WO2025157853A1 - Projection optical unit, and projection exposure system - Google Patents

Abstract

The invention relates to a projection optical unit (10), in particular an EUV projection optical unit, comprising a housing structure (128), wherein the housing structure (128) has: an interior space (140) which is at least partially enclosed by the housing structure (128); and support sections (146, 148, 150, 152) which extend outward from the housing structure (128), away from the interior space (140), wherein an optical element (102) of the projection optical unit (10) can be arranged at least partially within the interior space (140), wherein the housing structure (128) is a one-piece component, and wherein the housing structure (128) has a dimension of at least 2900 mm in at least one spatial direction (x, y, z).

Description

PROJECTION OPTICS AND PROJECTION EXPOSURE SYSTEM

The present invention relates to a projection optics system, in particular an EUV projection optics system, and a projection exposure system for EUV lithography with such a projection optics system.

The content of the priority application DE 10 2024 200 608.4 is incorporated in its entirety by reference.

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

Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed that use light with a wavelength in the range of 0.1 nm to 30 nm, particularly 13.5 nm. Since most materials absorb light at this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the previously used refractive optics, i.e., lenses.

The ongoing development of lithography systems, as mentioned above, toward higher numerical apertures to enable the imaging of smaller structures on the substrate is leading to ever larger optics. However, this also requires larger housings for these optics. This required increase in the installation space of such housings may require the assembly of several subcomponents into the housing. This assembly of subcomponents can have a negative impact on manufacturing costs, product performance, and lifetime performance. This must be improved.

Against this background, it is an object of the present invention to provide an improved projection optics. Accordingly, a projection optics system, in particular an EUV projection optics system, is proposed. The projection optics system comprises a housing structure, wherein the housing structure has an interior space which the housing structure encloses at least in sections, and support sections which extend out of the housing structure facing away from the interior space. An optical element of the projection optics system can be arranged at least in sections within the interior space. The housing structure is a one-piece component, and the housing structure has a dimension of at least 2,900 mm in at least one spatial direction.

Because the housing structure is a single-piece component, the need to join different sub-components to form the housing structure is eliminated. This minimizes the surface area of the housing structure, for example, to better meet vacuum and cleanliness requirements in the EUV environment. The single-piece design of the housing structure also reduces the number of joints and interfaces, thereby reducing the risk of leaks and corrosion. Furthermore, the single-piece construction allows for space-optimized force distribution.

The housing structure can, for example, be part of a housing of the projection optics. The projection optics is an optical system. Therefore, the terms "projection optics" and "optical system" can be interchanged here. The optical system is part of a projection exposure system for EUV lithography. The housing can be a so-called force frame of the optical system. The housing can be composed of several, for example, two, housing structures.

The housing structure is preferably shell-shaped or tub-shaped and encloses the interior space such that the interior space is arranged within the housing structure. However, this does not preclude the interior space from being open to the surroundings of the housing structure. For example, the interior space can be at least partially enclosed by a floor, two opposing side walls, a rear wall, and a front wall of the housing structure.

The optical element is in particular a mirror, preferably an EUV mirror.

However, the optical element can also be a lens. In particular, the optical element can be suspended in the housing structure or mounted on it. When the optical element is mounted, it is arranged at least partially within the interior space. However, this does not preclude the possibility that the optical element or sections of the optical element may protrude from the interior space and into the surroundings of the housing structure.

The term "single-piece" or "one-piece" is understood here to mean, in particular, that the housing structure is not constructed from multiple sub-components assembled together, but rather forms a single component. Accordingly, the housing structure can also be referred to as monolithic. Particularly preferably, the housing structure is a single-piece component. "Single-piece" in this case means that the housing structure is made entirely of the same material. The support sections are also formed in one piece, in particular from a single material, with the housing structure. Alternatively, the housing structure can be designed such that it can be converted into a welded construction.

Subcomponents can be firmly bonded to the housing structure. In bonded connections, the connecting parts are held together by atomic or molecular forces. Bonded connections are non-detachable connections that can only be separated by destroying the connecting elements and/or the connecting parts. Bonded connections can be achieved, for example, by soldering or welding. In particular, the housing structure is made of a metallic material. A light metal, preferably an aluminum alloy, can be used as the material for the housing structure.

The support sections can be block-shaped or cuboid-shaped. The support sections preferably extend outward from the aforementioned side walls, away from the interior. With the help of the support sections, the housing structure can be supported or mounted on suitable bearings, preferably on air bearings, in particular on so-called air mounts. The support sections thus serve to support the housing structure. The support sections can therefore also be referred to as bearing sections. The terms "support section" and "bearing section" are therefore interchangeable for the time being.

The housing structure is preferably assigned a coordinate system with a first spatial direction, the width direction or x-direction, a second spatial direction, the length direction or y-direction, and a third spatial direction, the height direction or z-direction. The directions are oriented perpendicular to one another. For example, the housing structure has a dimension of at least 2,900 mm along the y-direction. Along the x-direction, the housing structure can have a dimension of at least 1,000 mm, and along the z-direction, it can also have a dimension of at least 500 mm. In other words, the housing structure can have a length of more than 2,900 mm, a width of more than 1,000 mm, and a height of more than 500 mm.

According to one embodiment, the housing structure has stiffening ribs.

The number and orientation of the stiffening ribs are arbitrary. For example, two stiffening ribs can be provided. However, in principle, any number of stiffening ribs can be provided. The stiffening ribs increase the rigidity of the housing structure. "Stiffness" is understood here in particular to mean the resistance of a body, in this case the housing structure, to elastic deformation imposed by an external load, in particular by a force or moment, and conveys the relationship between the load on the body and its deformation. Stiffness is determined by the material of the body and its geometry. The stiffening ribs are in particular formed integrally or monolithically with the housing structure.

According to a further embodiment, the stiffening ribs run through the interior.

This means, in particular, that the stiffening ribs are arranged within the interior space. The stiffening ribs can, for example, form a truss-like structure within the interior space, which stiffens the housing structure. The stiffening ribs can be connected to one another.

According to a further embodiment, the stiffening ribs connect a first side wall and a second side wall of the housing structure to one another.

As previously mentioned, the housing structure may comprise, in addition to the first side wall and the second side wall, a base, a rear wall, and a front wall. The stiffening ribs may, in addition to the side walls, also connect the rear wall to the front wall, for example. Furthermore, it is also possible for different stiffening ribs to connect, for example, the side walls to each other, the front wall and the rear wall to each other, and/or the side walls to the Connect the rear wall and/or the front wall. In this case, the aforementioned truss-like structure of the stiffening ribs results.

According to a further embodiment, the first side wall and the second side wall are connected to each other by means of a bottom, a rear wall and a front wall of the housing structure.

The support sections, the first side wall, the second side wall, the base, the rear wall, and the front wall form the housing structure as a single-piece component, in particular as a single-piece component. The support sections are preferably formed as a single piece, in particular as a single-piece component, with the two side walls. Two such support sections can be assigned to each side wall.

According to a further embodiment, the housing structure further comprises cooling channels which run within the housing structure.

The cooling channels can, in particular, run through the first side wall, the second side wall, the base, the rear wall, and/or the front wall. This means, in particular, that the cooling channels can be arranged within the first side wall, the second side wall, the base, the rear wall, and/or the front wall. Furthermore, the cooling channels can also run through the stiffening ribs. In this case, the cooling channels are arranged within the stiffening ribs.

According to a further embodiment, the housing structure further comprises openings which break through the housing structure.

The openings can be provided, for example, on the first side wall, the second side wall, the base, the rear wall and/or the front wall. The openings can have different functions. The openings reduce, for example, the weight of the housing structure. Furthermore, electrical cables and/or liquid-carrying lines can be led through the openings. Furthermore, the optical element or components installed on the optical element can be led out of the housing or out of the housing structure, at least in sections, through the openings. A beam path of the optical system, which illumination radiation follows through the optical system, can also run through at least one opening or through several of the openings. According to a further embodiment, the housing structure has a dimension of at least 500 mm in at least one further spatial direction.

As previously mentioned, this means that the housing structure can have a length of more than 2,900 mm, a width of more than 1,000 mm, and a height of more than 500 mm. Alternatively, the housing structure can also have, for example, a length of more than 500 mm, a width of more than 2,900 mm, and a height of more than 1,000 mm. Furthermore, it is also possible for the housing structure to have a length of more than 1,000 mm, a width of more than 500 mm, and a height of more than 2,900 mm.

According to a further embodiment, the housing structure has an end face, wherein the support sections are arranged flush with the end face.

"Flush" here means, in particular, that the support sections and the end face lie in a common plane. The end face can be used to abut another housing structure, forming the housing. The end face is formed, in particular, by the side walls, the rear wall, the front wall, and the support sections. In other words, a respective upper edge or top side of the side walls, the rear wall, the front wall, and the support sections lie in a common plane in which the end face also lies or which is formed by the end face. The end face preferably lies in or parallel to a plane spanned by the x-direction and the y-direction.

According to a further embodiment, the housing structure has exactly four support sections.

Each side wall of the housing structure can be assigned exactly two support sections. This enables four-point support of the housing structure. However, more than four support sections can also be provided. The support sections can, for example, be block-shaped. With the help of the support sections, two housing structures can also be connected to one another to form the housing. To connect the two housing structures, the support sections have, for example, screw connections and/or pin connections. Precision interfaces with accuracies of less than 20 jun can be provided on the support sections. These precision interfaces can be used for positioning two housing structures to each other to form the housing and/or to position the optical element on the housing structure.

According to a further embodiment, the housing structure is shell-shaped.

"Shell-shaped" in this context means, in particular, that the housing structure encloses the aforementioned interior space at least in part. As mentioned above, however, the interior space is preferably open to the environment of the housing structure. If two housing structures are combined to form the housing, the housing preferably completely encloses the interior spaces of both housing structures. However, this does not preclude the interior space from being accessible from the environment through the aforementioned openings in the respective housing structure.

According to a further embodiment, the projection optics further comprises the optical element, wherein the optical element is arranged at least in sections within the interior of the housing structure.

The optical system can comprise multiple optical elements. However, only one optical element will be discussed below. The optical element is a mirror, in particular an EUV mirror. The optical element can be suspended in the housing structure and thus mounted to it.

According to a further embodiment, the projection optics further comprises at least two housing structures connected to one another, wherein the housing structures together form a housing of the projection optics.

The housing can be a support frame of the optical system as mentioned above. Preferably, the housing has exactly two housing structures that are connected to one another. The housing can accommodate the optical element. This means, in particular, that the optical element is arranged within the housing.

According to a further embodiment, the projection optics comprises a sensor frame, wherein the sensor frame is arranged at least in sections within the housing. In particular, the sensor frame is arranged within the interior spaces of the housing structures enclosed by the housing structures. The sensor frame can also be referred to as a sensor frame. The housing can be coupled to a fixed world by means of one or more coupling elements. Furthermore, the sensor frame can be coupled to the housing by means of one or more coupling elements. The coupling elements can comprise springs. A "fixed world" is understood here to be a region of the optical system that is immobile with respect to the housing. The optical element can be adjustable or aligned with an actuator unit in six degrees of freedom, namely three translational and three rotational degrees of freedom. The sensor frame serves as a reference for a change in the position of the optical element. The optical element is connected to the housing via the actuator unit. The optical element can be connected to the actuator unit via a coupling element, which in turn is connected to the housing via another coupling element. For example, a control unit is used to maintain a desired position of the optical element. The control unit can communicate with the actuator unit for this purpose. The control unit interacts with the sensor frame in such a way that, for example, sensors attached to the sensor frame measure the optical element. The control unit controls the actuator unit based on sensor signals from these sensors to maintain the desired position of the optical element.

Furthermore, a projection exposure system for EUV lithography with such projection optics is proposed.

The projection exposure system is an EUV lithography system. EUV stands for "Extreme Ultraviolet" and refers to a wavelength of working light between 0.1 nm and 30 nm.

"One" is not necessarily limited to a single element. Rather, multiple elements, such as two, three, or more, may be included. Any other counting term used here should not be understood as implying a limitation to the exact number of elements stated. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated. The embodiments and features described for the projection optics apply accordingly to the proposed projection exposure system and vice versa.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures.

Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography!

Fig. 2 shows a schematic view of an embodiment of an optical system for the projection exposure apparatus according to Fig. 1;

Fig. 3 shows a schematic plan view of the optical system according to Fig. 2;

Fig. 4 shows a further schematic view of the optical system according to Fig. 2;

Fig. 5 shows a further schematic view of the optical system according to Fig. 2;

Fig. 6 shows a schematic perspective view of an embodiment of a housing structure for the optical system according to Fig. 2;

Fig. 7 shows a schematic perspective partial sectional view of the housing structure according to Fig. 6;

Fig. 8 shows a schematic plan view of the housing structure according to Fig. 6;

Fig. 9 shows a schematic side view of the housing structure according to Fig. 6; and

Fig. 10 shows a schematic rear view of the housing structure according to Fig. 6. In the figures, identical or functionally equivalent elements are provided with the same reference numerals unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the remaining illumination system 2. In this case, the illumination system 2 does not include the light source 3.

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 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

For illustrative purposes, Fig. 1 shows a Cartesian coordinate system with an x-direction (x), a y-direction (y), and a z-direction (z). The x-direction (x) runs perpendicular to the drawing plane. The y-direction (y) runs horizontally, and the z-direction (z) runs vertically. The scanning direction in Fig. 1 runs along the y-direction (y). The z-direction (z) runs perpendicular to the object plane (6).

The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

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 can be displaced, in particular along the y-direction y, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other. 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 useful radiation, illumination radiation, or illumination light. The useful radiation 16 has, in particular, a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example an LPP source (Laser Produced Plasma, plasma generated with the aid of a laser) or a DPP source (Gas Discharged Produced Plasma, plasma generated by gas discharge). It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (FEL).

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

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

The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Only a few of these first facets 21 are shown in Fig. 1 as examples.

The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The first facets 21 can be designed as flat facets or, alternatively, as convexly or concavely curved facets.

As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

In the beam path of the illumination optics 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 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 optics 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 A1, EP 1 614 008 B1, and US Pat. No. 6,573,978.

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.

The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces. The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (EnglJ Fly's Eye Integrator).

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 10. In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last bundle-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path before the object field 5.

In a further embodiment of the illumination optics 4 (not shown), a transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which transmission optics contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and/or one or two mirrors for grazing incidence (GL mirrors, grazing incidence mirrors).

In the embodiment shown in Fig. 1, the illumination optics 4 has exactly three mirrors after the collector 17, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

In a further embodiment of the illumination optics 4, the deflection mirror 19 can also be omitted, so that the illumination optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is usually only an approximate imaging. The projection optics 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection illumination system 1.

In the example shown in Fig. 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The projection optics 10 is a double-obscured optic. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one rotational symmetry axis of the reflection surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 10 has a large object-image offset in the y-direction y between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

The projection optics 10 can, in particular, be anamorphic. It has, in particular, different image scales ßx, ßy in the x and y directions x, y. The two image scales ßx, ßy of the projection optics 10 are preferably (ßx, ßy) = (+/- 0.25, +/- 0.125). A positive image scale ß means an image without image inversion. A negative sign for the image scale ß means an image with image inversion.

The projection optics 10 thus leads to a reduction in the ratio 4'1 in the x-direction x, i.e. in the direction perpendicular to the scanning direction. The projection optics 10 leads to a reduction of 8D in the y-direction y, i.e. in the scanning direction.

Other magnifications are also possible. Magnifications with the same sign and absolutely identical in the x and y directions (x, y), for example, with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x- and y-directions x, y 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 design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions x, y are known from US 2018/0074303 A1.

Each of the second facets 23 is assigned to exactly one of the first facets 21 to form a respective illumination channel for illuminating the object field 5. This can, in particular, result in illumination according to the Köhler principle. The far field is divided into a plurality 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 assigned to them.

The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23, superimposed on one another, 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 superimposing different illumination channels.

By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the second facets 23 that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels. Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics 10 are described below.

The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 10 cannot usually be precisely illuminated with the second facet mirror 22. When imaging the projection optics 10, which telecentrically images the center of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the pairwise determined spacing of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

It is possible that the projection optics 10 have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

In the arrangement of the components of the illumination optics 4 shown in Fig. 1, the second facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the second facet mirror 22.

Fig. 2 shows a schematic view of an embodiment of an optical system 100 for the projection exposure apparatus 1. Fig. 3 shows a schematic plan view of the optical system 100. In the following, reference is made simultaneously to Figs. 2 and 3.

The optical system 100 can be a projection optics 10 as explained above or part of such a projection optics 10. Therefore, the optical system 100 can also be referred to as projection optics. However, the optical system 100 can It can also be an illumination system 2 as previously explained or part of such an illumination system 2. Therefore, the optical system 100 can alternatively also be referred to as an illumination system. However, it is assumed below that the optical system 100 is a projection optics system 10 or part of such a projection optics system 10. The optical system 100 is suitable for EUV lithography. However, the optical system 100 can also be suitable for DUV lithography.

The optical system 100 can comprise a plurality of optical elements 102, of which only one is shown in Figs. 2 and 3. Therefore, only one optical element 102 will be discussed below. The optical element 102 can be one of the mirrors M1 to M6. The optical element 102 comprises an optically effective surface 104, for example, a mirror surface. The optically effective surface 104 can be oriented upward or downward in the orientation of Fig. 2.

The optically effective surface 104 is provided on a front side 106 or on a rear side 108 of the optical element 102. It is assumed below that the optically effective surface 104 is provided on the front side 106. The optically effective surface 104 can be realized by means of a coating applied to the front side 106. The optically effective surface 104 is a mirror surface.

The optically effective surface 104 is suitable for reflecting illumination radiation 16, in particular EUV radiation, during operation of the optical system 100. The optically effective surface 104 can have an oval or elliptical geometry in the plan view according to Fig. 3. The optical element 102 can have a triangular geometry in the plan view according to Fig. 3. In principle, however, the geometry of the optical element 102 is arbitrary.

Facing away from the optically effective surface 104 or the front side 106, the optical element 102 has the rear side 108. The rear side 108 has no defined optical properties. This means, in particular, that the rear side 108 is not a mirror surface and therefore does not have any reflective properties. However, this is not absolutely necessary. As previously mentioned, the optically effective surface 104 can also be provided on the rear side 108.

The optical element 102 or the optically effective surface 104 has six degrees of freedom, namely three translational degrees of freedom each along the first spatial direction or x-direction x, the second spatial direction or y The optical element 102 has three spatial directions, one in the y direction and the third spatial direction or z direction, as well as three rotational degrees of freedom about the x direction, the y direction, and the z direction. This means that a position and an orientation of the optical element 102 or the optically effective surface 104 can be determined or described using the six degrees of freedom.

The "position" of the optical element 102 or the optically effective surface 104 is to be understood in particular as its coordinates or the coordinates of a measuring point provided on the optical element 102 with respect to the x-direction x, the y-direction y, and the z-direction z. The "orientation" of the optical element 102 or the optically effective surface 104 is to be understood in particular as its tilt with respect to the three spatial directions x, y, z. This means that the optical element 102 or the optically effective surface 104 can be tilted about the x-direction x, the y-direction y, and/or the z-direction z.

This results in six degrees of freedom for the position and orientation of the optical element 102 or the optically effective surface 104. A "position" of the optical element 102 or the optically effective surface 104 encompasses both its position and its orientation. The term "position" can therefore be replaced by the phrase "position and orientation," and vice versa.

In Fig. 2, solid lines indicate an actual position IL of the optical element 102 or the optically effective surface 104, and dashed lines and the reference symbols 102' or 104' indicate a desired position SL of the optical element 102 or the optically effective surface 104. The optical element 102 can be moved from its actual position IL to the desired position SL and vice versa. For example, the optical element 102 in the desired position SL meets certain optical specifications or requirements that the optical element 102 in the actual position IL does not meet.

To move the optical element 102 from the actual position IL to the desired position SL, the optical element 102 can be adjusted or aligned. "Adjusting" or "aligning" is understood here to mean, in particular, changing the position of the optical element 102. For example, the optical element 102 can be moved from the actual position IL to the desired position SL and vice versa. The adjustment or alignment of the optical element 102 can thus be performed in all six aforementioned degrees of freedom. Fig. 4 shows another schematic view of the optical system 100.

In addition to the optical element 102, the optical system 100 includes a housing 110 and a sensor frame 112 (EnglJ sensor frame). The housing 110 is, in particular, a so-called support frame (EnglJ force frame) of the optical system 100. Therefore, the terms "housing" and "support frame" can be used interchangeably in this context.

The housing 110 is coupled to a fixed world 116 by means of a coupling element 114. Several such coupling elements 114 can be provided. The sensor frame 112 is coupled to the housing 110 by means of a coupling element 118. Several such coupling elements 118 can be provided. The housing 110 thus supports the sensor frame 112. The coupling elements 114, 118 can comprise springs. In this case, a "fixed world" is understood to mean a region of the optical system 100 that is immobile with respect to the housing 110.

As previously mentioned, the optical system 100 can have a plurality of optical elements 102, of which only one is shown in Fig. 4. The optical element 102 can be adjusted or aligned in the aforementioned six degrees of freedom using an actuator unit 120. The sensor frame 112 serves as a reference for a change in the position of the optical element 102. The optical element 102 is connected to the housing 110 via the actuator unit 120. The optical element 102 can be connected to the actuator unit 120 via a coupling element 122, which in turn is connected to the housing 110 via a coupling element 124.

With the aid of a control and regulation unit 126, for example, a target position SL of the optical element 102 is maintained, as previously explained. The control and regulation unit 126 can communicate with the actuator unit 120 for this purpose. The control and regulation unit 126 interacts with the sensor frame 112 in such a way that, for example, sensors attached to the sensor frame 112 measure the optical element 102, wherein the control and regulation unit 126 controls the actuator unit 120 based on sensor signals from these sensors in order to maintain the target position SL of the optical element 102.

Fig. 5 shows another schematic view of the optical system 100. The optical system 100 is shown in Fig. 5 in a very simplified manner; for example, the optical element 102 is not shown. The optical system 100 can be constructed such that the sensor frame 112 is arranged at least partially within the housing 110. The sensor frame 112 can also be placed entirely within the housing 110. The housing 110 thus functions as a casing or enclosure for the sensor frame 112.

The sensor frame 112 can be made, at least in sections, from a ceramic material. The sensor frame 112 can be a one-piece component, in particular a single-piece component. "Single-piece" or "one-piece" in this case means that the sensor frame 112 is not composed of different subcomponents, but rather forms a continuous component. "Single-piece material" in this case means that the sensor frame 112 is made entirely from the same material.

The progressive development of projection exposure systems 1 as mentioned above towards higher numerical apertures in order to be able to image smaller structures on the wafer 13 tends to lead to ever larger optical elements 102. However, this also requires the housing 110 to be dimensioned larger.

This required increase in the installation space of the housing 110 can have a negative impact on manufacturing costs, product performance, and service life when multiple subcomponents are assembled. In the course of the development of projection exposure systems 1 with larger numerical apertures and the resulting introduction of larger dimensions of the housing 110, the goal of minimizing the small-scale assembly of the overall structure of the housing 110 is to be realized.

The housing 110 can be made of a metallic material, in particular a light metal. For example, an aluminum alloy can be used for the housing 110. The housing 110 is preferably multi-part. "Multi-part" in this case means, in particular, that the housing 110 can be composed of at least two subcomponents in the form of housing structures in order to be able to build the housing 110 around the sensor frame 112. However, the housing 110 is composed of as few subcomponents as possible. These aforementioned housing structures can be shell-shaped, in particular half-shell-shaped. Fig. 6 shows a schematic perspective view of an embodiment of a housing structure 128 for the housing 110. Fig. 7 shows a schematic perspective partial sectional view of the housing structure 128. Fig. 8 shows a schematic top view of the housing structure 128. Fig. 9 shows a schematic side view of the housing structure 128. Fig. 10 shows a schematic rear view of the housing structure 128. In the following, reference is made to Figs. 6 to 10 simultaneously.

The housing 110 can be constructed from several, for example, two, such housing structures 128. These housing structures 128 can be identical or different. Only one housing structure 128 will be discussed below. Assigned to the housing structure 128 is a coordinate system as previously mentioned, comprising a first spatial direction, width direction or x-direction x, a second spatial direction, length direction or y-direction y, and a third spatial direction, height direction or z-direction z. The directions x, y, z are oriented perpendicular to one another.

The housing structure 128 is a one-piece component, in particular a one-piece component made of the same material. For example, the housing structure 128 is made of an aluminum alloy. The housing structure 128 preferably has dimensions of at least 2,900 mm along the y-direction, at least 1,000 mm along the x-direction, and at least 500 mm along the z-direction. In other words, the housing structure 128 can have a length of more than 2,900 mm, a width of more than 1,000 mm, and a height of more than 500 mm.

The housing structure 128 is shell-shaped and comprises a base 130, two side walls 132, 134, which can be arranged parallel to one another, a rear wall 136, and a front wall 138. The rear wall 136 can be positioned perpendicular to the base 130. The front wall 138 can be oriented obliquely to the base 130. The housing structure 128 thus encloses a cavity or interior space 140. The interior space 140 is bounded by the base 130, the side walls 132, 134, the rear wall 136, and the front wall 138.

Reinforcing ribs 142, 144 may extend through the interior space 140. The number and orientation of the reinforcing ribs 142, 144 are arbitrary. For example, the reinforcing ribs 142, 144 may connect the side walls 132, 134 to one another. However, it is also possible for the reinforcing ribs 142, 144 to connect the rear wall 136 to the front wall 138. The optical element 102 (not shown) may be placed at least partially within the interior space 140. The stiffening ribs 142, 144 may also form a truss-like structure arranged within the interior space 140.

The stiffening ribs 142, 144 increase the rigidity of the housing structure 128. "Rigidity" is understood here in particular as the resistance of a body, in this case the housing structure 128, to elastic deformation imposed by an external load, in particular a force or moment, and conveys the relationship between the load on the body and its deformation. The rigidity is determined by the material of the body and its geometry.

A plurality of support sections 146, 148, 150, 152 can be provided on each side wall 132, 134. The support sections 146, 148, 150, 152 can be block-shaped. The support sections 146, 148, 150, 152 extend outward from the side walls 132, 134, away from the interior space 140. With the help of the support sections 146, 148, 150, 152, the housing structure 128 can be supported on suitable air bearings, in particular on so-called air mounts.

With reference to the housing structure 128, "integral" means, in particular, that the base 130, the side walls 132, 134, the rear wall 136, the front wall 138, and/or the support sections 146, 148, 150, 152 cannot be separated from one another in a non-destructive manner or without damaging them. In particular, "integral" means in this case that the housing structure 128 is not composed of different subcomponents, but rather that the base 130, the side walls 132, 134, the rear wall 136, the front wall 138, and the support sections 146, 148, 150, 152 form a common component, namely the housing structure 128.

The housing structure 128 has an end face 153, with which the housing structure 128 adheres to another housing structure (not shown) to form the housing 110. The end face 153 is formed by the side walls 132, 134, the rear wall 136, the front wall 138, and the support sections 146, 148, 150, 152. In other words, a respective upper edge or top side of the side walls 132, 134, the rear wall 136, the front wall 138, and the support sections 146, 148, 150, 152 lie in a common plane in which the end face 153 also lies or which is formed by the end face 153. The end face 153 lies in or parallel to a plane spanned by the x-direction x and the y-direction y. Any number of openings 154, 156, 158, 160 can be provided on the side walls 132, 134. Furthermore, an opening 162 can also be provided on the rear wall 136. Another opening 164 can extend from the rear wall 136 into the floor 130. Additionally, the floor 130 can have another opening 166. The stiffening ribs 142, 144 can also have openings 168, 170.

The openings 154, 156, 158, 160, 162, 164, 166, 168, 170 can have different functions. For example, the openings 154, 156, 158, 160, 162, 164, 166, 168, 170 reduce the weight of the housing structure 128. Furthermore, electrical cables and/or fluid-carrying lines can be routed through the openings 154, 156, 158, 160, 162, 164, 166, 168, 170.

In addition, the optical element 102 or components installed on the optical element 102 can be guided out of the housing 110 at least partially through the openings 154, 156, 158, 160, 162, 164, 166, 168, 170. A beam path of the optical system 100, which the illumination radiation 16 follows through the optical system 100, can also pass through at least one opening 154, 156, 158, 160, 162, 164, 166, 168, 170 or through several of the openings 154, 156, 158, 160, 162, 164, 166, 168, 170.

The housing structure 128 can be traversed by cooling channels 172, of which only one cooling channel 172 is shown very schematically in Fig. 9. The cooling channels 172 can be provided or mounted in or on the base 130, the side walls 132, 134, the rear wall 136, the front wall 138, and/or the stiffening ribs 142, 144.

The housing structure 128 is preferably shell-shaped and has an optimal stiffness-to-mass ratio to optimize dynamic performance. The housing structure 128 can preferably have monolithic stiffening ribs 142, 144 as previously mentioned. An exemplary dimension of the housing structure 128 is—as previously mentioned—greater than 2,900 mm in length, greater than 1,000 mm in width, and greater than 500 mm in height. The material used is preferably a metal alloy suitable for lightweight construction, such as an aluminum alloy.

The housing structure 128 may include an integrated cooling system, for example in the form of cooling channels 172. This may be achieved by monolithically incorporated cooling channels 172. The housing structure 128 has precision interfaces with accuracies of less than 20 jun. These precision interfaces can be used to position two housing structures 128 against each other to form the housing 110 and/or to position the optical element 102 on the housing structure 128. The exact shape of the housing structure 128, particularly taking into account the compliance and residual stress state of the housing structure 128, is defined by defining the bearing during an acceptance measurement.

The surface area of the monolithic housing structure 128 is minimized to ensure the vacuum and cleanliness requirements of the EUV environment. The minimized number of joints and interfaces due to the monolithic design reduces the risk of leaks and corrosion.

The housing structure 128 is structured in such a way that it can potentially be converted into a material-to-material soldered and/or welded construction. The housing structure 128 can also be structured in such a way that it can potentially be converted into a construction comprising subcomponents that are connected to one another in a force-fitting and/or form-fitting manner.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

LIST OF REFERENCE SYMBOLS

1 projection exposure system

2 Lighting system

3 Light source

4 Lighting optics

5 Object field

6 Object level

7 reticles

8 reticle holders

9 Reticle displacement drive

10 Projection optics

11 Image field

12 Image plane

13 wafers

14 wafer holders

15 W afer relocation drive

16 Lighting radiation

17 Collector

18 Intermediate focal plane

19 Deflecting mirrors

20 first facet mirror

21 first facet

22 second facet mirror

23 second facet

100 optical system

102 optical element

102’ optical element

104 optically effective area

104’ optically effective area

106 Front

108 Back

110 housings

112 sensor frames

114 Coupling element

116 solid world

118 coupling element

120 Actuator unit

122 coupling element 124 coupling element

126 Control and regulation unit

128 Housing structure

130 floor

132 side wall

134 side wall

136 rear wall

138 front wall

140 interior

142 Stiffening rib

144 Stiffening rib

146 support section

148 support section

150 support section

152 support section

153 frontal area

154 Breakthrough

156 Breakthrough

158 Breakthrough

160 Breakthrough

162 Breakthrough

164 Breakthrough

166 Breakthrough

168 Breakthrough

170 Breakthrough

172 cooling channel

ml mirror

M2 mirror

M3 mirror

M4 mirror

M5 mirror

M6 Mirror x x-direction y y-direction z-direction

Claims

PATENT CLAIMS 1. Projection optics (10), in particular EUV projection optics, with a housing structure (128), wherein the housing structure (128) has: an interior space (140) which the housing structure (128) encloses at least in sections, and Support sections (146, 148, 150, 152) which extend out of the housing structure (128) facing away from the interior space (140), wherein an optical element (102) of the projection optics (10) can be arranged at least in sections within the interior space (140), wherein the housing structure (128) is a one-piece component, and wherein the housing structure (128) has a dimension of at least 2,900 mm in at least one spatial direction (x, y, z). 2. Projection optics according to claim 1, wherein the housing structure (128) has stiffening ribs (142, 144). 3. Projection optics according to claim 2, wherein the stiffening ribs (142, 144) extend through the interior space (140). 4. Projection optics according to claim 2 or 3, wherein the stiffening ribs (142, 144) interconnect a first side wall (132) and a second side wall (134) of the housing structure (128). 5. Projection optics according to claim 4, wherein the first side wall (132) and the second side wall (134) are connected to one another by means of a bottom (130), a rear wall (136) and a front wall (138) of the housing structure (128). 6. Projection optics according to one of claims 1 - 5, further comprising cooling channels (172) extending within the housing structure (128). 7. Projection optics according to one of claims 1 - 6, further comprising openings (154, 156, 158, 160, 162, 164, 166, 168, 170) which break through the housing structure (128). 8. Projection optics according to one of claims 1 - 7, wherein the housing structure (128) has a dimension of at least 500 mm in at least one further spatial direction (x, y, z). 9. Projection optics according to one of claims 1 - 8, wherein the housing structure (128) has an end face (153), and wherein the support sections (146, 148, 150, 152) are arranged flush with the end face (153). 10. Projection optics according to one of claims 1 - 9, wherein the housing structure (128) has exactly four support sections (146, 148, 150, 152). 11. Projection optics according to one of claims 1 - 10, wherein the housing structure (128) is shell-shaped. 12. Projection optics according to one of claims 1 - 11, further comprising the optical element (102), wherein the optical element (102) is arranged at least in sections within the interior space (140) of the housing structure (128). 13. Projection optics according to claim 12, further comprising at least two housing structures (128) connected to one another, wherein the housing structures (128) together form a housing (110) of the projection optics (10). 14. Projection optics according to claim 13, further comprising a sensor frame (112), wherein the sensor frame (112) is arranged at least in sections within the housing (110). 15. Projection exposure system (1) for EUV lithography, comprising projection optics (10) according to one of claims 1-14.