WO2007128407A1

WO2007128407A1 - Illumination system for euv lithography as well as a first and second optical element for use in an illumination system of this type

Info

Publication number: WO2007128407A1
Application number: PCT/EP2007/003609
Authority: WO
Inventors: Martin Endres; Jens Ossmann
Original assignee: Carl Zeiss Smt Ag
Priority date: 2006-05-04
Filing date: 2007-04-25
Publication date: 2007-11-15
Also published as: TW200801843A; JP2009535827A; US20090041182A1; DE102006020734A1; JP2012178573A; JP5543516B2; EP2013663A1; US20150002925A1; JP4970533B2; US9671608B2; TWI414896B

Abstract

An illumination system for EUV lithography is used for illuminating a predetermined illumination field (2) of an object surface with EUV radiation (4). The illumination system has a source for the EUV radiation (4). A first optical element (7) is used to generate secondary light sources in the illumination system. A surface, impacted by EUV radiation (4), of the first optical element (7) is divided into a plurality of first facet elements (8 to 11). The latter are each associated with partial beams (12 to 15) of the EUV radiation (4). A second optical element (20) at the location of the secondary light sources is impacted by EUV radiation (4) over an impactable area via the first optical element (7), which impactable surface is divided into a plurality of second facet elements (21 to 24). The latter are each associated with at least one of the first facet elements (8 to 11) impacting the respective second facet element (21 to 24) to generate the secondary light sources. The second optical element (20) is at least part of an optical arrangement which images the first optical element (8 to 11) in a plane predetermined by the object surface. At least selections of the first facet elements (8 to 11) are configured and oriented in such a way that they are imaged in one of at least two partial fields (31, 32) of the illumination field (2) by the optical arrangement. The partial fields (31, 32) make up the entire illumination field (2), and intersection between the partial fields, if it exists at all, is always smaller than each of the partial fields contributing to the intersection. An illumination system is produced in which changing between various illumination settings is possible even when a second optical element is used which has fewer facet elements compared to the prior art.

Description

Illiiniination system for EUV lithography as well as a first and second optical element for use in an illumination system of this type

The invention relates to an illumination system for EUV lithography according to the preamble of claim 1. The invention also relates to a first and a second optical element for use in an illumination system of this type.

A generic illumination system with a corresponding first and second optical element is known from US 6 658 084 B2. Other illumination systems are known from DE 102 19 514 Al and from US 2007/0058274 Al . These publications describe the production of different illumination settings using displaceable field facet elements. With each of the different illumination settings, the object surface is illuminated with a different distribution of il- lumination angles. This known illumination system requires a very complex second optical element with a large number of pupil facets. Elements of this type are very expensive.

An object of the present invention is to develop an illumination system of the type mentioned at the outset in such a manner that it is possible to change between various illumination settings even when a second optical element is used which has fewer facet elements.

This object is achieved according to the invention by an illumination system having the features stated in the characterising part of claim 1.

It has been found, according to the invention, that it is not absolutely necessary to reproduce all the first facet elements in one and the same image area, but that it is possible to configure the illumination field as an assembly of individual partial fields which together make up the complete illumination field. In so doing, the entire illumination field is not illuminated via any of the partial fields. This basic approach allows the second facet elements to be used in a more flexible manner. These second facet elements may be irradi- ated by a plurality of first facet elements which are at a spatial distance from one another. The partial beams of EUV radiation emanating from the various first facet elements which act on one and the same second facet element are then imaged in the various partial fields. This makes it possible to image the partial beams of EUV radiation, associated with a plurality of first facet elements, by one and the same second facet element. This flexibility allows a second optical element with a small number of second facet elements, compared to the prior art, to be used for producing various illumination settings, while still allowing the production of an illumination setting, using a second optical element of this type, in which illumination set- ting a 1 : 1 assignment of the first and second facet elements is provided. Different illumination settings may therefore be produced without a loss of light and without exchanging optical components. A conventional setting, i.e. a homogeneous illumination of the second optical element may be produced while tightly filling the second optical element. Dividing the illumi- nation field into at least two partial fields makes it possible to preset an EUV intensity profile in the displacement direction of the object. It is possible, for example, to set as the default a Gaussian, Lorenzian, Trapezoidal or other profile. By displacing the object presetting the object surface perpendicularly to the partial field division of the illumination field, it is possi- ble to ensure that the object is illuminated over all partial fields, so that each partial field plays a part in illuminating a predetermined object point. This sequential illumination of object points over the partial fields may be utilised to achieve, for example, a desired activation of a sensitive wafer layer which is an example of an object surface to be illuminated. Displaceable first facet elements according to claim 2 lead to the possibility of automatically changing between various illumination settings.

The number of partial fields according to claim 3 is at the same time the minimally required number of partial fields. The result is a compact illumination field. Two, three or more first facet elements may be allocated to a second facet element to act thereon.

A division of the illumination field according to claim 4 allows a comparatively simply constructed optical arrangement. The partial fields are adjacent to one another particularly in a scan direction of a projection illumination installation, the illumination system being the component thereof. This ensures that a substrate to be illuminated, for example a wafer which is scanned by the illumination field, passes the at least two partial fields in succession.

Curved first facet elements or partial fields according to claim 5 reduce the requirements made on the optical arrangement.

An arrangement of the facet elements according to claim 6 reduces the requirements made on the imaging, since large angles may be avoided between the individual partial beams of the EUV radiation.

Second facet elements which may be displaced by an actuator according to claim 7 increase the flexibility of the illumination system.

An illumination system according to claim 8 has low losses. - A -

An arrangement according to claim 9 allows a 1 : 1 assignment of the first facet elements to the second facet elements.

Intersections according to claims 10 to 15 between the partial fields of the illumination field have proved to be advantageous for the practical realisation of the illumination system in particular for presetting a desired sequential illumination for the object surface.

The advantages of the illumination system according to claim 16 are the same as those of the illumination system according to claim 1.

A further object of the invention is the provision of a first as well as a second optical element for the illumination system according to the invention.

This object is achieved according to the invention by optical elements in accordance with claims 17 and 18.

The advantages of these optical elements are the same as those already mentioned above with reference to the illumination system according to the invention.

Embodiments of the invention are described in more detail hereinafter with reference to the drawings. In these are shown:

Fig. 1 schematically the beam path in an illumination system for EUV microlithography; Fig. 2 schematically components of the illumination system according to Fig. 1 , more specifically a first optical element, divided into a plurality of facet elements, to produce secondary light sources in the illumination system, a second optical element divided into a plu- rality of second facet elements at the location of the generated secondary light sources as well as an illumination field on an object surface, the second facet elements being illuminated to prepare a homogeneous, conventional illumination setting;

Fig. 3 a view similar to that of Fig. 2, the second face elements being illuminated to prepare an annular setting of a large diameter;

Fig. 4 a view similar to that of Fig. 2, the second facet elements being illuminated to prepare a homogeneous illumination setting with small illumination angles compared to the illumination setting of

Fig. 2;

Fig. 5 a view similar to that of Fig. 2, the second facet elements being illuminated to prepare an illumination setting in the manner of an x-dipole;

Fig. 6 a view similar to that of Fig. 2, the second facet elements being illuminated to prepare an illumination setting in the manner of a y- dipole;

Fig. 7 a view similar to that of Fig. 3 of another embodiment having curved first facet elements; Fig. 8 a view similar to that of Fig. 2 of another embodiment having a different magnification; and

Fig. 9 a view similar to that of Fig. 3 of the embodiment according to Fig. 8.

Fig. 1 shows an illumination system 1 for illuminating a predetermined illumination field 2 of an object surface 3 with extreme ultraviolet (EUV) radiation 4.

A plasma source is used as the source 5 for the EUV radiation 4. The wavelength of the EUV radiation is, for example, between 10 and 20 nm.

A cartesian coordinate system (x, y, z) is used in Fig. 1 and 2, reference be- ing made hereinafter to the coordinates (x, y, z). In Fig. 1 , the x direction extends perpendicularly to the plane of projection, the y direction extends to the right-hand side and the z direction extends downwards.

The EUV radiation emitted from the source 5 is initially collected by a col- lector 6 which reflects the EUV radiation like all the following steel guide components. The EUV radiation 4 emitted from the source 5 impinges on a first optical element 7, also termed a field scanning element. The first optical element 7 is used to produce secondary light sources in the illumination system 1. A reflecting surface, impacted by the EUV radiation 4, of the first optical element 7 is divided into a plurality of first facet elements, of which four first facet elements 8 to 1 1 are shown by way of example in Fig. 1. The latter are associated with partial beams 12 to 15 of the EUV radiation 4. The first facet elements are rectangular, the extent thereof being substantially greater in the x direction than in the y direction. A typical aspect ratio of the first face elements 8 to 1 1 (x:y) is 20: 1.

Each of the first facet elements 8 to 11 may be tilted between various set- ting positions about axes parallel to the x direction and y direction. For this purpose, each of the first facet elements 8 to 1 1 is connected to an associated actuator. In Fig. 1 , as a representative herefor, an actuator 16 is shown which, as indicated in dashed lines at 17, is mechanically connected to the first facet element 11 for tilting said facet element 1 1 selectively about one of the two axes (x/y). The actuator 16 is connected to a central control device 19 via a control line 18. Said control device 19 is connected with all the other actuators associated with the first facet elements 8 to 1 1 and with the first facet elements which are not shown via corresponding control lines (not shown).

Examples of arrangements of first facet elements are provided in Fig. 7 to 14 of US 2003/0086524 Al, to which reference is made in full.

A second optical element 20, also termed a pupil scanning element, is posi- tioned at the location of the secondary light sources generated by the first optical element 7, i.e. in an image plane to the source 5. Said second optical element 20 is impacted by the EUV radiation 4 via the first optical element 7. The impactable surface of the second optical element 20 is divided into a plurality of second facet elements, of which four facet elements 21 to 24 are shown by way of example in Fig. 1. The second facet elements 21 to 24 are each assigned to one of the first facet elements 8 to 1 1, so that a respective secondary light source is generated at the location of the respectively charged second facet elements 21 to 24. In the illustration according to Fig. 1 , the second facet element 21 is assigned to the first facet element 8, the second facet element 23 is assigned to the first facet element 9, the second facet element 22 is assigned to the first facet element 10 and the second facet element 24 is assigned to the first facet element 1 1.

Like the first facet elements 8 to 1 1 , the second facet elements 21 to 24 and the other facet elements of the second optical element 20 which are not shown may be tilted via actuators about axes parallel to the x and y directions. Fig. 1 schematically shows, as an example herefor, an actuator 25 which is associated with the second facet element 21 and which, as shown in dashed lines at 26, is mechanically connected to the second facet element 21 to tilt said second facet element 21. The actuator 25 is also in a signal connection with the control device 19 via a control line 18.

The first facet elements as well as the second facet elements are reflective elements.

The second optical element 20 is part of an optical arrangement 27 which comprises a plurality of optical components and forms an image of the first optical element 7 in a plane 30 predetermined by the object surface 3. Two other reflecting elements 28, 29 for EUV radiation belong to the optical arrangement 27, the reflecting element 28 downstream of the second optical element 20 reflecting the EUV radiation at a small angle of incidence, for example an incidence angle of 30°, and the reflecting element 29 positioned in the subsequent beam path of EUV radiation 4 reflecting the EUV radia- tion by glancing incidence.

Fig. 2 shows in a highly diagrammatic manner allocation relations between the first and the second facet elements during image formation in the illumination field 2. In this respect, the plane of projection of Fig. 2 is parallel to the x-y plane, and this also applies to the planes of projection of the following Fig. 3 to 9. For illustration purposes, the components shown in Fig. 2 to 9 have been rotated into the x-y plane. These components may in practice also be oriented in a different way. Components in Fig. 2 to 9 which are the same as those which have already been described above with reference to Fig. 1 , have the same reference numerals and will not be described again in detail.

Fig. 2 shows the four facet elements 8 to 1 1 representing all the first facet elements of the first optical element 7. Representing all the second facet elements of the second optical element 20, the second facet elements 21 to 24 are arranged as follows in Fig.2 for illustration purposes: the second facet elements 21 and 24 are components of an inner ring consisting of second facet elements. The second facet elements 22 and 23 are components of an outer ring of second facet elements. The overall round second optical element 20 has a plurality of such concentrically arranged rings of second facet elements. The second facet elements may be arranged in the manner of an evenly distributed x/y raster. Fig. 15 of US 2003/0086524 Al gives an example of this.

The allocation of the first facet elements 8 to 1 1 to the second facet elements 21 to 24 is such that it produces a homogeneous, conventional illumination setting. Together with other second facet elements which are not shown, all the second facet elements of the second optical element 20, i.e. not only the illustrated second facet elements 21 to 24, but also all other second facet elements of the associated raster are illuminated by a respective first facet element. The second optical element 20 is thus illuminated homogeneously. The first facet elements 8 and 10 are configured and oriented in such a manner that they are imaged in a lower partial field 31 of the illumination field 2 by the optical arrangement 27 in the arrangement of Fig. 2. The first facet elements 9 and 1 1 are configured and oriented in such a manner that they are imaged in the upper partial field 32 of the illumination field 2 by the optical arrangement 27. The two partial fields 31, 32 have the same surface area. The partial fields 31, 32 have the same aspect ratio as the first facet elements 8 to 1 1. The two partial fields 31 , 32 are slightly curved ar- cuately due to the imaging properties of the optical arrangement 27. The two partial fields 31, 32 make up the complete illumination field 2. In the idealised example shown in Fig. 2, the two partial fields 31, 32 are immediately adjacent to one another, without overlapping. In practice, the two partial fields 31, 32 overlap in such a manner that the intersection of the two partial fields 31, 32, i.e. the overlap region, is always smaller than the area of each partial field 31, 32.

In the embodiment according to Fig. 2, the first facet elements 8 to 1 1 are imaged in the image plane 30 with a negative magnification.

The division of the illumination field 2 into the two partial fields 31, 32 results in a portion of every second facet element being illuminated in each of the partial fields 31 , 32, so that in each partial field, illumination takes place at selected illumination angles of all illumination angles which are present in the illumination setting according to Fig. 2. Only a superpositioning of both partial fields 31 , 32 results in the object surface 3 being illuminated at all illumination angles of the illumination setting. This superpositioning is carried out by displacing the object surface 3 in the y direction. This displacement may be carried out continuously or in steps, in which case a step length must not be greater than the y extent of a partial field. In this way, each point on the object surface 3, which point passes through both partial fields 31 , 32, integrates the exposure effect of the EUV radiation radiated therein, so that following the passage, an illumination has been carried out from all illumination angles possible in the illumination setting.

Fig. 3 shows another illumination setting which is possible with the arrangement of Fig.1. This other illumination setting is what is known as a large annular setting. Starting from the situation according to Fig. 2, this large annular setting is set by tilting the first facet element 8 about its longi- tudinal axis parallel to the x direction and by tilting the second facet element 1 1 about its longitudinal axis parallel to the y direction. As a result of these tilting actions, the first facet element 8 now acts on the second facet element 23 and the first facet element 11 acts on the second facet element 22. The second facet element 22 is thus associated with two first facet ele- ments, more specifically the first facet elements 10 and 1 1. Accordingly, the second facet element 23 is associated with the first facet elements 8 and 9. The second facet elements 22, 23 are arranged in such a manner that in the illumination setting according to Fig. 3, they are thus acted on respectively by two different adjacent first facet elements, more specifically on the one hand the first facet elements 10 and 11 and on the other hand by the first facet element 8, 9. The second facet elements 21 , 24 are not acted on by the first optical element 7.

In Fig. 3, as in the setting according to Fig. 2, the lower partial field 31 is impacted by radiation from the first facet element 8 and 10. The upper partial field 32 is impacted by radiation from the first facet elements 9 and 1 1.

It is not necessary to displace the second facet elements 22, 23 when changing the illumination settings between those shown in Fig. 2 and 3. In the annular setting according to Fig. 3, the illumination angle varies between a minimum illumination angle different from zero and a maximum illumination angle.

Fig. 4 shows another illumination setting which may be produced with the arrangement according to Fig. 1 and 2. This is what is known as a small conventional setting with a maximum illumination angle which is smaller than the minimum illumination angle of the annular setting according to Fig. 3.

Compared to the setting of Fig. 2, in Fig. 4 the two first facet elements 9 and 10 are tilted in the x and y direction respectively. The first facet element 9, together with the first facet element 8 now acts on the second facet ele- ment 21. The first facet element 10, together with the first facet element 1 1 , now impacts on the second facet element 24. The second facet elements 22, 23 are not acted on by the first optical element 7.

As in the setting according to Fig.2, in Fig. 4 the lower partial field 31 is impacted by radiation from the first facet elements 8 and 10. The upper partial field 32 is impacted by radiation from the first facet elements 9 and 11.

It is unnecessary to displace the second facet elements 21 and 24 when changing between the illumination settings according to Fig. 2 and 4.

Fig. 5 shows another illumination setting which may be produced with the arrangement according to Fig. 1 and 2. This is an illumination setting in the manner of what is known as an x - dipole. In this case, illumination takes place in the x - z plane over a range of illumination angles which corre- sponds to the conventional setting according to Fig. 2. Perpendicularly hereto, i.e. in the y - z plane, illumination takes place in a region of smaller illumination angles which may increase outwardly.

In the setting according to Fig. 5, the beam path, starting from the first facet elements 10, 11, corresponds to the beam path of the setting according to Fig. 3. The radiation emanating from the first facet elements 8 and 9 jointly impact the second facet element 24, the radiation emanating from the first facet element 8 being imaged in the lower partial fields 31 and the radiation emanating from the first facet element 9 being imaged in the upper partial field 32.

During the transition between the illumination settings according to Fig. 2 and 5, it is necessary to tilt the second facet element 24 to ensure that the radiation emanating from the first facet elements 8 and 9 is in fact correctly imaged in the illumination field 2.

Fig. 6 shows another illumination setting which may be produced in the arrangement according to Fig. 1 and 2. This is an illumination setting in the manner of what is known as y-dipole mode. According to that carried out in connection with the setting of Fig. 5, the illumination angles in the illumination field are distributed in the setting of Fig. 6 in such a manner that there is an angle distribution in the y - z plane as in the conventional setting according to Fig. 2 and there is an illumination angle distribution in the x - z plane which corresponds to that in the y - z plane of the setting according to Fig. 5.

Compared to the setting of Fig. 2, to adjust the setting according to Fig. 6, not only must the first facet elements 8, 10 and 1 1 be tilted but also the sec- ond facet element 21 so that the radiation emanating from the first facet elements 10, 1 1 is correctly imaged in the illumination field 2.

In the setting according to Fig. 6, the first facet elements 8, 9 jointly eradi- ate the second facet element 23 and the first facet elements 10, 1 1 jointly eradiate the second facet element 21.

Fig. 7 shows another embodiment of an illumination system like the illumination system of Fig. 1 and 2, adjusted in to an illumination setting like the setting of Fig. 3. Components corresponding to those which have already been described above with reference to Fig. 1 to 6, have the same reference numerals and will not be described again in detail. In contrast to the rectangular first facet elements of the embodiments according to Fig. 1 and 2, the first optical element 7 of the arrangement according to Fig. 7 has slightly arcuately curved first facet elements 8 to 1 1.

The curved first facet elements 8 to 1 1 are imaged in the curved partial fields 31, 32 by the optical arrangement 27.

Fig. 8 and 9 show another embodiment of an illumination system 1. Components which correspond to those already described above with reference to Fig. 1 to 7 have the same reference numerals and are not described again in more detail.

In contrast to the embodiments according to fig. 1 to 7, the optical arrangement 27 of the embodiment according to Fig. 8 and 9, to which belong the second optical element 20 as well other reflective elements like the elements 28 and 29, (not shown) has a positive magnification. In the embodiment according to Fig. 8 and 9, this results in the first facet elements 9 and 1 1 now being imaged in the lower partial field 31 of the illumination field 2. The first facet elements 8 and 10 are imaged in the upper partial field 32.

Fig. 8 shows a conventional setting corresponding to that of Fig. 2. In re- spect of the guidance of the partial beams 12 to 15, the first facet element 8 is associated with the second facet element 23, the first facet element 9 is associated with the second facet element 21 , the first facet element 10 is associated with the second facet element 22 and the first facet element 1 1 is associated with the second facet element 24.

In the arrangement according to Fig. 8, Fig. 9 shows another illumination setting produced by tilting the first facet elements 9 and 1 1 , so that a large annular setting like the setting of Fig. 3 is produced. The second facet element 23 is jointly acted on by the two first facet elements 8 and 9. The sec- ond facet element 22 is jointly acted on by the two first facet elements 10 and 11.

The illumination system 1 is part of a projection illumination installation for microlithography, with which an object having the object surface, i.e. for example a mask or a reticle, is imaged on a wafer to produce integrated components, for example microprocessors or memory chips.

The first optical element 7 may be configured such that only specific first facet elements may be tilted by actuators, while other first facet elements are stationary. The second optical element 20 may also be equipped accordingly with tillable and stationary second facet elements. It also possible to equip the second optical element 20 in general with stationary second facet elements, in other words, not to provide a tilting option there. The number of first facet elements of the first optical element 7 is identical to the number of the second facet elements of the second optical element 20. Alternatively, it is possible to provide a second optical element 20, the number of facet elements thereof being greater or smaller than the number of the first facet elements of the first optical element.

In the embodiments described above, a maximum of two first facet elements 8 to 1 1 are associated with the second facet elements 21 to 24. It is also possible for more than two first facet elements to be associated in each case with a second facet element. The minimum number of the partial fields constructing the illumination field increases accordingly.

In principle, it is possible also to configure at least individual components of the illumination system as transmissive components.

Claims

1. Illumination system (1) for EUV lithography for illuminating a predetermined illumination field (2) of an object surface (3) with EUV radia- tion (4) a) with a first optical element (7) for producing secondary light sources in the illumination system ( 1), aa) which first optical element (7) is impacted by the EUV radiation (4), ab) the impacted surface of which first optical element (7) is divided into a plurality of first facet elements (8 to 11) which are each assigned to partial beams (12 to 15) of the EUV radiation

(4), b) with a second optical element (20) at the location of the secondary light sources generated by the first optical element (7), ba) which second optical element (20) is impacted with EUV radiation (4) via the first optical element (7), bb) the impactable surface of which is divided into a plurality of second facet elements (21 to 24) which are each assigned to at least one of the first facet elements (8 to 1 1) acting on the respective second facet element (21 to 24) to produce the secondary light sources, be) which is at least part of an optical arrangement (27) which images the first optical element (8 to 1 1) in a plane (30) prede- termined by the object surface (3), characterised in that c) at least two of the first facet elements (8 to 1 1) are configured and oriented such that they are imaged by the optical arrangement (27) in one and the same of at least two partial fields (31 , 32) of the illumination field (2) which make up the entire illumination field (2), an intersection between the partial fields (31, 32), if such an intersection exists, always being smaller than each of the partial fields (31, 32) contributing to the intersection.

2. Illumination system according to claim 1 for the selective illumination of a predetermined illumination field (2) of an object surface (3) with EUV radiation (4) in a setting selected from various predeterminable illumination settings, characterised in that be) at least selections of the first facet elements (8 to 1 1) may be moved between various setting positions by actuators (16) associated in each case with the selected first facet elements (8 to

H), bd) in each setting position of the movable first facet element (8 to 1 1), the partial beam (12 to 15) associated in each case therewith being deflected by the movable first facet element (8 to 11) to produce one of the predetermined illumination settings, e) at least one of the second facet elements (21 to 24) being positioned in such a manner that it may be acted on by at least two different first facet elements (8 to 1 1) in at least one of the predetermined illumination settings.

3. Illumination system according to claim 1 or 2, characterised by the configuration thereof such that the number of the partial fields (31, 32) corresponds to the maximum number of first facet elements (8 to 1 1) which are able to act on the same second facet element (12 to 24).

4. Illumination system according to any one of claims 1 to 3, characterised in that the illumination field is divided into at least two adjacent partial fϊelds (31 , 32) in the form of partial field strips, in particular with the same surface area.

5. Illumination system according to claim 4, characterised in that the first facet elements (8 to 1 1) and/or the partial fields (31 , 32) are curved.

6. Illumination system according to any one of claims 1 to 5, characterised in that at least one of the second facet elements (21 to 24) is arranged in such a way that it may be acted on by precisely two adjacent first facet elements (8 to 11).

7. Illumination system according to any one of claims 2 to 6, characterised in that at least one of the second facet elements (21 to 24) may be displaced between various setting positions using actuators (25) associated in each case with the selected second facet elements (21 to 24).

8. Illumination system according to any one of claims 1 to 7, characterised in that the first and/or second facet elements (8 to 1 1 ; 21 to 24) are configured as reflective elements.

9. Illumination system according to any one of claims 1 to 8, characterised in that the number of the first facet elements (8 to 1 1) is identical to the number of the second facet elements (21 to 24).

10. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31 , 32) is less than 95 % of the smallest partial field (31 , 32) contributing to the intersection.

1 1. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31, 32) is less than

90 % of the smallest partial field (31, 32) contributing to the intersection.

12. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31, 32) is less than

80 % of the smallest partial field (31, 32) contributing to the intersection.

13. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31, 32) is less than

60 % of the smallest partial field (31, 32) contributing to the intersection.

14. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31, 32) is less than

40 % of the smallest partial field (31 , 32) contributing to the intersection.

15. Illumination system according to any one of claims 1 to 9, characterised in that the intersection between the partial fields (31 , 32) is less than

20 % of the smallest partial field (31 , 32) contributing to the intersection.

16. Illumination system (1) for EUV lithography for illuminating a predetermined illumination field (2) of an object surface (3) with EUV radiation (4) a) with a first optical element (7) for producing secondary light sources in the illumination system (1), aa) which first optical element (7) is impacted by EUV radiation

(4), ab) the impacted surface of which first optical element (7) is divided into a plurality of first facet elements (8 to 1 1) which are each assigned to partial beams (12 to 15) of the EUV radiation

(4), b) with a second optical element (20) at the location of the secondary light sources generated by the first optical element (7), ba) which is impacted with EUV radiation (4) via the first optical element (7), bb) the impactable surface of which is divided into a plurality of second facet elements (21 to 24) which are each assigned to at least one of the first facet elements (8 to 11) acting on the respective second facet element (21 to 24) to generate the secondary light sources, be) which is at least part of an optical arrangement (27) which images the first optical element (8 to 1 1) in a plane (30) predetermined by the object surface (3), characterised in that at least two of the first facet elements (8 to 1 1) are imaged in the illumination field (2) via one and the same second facet element (21 to 24).

17. First optical element (7) for use in an illumination system (1) according to any one of claims 1 to 16.

18. Second optical element (20) for use in an illumination system (1) according to any one of claims 1 to 16.