Imaging EUV optical unit

Abstract

An imaging EUV optical unit (10) has a plurality of mirrors (M1 to M6) for guiding imaging light (16) along an imaging beam path from an object field (5) to an image field (11). The imaging optical unit (10) has a total apodization tilt APO Z3 which is less than 10%. A beam path intersection region (K1, K2, K3) is present between a first partial beam path (M1M2, M2M3) and a second partial beam path (M3M4, M4M5) in the imaging beam path. The first partial beam path (M1M2, M2M3) lies between a mirror (M1, M2) and a mirror (M2, M3) directly following said mirror in the imaging beam path. The second partial beam path (M3M4, M4M5) lies between a further mirror (M3M4) and a mirror (M4M5) directly following said further mirror in the imaging beam path. An object image shift (dOIS) is greater than 250 mm. The result is an imaging EUV optical unit having improved usability for an EUV projection exposure apparatus.

Description

[0001] Imaging EUV optics

[0002] The content of the German patent application DE 10 2024 207 939.1 is incorporated herein by reference.

[0003] The invention relates to an imaging EUV optic for guiding imaging light along an imaging beam path from an object field to an image field. Furthermore, the invention relates to an optical system with such an imaging optic, a projection exposure system with such an optical system, a method for producing a micro- or nanostructured component with such a projection exposure system, and a micro- or nanostructured component produced by this method.

[0004] Projection optics of the type mentioned above are known from US 7,151 592 B2, from WO 2016 / 188934 Al, from DE 10 2016 218 996 Al, from WO 2018 / 010960 Al, from DE 10 2015 209 827 Al, from DE 10 2012212 753 Al, from US 2010 / 0149509 Al and from US 4,964,706.

[0005] It is an object of the present invention to further develop an imaging EUV optic of the type mentioned at the outset in such a way that its usability for an EUV projection exposure system is improved.

[0006] According to a first aspect of the invention, the problem is solved by an imaging EUV optic with the features specified in claim 1.

[0007] According to the invention, it was discovered that an imaging optic with a low absolute total apodization tilt APO Z3 enables the desired uniform illumination of the image field via a single pupil of the imaging optic. Furthermore, it was discovered that the use of a beam path intersection area can advantageously lead to a reduction in the absolute value of the total apodization tilt Z3, since, due to the at least one beam path intersection area, contributions from the individual mirrors to the apodization tilt can have opposite signs. The large object-image offset avoids undesirable space constraints when using the imaging optic. The object-image offset can be greater than 400 mm, greater than 500 mm, greater than 600 mm, greater than 700 mm, greater than 800 mm, greater than 900 mm, and even greater than 1,000 mm.

[0008] The imaging optics can be used in a projection exposure system for lithography, particularly for EUV lithography, and can therefore be used with imaging light having a wavelength in the range of 5 nm to 30 nm, for example, 13.5 nm. The total apodization tilt can be less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2%, and, in particular, less than 1%. Typically, the total apodization tilt is greater than 0.001%. The at least one beam path intersection can occur between a first partial beam path between a first and a second mirror on the one hand, and another partial beam path between a third and a fourth mirror on the other hand, within the imaging beam path of the imaging optics.Alternatively or additionally, the beam path intersection area can be located between a first partial beam path between the first and second mirrors on the one hand, and another partial beam path between the fourth and fifth mirrors on the other, along the imaging beam path of the imaging optics. Again, alternatively or additionally, the beam path intersection area can be located between a first partial beam path between a second and a third mirror on the one hand, and another partial beam path between a fourth and a fifth mirror on the other, along the imaging beam path of the imaging optics.

[0009] The imaging optics can have more than one such beam path intersection area, for example two or three or, depending on the design, even more beam path intersection areas.

[0010] Exactly three beam path intersection areas according to claim 2 have proven effective in practice.

[0011] This applies accordingly to an object-image offset according to claim 3. An Nl-mirror embodiment of the imaging optics according to claim 4 has advantages with regard to the manufacturing effort of the mirrors and / or the adjustment effort. The imaging optics can be designed such that it does not have a grazing-incident mirror, i.e., no mirror that provides angles of incidence for imaging light greater than 45°.

[0012] A number of mirrors according to claim 5 has also proven effective in practice and represents a good compromise between aberration correction and overall transmission of the imaging optics. Depending on the design, the imaging optics can also have fewer than six mirrors, for example four or five mirrors, or more than six mirrors, for example seven, eight, nine, or ten mirrors, or even more mirrors if necessary.

[0013] An intermediate image according to claim 6 can, depending on the embodiment of the imaging optics, facilitate beam guidance along the imaging beam path. Furthermore, it can advantageously result in a reduced mirror area of ​​at least selected mirrors of the imaging optics. The intermediate image can be located along the imaging beam path between a fourth and a fifth mirror, or between a third and a fourth mirror of the imaging optics. The distance between the intermediate image and a final mirror of the imaging beam path before the image field can be more than 50% of the distance between this final mirror and the image field. This can contribute to generating a low overall apodization tilt.Furthermore, a suitable intermediate image arrangement can make it possible to keep the angle of incidence on mirrors of the imaging optics, which belong to partial beam paths of at least one crossing area, comparatively low, especially less than 20 degrees.

[0014] A total mirror surface area according to claim 7 reduces the manufacturing effort for the mirrors of the imaging optics. The total mirror surface area without overflow can be a maximum of 0.7 m². 2 , can be a maximum of 0.6 m 2 can be 0.58 m 2 The maximum length is 0.55 m. 2 The maximum distance is 0.5 m. 2 , at most 0.45 m 2 , can 0.43 m 2 amount to and can also be 0.42 m 2 The total mirror surface area is regularly greater than 0.2 m². 2The total mirror area represents the sum of all usable mirror areas of the majority of the mirrors. A total transmission of the imaging EUV optics according to claim 8 results in an advantageously high imaging light throughput. The total transmission is obtained by multiplying the individual mirror transmissions of the mirrors of the imaging optics. This total transmission can be greater than 6%, greater than 7%, greater than 8%, and can, for example, be 8.25%. When used with EUV imaging light, the total transmission is typically less than 20%.

[0015] An entrance pupil of the imaging EUV optics can be located in the beam path of the illumination and imaging light in front of the object field and thus be accessible to an optical component of an optical system of a projection exposure unit, of which the imaging EUV optics are a part, that is arranged in this beam path in front of the object field. Such an optical component can be a mirror, in particular a faceted mirror, of an illumination optic of the projection unit, for example a pupil faceted mirror.

[0016] The imaging EUV optics can have an accessible entrance pupil in a beam path of imaging light in front of the object field at a distance between 1 m and 4 m in front of the object field. The position of such an entrance pupil can be approximately the same in a meridional plane and in a sagittal plane perpendicular to it.

[0017] The imaging EUV optics can have a pupil plane in the beam path between the object field and the image field. The pupil or aperture plane can lie on one of the mirrors of the imaging EUV optics, in particular on an NL mirror.

[0018] The advantages of an optical system according to claim 9, a projection exposure system according to claim 10, a manufacturing method according to claim 11, and a micro- or nanostructured component according to claim 12 correspond to those already explained above with reference to the projection optics according to the invention. The EUV light source of the projection exposure system can be configured to produce a useful wavelength of at most 13.5 nm, less than 13.5 nm, less than 10 nm, less than 8 nm, less than 7 nm, and, for example, 6.7 nm or 6.9 nm. A useful wavelength of less than 6.7 nm, and particularly in the range of 6 nm, is also possible.

[0019] The projection exposure system can be used to manufacture, in particular, a semiconductor component, for example a memory chip.

[0020] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawing. The drawing shows:

[0021] Fig. 1 schematically shows a projection exposure system for EUV projection lithography in meridional section;

[0022] Fig. 2 also shows in a meridional section an embodiment of an imaging optic which is used as a projection lens in the projection exposure system according to Fig. 1, wherein an imaging beam path for principal rays, an upper and a lower coma ray of several selected field points is shown;

[0023] Fig. 3 shows a view of the imaging optics from viewing direction III in Fig. 2, wherein

[0024] Mirrors of the imaging optics are shown transparently for illustrative purposes, where this is necessary to make behind them visible;

[0025] Fig. 4 shows a further embodiment of the imaging optics in a representation similar to Fig. 2;

[0026] Fig. 5 shows a view of the imaging optics from the viewing direction V in Fig. 4, similar to Fig. 3; Fig. 6 shows a further embodiment of the imaging optics, similar to Fig. 2;

[0027] Fig. 7, in a representation similar to Fig. 3, shows a view of the imaging optics from viewing direction VII in Fig. 6.

[0028] The following section describes, with reference to Figure 1, the essential components of a projection exposure system 1 for microlithography. This description of the basic structure of the projection exposure system 1 and its components is not intended to be restrictive.

[0029] One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, a lighting optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the rest of the lighting system. In this case, the lighting system does not include the light source 3.

[0030] A reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in one scanning direction, via a reticule displacement drive 9.

[0031] Figure 1 shows a Cartesian xyz coordinate system for illustrative purposes. The x-direction runs perpendicular to the plane of the drawing. The y-direction runs horizontally, and the z-direction runs vertically. In Figure 1, the scan direction runs along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0032] The object field 5 can be semi-ring-shaped or rectangular.

[0033] The projection exposure system 1 includes a projection optic or imaging optic 10.

[0034] The projection optics 10 serve to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0035] The details of the imaging optics 10 used in the projection exposure system 1 are explained below with reference to Figures 2 ff.

[0036] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction, via a wafer transfer drive 15. When the projection exposure system 1 is configured as a scanner, this y-direction of movement is also referred to as the scan direction. The movement of the reticulum 7 via the reticulum transfer drive 9 and the movement of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0037] Radiation source 3 is an EUV radiation source. Radiation source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, imaging radiation, illumination light, or imaging light. The useful radiation has a wavelength in the range between 5 nm and 30 nm. Radiation source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. Radiation source 3 can be a free-electron laser (FEL). The radiation source can be a tin-based or xexon-based EUV radiation source.

[0038] The illumination radiation 16 emanating from the radiation source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated with the illumination radiation 16 at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0039] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector 17, and the illumination optics 4.

[0040] The illumination optics 4 comprise a first faceted mirror 19. If the first faceted mirror 19 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6, it is also referred to as a field faceted mirror. The first faceted mirror 19 comprises a plurality of individual first facets 20, which are hereinafter also referred to as field facets. Only a few of these facets are shown in Figure 1 as examples.

[0041] The first facets 20 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular border contour. The first facets 20 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0042] As is known, for example, from DE 10 2008 009 600 Al, the first facets 20 themselves can each be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 19 can in particular be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 Al.

[0043] Between the intermediate focus in the intermediate focal plane 18 and the first faceted mirror 19, a deflecting mirror US is located in the beam path of the illumination optics 4. This deflecting mirror can be a plane mirror or, alternatively, can have a beam-shaping effect. A second faceted mirror 21 is positioned downstream of the first faceted mirror 19 in the beam path of the illumination optics 4. If the second faceted mirror 21 is located in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted mirror 21 can also be positioned at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first faceted mirror 19 and the second faceted mirror 21 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 Al, EP 1 614 008 Bl and US 6,573,978.

[0044] The second facet mirror 21 comprises a plurality of second facets 22. The second facets 22 are also referred to as pupil facets in the case of a pupil facet mirror.

[0045] The second facets 22 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 Al in this regard.

[0046] The second facets 22 can have planar or alternatively convex or concave curved reflective surfaces.

[0047] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (Fly's Eye Integrator).

[0048] It can be advantageous not to arrange the second faceted mirror 21 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the pupil faceted mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0049] With the aid of the second faceted mirror 21 and, optionally, with an imaging optical assembly in the form of a transmission optic (not shown in Figure 1), the individual first facets 20 are imaged into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors arranged one behind the other in the beam path of the illumination optic 4. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (N1 mirrors) and / or one or two mirrors for grazing incidence (Gl mirrors). In the embodiment shown in Figure 1, the illumination optic 4 thus has exactly three mirrors after the collector 17: the deflecting mirror US, the first faceted mirror 19, and the second faceted mirror 21.

[0050] Insofar as the transmission optics are omitted after the second faceted mirror 21, the second faceted mirror 21 is the last beam-shaping or indeed the last mirror for the illumination radiation 16 in the beam path before the object field 5. An example of an illumination optics 4 without transmission optics is disclosed in Figure 2 of WO 2019 / 096654 Al.

[0051] The mapping of the first facets 20 by means of the second facets 22 or with the second facets 22 and a transmission optic into the object plane 6 is regularly only an approximate mapping.

[0052] The projection optics 10 comprise a plurality of mirrors, which are numbered according to their sequence in the beam path of the projection exposure system 1 in the following embodiments of the projection optics shown in Fig. 2 ff.

[0053] In the example shown in Figure 2, the projection optics 10 comprise six mirrors M1 to M6. Alternatives with four, five or another number of mirrors Mi are also possible.

[0054] The projection optics 10 are unobstructed optics. None of the mirrors M1 to M6 have a passage opening for the illumination radiation 16.

[0055] The projection optic 10 has an image-side numerical aperture of 0.33. Depending on the specific design of the projection optic 10, the image-side numerical aperture can range, for example, between 0.25 and 0.4. The image-side numerical aperture of the projection optic 10 can also assume other values ​​depending on the specific design.

[0056] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, e.g., with alternating layers of molybdenum and silicon. A ruthenium coating is also possible, particularly for coating mirrors for grazing incidence (GL mirrors).

[0057] The projection optics 10 result in a reduction in size by a ratio of 4:1 (β = 4.00). The magnification β is positive; therefore, the projection optics 10 does not produce an image inversion during projection. Alternatively, the projection optics 10 can also be designed in such a way that it produces an image inversion.

[0058] The sign convention for the image scale β is as follows: with a negative image scale, there is no intermediate image, not even in the form of a caustic, between the object field 5 and the image field 11, whereas with a positive image scale, there is indeed an intermediate image, possibly in the form of a caustic.

[0059] In yet another alternative design of the projection optics 10, this can, for example, lead to an image reversal in the x-direction, i.e., in the direction perpendicular to the scan direction y. A magnification β xIn the x-direction, the value is therefore -4.00. In the y-scan direction, this design of the projection optics can then lead to a reduction of 4:1, this time without image inversion (β). y = + 4.00).

[0060] In another embodiment, the projection optic 10 can also be anamorphic. It then exhibits different image scales β. x , ßy in the x and y directions.

[0061] The two image scales ß x , ß y the projection optics 10 are preferably located at (ß X , ßy) = (+ / - 4, + / - 8). Other scales are also possible. Scales with the same sign in the x and y directions are also possible.

[0062] The image field 11 has an x-dimension of 26 mm and a y-dimension of 2.8 mm. The x / y aspect ratio of the image field 11 is 9.3. Depending on the design of the projection optics 10, this aspect ratio can range, for example, between 2 and 20.

[0063] The image field can be designed in a partially ring shape.

[0064] Alternatively, the image field can also be rectangular.

[0065] Each pupil facet 22 is assigned to exactly one of the field facets 20 to form an illumination channel for illuminating the object field 5. This can result in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 by means of the field facets 20. The field facets 20 generate a plurality of images of the intermediate focus on the pupil facets 22 assigned to each of them.

[0066] The field facets 20 are each superimposed on the reticulum 7 by an associated pupil facet 22 to illuminate the object field 5. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0067] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, in particular the subset of pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill. A similarly desirable pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

[0068] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0069] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible.

[0070] The projection optics 10 are approximately telecentric in the x-direction on the object side.

[0071] In one variant, the projection optics have an entrance pupil EP (see Fig. 1) located in the beam path between 1500 mm and 3500 mm in the x-direction and also in the y-direction in front of the object field 5, and in particular in the range between 1800 mm and 2200 mm or between 2000 mm and 3500 mm. A plane of arrangement for this entrance pupil is shown in Figure 1 at EP. Therefore, if the pupil facet mirror 21 is arranged in the beam path of the illumination or imaging light 16 approximately 2 m in front of the object field 5, the pupil facet mirror 21 satisfies the positional condition "arrangement in the region of the entrance pupil of the projection optics".

[0072] If the entrance pupil is inaccessible, an arrangement plane of the pupil facet mirror 21 can be imaged into the entrance pupil with the help of further components of the illumination optics 4.

[0073] The entrance pupil of the projection optics 10 cannot always be illuminated exactly by the pupil facet mirror 21. When the projection optics 10 image the center of the pupil facet mirror 21 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature. It is possible that the projection optics 10 has different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, especially an optical component of the transmission optics, should be provided between the second facet mirror 21 and the reticule 7.With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0074] In the arrangement of the components of the illumination optics 4 shown in Figure 1, the pupil facet mirror 21 is tilted relative to the object plane 5. The second facet mirror 21 is further tilted relative to an arrangement plane defined by the first facet mirror 19.

[0075] Using the projection exposure system 1, at least a portion of the reticulum 7 in the object field 5 is imaged onto an area of ​​a photosensitive layer on the wafer 13 in the image field 11 for the lithographic fabrication of a micro- or nanostructured component, in particular a semiconductor component, for example a microchip. Depending on whether the projection exposure system 1 is configured as a scanner or a stepper, the reticulum 7 and the wafer 13 are moved continuously in the y-direction in scanner mode or stepwise in stepper mode, synchronized over time.

[0076] Depending on the design, individual components or component assemblies described above, such as the EUV collector 17, the illumination optics 4, or the projection optics 10, can also be components of a mask inspection device or a mask metrology device. A mask inspection system is generally known from US 10,042,248 B2, DE 102 20 815 A1, and WO 2012 / 101 269 A1.

[0077] The projection optics or imaging optics of such a mask inspection device or mask metrology device can be designed such that a magnifying projection or imaging from the object field 5 into the image field 11 takes place. Further details of the projection optics 10 are described below with reference to Figures 2 and 3.

[0078] The projection optics 10 have a total of six mirrors M1 to M6, all of which are designed as Ni mirrors (normal incidence mirrors). The imaging light 16 is incident on these Ni mirrors M1 to M6 at angles of incidence less than 45°. The maximum angle of incidence of the imaging light 16 striking the respective Ni mirror can be less than 40°, less than 35°, less than 30°, less than 25°, less than 20°, less than 15°, and less than 10°.

[0079] Information on the reflectivity of Ni mirrors (normal incidence mirrors) can be found in DE 101 55 711 A.

[0080] The mirrors M1 to M6 have no through-hole and are each used reflectively in a completely continuous area.

[0081] Figure 2 shows the calculated reflective surfaces of mirrors M1 to M6. The usable reflective surfaces of mirrors M1 to M6 are supported in a known manner by mirror bodies (not shown). The actual usable reflective surfaces of mirrors M1 to M6 comprise the reflective surfaces actually used for reflecting the imaging light 16, as well as a polishing overflow edge. The polishing overflow edge, which surrounds the reflective mirror surface actually used for reflection and projects at least 10 mm beyond this reflective mirror surface along its entire circumference, is thus incorporated into the usable reflective surfaces of mirrors M1 to M6. Therefore, between the reflective mirror surface and an area of ​​the mirror surface that is no longer polished, there is a projection of at least 10 mm in the form of the polishing overflow edge.

[0082] The image field 11 in the projection optics 10 is a ring field with a ring field radius of 80 mm.

[0083] The object plane 6 and the image plane 12 are approximately parallel to each other. The distance Z between the object plane 6 and the image plane 12 along the z-direction is 2,050 mm.

[0084] Between the object field 5 and the image field 11, the projection optics 10 have an intermediate image 23 in the form of an intermediate field area, which can also have the shape of a caustic. The intermediate image 23 lies in the imaging beam path of the imaging light 16 between the mirrors M4 and M5.

[0085] Fig. 3 shows a view of the projection optics 10 along the z-coordinate. This view is defined according to the specification of the xyz coordinate system such that the projection optics

[0086] 10 is viewed from a direction opposite to the z-coordinate direction. For illustration, all mirrors M1 to M6 are shown transparently, so that any mirrors Mi behind them are also visible with their entire edges.

[0087] The object-image offset dois is 1,101 mm. The object-image offset dois is calculated between a central field point of object field 5 and a central field point of image field 5.

[0088] 11 measured perpendicular to a normal N to the image plane 12. This object-image offset dois is smaller than the distance Z, and therefore also smaller than the spatial distance between the object field 5 and the image field 11.

[0089] The object-image offset (dois) is greater than 250 mm, depending on the design of the projection optics.

[0090] The total transmission of the projection optics 10, which results from the product of the EUV reflectivities of the mirrors M1 to M6 for the illumination light 16 along the imaging beam path through the projection optics 10, is 8.25% for the projection optics 10 according to Figure 2. On average, each individual mirror M1 to M6 therefore has a reflectivity of 66%.

[0091] The total transmission of mirrors M1 to M6, i.e., the total transmission of the projection optics 10, is therefore greater than 8%. The projection optics 10 is approximately telecentric on the object side. The distance between an entrance pupil in the yz meridional plane on the one hand and in the xz plane on the other hand and the object plane 6 is very large in each case, amounting to approximately 10 m in the yz plane (position of the entrance pupil (y)) and approximately 18 m in the xz plane (position of the entrance pupil (x)).

[0092] In the imaging light beam path before the intermediate image 23, the projection optics 10 has a pupil plane between the mirrors M3 and M4. The aperture of the projection optics 10 can be limited by means of an aperture diaphragm that limits the imaging beam path, particularly at its edges, and is arranged in the region of this pupil plane. If necessary, internal obscuration can also be defined by means of a corresponding aperture section. The aperture diaphragm can be designed as a multi-part diaphragm, e.g., a three-part diaphragm. A corresponding multi-part diaphragm is known from DE 10 2016 218 996 A1 and from WO 2016 / 188934 A1.

[0093] The z-distance between mirror M5 and image field 11 is 70 mm.

[0094] The entire projection optics assembly 10 can be housed in a cuboid with xyz edge lengths of 486 mm, 1272 mm, and 1649 mm. The thicknesses of the mirrors M1 to M6, i.e., the thicknesses of the respective mirror substrates, are not taken into account in the calculation of this installation space.

[0095] The projection optics 10 are telecentric on the image side.

[0096] Mirrors M1 to M6 are coated with a layer that optimizes their reflectivity for the imaging light. This layer can be a multilayer coating, with successive layers made of different materials. Alternating layers of materials can also be used. A typical multilayer coating may consist of fifty bilayers, each comprising a layer of molybdenum and a layer of silicon, or a layer of boron and a layer of lanthanum. Layers containing lanthanum nitride and / or boron, particularly B4C, can also be used.

[0097] The projection optics 10 has a total of three beam path intersection regions between partial beam paths of the imaging beam path, each between one of the mirrors Mi and the mirror Mi+1 directly following it in the imaging beam path. The respective intersecting partial beam paths are subsequently referred to as MiMi+1 and are defined as the partial beam path of the imaging beam path between the mirror Mi and the directly following mirror Mi+1.

[0098] This involves a beam path intersection area Kl between a first partial beam path M1M2 between mirror M1 and mirror M2 on the one hand, and a second partial beam path M3M4 between mirror M3 and the subsequent mirror M4 on the other. A further beam path intersection area K2 lies between partial beam path M1M2 and partial beam path M4M5. The third beam path intersection area K3 lies between partial beam path M2M3 and partial beam path M4M5.

[0099] The intersection areas K2 and K3 of the projection optics 10 overlap each other, with an overlap area between these beam path intersection areas K2 and K3 being larger than half the extent of the respective beam path intersection areas K2 and K3.

[0100] Due to these beam path intersection areas Kl to K3, the mirror M4 lies between the object field 5 and the mirror M2 when viewed along the y-direction.

[0101] The intermediate image 23 lies in the beam path intersection area K2 and also in the beam path intersection area K3.

[0102] Due to these beam path intersection regions Kl to K3, a comparatively small apodization tilt APO Z3 results in the projection optics 10. The apodization tilt APO Z3 describes a linear intensity profile in the y-direction (meridional) across the pupil of the projection optics 10. It can be approximately determined by the intensity I of the imaging light 16 after reflectivity at the mirror Mi of three rays from the central field point: the principal ray (PS), the upper coma ray (OC), and the lower coma ray (LC). The apodization tilt APO Z3 in % is calculated from these rays as

[0103] IOK denotes the intensity I of the upper coma ray after reflection at mirror Mi. IUK denotes the intensity of the lower coma ray UK after reflection at mirror Mi. Ins denotes the intensity of the principal ray HS after reflection at mirror Mi.

[0104] The apodization tilt of the APO Z3 has a negative sign when the intensity of the upper mirror (OK) is lower than that of the lower mirror (UK). This regularly occurs due to the reflectivity properties of the coatings on mirrors M1 to M6 when the angle of incidence of the upper mirror is greater than that of the lower mirror.

[0105] The cumulative total apodization tilt of the APO Z3 projection optics is 3.71%, which is absolutely less than 10%.

[0106] Table 1 below summarizes parameters of the projection optics 10. In addition to the data already explained above, Table 1 also gives values ​​for the angle of a main ray from a central field point to the z-axis (5.99°), as well as a usable étendue of the projection optics and a mean wavefront error (RMS). The mean wavefront error (RMS) for the projection optics 10 is 9.5 mK. This mean wavefront error is therefore less than 50 mA, less than 25 mA, less than 20 mA, less than 15 mA, and, in particular, less than 10 mV across the entire used image field 11.

[0107] Table 1 for Fig. 2

[0108] The following Table 2a summarizes geometric data of the projection optics 10, namely x, y, and z coordinate values ​​of the fields, the mirrors, and the aperture diaphragm of the projection optics 10, where the origin of the coordinate system is defined as the center of the image field 11. The centers of the fields, the mirrors, and the aperture diaphragm are all located at the x-coordinate 0. The last mirror M6 in the imaging beam path, which defines the image-side numerical aperture, has its center at the x, y-coordinate values ​​0, 0.

[0109] Table 2a for Fig. 2

[0110] Table 2b summarizes how the mirrors and the aperture diaphragm are tilted about the three coordinate axes.

[0111] Table 2b for Fig. 2

[0112] The following tables 3a, 3b summarize the parameters “maximum angle of incidence”, “reflection surface extent in x-direction”, “reflection surface extent in y-direction” and “maximum mirror diameter” for the mirrors M1 to M6 of the projection optics 10.

[0113] Table 3a for Fig. 2

[0114] Table 3b to Fig. 2 The mirror with the largest reflective surface area is the last mirror M6.

[0115] All mirrors have an average transmission greater than 62%.

[0116] The projection optics 10, without polishing overflow, has a total mirror surface area that represents the sum of the usable mirror surfaces of mirrors M1 to M6, which is 0.42 m². 2 Including a 50 mm wide polishing overflow, the projection optic 10 has a total mirror area of ​​0.74 m². 2 .

[0117] The mirrors M1 to M6 are designed as freeform surfaces that cannot be described by a rotationally symmetric function. Other configurations of the projection optics 10 are also possible, in which at least one of the mirrors M1 to M6 is designed as a rotationally symmetric asphere. All mirrors M1 to M6 can also be designed as such aspheres.

[0118] A freeform surface can be described by the following freeform surface equation (equation 1):

[0119] + ... co

[0120] The following holds for the parameters of this equation (1):

[0121] Z is the height of the freeform surface at point x, y, where x 2 + y 2 = r 2 . r is the distance to the reference axis of the freeform surface equation (x = 0; y = 0).

[0122] In the freeform surface equation (1) Ci, C2, C3... denote the coefficients of the freeform surface series expansion in the powers of x and y.

[0123] In the case of a conical base, c x , c y a constant that corresponds to the vertex curvature of a corresponding asphere. Therefore, c x = 1 / R X (1 / RDX) and c y = 1 / R y (1 / RDY). k x and k y (CCX, CCY) each correspond to a conical constant of a corresponding asphere. Equation (1) thus describes a biconical freeform surface. An alternative freeform surface can be generated from a rotationally symmetric reference surface. Such freeform surfaces for reflective surfaces of the mirrors of projection optics in projection exposure systems for microlithography are known from the

[0124] US 2007 0 058 269 Al.

[0125] Alternatively, a freeform surface can be described by the following freeform surface equation (equation 2):

[0126] , . ( sin(m ■ <p), falls m ungerade mit s(m ■ (p) = , . tcos(m ■ (p), falls m gerade

[0127] Z denotes the swash level Z (h, cp) of the freeform surface at a point (h, cp), represented in polar coordinates. p = 1 / R denotes the curvature of the reference sphere. h0 denotes the normalization height in mm.

[0128] Q denotes the Forbes polynomial of degree Z for azimuthal order 0, c l+1 denotes the corresponding coefficient.

[0129] Q™ denotes the Forbes polynomial of degree n for azimuthal order m, a p denotes the corresponding coefficient for meridional symmetric terms. Here, p = (m + n + 1) + n — 1 with azimuthal order m and radial order n.

[0130] For the description of Forbes freeform surfaces and Forbes polynomials, reference is also made to DE 10 2018 214 437 Al and the references mentioned therein.

[0131] The coordinates of the mirrors are given with respect to a coordinate system defined such that an origin of the xyz coordinate system lies at a center of the image field on the wafer, with a z-axis of this coordinate system being perpendicular to the image plane and pointing from the center of the image field towards the last aperture-limiting mirror of the imaging optics, with the y-axis of the coordinate system being oriented such that the reticule lies at positive y-coordinates.

[0132] Alternatively, freeform surfaces can also be described using two-dimensional spline surfaces. Examples include Bézier curves or non-uniform rational basis splines (NURBS). Two-dimensional spline surfaces can be described, for example, by a grid of points in an xy-plane and their corresponding z-values, or by these points and their associated slopes. Depending on the specific type of spline surface, the complete surface is obtained by interpolation between the grid points using, for example, polynomials or functions that have certain properties regarding their continuity and differentiability. Examples of such functions are analytic functions.

[0133] The optical design data of the reflective surfaces of the mirrors M1 to M6 of the projection optics 10 can be found in the following further tables.

[0134] Table 4 (Tables 4a / 4b. . .) tabulates separately for mirrors M1 to M6 the parameters RDX, RDY, CCX, CCY and, sorted according to the powers in x and y, the values ​​of the coefficients CI, C2, C3 . . . of the freeform surface series expansion according to the above equation (1).

[0135] Table 4a for Fig. 2

[0136] Table 4b for Fig. 2

[0137] Table 5 below summarizes system data for the projection optics 10 in connection with the apodization tilt APO Z3. Tabulated for each of the mirrors M1 to M6 are the transmissions of the principal ray (HS), the upper coma ray (OK), and the lower coma ray (UK), the value for the apodization tilt APO Z3 calculated according to the formula above, and the respective angle of incidence for the upper coma ray (AOI OK) and for the lower coma ray (AOI UK) for that mirror M1.

[0138] Table 5 for Fig. 2

[0139] Due to the beam path intersection areas Kl to K3, it follows that negative values ​​result for the apodization tilt APO Z3 at mirrors M1, M3 and M6, and positive values ​​for mirrors M2, M4 and M5, which leads to a compensating effect of the apodization tilts with regard to their contribution to the total apodization tilt APO Z3, which then has an advantageously small absolute value of 3.71%.

[0140] With reference to Figures 4 and 5, a further embodiment of a projection optic or imaging optic 25 is described below, which can be used in place of the projection optic 10 of the embodiment according to Figures 2 and 3 in the projection exposure system 1. Components and functions that correspond to those already explained above in connection with Figures 1 to 3 bear the same reference numerals and are not discussed again in detail.

[0141] Regarding the basic guidance of the illumination light 16 along the imaging beam path, the projection optics 25 correspond to the projection optics 10. The mean wavefront error (RMS) of the projection optics 25 is 8.3 mK. The total transmission of the projection optics 25 is 8.4%. The total apodization tilt (APO Z3) of the projection optics 25 is 3.94%. The distance between the object plane 6 and the image plane 12 of the projection optics 25 is 2,130.66 mm. The object-image offset (dois) of the projection optics 25 is 1,192 mm. The total mirror area without overflow is 0.43 m². 2 Including a 50 mm overflow, the total mirror surface area is 0.74 m². 2 .

[0142] In the projection optics 25, the pupil plane lies in the imaging beam path between mirrors M5 and M6. A three-part aperture diaphragm can be positioned there to define the pupil boundary.

[0143] In the projection optics 25, an entrance pupil is located in the imaging beam path in front of the object field 5. The pupil facet mirror 21 of the illumination optics 4 of the projection exposure system 1 can be arranged directly there, so that no intermediate transmission optics are required.

[0144] In the projection optics 25, as in the projection optics 10, there are three beam path crossing areas, namely the beam path crossing area Kl between the partial beam paths M1M2 on the one hand and M3M4 on the other, the beam path crossing area K2 between the partial beam paths M1M2 on the one hand and M4M5 on the other, and the beam path crossing area K3 between the partial beam paths M2M3 on the one hand and M4M5 on the other.

[0145] The intermediate image 23 lies in the imaging beam path between mirrors M3 and M4 in the projection optics 25. The intermediate image 23 lies in the beam path intersection area Kl.

[0146] For the overlap of the beam path intersection areas K2 and K3, what has been stated above for the projection optics 10 also applies to the projection optics 25.

[0147] The following tables summarize parameters and the optical design of the projection optics 25. These tables correspond in structure to those already explained above in connection with Figures 2 and 3.

[0148] Table 1 for Fig. 4

[0149] Table 2a for Fig. 4

[0150] Table 2b for Fig. 4

[0151] Table 3a for Fig. 4

[0152] Table 3b for Fig. 4

[0153] Table 4b for Fig. 4

[0154] Table 5 for Fig. 4

[0155] With reference to Figures 6 and 7, a further embodiment of a projection optic or imaging optic 26 is described below, which can be used in place of the projection optic 10 of the embodiment according to Figures 2 and 3 in the projection exposure system 1. Components and functions that correspond to those already explained in the preceding context with reference to Figures 1 to 5 bear the same reference numbers and are not discussed again in detail.

[0156] The basic imaging beam path of projection optics 26 corresponds to that of projection optics 10.

[0157] The image field 11, also in the projection optics 26, is a ring field with a field radius of 80 mm. The xy dimensions of the image field 11 are 26 mm x 2.7 mm. The mean wavefront error (RMS) of the projection optics 26 is 7.1 mK. The total transmission is 8.3%. The total apodization tilt of the APO Z3 is 0.99%.

[0158] The projection optics 26 have a distance of 2,050 mm between the object plane 6 and the image plane 12. The object-image offset is 1,162 mm. The total mirror area (excluding overflow) is 0.58 m². 2 Including a 50 mm overflow, the total mirror surface area of ​​the projection optics is 26 x 0.94 m². 2In the projection optic 26, a pupil plane is again located in the imaging beam path between mirrors M5 and M6 and is designed as a multi-part aperture diaphragm. In the projection optic 26, an entrance pupil is located in the imaging beam path in front of the object field 5 at a distance of approximately 2.5 m. Thus, an accessible entrance pupil is also present here. The second faceted mirror 21, for example, can be positioned at the location of this entrance pupil.

[0159] The intermediate image 23 lies in the projection optics 26 between the mirrors M3 and M4, near mirror M3 and at the edge of the beam path intersection area Kl.

[0160] The projection optics 26 in turn has three beam path intersection areas, namely a beam path intersection area Kl between the partial beam paths M1M2 and M3M4, a beam path intersection area K2 between the partial beam paths M1M2 and M4M5 and a beam path intersection area K3 between the partial beam paths M2M3 and M4M5.

[0161] In projection optics 26, the intersection areas K2 and K3 overlap. In projection optics 26, the intersection areas Kl and K2 also overlap.

[0162] The following tables summarize parameters and the optical design of the projection optics 26. These tables correspond in structure to those already explained above in connection with Figures 2 and 3.

[0163] Table 2a for Fig. 6 Image field 0.00 I _ 0.00 I

[0164] Table 2b for Fig. 6

[0165] Table 3a for Fig. 6 Table 3b for Fig. 6

[0166] Table 4a for Fig. 6

[0167] Table 4b for Fig. 6

[0168] Table 5 for Fig. 6

[0169] The projection optics 10, 25 and 26 described above all have an image-side numerical aperture of at least 0.3. These described projection optics all have an image-side numerical aperture of less than 0.5 and, in particular, less than 0.4.

[0170] Depending on the design of the projection optics described above, at least one system manipulator may be provided to correct at least one imaging error of the projection optics. This may be a mirror of the projection optics that can be displaced along at least one degree of freedom of translation and / or rotation, particularly by means of an actuator. Alternatively or additionally, the system manipulator may be implemented by at least one deformable mirror. This may be, in particular, a mirror that is arranged in the imaging beam path near an intermediate image of the imaging optics. Such a system manipulator may have at least one actuator that is in signal communication with a central control unit of the projection optics and / or the optical system and / or the projection exposure system.

[0171] To produce a micro- or nanostructured component, the projection exposure system 1 is used as follows: First, the reflection mask 7 or the reticle and the substrate or wafer 13 are provided. Then, a structure on the reticle 7 is projected onto a photosensitive layer of the wafer 13 using the projection exposure system 1. Developing the photosensitive layer then creates a micro- or nanostructure on the wafer 13, thus producing the microstructured component.

Claims

Patent claims 1. Imaging EUV optics (10; 25; 26) with a plurality of mirrors (M1 to M6) for guiding imaging light (16) along an imaging beam path from an object field (5) to an image field (11), wherein the imaging optics (10; 25; 26) has a total apodization tilt APO Z3 that is absolutely less than 10%, with at least one beam path crossing area (Kl, K2, K3) between a first partial beam path (M1M2; M2M3) between a mirror (M1; M2) and a mirror (M2; M3) directly following this mirror in the imaging beam path, and a second partial beam path (M3M4; M4M5) between another mirror (M3; M4) and a mirror (M4; M5) directly following this further mirror in the imaging beam path, with an object-image offset (dois) that is greater is 250 mm.

2. Imaging optics according to claim 1, characterized by three different beam path crossing regions (Kl to K3), each between at least one beam path crossing region (Kl, K2, K3) between a first partial beam path (M1M2; M2M3) between a mirror (M1; M2) and a mirror (M2; M3) directly following this mirror in the imaging beam path and a second partial beam path (M3M4; M4M5) between a further mirror (M3; M4) and a mirror (M4; M5) directly following this further mirror in the imaging beam path.

3. Imaging optics according to claim 1 or 2, characterized in that the object-image offset is greater than 1,000 mm.

4. Imaging optics according to one of claims 1 to 3, characterized in that all mirrors (M1 to M6) of the imaging optics (10; 25; 26) are designed as Ni mirrors.

5. Imaging optics according to one of claims 1 to 4, characterized in that the imaging optics has exactly six mirrors (M1 to M6).

6. Imaging optics according to one of claims 1 to 5, characterized by exactly one intermediate image (23) between the object field (5) and the image field (11).

7. Imaging optics according to one of claims 1 to 6, characterized by a total mirror surface without overflow, which is at most 1 m² 2 amounts.

8. Imaging optics according to one of claims 1 or 7, characterized by a total transmission greater than 5%.

9. Optical system with an illumination optic (4) for illuminating the object field (5) with the imaging light (16), with an imaging optic (10) according to one of claims 1 to 8.

10. Projection exposure system with an optical system according to claim 9 and with an EUV light source (3).

11. Method for manufacturing a structured component comprising the following process steps: Providing a reticule (7) and a wafer (13), Projecting a structure on the reticulum (7) onto a photosensitive layer of the wafer (13) using the projection exposure system according to claim 10, generating a micro- or nanostructure on the wafer (13).

12. Structured component, manufactured according to a method according to claim 11.

Images