Pupil facet mirror, lighting optics and optical system for a projection lighting system

Description

[0001] The invention relates to an optical system for a projection exposure system, a pupil facet mirror for an illumination optic, and an illumination optic. The invention further relates to a projection exposure system for microlithography. Finally, the invention relates to a method for exposing a wafer using a projection exposure system.

[0002] DE 10 2014 223 453 A1 discloses a lighting optic for projection lithography.

[0003] Projection exposure systems with high numerical apertures are known from the prior art. However, large angles of incidence of the illumination radiation can lead to shadowing effects due to the mask structures.

[0004] One object of the invention is to improve an optical system for a projection exposure system.

[0005] This problem is solved by an optical system according to claim 1.

[0006] In a particular embodiment of the optical system, the angular space of the illumination radiation of the projection optics at the reticle is twice as large in a first direction as the angular space of the illumination radiation of the illumination optics. This first direction runs parallel to the scan direction of the projection exposure system. In the illumination optics, the scan direction can be identified based on the extent of the illuminated reticle: The reticle is significantly shorter in the scan direction than in a direction orthogonal to it.

[0007] A halving of the angular space in a first direction can be achieved, in particular, by ensuring that the opening of the illumination beam in the projection optics path results in a circular angular space on the wafer, while the opening of the illumination beam for illuminating the reticulum in the first direction is reduced by half. In the case of astigmatic imaging by the projection optics, the angular space of the illumination beam in the projection optics path can be elliptical.

[0008] When referring to the opening or angular space of the beam of illumination radiation in the beam path of the projection optics, this only refers to those rays that lie within the aperture captured by the projection optics, i.e., those rays that can reach the wafer.

[0009] In the first direction, the numerical aperture of the illumination optics is, in particular, exactly half the size of the numerical aperture of the projection optics.

[0010] According to the invention, it was discovered that this reduces the maximum angle of incidence of the illumination radiation on the reticulum. The consequence of halving the illumination pupil on the image of the reticulum can be compensated for by a subsequent second exposure with the other half of the illumination pupil. This will be described in more detail below.

[0011] According to a further aspect of the invention, the reticle is tilted relative to the beam path of the illumination radiation such that its surface normal lies completely within the beam of the illumination radiation of the projection optics. Due to the different opening angles of the illumination radiation incident on the reticle and that reflected by the reticle, the surface normal of the reticle is no longer symmetrically located between the beam of the illumination optics and that of the projection optics, but rather lies completely within the beam of the projection optics.

[0012] According to another aspect of the invention, the optical system comprises a semicircular pupil facet mirror. The pupil facet mirror is described in more detail below.

[0013] According to another aspect of the invention, the optical system comprises a projection optic with an object-side numerical aperture of at least 0.55, in particular at least 0.7.

[0014] According to a further aspect of the invention, the angular space of the illumination radiation of the projection optics at the reticle is equal in a second direction to the angular space of the illumination radiation of the illumination optics. The second direction is, in particular, oriented perpendicular to the first direction.

[0015] To resolve structures of the reticle at the resolution limit, only a part of one of the first two diffraction orders of the illumination radiation reflected at the reticle is used to project the reticle onto the wafer.

[0016] In the beam of the projection optics, in addition to the illumination radiation specularly reflected at the reticle (i.e., the zeroth diffraction order), only a portion of either the +1st or the -1st diffraction order is contained. The +1st / -1st diffraction order may be partially, or even completely, contained in the beam of the projection optics. This applies accordingly to higher diffraction orders.

[0017] According to a further aspect of the invention, both the reticule and the wafer are rotatable by 180° each. In particular, they are mounted on a reticule or wafer holder so as to be rotatable accordingly.

[0018] This allows the reticulum to be illuminated with the other half of the illumination pupil. In this process, the same mask structures—that is, the same mask embedded in the reticulum—are imaged onto the same areas of the wafer. This differs from both double exposure, where different masks are successively imaged onto the same area of ​​the wafer using different illumination pupils, and double patterning, where the photoresist applied to the wafer undergoes development between two exposures of the same area.

[0019] According to another aspect of the invention, the projection optics has a plurality of mirrors, wherein the first two mirrors, in particular the first three mirrors, in particular the first four mirrors in the beam path of the projection optics have a simply connected reflective surface.

[0020] This eliminates the need for a fractional reflective surface in these projection optics mirrors.

[0021] Avoiding a fractionated reflection surface makes it possible, in particular, to separate the beam paths between the reticle and the illumination optics from those between the reticle and the projection optics.

[0022] Further objectives of the invention are to improve a lighting optic for a projection exposure system and a pupil facet mirror for a lighting optic of a projection exposure system.

[0023] These tasks are solved by an illumination optic designed in such a way that only half an illumination pupil is available for illuminating the reticulum, and a pupil facet mirror with a semicircular design.

[0024] The illumination optics have an output aperture which is smaller in a first direction than in a second direction perpendicular to it. The ratio of the diameters of the output aperture of the illumination optics in the first and second directions is at most 0.7, in particular at most 0.6. It may, in particular, be 0.5.

[0025] This can be achieved, in particular, by truncating half of a circular exit aperture. This is possible especially through a suitable design of the pupil facet mirror. The illumination optics, in particular, have a semicircular aperture.

[0026] The pupil facet mirror can also be semi-elliptical. This means that it has the shape of half a symmetrically divided ellipse.

[0027] The shape of the pupil facet mirror refers in particular to its envelope, that is, the shape of its smallest convex envelope. This shape especially defines the area in which the pupil facets can be arranged.

[0028] According to another aspect of the invention, an illumination optic which provides only half an illumination pupil for illuminating the reticulum is formed by an aperture for blocking half of the illumination pupil.

[0029] According to the invention, it has been found that by providing only half of the illumination pupil, the opening of the beam of light illuminating the reticulum in one direction can be reduced by half. This reduces the maximum angle of incidence of the illumination radiation on the mask. In particular, this reduces shadowing effects.

[0030] Another objective of the invention is to improve a projection exposure system for microlithography.

[0031] This task is solved by a projection exposure system with an optical system as described above.

[0032] The advantages arise from those already described.

[0033] The projection exposure system is, in particular, an EUV projection exposure system. It includes, in particular, a radiation source for generating illumination radiation in the EUV range, especially in the wavelength range of less than 30 nm, and specifically for illuminating light with a wavelength of 13.5 nm or 7 nm.

[0034] Another object of the invention is to improve a method for exposing a wafer using a projection exposure system.

[0035] This task is solved by a method in which a reticule is projected onto the wafer twice in succession, with the reticule and the wafer being rotated 180° around the optical axis between the two exposure steps.

[0036] In this way, it is possible to use the two halves of an illumination pupil sequentially to illuminate the reticulum and image its structures onto the wafer. This compensates for, and in particular essentially completely compensates for, the effect of the previously described pupil bisection.

[0037] The process is a double exposure process.

[0038] Due to the reduced shadowing effects combined with high numerical aperture, especially of the projection optics, the precision of the structures on the wafer can be further improved.

[0039] Further details and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the figures. These show: Fig. 1 schematically shows a meridional section through a projection exposure system for microlithography, Fig. 2 schematically shows a top view of the pupil facet mirror of the illumination optics of the projection exposure system according to Fig. 1 , Fig. 3 a section enlargement of area III in the beam path of the projection exposure system according to Fig. 1 , Fig. 4 schematically shows a section along line IV-IV according to Fig. 3 through the beams of the illumination radiation of the illumination optics and the projection optics in the area of ​​the reticle, Fig. 5 schematically the arrangement of reticle and wafer in a first exposure step and Fig. 6 schematically the arrangement of reticle and wafer in a subsequent second exposure step.

[0040] The following section describes, by way of example, the general details of a projection exposure system 1 known per se for microlithography. Reference is made to DE 10 2012 220 597 A1, which is hereby fully incorporated into the present application. This reference is not to be understood as limiting. Deviations in various details of the projection exposure system 1 are possible.

[0041] A projection exposure system 1 for microlithography is used to produce a micro- or nanostructured electronic semiconductor device. A radiation source 2 emits EUV radiation used for illumination in the wavelength range, for example, between 5 nm and 30 nm. The radiation source 2 can be a GDPP source (gas discharge produced plasma) or an LPP source (laser produced plasma). A radiation source based on a synchrotron or a free electron laser (FEL) can also be used for the radiation source 2. Information on such a radiation source can be found, for example, in US 6,859,515 B2. For illumination and imaging within the projection exposure system 1, EUV illumination light or illumination radiation in the form of an imaging light bundle 3 is used.The imaging light beam 3 passes through a collector 4 after the radiation source 2. This collector can be, for example, a nested collector with a multi-shell structure known from the prior art, or alternatively, an ellipsoidally shaped collector arranged behind the radiation source 2. A corresponding collector is known from EP 1 225 481 A. The radiation source 2 and the collector 4 can be components of a radiation source module 8.

[0042] After passing through collector 4, the EUV illumination light 3 first passes through an intermediate focal plane 5, which can be used to separate the imaging light bundle 3 from unwanted radiation or particle components. After passing through the intermediate focal plane 5, the imaging light bundle 3 first encounters a field facet mirror 6 with field facets 7. The field facet mirror 6 represents a first facet mirror of the projection exposure system 1.

[0043] To facilitate the description of spatial relationships, a Cartesian global xyz coordinate system is shown in the drawing. The x-axis runs in the Fig. 1 perpendicular to and extending from the plane of the drawing. The y-axis runs in the Fig. 1 to the right. The z-axis runs in the Fig. 1 up.

[0044] The field facets 7 can be switched between three different tilt positions each. Depending on the design of the field facet mirror 6, all or some of the field facets 7 can also be switched between more than three different tilt positions. For this purpose, each field facet is connected to an actuator. The actuators of all tiltable field facets 7 can be controlled via a central control unit.

[0045] After reflection at the field facet mirror 6, the imaging light bundle 3, divided into imaging light sub-bundles assigned to the individual field facets 7, strikes a pupil facet mirror 10, which will be described in more detail below. The respective imaging light sub-bundle of the entire imaging light bundle 3 is guided along one imaging light channel.

[0046] Fig. 2 Figure 1 schematically shows an exemplary facet arrangement of pupil facets 11 of the pupil facet mirror 10. The pupil facet mirror 10 represents a second facet mirror of the projection exposure system 1. The pupil facets 11 are arranged on a carrier plate of the pupil facet mirror 10. The pupil facets 11 are arranged row by row and column by column in an x / y grid. Alternatively, the pupil facets 11 are arranged on a hexagonal grid. The pupil facets 11 have square reflective surfaces. Other shapes of reflective surfaces are also possible, for example, rectangular, round, or polygonal, such as hexagonal or octagonal. Diamond-shaped arrangements of pupil facets 11 are also possible.

[0047] Each imaging light sub-bundle of the EUV illumination light 3, reflected by one of the field facets 7 in one of the three tilt positions, is assigned exactly one pupil facet 11, so that each pair of facets illuminated by exactly one of the field facets 7 and exactly one of the pupil facets 11 defines the imaging light channel for the corresponding imaging light sub-bundle of the EUV illumination light 3. In each tilt position of the respective field facet 7, exactly one pupil facet 11 is assigned to this field facet 7 for deflecting the EUV illumination light 3 towards this pupil facet 11.

[0048] The channel-wise assignment of the pupil facets 11 to the field facets 7 is determined by the desired illumination provided by the projection exposure system 1. Due to the different tilt positions of the field facets, each of the field facets 7 can therefore specify different imaging light channels. Each of the field facets 7 is assigned a set of pupil facets 11 corresponding to the number of tilt positions across all its tilt positions.

[0049] In an alternative configuration, the field facets 7 can also be switched between two tilt positions, between four tilt positions, or between even more tilt positions, thereby defining one imaging light channel each. The number of pupil facets 11 in the respective pupil facet set is correspondingly greater.

[0050] The field facet mirror 6 can have field facets 7 that can be switched between several tilt positions, or field facets 7 that are not switchable but are fixedly assigned to a specific pupil facet. Such a variant with non-switchable field facets 7 is used particularly when the various predefined illumination settings overlap in such a way that light from certain identical directions is required for all predefined illumination settings, so that certain pupil facets are always illuminated by the EUV illumination light, regardless of the predefined illumination setting.

[0051] In the Fig. 2 The pupil facets 11 of the pupil facet mirror 10 that are illuminated by the illuminating light 3 due to a momentary tilting of the field facets 7 are highlighted as an example. This is shown as an example in the Fig. 2 An illumination setting that corresponds to half an x-dipole setting, specifically one of the poles of such an x-dipole setting. This illumination setting corresponds to an illumination angle distribution that can be specified via the projection exposure system 1. The pupil facets 11 illuminated by the illumination light 3 form at least one contiguous pupil facet group in every illumination setting. In principle, depending on the current tilt positions of the field facets 7, illumination settings with non-contiguous distributions of pupil facets 11 illuminated by the illumination light 3 can also be realized. Mixed forms of illumination settings with at least one contiguous pupil facet group and with at least one isolated pupil facet 11 are also possible.Such an illumination setting, featuring individually illuminated pupil facets 11, can be implemented in cases where there is a significantly larger number of pupil facets compared to the number of field facets, with the smaller number of field facets being used to illuminate the pupil facets on the pupil facet mirror 10 as evenly as possible. If the illumination setting includes at least one contiguous group of pupil facets, this group contains at least two pupil facets 11.

[0052] Via the pupil facet mirror 10 ( Fig. 1 The field facets 7 are projected onto an object plane 16 of the projection exposure system 1 by a downstream transmission optic 15 consisting of three EUV mirrors 12, 13, 14. The EUV mirror 14 is designed as a grazing-incidence mirror. A reticle 17 is arranged in the object plane 16, from which an illumination area is lit by the EUV illumination light 3. This illumination area coincides with an object field 18 of a downstream projection optic 19 of the projection exposure system 1. The illumination area is also referred to as the illumination field. Depending on the specific design of the illumination optic of the projection exposure system 1, the object field 18 is rectangular or arc-shaped. The imaging light channels are superimposed in the object field 18. The EUV illumination light 3 is reflected by the reticle 17.The reticule 17 is held by a reticule holder 17a, which can be moved along the displacement direction y by means of a schematically indicated object displacement drive 17b.

[0053] The transmission optics 15 can be dispensed with if the pupil facet mirror 10 is arranged directly in an entrance pupil of the projection optics 19.

[0054] The projection optics 19 image the object field 18 in the object plane 16 onto an image field 20 in an image plane 21. A wafer 22, which carries a light-sensitive layer, is arranged in this image plane 21. This layer is exposed during the projection exposure by the projection exposure system 1. The wafer 22, i.e., the substrate onto which the image is projected, is held by a wafer holder 22a, which can be moved along the displacement direction y by means of a wafer displacement drive 22b (also shown schematically) synchronously with the displacement of the reticule holder 17a. During the projection exposure, both the reticule 17 and the wafer 22 are scanned synchronously in the y-direction. The projection exposure system 1 is designed as a scanner. The scan direction y is the object displacement direction.

[0055] The field facet mirror 6, the pupil facet mirror 10 and the mirrors 12 to 14 of the transmission optics 15 are components of an illumination optics 23 of the projection exposure system 1.

[0056] Together with the projection optics 19, the lighting optics 23 form an optical system 24 of the projection exposure system 1.

[0057] Together with the radiation source module 8, the lighting optics 23 form a lighting system 25 of the projection exposure system 1.

[0058] Further details of the projection exposure system 1, in particular the illumination optics 23, especially the pupil facet mirror 10, are described below.

[0059] The illumination optics 23 can preferably have a high numerical aperture, in particular a numerical aperture of at least 0.55, in particular at least 0.65, in particular at least 0.7. However, according to the invention, it was recognized that large angles of incidence of the illumination radiation in the region of the reticle 17 can lead to undesirable shadowing effects.

[0060] For reasons related to the guidance of the illumination radiation, the beam path of the illumination radiation in the illumination optics 23 is usually tilted relative to a normal 26 of the reticle 17 such that the beam path of the illumination optics 23 does not overlap with the beam path of the projection optics 19. In particular, the beam path of the illumination optics 23 is tilted such that it does not overlap with the beam of light specularly reflected by the reticle 17, i.e., the illumination radiation diffracted into zero order, in the beam path of the projection optics 19.

[0061] Shadowing effects can be at least partially compensated for by an anamorphic design of the projection optics 19. However, this leads to a reduction in the transmitted information and thus to a reduction in the throughput of the projection exposure system 1. The invention described here can be combined with an anamorphic design of the projection optics 19. An advantageous design will be discussed later.

[0062] According to the invention, it is provided that the maximum angle of incidence of the illumination radiation at the reticulum 17 is reduced by reducing the opening of the beam 3 of the illumination radiation in the beam path of the illumination optics 23 at the reticulum 17.

[0063] This can be achieved, for example, by using only a semicircular pupil facet mirror 10 instead of a circular pupil facet mirror 10 (see Fig. 2 ) is used.

[0064] In the Fig. 3 und 4 The beam 27 of the illumination optics 23 in the region of reticle 17 and the beam 28 of the projection optics 19 in the region of reticle 17 are shown schematically and by way of example. A dashed line 29 clarifies in the Fig. 4 the drawing plane of the Fig. 3 .

[0065] The maximum extent of the beam 27 of the illumination optics 23 is shown in particular, that is, the object-side aperture of the illumination optics 23, as well as that of the projection optics 19. The corresponding area is not necessarily completely filled with illumination radiation (see, for example, the exemplary illustration in Fig. 2 ).

[0066] As in the Fig. 3 und 4 As shown by way of example, the opening angle b(BO) of the beam 27 of the illumination optics 23 can be exactly half as large as the opening angle b(PO) of the beam 28 of the projection optics 19 in a first direction.

[0067] The first direction can be, in particular, the y-direction, that is, the scan direction.

[0068] In a second direction perpendicular to this, the radiation beams 27, 28 of the illumination radiation can have identical opening angles in the beam path of the illumination optics 23 and in the beam path of the projection optics 19 (see Fig. 4 ).

[0069] Furthermore, it is planned to tilt the beam 27 of the illumination radiation in the illumination optics 23 relative to the reticulum 17 in such a way that the maximum angle of incidence b in_max of the illumination radiation at the reticulum 17 is exactly as large as the maximum angle of reflection b aus_max of the illumination radiation specularly reflected at the reticulum 17.

[0070] Because of the different openings of the beam bundles 27, 28 in the beam path of the illumination optics 23 and in the beam path of the projection optics 19, this results in the surface normal 26 at the reticulum 17 lying completely in the area of ​​the beam bundle 28 of the projection optics 19.

[0071] When using an anamorphic projection optic 19, a particularly advantageous embodiment consists in selecting the magnification scales such that the total angular extent is identical in the x and y directions. The extent of the radiation beam 28 of the illumination radiation in the beam path of the projection optic 19 in angular space can be 50% larger in the x direction than in the y direction. This results in the maximum angle of a ray relative to the normal of the reticle being independent of its direction.

[0072] Although the surface normal 26 of the reticle 17 lies completely in the beam path of the projection optics 19, the first two mirrors, in particular the first three mirrors, and especially the first four mirrors in the beam path of the projection optics 19 can have a simply connected reflective surface. In particular, they have a reflective surface which is not fractionated.

[0073] In the Fig. 4 It is shown by way of example that the specularly reflected zeroth order of the illumination radiation is completely contained (hatched area 30) in the beam 28 of the projection optics 19. The beam 28 of the projection optics 19 also contains higher-order components (unhatched area 31). However, the beam 28 of the projection optics 19 only contains higher-order components that lie on one side of the zeroth-order area 30, particularly in the y-direction. The higher-order components lie specifically in a region between the beam 27 of the illumination optics 23 and its specular reflection.

[0074] Again Fig. 4 As can be further determined, the reduction of the aperture of the beam 27 of the illumination optics 23 only takes place in the first direction, in particular the y-direction. In a second, perpendicular direction, in particular the x-direction, no reduction of the aperture of the beam 27 takes place.

[0075] The beam 27 of the illumination optics 23 thus has different maximum dimensions. In an anamorphic system, the maximum dimensions are to be taken relative to the numerical aperture of the projection optics in the corresponding direction.

[0076] According to the invention, it was discovered that the effect of the previously described halving of the illumination pupil on the imaging of the reticulum 17 onto the wafer 22 can be compensated for by a double exposure. In this double exposure, the two complementary halves of the illumination pupil are used sequentially to image the reticulum 17 onto the wafer 22. The optical system 24 of the projection exposure unit 1 remains unchanged, while the reticulum 17 and the wafer 22 are rotated about the optical axis. In particular, the reticulum 17 and the wafer 22 are rotated by 180° about the optical axis. The arrangements of the reticulum 17 and the wafer 22 in the two exposure steps are shown by way of example in the Fig. 5 und 6 depicted.

[0077] It should be noted that the double exposure described above can be advantageous, but is not necessary. Without this double exposure, a focus error or a z-position error of the reticles and / or wafer leads to a shift and washout of the structures produced on the wafer. The described double exposure can significantly reduce this shift, but this can be accompanied by an increase in the washout of the structures. Depending on the intended application of the projection exposure system, the described double exposure may therefore be necessary, advantageous but not necessary, or even disadvantageous.

[0078] The reticule holder 17a is used to rotate the reticule 17.

[0079] The wafer holder 22a is used to rotate the wafer 22.

[0080] From the perspective of reticulum 17, its structures are illuminated with complementary halves of the illumination pupil in each of the two exposure steps.

[0081] Using the solution described above, the maximum angle of incidence / emission of the illumination radiation at the reticulum can be reduced by 25%.

Claims

1. Optical system (24) for a projection exposure apparatus (1), comprising 1.1 an illumination optical unit (23) for transferring illumination radiation to a reticle (17), and 1.2 a projection optical unit (19) for projecting the reticle (17) onto a wafer (22), characterized in that 1.

3. the angle space of the illumination radiation of the illumination optical unit (23) and of the projection optical unit (19) at the reticle (17) is designed such that only one of the two first orders of diffraction of the illumination radiation reflected off the reticle (17) is contained in the beam of the projection optical unit (19).

2. Optical system (24) according to Claim 1, characterized in that the angle space of the illumination radiation of the projection optical unit (19) at the reticle (17) is twice as large in a first direction as the angle space of the illumination radiation of the illumination optical unit (23).

3. Optical system (24) according to Claim 1 or 2, characterized in that the reticle (17) is tilted relative to the beam path of the illumination radiation in such a way that its surface normal (26) lies entirely in the beam of the illumination radiation of the projection optical unit (19).

4. Optical system (24) according to one of Claims 1 to 3, characterized by a pupil facet mirror (10) having a semicircular embodiment.

5. Optical system (24) according to one of Claims 1 to 4, characterized in that the projection optical unit (19) has an object-side numerical aperture of at least 0.55.

6. Optical system (24) according to one of Claims 1 to 5, characterized in that the angle space of the illumination radiation of the projection optical unit (19) at the reticle (17) is the same size in a second direction as the angle space of the illumination radiation of the illumination optical unit (23).

7. Optical system (24) according to one of Claims 1 to 6, characterized in that the projection optical unit (19) has a plurality of mirrors, wherein the first two mirrors in the beam path of the projection optical unit (19) have a simply contiguous reflection surface.

8. Optical system (24) according to one of Claims 1 to 7, characterized in that the envelope of the beams of the projection optical unit (19) and the envelope of the beams of the illumination optical unit (23) do not overlap.

9. Pupil facet mirror (10) for an illumination optical unit (23) of an optical system according to one of Claims 1 to 8, characterized by a semicircular embodiment.

10. Pupil facet mirror (10) according to Claim 9, characterized by a plurality of pupil facets (10) which are arranged in an x / y grid or on a hexagonal grid.

11. Pupil facet mirror (10) according to one of Claims 9 and 10, characterized in that the pupil facets (10) have square, round, hexagonal or octagonal reflection surfaces.

12. Illumination optical unit (23) for an optical system (24) according to one of Claims 1 to 8, having an exit-side maximum aperture, which is at most 70% as large in a first direction as in a second direction perpendicular thereto, characterized by a pupil facet mirror (10) according to one of Claims 9 to 11.

13. Microlithographic projection exposure apparatus (1) comprising 13.

1. an optical system (24) according to one of Claims 1 to 8, and 13.

2. a radiation source (2) for generating illumination radiation.

14. Method for illuminating a wafer (22) with the aid of a projection exposure apparatus (1), comprising the following steps: 14.

1. providing a projection exposure apparatus (1) with an optical system according to one of Claims 1 to 8, 14.

2. providing a reticle (17) in an object plane (16) of the projection exposure apparatus (1), 14.

3. providing a wafer (22) in an image plane (21) of the projection exposure apparatus (1), 14.

4. first projecting of the reticle (17) onto the wafer (22) with the aid of the projection exposure apparatus (1), 14.

5. wherein, for illuminating the reticle (17) by means of the projection exposure apparatus (1), an illumination angle distribution is specified which corresponds to precisely one of the poles of a dipole setting.

15. Method according to Claim 14, characterized by the following steps: 15.

5. rotating the reticle (17) and the wafer (22) through 180° in each case about the optical axis, 15.

6. second projecting of the reticle (17) onto the wafer (22) with the aid of the projection exposure apparatus (1).