Optical arrangement

Abstract

An optical arrangement (100, 200, 300) for a lithography apparatus (1), in particular an EUV lithography apparatus (1), comprising an optical element (102, 202, 302); and a housing (104, 204, 304) adjoining the optical element (102, 202, 302); wherein a housing surface (110, 210, 310) has an alternately concave-convex surface structure (118, 21, 318) in a transition region (114, 214, 314), where the housing (104, 204, 304) forms a concave shape (112, 212, 312) together with the optical element (102, 202, 302), and / or adjacent to the transition region (114, 214, 314).

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1

[0003] OPTICAL ARRANGEMENT

[0004] The present invention relates to an optical arrangement and a lithography apparatus having such an optical arrangement, in particular for EUV lithography.

[0005] The content of the priority application DE 102025 106829.1 is incorporated by reference in its entirety.

[0006] Microlithography is used to produce microstructured components, such as for example integrated circuits. The microlithography process is carried out using a lithography apparatus having an illumination system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is projected here by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and is arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0007] Driven by the need for ever smaller structures in the fabrication of integrated circuits, EUV lithography apparatuses that use light at a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm, are currently under development. Since most materials absorb light at this wavelength, such EUV lithography apparatuses require the use of reflective optics units, i.e. mirrors, instead of refractive optics units, i.e. lenses, as used previously.

[0008] In order to reduce or avoid outgassing from materials used, gaseous hydrogen (H2) is applied to the interior of an EUV lithography apparatus, for example with an internal pressure of 3'10 pascal. Individual hydrogen atoms typically have an ionization energy of 13.6 eV, and hydrogen atoms bound in an H2 molecule have an ionization energy of 15.4 eV. Since the EUV radiation photons have an energy of e.g. 91.84 eV, ionization occurs when a photon is incident on an H2 molecule, with the released electron receiving an energy of 76.44 eV and the atomic nucleus accordingly receiving an energy of 0.6 eV or 2.4 eV. The electron moves away from the H2+molecule at high speed. If the ionization takes place in a space or a concave shape defined jointly by an optical element and a housing which houses the optical element (in technical terms: a mini environment), then the walls enclosing the space are electrostatically charged with negative charge. As a consequence, the slower hydrogen ions are attracted to the walls. This ion flow is used for example to clean the optical element. In a concave transition region, the concave shape leads to a weaker electric field, with the result that comparativelyCarl Zeiss SMT GmbH

[0009] 2

[0010] many ions are incident on an edge region of the optical element. Hence, cleaning is less effective in the edge region.

[0011] Several solutions are known in the technical field of cleaning action by means of hydrogen plasma.

[0012] DE 102016208850 Al discloses a projection exposure apparatus, wherein movable, finger-like and electrically conductive conditioning elements are arranged just above a surface of an optical element in order to guide positively charged hydrogen ions into a region of the optical element where EUV radiation is incident.

[0013] DE 102017213406 Al discloses an optical element, wherein an edge-free surface is delimited by an edge. An illuminated region is situated within the edge-free surface. The edge may be configured as a rounded-off portion or as a chamfer.

[0014] DE 102021213613 Al discloses a force frame for a projection exposure apparatus. A surface of the force frame is coated with getter material intended to bind hydrogen outgassing contaminants (hydrogen induced outgassing (HIO) elements), especially Si, Mg, Sn or Zn hydrides. In this context, an average roughness Raof between 0.1 pm and 1.0 pm is advantageous for adhesion of the coating. For this purpose, the intention is to roughen the surface, for example by grinding, milling, mechanical microstructuring, laser structuring, wet chemical pretreatment, plasma etching or deposition of a structured coating.

[0015] DE 102021202 770 Al discloses a method for generating a plasma from a gas by means of a beam, especially an electron-containing beam, from an additional beam source not used for the generation of used light.

[0016] DE 102022213 753 Al discloses an apparatus for protecting a surface of an optical component against damage due to incident ions. This surface to be protected is a first electrode which has multiple gaps. Second electrodes come into contact with a plasma through these gaps. The first electrode and the second electrodes are insulated from each other and connected via a voltage source. The second electrodes project beyond the surface to be protected and have an acicular design.

[0017] Against this background, a problem addressed by the present invention is that of providing an improved optical arrangement, in particular with an option forCarl Zeiss SMT GmbH

[0018] 3

[0019] setting an ion flow ratio between a) an ion flow to the optical element in an edge region with respect to the housing and b) an ion flow to the housing in an edge region with respect to the optical element.

[0020] Accordingly, an optical arrangement for a lithography apparatus, in particular an EUV lithography apparatus or a DUV lithography apparatus, is proposed. The optical arrangement has an optical element and a housing. The housing adjoins the optical element. There is a transition region where the housing forms a concave shape together with the optical element. A housing surface has an alternately concave-convex surface structure in the transition region and / or adjacent to the transition region.

[0021] EUV stands for "extreme ultraviolet" and denotes a wavelength of the operating light between 0.1 nm and 30 nm, in particular 13.5 nm. DUV stands for "deep ultraviolet" and denotes a wavelength of the operating light between 30 nm and 250 nm. Thus, the optical apparatus, in particular the optical element, is at least suitable for the respective operating light. In a DUV lithography apparatus, the optical arrangement may be advantageously used, for example, in conjunction with a device for cleaning deposits by means of plasma generated in a targeted manner.

[0022] The housing "adjoining" the optical element should preferably be understood to mean that the housing abuts against the optical element, that there is a gap of up to 5 mm between the optical element and the housing, and / or that a thin layer made of a material other than a material or carrier material or matrix material of the optical element and other than a material of the housing is interposed between the housing and the optical element. In particular, this may be a layer prepared for vibration damping and / or a layer prepared to compensate for different thermal expansion behaviours of the housing and of the optical element.

[0023] The alternately concave-convex surface structure has convex regions and, in each case, a concave region between them. A strength of the electric field in the concave transition region can be set by means of the surface structure or more precisely by means of the convex regions of the surface structure. (This relates to the electric field caused or brought about during operation by the charge separation of the plasma, with the plasma - preferably H2 plasma - usually being generated by the EUV radiation.)

[0024] A region is said to be "convex" if the connecting line between any two points runs within the region. If a region is not convex, it is said to be "concave".Carl Zeiss SMT GmbH

[0025] 4

[0026] The housing can be said to have a housing surface. The housing surface of the housing can be said to adjoin the optical element. The housing and the optical element can be said to form a mini environment. The housing can be said to surround the optical element. The housing can be said to form a shielding screen around the optical element.

[0027] The transition region denotes a transition from an approximately flat plane, formed by an optically effective surface of the optical element in particular, into an edge protruding from the plane. The transition region can also be said to describe a transition from a front side or a plane of an optically effective surface of the optical element into an edge projecting from the optical element. The edge is formed by the housing, which is preferably in one piece but may also be made of multiple pieces. In particular, the edge is formed by a wall of the housing. The transition can be described as a geometric transition or as a geometric designation. The transition region may coincide with a boundary between the components and / or assemblies of optical element and housing, but the transition region may also be formed predominantly or in full by the housing.

[0028] The term "concave shape", formed jointly by the housing and the optical element, refers to the geometric shape of the (optical) arrangement. The housing and the optical element can also be said to form a concavely shaped assembly. It may be important that the same shape can be referred to as "convex shape" if it relates to a gas and / or plasma. In other words: the concave shape of the arrangement is filled by a convexly shaped gas and / or plasma.

[0029] To strengthen a linguistic distinction between the "concave" shape of the (optical) arrangement and the "convex" shape of the gas and / or plasma volume on the one hand and the "concave-convex" surface structure on the other hand, it is possible to describe the arrangement as a "globally concave" shape, whereas the surface structure can be described as "locally concave-convex". An amplitude of the concave-convex surface structure is typically smaller than an amplitude of the concave shape of the arrangement by at least one order of magnitude.

[0030] The concave shape jointly formed by the housing and the optical element may have an opening angle between the housing surface and a base plane. For example, the base plane is defined by a circumferential edge of the optical element. For example, the base plane is a central plane of an optically effective surface of the optical element. For example, the base plane is a central plane of a reflection surface of the optical element. The opening angle is preferably greaterCarl Zeiss SMT GmbH

[0031] 5

[0032] than 90° with respect to this base plane in order to avoid a reflection back to the upstream optical element. In the case of grazing incidence, the opening angle may be up to 180° with respect to the base plane (extreme case). The aforementioned opening angle might vary in a circumferential direction around a main axis of the optical element, and so an opening in the housing, said opening being spaced apart from the optical element, is wider in one cross-sectional plane and narrower in another cross-sectional plane. The aforementioned opening angle range is suitable for grazing light incidence (wide opening angle) on the one hand and for perpendicular light incidence (narrow opening angle) on the other. It can also be said that the housing may project from the optical element in a manner ranging from funnel-shaped to tubular. The housing may also be said to house the optical element in a manner ranging from bowl-shaped to cylindrical.

[0033] By preference, the surface structure surrounds the optical element. By preference, the transition region including the surface structure surrounds the optical element. For example, the transition region and the surface structure may in each case surround the optical element in the manner of a ring. The surface structure can be said to be formed around an optically effective surface in the manner of a ring and / or formed around an axis perpendicular to the optically effective surface in the manner of a ring. Hence, the intensification of the electric field can be set all around the optical element.

[0034] The surface structure may form a free surface. In other words: the surface structure is preferably uncoated. Since the surface structure is configured to generate a specific field strength of the electric field, it is preferably in direct contact with a gas and / or plasma on the inside within the concave shape of the arrangement such that an intensification or increase in the electric field strength is not attenuated.

[0035] The housing surface and the surface structure may be formed in one piece. For example, the surface structure is introduced into a housing wall which has the housing surface. This ensures gap -free contact between the housing surface and the surface structure.

[0036] The housing surface and the surface structure and preferably also the optical element may be electrically connected to a potential. The electric field is caused by the EUV-induced charge separation in the hydrogen gas, and so the electric charge of the surfaces facing the plasma sets in without further action. However, potential equalization is advantageous in relation to an improvement in a homogeneity of the electric field.Carl Zeiss SMT GmbH

[0037] 6

[0038] The housing surface and the surface structure may be made of stainless steel. Stainless steel is very conductive and very insensitive at the same time, and it is therefore a preferred material for the housing. The housing surface may be blackened, for example oxidized, in order to improve (i.e. reduce) a reflectivity of the surface.

[0039] As seen from the optical element, the housing surface may have a smooth region away from the surface structure. A smooth region can be understood to be a region without amplitudes, and / or a region whose amplitudes are at most 1 / 10 of the amplitudes of the surface structure. The electric field is (also) set by the contrast between the surface structure and the smooth region. Thus, the smooth region leads to a relatively larger electric field strength in the transition region.

[0040] The housing surface may have a smooth region between the optical element and the surface structure. Especially where the housing, from the optical element, extends initially in the base plane before it transitions into a projecting region in the transition region, it may be the case that no concave-convex surface structures are provided between the transition region and the optical element for increasing an electric field strength in the transition region.

[0041] The surface structure may have a width of 5 cm to 50 cm, more preferably of 10 cm to 25 cm. The width preferably denotes a radial extent or an extent along a radial base line of the surface, starting from the optical element or a main axis of the optical element. The wider the surface structure, the smaller the intensification of the electric field strength in the transition region in comparison with the remainder of the wall / optical element. The aforementioned surface structure widths have exhibited good intensification in field strength simulations.

[0042] The surface structure may have an amplitude of 0.05 mm to 50 mm and preferably of 0.1 mm to 20 mm. The aforementioned amplitudes have exhibited good intensification in simulations. On the one hand, a sharpness of the respective tip of the respective convex region is important for local intensification of the electric field, and, on the other hand, the convex regions should be close together and producible. Against this background, the aforementioned amplitude ranges represent a compromise assessed as good.

[0043] As viewed in cross section along a radial direction with respect to the optical element, the surface structure may have a regular profile. In other words, theCarl Zeiss SMT GmbH

[0044] 7

[0045] profile of the surface structure follows a predetermined rule and is manufactured in a targeted manner. Such a profile can be determined well by means of the underlying rule.

[0046] As viewed in cross section along a radial direction with respect to the optical element, the surface structure may have a periodic profile. A quasi-uniform intensification of the electric field strength can be achieved in this way.

[0047] Preferred examples of the profile of the surface structure are a zigzag-shaped profile and a wave-shaped profile. The wave-shaped profile is preferably a sinusoidal profile, with these terms for example including a sine function, a sine function of a quadratic function, a quadratic function of a sine function and the like. What applies to the convex regions of the surface structure, i.e. the portions protruding into the gas and / or plasma, is that these are preferably pointed.

[0048] In cross section along a radial direction with respect to the optical element, the surface structure may have an aperiodic profile, with preferably a respective distance between in each case two adjacent convex regions increasing with increasing distance from the transition region and / or with increasing distance from an imaginary intersection of the transition region. For example, an aperiodic profile may be understood to mean a sine function with a decreasing or increasing period. For example, an aperiodic profile may be understood to mean an irregular profile. An aperiodic profile may be understood to mean both a profile with different amplitudes and a profile with amplitudes of equal height.

[0049] The convex regions of the surface structure may extend an equal distance into the concave shape. This can lead to a uniform intensification of the electric field strength and for example is particularly suitable for a gradual transition from the base plane into the wall. The convex regions, for example toward the edges of the surface structure, may also extend less far into the concave shape. This may lead to a greater intensification of the electric field strength in the centre of the surface structure and for example is particularly suitable for a sharp to abrupt transition from the base plane into the wall.

[0050] For example, the "intersection" is defined between the base plane, which is defined by a circumferential edge of the optical element and / or is a central plane of an optically effective surface and / or reflection surface, and a mean profile of the housing surface in the cross section considered. The "intersection" may be a constructive or imaginary line or such a point, whereas the "transition" describes an actual shape or a change in the profile of said shape.Carl Zeiss SMT GmbH

[0051] 8

[0052] In a radial direction with respect to the optical element, the surface structure may have 2 to 30 and preferably 6 to 20 convex regions. For these numbers, simulations have exhibited a good intensification of the electric field strength in each case, with the precise number of convex regions depending on the respective design of the concave shape of the arrangement.

[0053] The housing may abut against the optical element, and / or the housing may support the optical element. The aforementioned embodiments ensure particularly close contact between the optical element and the housing, and so this hardly influences an electric field strength in a boundary region between these parts.

[0054] According to another aspect of the invention, a projection optics unit is proposed for a projection exposure apparatus, specifically for an EUV projection exposure apparatus or a DUV projection exposure apparatus in particular. The projection exposure apparatus has at least one proposed optical arrangement. The embodiments and features described for the proposed optical arrangement apply correspondingly to the proposed projection exposure apparatus, and vice versa.

[0055] According to another aspect of the invention, an illumination system is proposed for a projection exposure apparatus, specifically for an EUV projection exposure apparatus or a DUV projection exposure apparatus in particular, and preferably for a lithography apparatus. The illumination system has at least one proposed optical apparatus. The embodiments and features described for the proposed optical arrangement apply correspondingly to the proposed illumination system, and vice versa.

[0056] According to another aspect of the invention, a lithography apparatus is proposed, specifically an EUV lithography apparatus or a DUV lithography apparatus in particular. The proposed lithography apparatus has at least one optical arrangement as described above. The embodiments and features described for the proposed optical arrangement apply correspondingly to the proposed lithography apparatus, and vice versa.

[0057] According to another aspect of the invention, an inspection apparatus is proposed for inspecting a shape, a position and / or a geometry of an optical element. The proposed inspection apparatus is prepared in particular for inspecting or checking an optical element or a wafer stage or a mask. An example of such an inspection apparatus is shown in DE 102012220518A1. The proposed inspectionCarl Zeiss SMT GmbH

[0058] 9

[0059] apparatus contains at least one proposed optical arrangement. The embodiments and features described for the proposed optical arrangement apply correspondingly to the proposed inspection apparatus, and vice versa.

[0060] "A(n) / one" should not necessarily be understood as a restriction to exactly one element in the present case. Rather, a plurality of elements, such as two, three or more, may also be provided. Any other numeral used here should also not be understood as a restriction to exactly the stated number of elements. Rather, unless indicated otherwise, numerical deviations upward and downward are possible.

[0061] Further possible implementations of the invention also comprise combinations not explicitly mentioned of features or embodiments described hereinabove or hereinafter with regard to the exemplary embodiments. A person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the invention.

[0062] Further advantageous configurations and aspects of the invention are the subject of the dependent claims and of the exemplary embodiments of the invention that are described hereinafter. The invention will be explained in more detail hereinafter on the basis of preferred embodiments with reference to the appended figures.

[0063] Fig. 1 shows a schematic meridional section of a projection exposure apparatus for EUV projection lithography!

[0064] Fig. 2 schematically shows a surface profile of an optical element and of a housing of an optical arrangement in a cross-sectional view which extends radially with respect to a main axis, to be precise in accordance with a further embodiment of the invention!

[0065] Fig. 3 shows a schematic perspective view of an optical arrangement according to a next embodiment of the invention!

[0066] Fig. 4 schematically shows a surface profile of an optical element and of a housing of an optical arrangement in a cross-sectional view which extends radially with respect to a main axis, to be precise in accordance with a further embodiment of the invention!Carl Zeiss SMT GmbH

[0067] 10

[0068] Fig. 5 schematically shows a cross section of a gas and plasma volume for the purpose of illustrating an ion flow simulation!

[0069] Fig. 6 shows a graph of an ion flow ratio as a function of a number of convex regions in a surface structure according to an ion flow simulation!

[0070] Fig. 7 shows a graph of an ion flow ratio as a function of an amplitude of convex regions in a surface structure according to an ion flow simulation!

[0071] Fig. 8 shows a graph of an ion flow ratio as a function of a peak sharpness of convex regions in a surface structure according to an ion flow simulation! and

[0072] Fig. 9 schematically shows a plurality of different peaked or sharp profiles for a convex region.

[0073] In the figures, identical or functionally identical elements have been provided with the same reference signs, unless indicated otherwise. It should also be noted that the illustrations in the figures are not necessarily true to scale.

[0074] Fig. 1 shows an embodiment of a projection exposure apparatus 1 (lithography apparatus), in particular an EUV lithography apparatus. An embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light or radiation source 3, an illumination optics unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not comprise the light source 3.

[0075] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable by way of a reticle displacement drive 9, in particular in a scanning direction.

[0076] Fig. 1 depicts, by way of elucidation, a Cartesian coordinate system with an x-direction x, a ydirection y and a z-direction z. The x-direction x runs perpendicularly into the plane of the drawing. The ydirection y runs horizontally, and the z-direction z runs vertically. The scanning direction runs in the ydirection y in Fig. 1. The z-direction z runs perpendicularly to the object plane 6.

[0077] The projection exposure apparatus 1 comprises a projection optics unit 10. The projection optics unit 10 is used to image the object field 5 into an image field 11Carl Zeiss SMT GmbH

[0078] 11

[0079] 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.

[0080] 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 in the ydirection y. 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 may be mutually synchronized.

[0081] The light source 3 is an EUV radiation source. The light source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. The used radiation 16 has in particular a wavelength in the range between 5 nm and 30 nm. The light source 3 may be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotronbased radiation source. The light source 3 may be a free electron laser (FEL).

[0082] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 may be a collector having one or more ellipsoidal and / or hyperboloidal reflection surfaces. The illumination radiation 16 may be incident on the at least one reflection surface of the collector 17 with grazing incidence (Gl), i.e. at angles of incidence of greater than 45°, or with normal incidence (Nl), i.e. at angles of incidence of less than 45°. The collector 17 may be structured and / or coated, firstly to optimize its reflectivity for the used radiation and secondly to suppress extraneous light.

[0083] 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 may represent a separation between a radiation source module, having the light source 3 and the collector 17, and the illumination optics unit 4.

[0084] The illumination optics unit 4 comprises a deflection mirror 19 and, arranged downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a planar deflection mirror or alternatively a mirror with a beam-influencing effect that goes beyond the pure deflection effect. In addition to that or in an alternative, the deflection mirror 19 may be embodied as a spectral filter that separates a used light wavelength of the illumination radiation 16Carl Zeiss SMT GmbH

[0085] 12

[0086] from extraneous light of a wavelength differing therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optics 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 can also be referred to as field facets. Only some of these first facets 21 are illustrated in Fig. 1 by way of example.

[0087] The first facets 21 may be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partly circular edge contour. The first facets 21 may take the form of planar facets or alternatively convexly or concavely curved facets.

[0088] As is known from DE 102008009600 Al, for example, the first facets 21 themselves may each also be composed of a multiplicity of individual mirrors, in particular a multip licity of micromirrors. The first facet mirror 20 may in particular take the form of a microelectromechanical system (MEMS system). For details, reference is made to DE 102008009600 Al.

[0089] The illumination radiation 16 travels horizontally, i.e. in the ydirection y, between the collector 17 and the deflection mirror 19.

[0090] In the beam path of the illumination optics unit 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 may also be spaced apart from a pupil plane of the illumination optics 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 614008 Bl and US 6,573,978.

[0091] 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.

[0092] The second facets 23 may 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 2008009600 Al.

[0093] The second facets 23 may have planar or alternatively convexly or concavely curved reflection surfaces.Carl Zeiss SMT GmbH

[0094] 13

[0095] The illumination optics unit 4 thus forms a doubly faceted system. This fundamental principle is also referred to as a fly's eye integrator.

[0096] It may 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 optics unit 10. In particular, the second facet mirror 22 may be arranged so as to be tilted in relation to a pupil plane of the projection optics unit 10, as described for example in DE 102017220586 Al.

[0097] The second facet mirror 22 is used to image the individual first facets 21 into the object field 5. The second facet mirror 22 is the last beam-shaping mirror or else actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

[0098] In a further embodiment (not illustrated) of the illumination optics unit 4, a transfer optics unit contributing in particular to the imaging of the first facets 21 into the object field 5 may be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optics unit may comprise exactly one mirror, or alternatively two or more mirrors arranged one behind another in the beam path of the illumination optics unit 4. The transfer optics unit may in particular comprise one or two normal-incidence mirrors (NI mirrors) and / or one or two grazing-incidence mirrors (GI mirrors).

[0099] In the embodiment shown in Fig. 1, the illumination optics unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

[0100] In a further embodiment of the illumination optics unit 4, the deflection mirror 19 may also be omitted, and so the illumination optics unit 4 can then have exactly two mirrors downstream of the collector 17, specifically the first facet mirror 20 and the second facet mirror 22.

[0101] 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 optics unit, is generally only approximate imaging.

[0102] The projection optics 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.Carl Zeiss SMT GmbH

[0103] 14

[0104] In the example illustrated in Fig. 1, the projection optics 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 optics 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 optics unit 10 has an image-side numerical aperture that is greater than 0.5 and may also be greater than 0.6 and may be, for example, 0.7 or 0.75.

[0105] Reflection surfaces of the mirrors Mi may take the form of free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi may be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics unit 4, the mirrors Mi may have highly reflective coatings for the illumination radiation 16. These coatings may be in the form of multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0106] The projection optics unit 10 has a large object-image shift in the ydirection y between a ycoordinate of a centre of the object field 5 and a ycoordinate of the centre of the image field 11. This object-image shift in the ydirection y may be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.

[0107] The projection optics unit 10 may in particular have an anamorphic form. In particular, it has different imaging scales Bx, By in the x-direction x and y direction y. The two imaging scales Bx, By of the projection optics unit 10 are preferably (Bx, By) = (+ / -0.25, + / -0.125). A positive imaging scale B means imaging without image inversion. A negative sign for the imaging scale B means imaging with image inversion.

[0108] The projection optics unit 10 consequently leads to a reduction in size with a ratio of 4'1 in the x-direction x, i.e. in a direction perpendicular to the scanning direction.

[0109] The projection optics unit 10 leads to a reduction in size of 8H in the ydirection y, i.e. in the scanning direction.

[0110] Other imaging scales are likewise possible. Imaging scales with the same sign and the same absolute value in the x-direction x and ydirection y are also possible, for example with absolute values of 0.125 or of 0.25.Carl Zeiss SMT GmbH

[0111] 15

[0112] The number of intermediate image planes in the x- direction x and in the y-direction y in the beam path between the object field 5 and the image field 11 may be the same or may differ, depending on the design of the projection optics unit 10. Examples of projection optics units with different numbers of such intermediate images in the x-direction x and the ydirection y are known from US 2018 / 0074303 Al.

[0113] In each case, one of the second facets 23 is assigned to exactly one of the first facets 21 in order to form a respective illumination channel for illuminating the object field 5. This may in particular produce illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 using the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 respectively assigned to them.

[0114] The first facets 21 are each imaged onto the reticle 7 by an assigned second facet 23 with images overlaid over one another for the purpose of illuminating 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 may be achieved by overlaying different illumination channels.

[0115] An arrangement of the second facets 23 may geometrically define the illumination of the entrance pupil of the projection optics unit 10. The intensity distribution in the entrance pupil of the projection optics unit 10 may be set by selecting the illumination channels, in particular the subset of the second facets 23 that guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0116] A likewise preferred pupil uniformity in the region of portions of an illumination pupil of the illumination optics unit 4 that are illuminated in a defined manner may be achieved by a redistribution of the illumination channels.

[0117] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics unit 10 are described below.

[0118] The projection optics unit 10 may have in particular a homocentric entrance pupil. The latter may be accessible. It may also be inaccessible.Carl Zeiss SMT GmbH

[0119] 16

[0120] The entrance pupil of the projection optics unit 10 regularly cannot be exactly illuminated with the second facet mirror 22. In the case of imaging by the projection optics unit 10 that telecentrically images the centre of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. 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 is the entrance pupil or an area conjugate thereto in real space. In particular, this area exhibits a finite curvature.

[0121] It may be the case that the projection optics 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 optics 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.

[0122] In the arrangement of the components of the illumination optics unit 4 illustrated in Fig. 1, the second facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optics unit 10. The first 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. 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.

[0123] Fig. 2 schematically shows a cross section of an optical arrangement 100. The optical arrangement 100 has an optical element 102 and a housing 104. The housing 104 supports the optical element 102. A main axis H of the optical element 102 lies in plane of the drawing of the cross section.

[0124] For example, the optical element 102 is one of the mirrors Ml to M6 or one of the facet mirrors 20, 22. The optical element 102 has at least one optically effective surface 106 (in technical terms: optical footprint) on which the illumination radiation 16 (operating light) is incident and which is a mirror surface, for example.

[0125] The housing 104 has a wall 108. The wall 108 surrounds the optical element 102 like a protruding edge. In this case, a housing surface 110 makes an angle W of 90° to 170° with the optically effective surface 106.Carl Zeiss SMT GmbH

[0126] 17

[0127] Hence, the housing 104 and the optical element 102 form a concave shape 112. This could also be referred to as a concave overall shape 112. The concave shape forms what is known as a mini-environment, which is intended to provide the best-possible protection or shield for remaining parts of a lithography apparatus (and / or projection optics unit, projection exposure apparatus, inspection apparatus or the like), for example against the electrostatic effect of the charge-separated plasma.

[0128] There is a transition region 114 where the optically effective surface 106, which extends in a base plane 116, transitions into the wall 108. The housing surface 110 has a surface structure 118 in this transition region 114 and adjacent to this transition region 114.

[0129] The wall 108 may adjoin the optical element 104 at an angle such that the transition region 114 includes both a part of the optical element 104 and a part of the wall 108. In this case, the surface structure 118 is part of the housing surface 110.

[0130] The surface structure 118 is alternately concave-convex. It has at least two convex regions 120 which project inwardly into the concave shape 112. A concave region 122 is situated at least between two respective convex regions 120. As shown in detail below, the inventor has discovered that the sharpness or pointedness of the convex regions 120 in particular intensifies the electrostatic field that forms during operation.

[0131] A smooth surface portion 124 is situated outside of the surface structure 118 in the radial direction. The housing surface 110 thus has the concave-convex surface structure 118 and the smooth surface portion 124.

[0132] The surface structure 118 is formed in one piece with the housing 104 and with the housing surface 110. For example, the surface structure 118 and the smooth surface portion 124 are milled or shaped by milling. For example, a profile cutter can be used for the surface structure 118.

[0133] The surface structure 118 is a free surface so that it can influence the electric field unimpeded. The entire housing surface 110 including the surface structure 118 is not coated.Carl Zeiss SMT GmbH

[0134] 18

[0135] The housing 104 and the optical element 102 are connected to an electric potential. During operation, there is thus a uniform distribution of the electrons which pass from the plasma into the housing 104 and the optical element 102.

[0136] Fig. 3 shows a perspective view of an optical arrangement 200 in accordance with a very schematic embodiment. The optical arrangement 200 has different proportions and numbers than the optical arrangement 100. The optical arrangement 200 has an optical element 202 with an optically effective surface 206. Moreover, the optical arrangement 200 has a housing 204 which forms a wall 208. Hence, a concave shape 212 arises. At and next to a transition region 214, a housing surface 210 has a surface structure 218 composed of multiple convex regions 220 and concave regions 222 therebetween. A smooth portion 224 is found further out. Otherwise, what is described with respect to the above embodiment applies.

[0137] Fig. 4 shows a further optical arrangement 300 in a cross-sectional illustration. In contrast to the optical arrangements 100 and 200, the housing 304, starting from the optical element 302, initially extends in the same base plane 316 before the wall 308 forms the concave basic shape 312. Since the housing surface 310 thus extends in both directions of the transition region 314, the surface structure 318 is also present on both sides of the transition region 314 or of a transition point or of an intersection point. Otherwise, what is described with respect to the other embodiments applies.

[0138] Figs 5 to 8 are now used to present simulation results relating to the ion flow ratio as a function of different parameters.

[0139] The assumption is made that a surface structure has a profile curve f in cross section, said profile curve depending on a spatial coordinate s, which is assumed along an assumed idealized or surface-profile-free curve:

[0140] f(s) = A * sin( s * n * n / smax )2 p

[0141] Here: A is an amplitude, n is a number of convex regions (in technical terms: peaks), Smax is an overall distance and p is a measure of a curvature of the profile in the respective convex region.

[0142] A local curvature in the convex region can be expressed as:

[0143] K = f"(s) * ( 1 + f2(s) )A-( 3 / 2 )

[0144] Here, f'2(s) is a square of a first derivative of the profile curve f(s) and f"(s) is a second derivative of the profile curve.Carl Zeiss SMT GmbH

[0145] 19

[0146] The curvature K influences a field increase of the electric field according to:

[0147] n • V E = — 2KE

[0148] An electric charge carrier current J is thus in turn describable by:

[0149] J = ni * Zi * g * E

[0150] Here: m denotes a particle density in 1 / m3, Zi denotes an ion charge in coulomb, jx denotes an electron mobility in the electric field in m2 / (V*s) and E is precisely the electric field strength in V / m.

[0151] On this basis, the inventor has examined multiple parameters by means of a simulation model (in COMSOL Multiphysics) (plasma simulations with drift, diffusion approximation at 5 Pa H2). An exemplary gas and plasma volume is illustrated in Fig. 5. Hence, the optical element is situated at the lower edge, and the wavy line at the right-hand edge forms the surface structure of the housing surface of the housing.

[0152] In Figs 6 to 8, the solid line represents the ion flow £ toward the optical element, and the dashed line represents the ion flow £ toward the surface structure, to be precise in ions per second.

[0153] Fig. 6 represents the ion flows £ for different numbers n of convex regions. It is clearly evident that, given the boundary conditions of this simulation, approx. 30% more ions are incident on the optical element than on the housing surface when there are no convex regions and that more ions are incident on the housing surface than on the optical element from n = 7 convex regions onward.

[0154] Fig. 7 represents the ion flows £ for different amplitudes of the convex regions. It is evident that in the case of an amplitude of 0.1 cm, only approximately half as many ions are incident on the housing surface as on the optical element. It is clearly evident that in the case of an amplitude of 2.1 cm, the ions incident on the housing surface and on the optical element are almost similar in number.

[0155] Fig. 8 represents the ion flows £ for convex regions of varying sharpness. It is evident that in the case of an exponent of 2*1 and 2*10, the ion flow toward the housing surface is significantly below the ion flow to the optical element. The ion flows are the same in terms of absolute value approximately at an exponent of 2*35, and the ion flow to the housing surface is greater than the ion flow to the optical element at higher exponents. Fig. 9 illustrates the corresponding profile curves in a cross-sectional view for comparison purposes.Carl Zeiss SMT GmbH

[0156] 20

[0157] The simulation results thus demonstrate that the ion flow ratio can be set by means of the alternately convex-concave surface structure at / next to the transition region. Naturally, the specific numbers vary with the specific configuration of the respective optical arrangement.

[0158] In the above description, the surface structure has always been described as rotationally symmetric or at least circumferential. However, it should also be mentioned that the surface structure may, in addition to that or in an alternative, have a circumferentially periodic or aperiodic form.

[0159] By preference, the surface structure is closed in the manner of a ring in the circumferential direction. However, the surface structure may also be interrupted one or more times in the circumferential direction.

[0160] Although the present invention has been described on the basis of exemplary embodiments, it may be modified in a variety of ways.Carl Zeiss SMT GmbH

[0161] 21

[0162] LIST OF REFERENCE SIGNS

[0163] 1 Projection exposure apparatus

[0164] 2 Illumination system

[0165] 3 Light source

[0166] 4 Illumination optics unit

[0167] 5 Object field

[0168] 6 Object plane

[0169] 7 Reticle

[0170] 8 Reticle holder

[0171] 9 Reticle displacement drive

[0172] 10 Projection optics unit

[0173] 11 Image field

[0174] 12 Image plane

[0175] 13 Wafer

[0176] 14 Wafer holder

[0177] 15 Wafer displacement drive

[0178] 16 Illumination radiation

[0179] 17 Collector

[0180] 18 Intermediate focal plane

[0181] 19 Deflection mirror

[0182] 20 First facet mirror

[0183] 21 First facet

[0184] 22 Second facet mirror

[0185] 23 Second facet

[0186] 100, 200, 300 Optical arrangement

[0187] 102, 202, 302 Optical element

[0188] 104, 204, 304 Housing

[0189] 106, 206, 306 Optically effective surface

[0190] 108, 208, 308 Wall

[0191] 110, 210, 310 Housing surface

[0192] 112, 212, 312 Concave shape

[0193] 114, 214, 314 Transition region

[0194] 116, 316 Base plane

[0195] 118, 218, 318 Alternately convex-concave surface structure 120, 220, 320 Convex region of the surface structure 122, 222, 322 Concave region of the surface structure 124, 224, 324 Smooth region

[0196] Amplitude

[0197] H Main axisCarl Zeiss SMT GmbH

[0198] Ml Mirror

[0199] M2 Mirror

[0200] M3 Mirror

[0201] M4 Mirror

[0202] M5 Mirror

[0203] M6 Mirror

[0204] W Angle

[0205] fi Ion flow

[0206] n Number of convex regions p Measure of curvature s Spatial coordinate

Claims

Carl Zeiss SMT GmbH23CLAIMS1. Optical arrangement (100, 200, 300) for a lithography apparatus (1), comprisingan optical element (102, 202, 302);a housing (104, 204, 304) adjoining the optical element (102, 202, 302); and a housing surface (110, 210, 310) which has an alternately concave-convex surface structure (118, 21, 318) in a transition region (114, 214, 314), where the housing (104, 204, 304) forms a concave shape (112, 212, 312) together with the optical element (102, 202, 302), and / or adjacent to the transition region (114, 214, 314).

2. Optical arrangement (100, 200, 300) according to Claim 1, characterized in that the surface structure (118, 21, 318) surrounds the optical element (102, 202, 302).

3. Optical arrangement (100, 200, 300) according to Claim 1 or 2, characterized in that the surface structure (118, 21, 318) forms a free surface.

4. Optical arrangement (100, 200, 300) according to any of Claims 1 to 3, characterized in that the housing surface (110, 210, 310) is formed in one piece with the surface structure (118, 218, 318).

5. Optical arrangement (100, 200, 300) according to any of Claims 1 to 4, characterized in that the housing surface (110, 210, 310) and the surface structure (118, 218, 318) and preferably also the optical element (102, 104, 304) are electrically connected to a potential.

6. Optical arrangement (100, 200, 300) according to any of Claims 1 to 5, characterized in that the housing surface (110, 210, 310) and the surface structure (118, 218, 318) are made of stainless steel.

7. Optical arrangement (100, 200, 300) according to any of Claims 1 to 6, characterized in that as seen from the optical element, the housing surface (110, 210, 310) has a smooth region (124, 224, 324) away from the surface structure (118, 218, 318).

8. Optical arrangement (100, 200, 300) according to any of Claims 1 to 7, characterized in that the housing surface has a smooth region between the optical element and the surface structure.Carl Zeiss SMT GmbH249. Optical arrangement (100, 200, 300) according to any of Claims 1 to 8, characterized in that the surface structure (118, 218, 318) has a width of 5 cm to 50 cm, more preferably of 10 cm to 25 cm.

10. Optical arrangement (100, 200, 300) according to any of Claims 1 to 9, characterized in that the surface structure (118, 218, 318) has an amplitude of 0.05 mm to 50 mm and preferably of 0.1 mm to 20 mm.

11. Optical arrangement (100, 200, 300) according to any of Claims 1 to 10, characterized in that as viewed in cross section along a radial direction with respect to the optical element (102, 202, 302), the surface structure (118, 218, 318) has a regular profile, in particular a periodic profile, preferably a zigzag¬ shaped and / or a wave-shaped profile and more preferably a sinusoidal profile.

12. Optical arrangement (100, 200, 300) according to any of Claims 1 to 11, characterized in that as viewed in cross section along a radial direction with respect to the optical element (102, 202, 302), the surface structure (118, 218, 318) has an aperiodic profile, with preferably a respective distance between in each case two adjacent convex regions (120, 220, 320) increasing with increasing distance from the transition region (114, 214, 314).

13. Optical arrangement (100, 200, 300) according to any of Claims 1 to 12, characterized in that the surface structure (118, 218, 318) has 2 to 30 and preferably 6 to 20 convex regions (120, 220, 320) in a radial direction with respect to the optical element.

14. Optical arrangement (100, 200, 300) according to any of Claims 1 to 13, characterized in that the housing (104, 204, 304) abuts against the optical element (102, 202, 302), and / or the housing (104, 204, 304) supports the optical element.

15. Lithography apparatus (1), comprising an optical arrangement (100, 200, 300) according to any of Claims 1 to 14.

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