EUV polarization device comprising an EUV polarizer

Abstract

An EUV polarization device (25) has a polarizer (24) for polarizing EUV used light (16) with a predefined used wavelength range. The EUV polarization device (25) has a target component transmission for a target polarization component (Pg) and an attenuation transmission for an attenuation polarization component (Pb) of the EUV used light (16). The attenuation polarization component (Pb) is perpendicular to the target polarization component (Pg). The target component transmission (tg) is greater than the attenuation component transmission (tb). The attenuation component transmission (tb) is greater than 3%. The result is an EUV polarization device which, when used in a projection exposure apparatus, can meet high requirements for edge roughness of imaged object structures and / or high requirements for an edge placement error when imaging corresponding object edges.

Description

[0001] EUV polarization device comprising an EUV polarizer

[0002] The content of the German patent application DE 10 2024 211 716.1 is incorporated by reference herein.

[0003] The invention relates to an EUV polarization device comprising an EUV polarizer for polarizing EUV used light with a predefined used wavelength range. Furthermore, the invention relates to an illumination optical unit comprising such an EUV polarization device, a projection optical unit comprising such an EUV polarization device, an optical system comprising such an illumination optical unit and / or such a projection optical unit, a projection exposure apparatus comprising such an optical system, a method for producing a microstructured or nanostructured component by means of such a projection exposure apparatus, and a microstructured or nanostructured component produced by means of such a production method.

[0004] A microlithographic projection exposure apparatus comprising an EUV polarizer is known from US 7,982,844 B2 and DE 10 2019 200 193 B3. DE 10 2010 001 336 B3 discloses an arrangement and a method for characterizing polarization properties of an optical system. DE 10 2023 204 665 Al discloses an EUV reflectometer and a method for determining reflection properties of a sample surface. DE 10 2008 002 749 Al discloses a microlithographic illumination optical unit.

[0005] A problem addressed by the present invention is that of providing an EUV polarization device by means of which a lithographic projection exposure is achieved when using the EUV polarization device in a projection exposure apparatus meeting high requirements of edge roughness of imaged object structures and / or meeting high requirements of edge placement error when imaging corresponding object edges.

[0006] This problem is solved according to the invention by an EUV polarization device having the features specified in Claim 1.

[0007] According to the invention, it has been recognized that in an EUV polarization device for use in a corresponding projection exposure apparatus, it is not necessary to work towards an optimally large suppression ratio. Rather, it can be advantageous for achieving a predefined good edge roughness and / or a predefined good edge placement error if an attenuation component transmission of the EUV polarizer of the EUV polarization device is greater than a predefined lower limit value and in particular is greater than 3%. Depending on the embodiment of the EUV polarizer, the attenuation component transmission can also be greater than 4%, can be greater than 5%, can be greater than 6%, can be greater than 7%, can be greater than 8%, can be greater than 9% and can also be greater than 10%. A corresponding design of the EUV polarizer results in an advantageously high throughput with the EUV used light in the predefined used wavelength range. The EUV polarization device can have exactly one EUV polarizer or else a plurality of EUV polarizers.

[0008] The target polarization component can be a p-polarization component. The attenuation polarization component can be an s-polarization component.

[0009] An attenuation component transmission according to Claim 2 leads to a particularly advantageous combination of imaging quality parameters such as those of the low edge roughness and the low edge placement error on the one hand and a high EUV used light throughput on the other hand. An upper limit of the attenuation component transmission can be at 25% and can also be at 20% transmission of the EUV used light in the predefined used wavelength range. Depending on the embodiment of the EUV polarization device, the lower limit of the attenuation component transmission can also be at 4%, at 5%, at 6%, at 7%, at 8%, at 9%, at 10%, at 12%, at 15% or even at 17%.

[0010] A layer stack construction according to Claim 3 leads to reproducible and precisely settable values for the target component transmission on the one hand and for the attenuation component transmission on the other hand.

[0011] This applies particularly to numbers of bilayers in the layer stack according to Claim 4.

[0012] Angles of incidence according to Claim 5 have been found to be particularly advantageous for achieving a good combination of imaging quality parameters on the one hand and throughput on the other hand. The angle of incidence can be in the range of 42° and 43° and can be 42.7°, for example.

[0013] Layer materials according to Claim 6 have proved worthwhile in practice.

[0014] Layer thicknesses within the bilayers according to Claims 7 and 8 have been found to be particularly advantageous, depending on the combination of layer materials used, for example with the use of the combination of first layer material silicon, second layer material molybdenum or with the use of the combination of first layer material silicon and second layer material ruthenium. A protective layer botom layer and / or a protective layer top layer according to Claim 9 has been found to be advantageous for avoiding an undesirable reactive change of the layer materials. The protective layer material can be one of the layer materials, for example ruthenium. Alternatively, the protective layer material can also be a different material than the layer materials of the bilayers, for example a silicon, in particular MoSi2.

[0015] A support layer according to Claim 10 increases a stability of the EUV polarizer. What has been explained above for the protective layer materials is applicable to the support layer materials. Silicon can also be used as a support layer material.

[0016] The support layer can also have a protective layer function. Conversely, the protective layer can also have a support layer function.

[0017] A polarizer mount according to Claim 11 enables a precise predefinition of an angle of incidence of the EUV used light on the EUV polarizer. The polarizer mount can be displaceable manually and / or in a driven maimer for the purpose of predefining the angle of incidence. Insofar as a drive is used for the polarizer mount, this drive can be signal-connected to an openloop control device and / or to a closed-loop control device of the projection exposure apparatus. Insofar as intensities of the target polarization component transmited by the EUV polarizer and / or of the transmited atenuation polarization component are detectable in the projection exposure apparatus by means of corresponding measuring devices, in particular using corresponding analysers, controlled operation of an angle of incidence position of the EUV polarizer can be effected, which position is set by way of the polarizer mount. The advantages of an illumination optical unit according to Claim 12, of a projection optical unit according to Claim 13, of an optical system according to Claim 14, of a projection exposure apparatus according to Claim 15, of a production method according to Claim 16 and of a micro structured or nano structured component according to Claim 17 correspond to those which have already been explained above with reference to the EUV polarization device. The component can be a microchip, in particular a memory chip.

[0018] At least one exemplary embodiment of the invention is described hereinafter with reference to the drawing. In the drawing:

[0019] Fig. 1 schematically shows, in meridional section, a projection exposure apparatus for EUV projection lithography, having an EUV polarization device comprising an EUV polarizer for polarizing EUV used light;

[0020] Figs 2 to 4 show variants of the EUV polarizer, each having a layer stack of two alternating layer materials with a plurality of bilayers;

[0021] Fig. 5 shows a variant of the EUV polarizer with a bottom layer and with a top layer composed of a protective layer material;

[0022] Fig. 6 shows a variant of the EUV polarizer in which the protective layer material simultaneously constitutes one of the layer materials of the bilayers; Fig. 7 shows a variant of the EUV polarizer with a first and a last layer of the layer stack, embodied as support layer, wherein the material of the support layer simultaneously constitutes one of the layer materials of the bilayers of the layer stack;

[0023] Fig. 8 shows, in an illustration similar to Fig. 7, a variant of the EUV polarizer with support layers fabricated from a different layer material than the layer materials of the bilayers of the layer stack;

[0024] Fig. 9 shows a variant of the EUV polarizer according to Fig. 8 with additional end-side protective-layer sublayers;

[0025] Fig. 10 shows a variant of the EUV polarizer according to Fig. 9 with an additional bottom layer and an additional top layer composed of protective layer material of the end-side protective-layer sublayers;

[0026] Fig. 11 shows in a diagram possible combinations of a target component transmission tgfor a target polarization component of the EUV used light on the one hand and an attenuation component transmission tb for an attenuation polarization component of the EUV used light on the other hand for a first material combination of layer materials for bilayers of the layer stack of the EUV polarizer, wherein isolines of an edge roughness LER are additionally depicted for different structure periods p; Fig. 12 shows, for a different material combination of layer materials of the bilayers of the layer stack of a variant of the EUV polarizer in a diagram similar to Fig. 11, once again possible combinations of the target component transmission tgand the attenuation component transmission tb, wherein isolines of an edge placement error EPE are additionally depicted, and wherein the edge placement error EPE is influenced by error parameters which take account of photoresist properties and a uniformity error of the illumination system; and

[0027] Fig. 13 shows, in an illustration similar to Fig. 12, the possible component transmissions, this time with depicted isolines of the edge placement error EPE which is additionally influenced by a vibration contribution of components of the projection exposure apparatus as a source of error.

[0028] The essential constituent parts of a microlithographic projection exposure apparatus 1 are first described by way of example hereinafter with reference to Figure 1. The description of the basic set-up of the projection exposure apparatus 1 and the constituent parts thereof should be understood here to be non-limiting.

[0029] One embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light or radiation source 3, an illumination optical unit 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 module separate from the rest of the illumination system. In this case, the illumination system does not comprise the light source 3. An object arranged in the object field 5 on the basis of the example of a reticle 7 is exposed. The reticle 7 is held by a reticle or object holder 8. The reticle holder 8 is displaceable by way of a reticle or object displacement drive 9 in particular in a scanning direction.

[0030] A Cartesian xyz-coordinate system is depicted in Figure 1 for explanation purposes. The x-direction runs perpendicularly to the plane of the drawing into the latter. The y-direction runs horizontally, and the z-direction runs vertically. The scanning direction runs along the y-direction in Fig. 1. The z-direction runs perpendicularly to the object plane 6.

[0031] The projection exposure apparatus 1 comprises a projection optical unit 10. The projection optical unit 10 serves as an imaging optical unit for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. Alternatively, an angle between the object plane 6 and the image plane 12 that differs from 0° is also possible.

[0032] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by way of a wafer displacement drive 15 in particular along the y-direction. The displacement, firstly, of the reticle 7 by way of the reticle displacement drive 9 and, secondly, of the wafer 13 by way of the wafer displacement drive 15 can be implemented so as to be synchronized with one another.

[0033] The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, used light, illumination radiation or illumination light. Insofar as the illumination light 16 is guided by the projection optical unit 10, the illumination light 16 is also referred to as imaging light. The used radiation has in particular a wavelength in the range of between 5 nm and 30 nm. A wavelength range of the illumination light 16 that is used for the projection exposure is referred to as the used wavelength range. For example, this used wavelength range can be around 13.5 nm (e.g. 13.5 nm + / - 0.1 nm). The radiation source 3 can be a plasma source, for example an LPP (Laser Produced Plasma) source or a GDPP (Gas Discharge Produced Plasma) source. It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

[0034] 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 with a plurality of ellipsoidal and / or hyperboloidal reflection surfaces. The illumination radiation 16 can be incident on the at least one reflection surface of the collector 17 with grazing incidence (GI), i.e. at angles of incidence of greater than 45°, or with normal incidence (NI), i.e. at angles of incidence of less than 45°. The collector 17 can be structured and / or coated on the one hand for optimizing its reflectivity for the used radiation and on the other hand for suppressing extraneous light.

[0035] Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can constitute a separation between a radiation source module, having the radiation source 3 and the collector 17, and the illumination optical unit 4.

[0036] The illumination optical unit 4 comprises a deflection mirror 19 and, disposed downstream thereof in the beam path, a first facet mirror 20, which is illustrated in a plan view in Fig. 2. The deflection mirror 19 can be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond the pure deflection effect. Additionally or alternatively, the deflection mirror 19 can be embodied as a spectral filter that separates a used light wavelength of the illumination radiation 16 from extraneous light of a wavelength differing therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which are also referred to below as field facets. Only some of these facets 21 are illustrated in Fig. 1 by way of example.

[0037] As illustrated in Fig. 2, the first facets 21 can be embodied as macroscopic facets, in particular as rectangular facets or else as facets with an arcuate or partly circular edge contour. The first facets 21 can be embodied as plane facets or alternatively as convexly or concavely curved facets.

[0038] As is known from DE 10 2008 009 600 Al, for example, the first facets 21 themselves can each also be composed of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 can be configured in particular as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 Al.

[0039] Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, i.e. along the y-direction.

[0040] In the beam path of the illumination optical unit 4, there is disposed downstream of the first facet mirror 20 a second facet mirror 22, which is illustrated in a schematic plan view in Fig. 3. If the second facet mirror 22 is arranged in a pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 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.

[0041] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0042] The second facets 23 can likewise be macroscopic facets, which can for example have a round, rectangular or else hexagonal boundary, or can alternatively be facets composed of micromirrors. In this regard, reference is likewise made to DE 10 2008 009 600 Al.

[0043] The second facets 23 can have plane or alternatively convexly or concavely curved reflection surfaces.

[0044] The illumination optical unit 4 thus forms a doubly faceted system. This basic principle is also referred to as a fly's eye condenser (fly's eye integrator).

[0045] It can be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optical unit 10. In particular, the pupil facet mirror 22 can be arranged so as to be tilted relative to a pupil plane of the projection optical unit 10, as described for example in DE 10 2017 220 586 Al. The individual first facets 21 are imaged into the object field 5 with the aid of the second facet mirror 22. The second facet mirror 22 is the last beamshaping mirror or else actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

[0046] In a further embodiment (not illustrated) of the illumination optical unit 4, a transfer optical unit contributing in particular to the imaging of the first facets 21 into the object field 5 can be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optical unit can have exactly one mirror, or alternatively two or more mirrors arranged one behind another in the beam path of the illumination optical unit 4. The transfer optical unit can in particular comprise one or two normal-incidence mirrors (NI mirrors) and / or one or two grazing-incidence mirrors (GI mirrors).

[0047] In the embodiment shown in Fig. 1, the illumination optical unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

[0048] In a further embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, and so the illumination optical unit 4 can have exactly two mirrors downstream of the collector 17 in that case, specifically the first facet mirror 20 and the second facet mirror 22.

[0049] The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or using the second facets 23 and a transfer optical unit is regularly only approximate imaging. An EUV polarizer 24 of an EUV polarization device 25 is arranged in the beam path of the EUV used light 16 between the two facet mirrors 20, 22. The EUV polarizer 24 serves for polarizing the EUV used light 16 in the used wavelength range.

[0050] The EUV polarizer 24 is operated in transmission for the EUV used light 16.

[0051] The EUV polarizer 24 has a target component transmission for a target polarization component Pgof the EUV used light 16 with a polarization direction perpendicular to the drawing plane of Fig. 1 and an attenuation component transmission for an attenuation polarization component Pb of the EUV used light 16 with a polarization direction in the drawing plane of Fig. E

[0052] The target polarization component Pgon the one hand and the attenuation polarization component Pb on the other hand of the EUV used light 16 are respectively indicated in Fig. 1 after passing through the EUV polarizer 24.

[0053] The attenuation polarization component Pb is perpendicular to the target polarization component Pg.

[0054] A target component transmission tgof the EUV polarizer 24 is greater than the attenuation component transmission tb, which will also be explained below.

[0055] The EUV polarizer 24 has an optical entrance surface 26 and an optical exit surface 27. Both surfaces 26, 27 can extend parallel to one another or else, in order to avoid disturbing reflections, can be at a slight wedge angle to one another, which angle is regularly less than 1°.

[0056] The EUV polarizer 24 is arranged so as to be tilted with respect to a beam direction of the EUV used light 16, so that the EUV used light 16 is incident non-perpendicularly on the entrance surface 26 and also non- perpendicularly on the exit surface 27 of the EUV polarizer 24.

[0057] A typical angle of incidence a of the used EUV light 16 on the surfaces 26, 27 of the EUV polarizer 24 can be in the range of between 20° and 70°, for example in the range of between 30° and 60°. This angle of incidence a is regularly significantly, i.e. by more than 1.5°, by more than 3°, by more than 5° or else by more than 10°, different from the Brewster angle of optical material of the EUV polarizer for the EUV used light 16. Depending on the polarizer embodiment, the angle of incidence can also differ just slightly from the Brewster angle, for example in the range of between 0.1° and 2°. The angle of incidence can be smaller than the Brewster angle by the aforementioned angle ranges.

[0058] The EUV polarizer 16 is held by a polarizer mount 28, which can be a mounting for the EUV polarizer 25.

[0059] The polarizer mount 28 serves for predefining the angle of incidence a. The polarizer mount 28 is operatively connected to a polarizer tilt drive 29. The polarizer tilt drive 29 is used to set the angle of incidence a.

[0060] The polarizer tilt drive 29 and also further components of the projection exposure apparatus 1 are signal-connected to a central open-loop / closed- loop control device 30 of the projection exposure apparatus 1. Depending on the embodiment of the EUV polarization device 25, the latter can comprise exactly one EUV polarizer 24 or else a plurality of EUV polarizers. If a plurality of EUV polarizers are used, the EUV used light 16 can impinge on them with the same angle of incidence a or with different angles of incidence.

[0061] Exemplary embodiments for the EUV polarizer 24 are explained in even greater detail below with reference to Figures 2 to 13.

[0062] The projection optical unit 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

[0063] The mirror M3 of the projection optical unit 10 is a near-pupil mirror. The arrangement plane of the mirror M3 is thus near a pupil plane of the optical system of the projection exposure apparatus 1.

[0064] The following applies to the near-pupil mirror M3 :

[0065] P(M3) > 0.6

[0066] With regard to the definition of the parameter P characterizing pupil proximity, reference is made to WO 2009 / 024 164 Al.

[0067] In the example illustrated in Figure 1, the projection optical unit 10 comprises six mirrors Ml to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are likewise possible. The projection optical unit 10 is a doubly obscured optical unit. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6 and for example can be 0.7 or 0.75.

[0068] Between the mirrors M2 and M3 of the projection optical unit 10, a further possible position for the EUV polarizer 24 is illustrated using dashed lines in Fig. 1.

[0069] Here, in an alternative variant, at least one additional EUV polarizer 24 in addition to the EUV polarizer 24 can also be arranged between the two facet mirrors 20, 22. Even further alternatively or additionally possible arrangement positions can be used, for example between the mirrors Ml and M2 or else between the mirrors M3 and M4 of the projection optical unit 10. Depending on the embodiment of the EUV polarization device 25, a plurality of EUV polarizers can also be arranged in the used light beam path of the projection optical unit 10. Alternatively or additionally, it is possible to arrange different parts or portions of an EUV polarizer arranged in the used light beam path of the projection optical unit 10 with different orientation, i.e. with different tilting, next to one another in the beam path. The arrangement of the at least one EUV polarizer in the used light beam path of the polarization optical unit can be such that a tangential polarization of the used light is present in a pupil of the projection optical unit 10. The at least one EUV polarizer arranged in the beam path of the projection optical unit 10 can be arranged adjacent to a mirror Mi (i = 1, 2, . . .) arranged in the vicinity of a pupil plane of the projection optical unit 10. Reflection surfaces of the mirrors Mi can be embodied as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optical unit 4, the mirrors Mi can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0070] The projection optical unit 10 has a large object-image offset in the y- direction between a y-coordinate of a centre of the object field 5 and a y- coordinate of the centre of the image field 11. This object-image offset in the y-direction can be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.

[0071] The projection optical unit 10 can be embodied in particular in anamorphic fashion. In particular, it has different imaging scales 0X, pyin the x- and y- directions. The two imaging scales 0X, pyof the projection optical unit 10 are preferably (px, py) = (+ / -0.25, + / -0.125). A positive imaging scale P means imaging without image inversion. A negative sign for the imaging scale P means imaging with image inversion.

[0072] The projection optical unit 10 thus leads to a reduction in size with a ratio of 4: 1 in the x-direction, i.e. in a direction perpendicular to the scanning direction.

[0073] The projection optical unit 10 leads to a reduction in size of 8: 1 in the y- direction, i.e. in the scanning direction. Other imaging scales are likewise possible. Imaging scales with the same signs and the same absolute values in the x- and y-directions, for example with absolute values of 0.125 or 0.25, are also possible.

[0074] The number of intermediate image planes in the x-direction and in the y- direction in the beam path between the object field 5 and the image field 11 can be the same or can be different, depending on the embodiment of the projection optical unit 10. Examples of projection optical units with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 Al.

[0075] In each case one of the pupil facets 23 is assigned to exactly one of the field facets 21 for the purpose of forming a respective illumination channel for illuminating the object field 5. In particular, this can result in illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 respectively assigned thereto.

[0076] The field facets 21 are each imaged by an assigned pupil facet 23 onto the reticle 7 in a maimer overlaid on one another in order to illuminate the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different illumination channels.

[0077] The illumination of the entrance pupil of the projection optical unit 10 can be defined geometrically by way of an arrangement of the pupil facets 23 impinged on by the illumination light 16. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels, in particular the subset of the pupil facets which guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0078] A likewise preferred pupil uniformity in the region of portions of an illumination pupil of the illumination optical unit 4 that are illuminated in a defined maimer can be achieved by a redistribution of the illumination channels.

[0079] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optical unit 10 are described below.

[0080] The projection optical unit 10 can have in particular a homocentric entrance pupil. The latter can be accessible. It can also be inaccessible.

[0081] The entrance pupil of the projection optical unit 10 regularly cannot be exactly illuminated using the pupil facet mirror 22. The aperture rays often do not intersect at a single point in the event of imaging by the projection optical unit 10 that telecentrically images the centre of the pupil facet mirror 22 onto the wafer 13. However, it is possible to find an area in which the spacing of the aperture rays that is determined in pairs becomes minimal. This area constitutes the entrance pupil or an area conjugate thereto in real space. In particular, this area exhibits a finite curvature.

[0082] It may be the case that the projection optical unit 10 has different poses of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, in particular an optical component of the transfer optical unit, should be provided between the second facet mirror 22 and the reticle 7. With the aid of this optical element, the different poses of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0083] In the arrangement of the components of the illumination optical unit 4 illustrated in figure 1, the pupil facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optical unit 10. The field facet mirror 20 is arranged so as to be tilted with respect to the object plane 6. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the deflection mirror 19.

[0084] The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the second facet mirror 22.

[0085] With reference to Fig. 2, an embodiment of the EUV polarizer 24 is explained in greater detail below.

[0086] The EUV polarizer 24 is embodied as a layer stack of alternating layer materials with, in the illustrated case, a total of four bilayers Bi, B2, B3 and B4. According to the embodiment of the EUV polarizer, the number of bilayers Bi is actually higher and lies in particular in the range of between 5 and 15 (Bi . . .BN; 5 < N; 5 < N < 15).

[0087] Each of the bilayers Bi has a first layer Bi1composed of a first layer material and a second layer Bi2composed of a further layer material different from the first layer material. The first layer material is molybdenum in the embodiment according to Fig. 2. The second layer material is silicon in the embodiment according to Fig. 2. In the EUV polarizer 24 according to Fig. 2, the layer stack 31 is designed for an angle of incidence a in the range of between 40° and 45°, in particular in the range of between 42° and 43°, for example for an angle of incidence a of 42.7°.

[0088] The respective second layer Bi2of the bilayers has a thickness in the range of between 5.8 nm and 6.1 nm. The second layer thickness is in the range of between 3.5 nm and 4.0 nm. These layer thicknesses are illustrated in exaggerated fashion in Fig. 2. The respective layer thickness is measured perpendicular to the layer extent, i.e. for example perpendicular to the entrance surface 26 and / or perpendicular to the exit surface 27.

[0089] In the embodiment according to Fig. 2, the EUV polarizer 24 has a leading layer Bi1composed of the first layer material and also forming the entrance surface 26, and a last layer BN2composed of the second layer material and also forming the exit surface 27. In total, N (N = 4) complete bilayers Bi are thus present.

[0090] With reference to Fig. 3, a description is given below of a further embodiment of an EUV polarizer 32, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 and 2 bear the same reference signs and will not be discussed in detail again.

[0091] In the embodiment according to Fig. 3, preceding the layer Bi1, which in the embodiment according to Fig. 2 constitutes the leading layer of the layer stack 31, yet another layer Bo2composed of the second layer material silicon is applied, so that the EUV polarizer 32 has a respective layer Bo2, BN2composed of the second layer material silicon on the entrance and exit sides.

[0092] With reference to Fig. 4, a description is given below of a further embodiment of an EUV polarizer 33, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 3 bear the same reference signs and will not be discussed in detail again.

[0093] In the case of the EUV polarizer 33 according to Fig. 4, layers Bi1, BN1each composed of the first layer material molybdenum are present both on the entrance and on the exit side. On the exit side, therefore, after a bilayer BN-I, an incomplete bilayer comprising an exit-side layer BN1is also present.

[0094] With reference to Fig. 5, a description is given below of a further embodiment of an EUV polarizer 34, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 4 bear the same reference signs and will not be discussed in detail again.

[0095] With regard to the bilayer layer construction of the layer stack 31, the EUV polarizer 34 according to Fig. 5 corresponds to the EUV polarizer 24 according to Fig. 2. The EUV polarizer 34 additionally has a bottom layer 35 preceding the entrance-side first layer Bi1and a top layer 36 on the exit side after the last layer BN2. Both the bottom layer 35 and the top layer 36 are composed of a protective layer material. The protective layer material can be ruthenium. In addition to the bottom layer 35 and the top layer 36, the EUV polarizer 34 also has end-side protective-layer sublayers 37, 38, which cover the layer stack 31 of the EUV polarizer 34 towards the lateral end sides, i.e. towards the polarizer mount 28, which is not illustrated in Fig. 5. Further corresponding end-side protective-layer sublayers can be arranged above and below the drawing plane of Fig. 5, so that the layer stack with the bilayers Bi is completely surrounded on all six sides by protective layer material, i.e. is completely enveloped by the latter.

[0096] With reference to Fig. 6, a description is given below of a further embodiment of an EUV polarizer 39, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 5 bear the same reference signs and will not be discussed in detail again.

[0097] In the EUV polarizer 39 according to Fig. 6, ruthenium is used as second layer material instead of molybdenum. With regard to its layer construction between the entrance surface 26 and the exit surface 27, the layer stack 31 of the EUV polarizer 39 corresponds to the layer construction of the EUV polarizer 32 according to Fig. 3. The ruthenium layers Bi1and BN1, which terminate the layer stack 31 of the EUV polarizer 39 on the entrance and exit sides, simultaneously constitute the bottom layer 35 and the top layer 36 composed of the protective layer material (cf. embodiment according to Fig- 5).

[0098] Ruthenium is simultaneously the protective layer material in the EUV polarizer 39. In addition, the EUV polarizer 39 has the end-side protective- layer sublayers 37, 38, once again in accordance with the embodiment according to Fig. 5. These protective-layer sublayers 37, 38 are likewise composed of ruthenium.

[0099] The layer construction of the layer stack 31 of the EUV polarizer 39 corresponds in principle to that according to Fig. 4, with ruthenium now being used as first layer material instead of molybdenum.

[0100] In the case of the EUV polarizer 39 according to Fig. 6, the second layer material silicon is thus surrounded by the protective layer material ruthenium on the entrance side, on the exit side and also on the end sides.

[0101] With reference to Fig. 7, a description is given below of a further embodiment of an EUV polarizer 40, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 6 bear the same reference signs and will not be discussed in detail again.

[0102] A layer construction of the EUV polarizer 40 according to Fig. 7 corresponds in principle to that of the EUV polarizer 32 according to Fig.

[0103] 3. In contrast thereto, an entrance-side layer Bo2firstly and an exit-side layer BN2, each composed of silicon, are significantly thicker in terms of the layer thickness, for example more than 50% thicker, than the further layers Bi2to BN-I2composed of the second layer material silicon.

[0104] The thicker entrance- and exit-side layers Bo2and BN2composed of the second layer material constitute support layers for the layer stack 31 of the EUV polarizer 40. With reference to Fig. 8, a description is given below of a further embodiment of an EUV polarizer 41, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 7 bear the same reference signs and will not be discussed in detail again.

[0105] Instead of support layers Bo2, BN2composed of the second layer material, the EUV polarizer 41 according to Fig. 8 has, on the entrance side and on the exit side, support layers 42, 43 composed of a support layer material different from the layer materials of the respective bilayers Bi. This can be a silicide, for example MoSi2. These support layers 42, 43 can simultaneously constitute protective layer bottom and top layers corresponding to the bottom layer 35 and the top layer 36 of the embodiment according to Fig. 5.

[0106] Between the support layers 42, 43, a layer stack construction of the EUV polarizer 41 corresponds to that according to Fig. 4.

[0107] With reference to Fig. 9, a description is given below of a further embodiment of an EUV polarizer 44, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 8 bear the same reference signs and will not be discussed in detail again. In contrast to the EUV polarizer 41 according to Fig. 8, the EUV polarizer 44 has additional end-side protective-layer sublayers 37, 38 in accordance with the embodiment according to Fig. 5 or 6.

[0108] With reference to Fig. 10, a description is given below of a further embodiment of an EUV polarizer 45, which can be used instead of the EUV polarizer 24 in the EUV polarization device 25. Components and functions corresponding to those which have already been explained above with reference to Figs 1 to 9 bear the same reference signs and will not be discussed in detail again.

[0109] In contrast to the EUV polarizer 44 according to Fig. 9, the EUV polarizer 45 according to Fig. 10 has, on the entrance and exit sides, layers also covering the two support layers 42, 43, specifically a bottom layer 35 and a top layer 36, once again composed of a protective layer material, for example ruthenium, in accordance with the embodiment according to Fig. 5.

[0110] Fig. 11 illustrates transmission ratios and achievable edge roughnesses when using the EUV polarization device 25 comprising an EUV polarizer, having a layer stack composed of molybdenum / silicon bilayers. The illustration shows the attenuation component transmission tb on the abscissa and the target component transmission tgon the ordinate. This tb / tgdiagram highlights that range of transmission pairings (tb, tg) which can be achieved by appropriate choice of numbers of bilayers (number periods), angles of incidence a and also layer thicknesses of the first and second layers of the respective bilayer. In the diagram illustration according to Fig. 11, this range (tb, tg) has an area shape similar to the cross-section of an aerofoil. The transmission pairing area range extends from the value (0,0), for the case where a complete absorber is used as polarizer, to the value (1,1), for the case where the EUV polarizer does not influence the EUV used light 16 at all.

[0111] An upper edge curve Toptof this range (tb, tg) is of practical relevance. That involves those values of the overall range with the largest target component and attenuation component transmissions.

[0112] Fig. 11 additionally depicts isolines of an edge roughness LER, LERi to LERs, which reproduce transmission pairings (tb, tg) with the same edge roughness LER for different structure periods p that are present on the reticle 7 and are to be imaged by means of the projection exposure apparatus 1. The legend in the diagram of Fig. 11 presents the relation between the respective LER isoline LERi and the associated structure period p.

[0113] In principle, the following relationship applies to the edge roughness LER:

[0114] (1)

[0115] In this case, X is the wavelength of the EUV used light, and p is the structure period of structures to be imaged on the reticle 7.

[0116] For a structure period p = 9.52 nm (isoline LERs), the respective variant of the EUV polarizer results in attainable transmission pairings on the curve Topt which lie above the isoline LERs, and so, on account of the higher transmissions along the curve Toptin comparison with the isoline LERs, for example for the pairing (tb, tg) = (0.15; 0.6), an improved structure imaging should be expected.

[0117] Fig. 12 shows, in a diagram illustration similar to Fig. 11, ratios once again for a molybdenum / silicon bilayer layer pairing, with depiction in this case of isolines EPEi for an edge placement error EPE taking into account specific sources of error during structure imaging. The smaller the index i for the isolines EPEi, the smaller the associated edge placement error.

[0118] The following applies to the edge placement error EPE:

[0119] In this case, NILS stands for the image contrast, to which in turn the following applies:

[0120] (3)

[0121] The parameters cl, c2 and c3 describe sources of error during structure imaging.

[0122] The parameter cl substantially depends on the properties of the photoresist used. The effects of a uniformity error of the illumination system are all the greater, the poorer the image contrast; such errors form a part of the parameter c3. If the projection exposure apparatus 1 wobbles, i.e. components of the projection exposure apparatus 1 vibrate or oscillate, the structures may be printed in the wrong place, and the extent of the displacement depends only on the intensity of the wobbling, but not on the image contrast; such errors form a part of the parameter c2.

[0123] The edge placement error EPE takes account of both stochastic local contributions to the edge roughness and other, especially deterministic, non-local effects that are only partially dependent on the image contrast. Local contributions relate to spatial frequencies on a sub-micrometre scale. Non-local contributions relates to spatial frequencies in the range of 100 pm and greater.

[0124] Fig. 12 takes account of the parameters cl (photoresist) and c3 (uniformity error). The isolines EPEi are calculated in Fig. 12 taking into account the constraints c2 / cl = 0 and c3 / cl = 2.

[0125] A smallest edge placement error EPEi results for a value pairing (tg~ 0.5; tb ~ 0.05) highlighted in Fig. 12.

[0126] Fig. 13 shows, in a diagram that otherwise corresponds to Fig. 12, the achievable range of transmission pairings (tg, tb), in this case with isolines for the edge placement error EPEi calculated according to other error prerequisites. The calculation of the edge placement error with the aid of formula (2) above takes account of all three error contributions parametrized via the parameters ci, C2, C3, i.e. photoresist error (ci), uniformity error (cs) and vibration error (C2). In the calculation of the isolines EPEi to EPEs in Fig. 13, C2 / C1 = 0.2 and C3 / ci = 0.2 were used as constraints.

[0127] Taking these sources of error into account gives rise to a pairing (tg~ 0.62, tb ~ 0.16) as a value pairing for the target component transmission ti, firstly, and the attenuation component transmission tb, secondly, which is to be predefined by means of the EUV polarizer in the EUV polarization device 25 in order that an optimally small placement error EPE results. At the optimum of the curve EPEi according to Fig. 12, therefore, quite strong polarization is effected by means of the respective EUV polarizer, whereas at the optimum on the curve EPE2 according to Fig. 13, comparatively weak polarization is effected since the attenuation component transmission tb is also greater than 10%.

[0128] Table 1 below tabulates value pairs on this curve Toptstarting from values at the value pairing (1, 1) through to values near the value pairing (0,0). Table 1

[0129] In addition to the values for the target component transmission tgand the attenuation component transmission tb, the table tabulates the number of periods, i.e. the number of bilayers Bi, the respective angle of incidence a and also the thicknesses of the first layer material silicon and the second layer material molybdenum, in each case in nanometres.

[0130] Advantageous transmission pairings tg, tb result in particular for silicon thicknesses in the range of between 5.8 nm and 6.1 nm and for molybdenum thicknesses in the range of between 3.5 nm and 4.0 nm.

[0131] Table 2 below tabulates a corresponding curve Toptfor a combination of layer materials ruthenium / silicon.

[0132] Table 2

[0133] In this combination of layer materials ruthenium / silicon, advantageous transmission pairings tg, tb result for silicon layer thicknesses in the range of between 6.5 nm and 6.8 nm and for ruthenium layer thicknesses in the range of between 2.8 nm and 3.3 nm. In order to produce a micro- or nanostructured component, the projection exposure apparatus 1 is used as follows: First, the reflection mask 7 or the reticle and the substrate or the wafer 13 are provided. Depending on a structure period p to be imaged on the reticle 7 and depending on error influencing variables of a light-sensitive layer of the wafer 13 (photoresist), an illumination uniformity to be measured and measured oscillations or vibrations of the projection exposure apparatus 1, there then follows a selection and an adjustment of the respective EUV polarizer of the EUV polarization device 25 in the beam path of the EUV used light 16 in order that a predefined value for an edge roughness LER of an imaging and / or for an edge placement error EPE is achieved. Subsequently, the structure on the reticle 7 is projected onto the light-sensitive layer of the wafer 13 with the aid of the projection exposure apparatus 1. Then, a micro structure or nanostructure on the wafer 13, and hence the microstructured component, is produced by developing the light-sensitive layer. A semiconductor microchip, in particular a memory chip, can be produced by this means.

Claims

1. Patent Claims1. EUV polarization device (25) comprising an EUV polarizer (24; 32;33; 34; 39; 40; 44; 45) for polarizing EUV used light (16) with a predefined used wavelength range, with a target component transmission (tg) for a target polarization component (Pg) of the EUV used light (16), with an attenuation transmission (tb) for an attenuation polarization component (Pb) of the EUV used light (16), wherein the attenuation polarization component (Pb) is perpendicular to the target polarization component (Pg), wherein the target component transmission (tg) is greater than the attenuation component transmission (tb), wherein the attenuation component transmission (tb) is greater than 3% when the EUV polarization device is used in a projection exposure apparatus.

2. EUV polarization device according to Claim 1, characterized in that the attenuation component transmission (tb) is in the range of between 3% and 30%.

3. EUV polarization device according to Claim 1 or 2, wherein the EUV polarizer (24; 32; 33; 34; 39; 40; 44; 45) has a layer stack (31) of alternating layer materials comprising at least one bilayer (Bi), wherein the bilayer (Bi) has: a first layer (Bi1) composed of a first layer material, a further layer (Bi2) composed of a further layer material different from the first layer material.

4. EUV polarization device according to Claim 3, characterized in that the layer stack (31) has between five and 15 of the bilayers (Bi).

5. EUV polarization device according to any of Claims 1 to 4, designed for an angle of incidence of the EUV used light (16) on the EUV polarizer (24; 32; 33; 34; 39; 40; 44; 45) in the range of between 40° and 45°.

6. EUV polarization device according to any of Claims 4 to 6, characterized by silicon as one of the layer materials and / or by molybdenum or ruthenium as a further of the layer materials.

7. EUV polarization device according to Claim 6, characterized in that the layer composed of the first layer material has a thickness in the range of between 5.8 nm and 6.1 nm or in the range of between 6.5 nm and 6.8 nm.

8. EUV polarization device according to Claim 6 or 7, characterized in that the further layer composed of the further layer material has a thickness in the range of between 3.5 nm and 4.0 nm or in the range of between 2.8 nm and 3.3 nm.

9. EUV polarization device according to any of Claims 1 to 8, characterized in that the EUV polarizer (34; 27; 41; 44; 45) has a bottom layer (35; 42) and / or a top layer (36; 43) composed of a protective layer material.

10. EUV polarization device according to any of Claims 1 to 9, characterized in that the EUV polarizer (40; 41; 44; 45) has at leastone support layer (Bo2, BN2; 42, 43), arranged as the first and / or last layer of the layer stack (31).

11. EUV polarization device according to any of Claims 1 to 10, characterized by a polarizer mount (28) for predefining an angle of incidence (a) of the EUV used light (16) on the EUV polarizer (24; 32; 33; 34; 39; 40; 44; 45).

12. Illumination optical unit (4) for illuminating an object field (5), in which an object (7) is arrangeable, with EUV used light (16), having an EUV polarization device (25) according to any of Claims 1 to 11.

13. Projection optical unit (10) for imaging an object field (5), in which an object (5) is arrangeable, into an image field (11), which is arrangeable on a wafer (13), with EUV used light (16), having an EUV polarization device (25) according to any of Claims 1 to 11.

14. Optical system comprising an illumination optical unit according to Claim 12 and / or comprising a projection optical unit according to Claim 13.

15. Projection exposure apparatus comprising an optical system according to Claim 14 and comprising a light source (3) for the illumination light (16).

16. Method for producing a structured component by means of a projection exposure apparatus according to Claim 15, comprising the following steps:providing the projection exposure apparatus, an object (7) to be imaged and a wafer (3) coated with a light-sensitive layer, determining a structure period (p) to be imaged which is present on the object (7), - determining structure imaging error contributions (cl, c2, c3) of the projection exposure apparatus (1), depending on the determined structure period (p) and / or depending on at least one determined error contribution (cl, c2, c3): selecting an EUV polarization device (25) comprising an EUV polarizer according to any of Claims 1 to 11 including a predefinition of an angle of incidence (a) for the EUV used light (16), projecting the structure to be imaged on the object (7) onto the light-sensitive layer of the wafer (13) with the aid of the projection exposure apparatus (1) having the selected EUV polarization device (25), developing the light-sensitive layer to create the structured component.

17. Component, produced according to a method according to Claim 16.

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