix the mirror position. 
     The interchangeable subunit  58  illuminates an external annular area  65  of the pupil facet mirror  13 . The interchangeable subunit  57  illuminates an adjacent annular area  66  of the pupil facet mirror  13  adjoining the inside of the external annular area  65 . When the interchangeable subunits  57 ,  58  are in use, the areas  31  and  54  of the pupil facet mirror  13  are not illuminated. 
     When the interchangeable subunits  50 ,  51  are interchanged with the second interchangeable subunits  57 ,  58 , a conventional illumination setting is thus interchanged with an annular illumination setting. 
       FIG. 11  shows a field facet mirror  67 . Elements which correspond to those described previously with reference to  FIGS. 1 to 10  are designated by the same reference numbers, and are not described again. 
     The field facet mirror  67  is provided with a stationary subunit  68  and two interchangeable subunits  69 ,  70 . Unlike the edge boundaries of the interchangeable subunits  29  or, alternatively,  50 ,  51 ,  57 ,  58 , which have the shape of a segment, the boundaries of the interchangeable subunits  69 ,  70  are of rectangular shape. The interchangeable subunit  70  shown at the bottom of  FIG. 11  illuminates the central area  31  of the pupil facet mirror  13 . The interchangeable subunit  69  shown at the top of  FIG. 11  illuminates two opposite areas  71 ,  72  adjoining the central area  31 . The area  71  is disposed above the central area  31  in  FIG. 13 , while the area  71  is disposed below the central area  31  in  FIG. 13 . 
     Residual areas  73 ,  74  are illuminated by the stationary subunit  68  so as to obtain a conventional illumination by all areas  31 ,  71 ,  72 ,  73 ,  74 . The conventional illumination, also referred to as a conventional setting, corresponds to a circular illumination with an intensity as uniform as possible within the circle. The residual areas  73 ,  74  form adjacent boundary areas having the shape of a segment and adjoining the central area  31 . 
     A changing device  75  for the field facet mirror, whose structure otherwise corresponds to that of the changing device  56 , is provided with further interchangeable subunits  76 ,  77  in addition to the interchangeable subunits  69 ,  70 . The interchangeable subunit  76  is shown on the left-hand side of  FIG. 12 , while the interchangeable subunit  77  is shown on the right-hand side of  FIG. 12 . Corresponding to the above descriptions with regard to the changing device  56 , the changing device  75  is used to interchange the interchangeable subunits  69 ,  70  with the interchangeable subunits  76 ,  77 . In order to do so, the changing device  75  is rotated about the central swivel axis  62  by 90° in the clockwise direction, i.e. away from the position shown in  FIG. 12 . When the interchangeable subunits are interchanged, the interchangeable subunit  76  thus takes the place of the interchangeable sub-unit  69 , while the interchangeable subunit  77  takes the place of the interchangeable subunit  70 . The interchangeable subunit illuminates two opposite external boundary areas  78 ,  79  of the pupil facet mirror which are shown on the left- and right-hand sides of  FIG. 14  and have the shape of a pitch circle. The interchangeable subunit  77  illuminates two opposite adjacent boundary areas  80 ,  81  of the pupil facet mirror  13  shown on the left- and right-hand sides of  FIG. 14 , the adjacent boundary areas  80 ,  81  having the shape of a pitch circle and adjoining the outer boundary areas  78 ,  79 . When the interchangeable subunits  76 ,  77  are in use, the areas  31  as well as  71 ,  72  of the pupil facet mirror  13  are not illuminated. 
     Thus, by inserting the interchangeable subunits  76 ,  77  into the pupil facet mirror  67 , a dipole illumination is obtained which provides for two symmetrically illuminated areas (dipole setting). 
       FIG. 15  shows a field facet mirror  82 . Elements which correspond to those described previously with reference to  FIGS. 1 to 14  are designated by the same reference numbers, and are not described again. 
     The arrangement of the field facets  11  in the field facet mirror  82  corresponds to the arrangement in the field facet mirror  10 . The field facet mirror  82  is provided with a stationary subunit  83  and two interchangeable sub-units  84 ,  85 . The interchangeable subunit  84  is shown at the top of  FIG. 15 , while the interchangeable subunit  85  is shown at the bottom of  FIG. 15 . The interchangeable subunits  84 ,  85  have different sizes and are thus provided with a different number of field facets  11 . The interchangeable subunit  84  shown at the top of  FIG. 15  has three groups  19  of field facets formed by the upper groups situated in the columns  21 ,  22 ,  23  of field facets. 
     The interchangeable subunit  85  shown at the bottom of  FIG. 15  is configured as the lower boundary of the columns  21 ,  22 ,  23  of field facets. In the column  21  of field facets, the interchangeable subunit  85  possesses one group  19  of field facets and the residual group  26 . In the column  22  of field facets, the interchangeable subunit  85  comprises two groups  19  of field facets. In the column  23  of field facets, the interchangeable subunit  85  possesses one group  19  of field facets and the residual group  26 . 
     Corresponding to their different sizes and, therefore, different numbers of field facets  11 , the interchangeable subunits  84 ,  85  thus also illuminate areas of different sizes of the pupil facet mirror  13 . This proves useful in situations where the central area  31 , for example, is provided with a larger number of pupil facets  14  than the adjacent annular area  54  (see  FIG. 10 ). 
     A changing device  86  for the field facet mirror  82  is provided with further interchangeable subunits  87 ,  88  in addition to the interchangeable subunits  84 ,  85 . Except for the configuration of the interchangeable subunits  84 ,  85 ,  87 ,  88 , the structure of the changing device  86  corresponds to that of the changing device  56 . 
     The external contour of the interchangeable subunit  87  corresponds to that of the interchangeable subunit  84 . Moreover, the external contour of the interchangeable subunit  88  corresponds to that of the interchangeable sub-unit  85 . As previously described in connection with the changing device  56 , the interchangeable subunits  84 ,  85  are also interchangeable with the interchangeable subunits  87 ,  88  via the changing device  86 , i.e. by rotating the changing device  86  about the swivel axis  60  by 90° in the clockwise direction. The interchangeable subunits  87 ,  88  illuminate other areas on the pupil facet mirror  13  than the interchangeable subunits  84 ,  85 . This way, the changing device  86  also offers the possibility of changing between different illumination settings. 
     Some embodiments of a changing device can also be provided with a larger number of interchangeable subunits, thus allowing for a change between more than two interchangeable subunit configurations in a corresponding field facet mirror. Such a changing device (not shown) can be used to change, for example, between a conventional setting, an annular setting and a dipole setting. Depending on the configuration of the interchangeable subunits, the interchange of the interchangeable subunits also provides for other illumination settings, for example a quadrupole illumination setting, a conventional illumination setting with different maximum illumination angles (different sigma), or other, more exotic illumination settings. Dipole, quadrupole and annular illumination settings in a projection exposure apparatus, in particular in connection with EUV illumination radiation, provide for the imaging of finer structures than generally possible with conventional settings. The areas illuminated by the interchangeable subunits or the stationary subunit have the shape that is required in order to configure the individual illumination setting. In addition to the area shapes already described above, illumination of areas that have the shape of a sector, for example, or are provided with an entirely different contour at the boundaries is also possible. 
     It is also possible to provide more than two interchangeable subunits per field facet mirror. 
     As an alternative to a tangential changing device  44  as indicated in  FIG. 1  or to a circular changing device  56 ,  75 ,  86 , it is also possible to provide a linear changing device in which the individual interchangeable subunits are arranged on a carriage that is displaceable in a longitudinal direction, e.g. in the direction perpendicular to the drawing plane of  FIG. 1 . 
     The interchangeable subunits shown here are provided with several field facets  11  each which are combined in groups of field facets. In some embodiments, provision can be made for interchangeable subunits having only a single field facet  11 . 
     Manufacturing of a microstructured or nanostructured element takes place by positioning the structure to be imaged, i.e. the pattern to be imaged, of the reticle  2  into the object field of the reticle or object plane. The wafer  4  is positioned in the image field of the image plane or wafer plane  5 . While the projection exposure apparatus  1  is in use, the pattern on the reticle  2  is projected onto an illumination light-sensitive layer of the wafer  4 . This layer can then be developed so as to manufacture the microstructured or nanostructured element. 
     The facet mirror, which is provided with the interchangeable subunits and also referred to as the field facet mirror in the embodiments described above, is implemented in a first configuration of subunits. As soon as another illumination setting is required, a subunit of the facet mirror is interchanged with an interchangeable subunit, thus modifying the configuration of subunits of the facet mirror. Subsequently, another projection cycle is carried out, the subunits of the facet mirror being arranged in a second configuration. 
     When changing between two illumination settings, it is possible to interchange exactly one subunit of the field facet mirror. However, it is also possible to interchange at least two subunits in order to change the illumination setting. 
     Other embodiments are in the claims.