DE102024200212A1 - shielding element, optical system and projection exposure system - Google Patents

Abstract

A shielding element (126) for shielding components (102, 102') of a projection exposure system (1), comprising a sheet-metal base section (136) and a plurality of fastening points (128, 130, 132, 134, 158, 160, 162, 216) provided on the base section (136) for fastening the shielding element (126) to a support structure (120), wherein the fastening points (128, 130, 132, 134, 158, 160, 162, 216) have different numbers of degrees of freedom.

Description

The present invention relates to a shielding element for the magnetic and/or thermal shielding of components of a projection exposure system, an optical system with such a shielding element and a projection exposure system with such a shielding element and/or such an optical system.

Microlithography is used to produce microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system that has 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, such as a silicon wafer, that is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system in order to transfer the mask structure onto the light-sensitive coating of the substrate.

Driven by the pursuit of ever smaller structures in the manufacture of integrated circuits, EUV lithography systems, which use light with a wavelength in the range of 0.1 nm to 30 nm, in particular 13.5 nm, and DUV lithography systems, which use light with a wavelength in the range of 30 nm and 250 nm, are currently being developed. In particular, such EUV lithography systems require the use of reflective optics, i.e. mirrors, instead of - as previously - refracting optics, i.e. lenses, due to the high absorption of light of this wavelength by most materials.

In order to protect components, such as a mirror as mentioned above, of such an EUV lithography system from magnetic fields, shielding elements can be used. It is desirable that the shielding elements take up as little space as possible. Furthermore, it is necessary to attach the shielding elements to a fixed support structure in such a way that they are neither mechanically underdetermined nor mechanically overdetermined.

Against this background, an object of the present invention is to provide an improved shielding element.

Accordingly, a shielding element for shielding components of a projection exposure system is proposed. The shielding element comprises a sheet-metal-shaped base section and a plurality of fastening points provided on the base section for fastening the shielding element to a support structure, wherein the fastening points have different numbers of degrees of freedom.

Because the base section is made of sheet metal, the shielding element can also be used when there is little available installation space. Because the fastening points have different degrees of freedom, it is possible to attach the shielding element to the supporting structure in such a way that the shielding element is neither mechanically underdetermined nor mechanically overdetermined.

The shielding element is particularly suitable for magnetic and/or thermal shielding of the components. In addition, the shielding element can also function for electromagnetic shielding or for shielding against stray light. The shield can also function as a so-called HiO getter (hydrogen induced outgassing). In its function as a HiO getter, the effect of hydrogen-induced outgassing on the components can be prevented or at least reduced.

The components can include, for example, optical elements, in particular mirrors. The shielding element can be used for both EUV lithography and DUV lithography. The fact that the base section is "sheet-shaped" is to be understood in particular in the present case to mean that the base section has two main extension directions, along which the base section has a significantly larger geometric extension than along a thickness direction of the base section. For example, the base section can have a thickness of a few tenths of a millimeter to a few millimeters.

The shielding element or the base section is preferably made of a metallic material. In particular, the base section can be made of a nickel-iron alloy, such as FeNi48 or FeNi50. To prevent corrosion, the shielding element or the base section can be coated. A nickel-phosphorus coating (NiP), for example, is used as the coating.

The number of fastening points is arbitrary. For example, exactly four fastening points can be provided on the base section. In the simplest case, one of the fastening points can be a hole through the base section. Each fastening point can be provided with a fastening element, in particular in the form of a Screw, with the help of which the shielding element is connected, in particular screwed, to the supporting structure.

The support structure can be a support frame (English: force frame) of an optical system, in particular a projection optics, of the projection exposure system. The shielding element is part of the optical system. The previously mentioned components, in particular in the form of optical elements, are also part of the optical system. The components are at least partially covered by the shielding element or arranged within the shielding element. The optical system can have several such shielding elements. All shielding elements of the optical system together form a shield of the optical system.

The shielding element or the base section is assigned a coordinate system with a first spatial direction or x-direction, a second spatial direction or y-direction and a third spatial direction or z-direction. Any object in this coordinate system has six degrees of freedom, namely three translational degrees of freedom along the x-direction, the y-direction and the z-direction and three rotational degrees of freedom around the x-direction, the y-direction and the z-direction. This means that a position and an orientation of this aforementioned object in the coordinate system can be determined or described using the six degrees of freedom.

In the simplest case, for example, one of the fastening points has exactly one degree of freedom, for example a rotational degree of freedom. However, the fastening points can also have two, three, four or more than four degrees of freedom. For example, one fastening point has exactly one degree of freedom, another fastening point has exactly two degrees of freedom and two further fastening points each have exactly three degrees of freedom. In this latter case, the shielding element preferably has exactly four fastening points.

The shielding element can be kinematically underdetermined or kinematically overdetermined. Kinematic overdetermination defines the thermal center of the shielding element less than an isostatic solution where neither kinematic overdetermination nor kinematic underdetermination exists. The term "thermal center" is used here as follows. When a solid body is subjected to a thermal change, an expansion of the body occurs, which changes the dimensions and possibly the shape of the body and the position of its points. Under certain circumstances, a point belonging to the space associated with the body may experience no displacement at all. This aforementioned point is called the thermal center.

The shielding element can also be used in very limited installation space. As mentioned above, the shielding element preferably has an anti-corrosion coating. The shielding element can have any number of fastening points. So many fastening points can be used that there is static overdetermination. In particular, unwanted vibrations of the shielding element can be prevented or suppressed by additional fastening points. According to one embodiment, the base section has several areas that are connected to one another at one or more bending edges.

The base section can have any number of folds and/or areas. The base section can also have one or more curves per area. In particular, the base section has a first area and a second area that is bent at a bending edge relative to the first area. For example, the second area is arranged perpendicular to the first area. The bending edge can be used to stiffen the shielding element. The shielding element can basically have any three-dimensional geometry. For this purpose, the base section can be bent at several bending edges.

According to a further embodiment, at least one of the fastening points has a bore with a countersink.

For example, a head section of a fastening element for fastening the shielding element to the support structure can be accommodated in the countersink. This allows the head section to be arranged flush with a front side of the shielding element. This makes it possible to use the shielding element even when the available installation space is limited. Fastening points can also be provided without such a countersink.

According to a further embodiment, the bore is an elongated hole, wherein in particular a countersink is provided on the bore.

Alternatively, the hole can also be circular. In the case that the hole is a slot, a translational degree of freedom can be set along this slot. In addition to this translational degree of freedom, a rotational degree of freedom around the fastening element is possible.

According to a further embodiment, at least one of the fastening points has a coupling section, wherein the coupling section is connected to the base section by means of spring sections.

The coupling section is movable relative to the base section, in particular translationally movable. When the coupling section moves relative to the base section, the spring sections are deformed elastically, in particular spring-elastically. In the present case, an “elastic” deformation of the spring sections means that the spring sections can be brought from an undeformed or undeflected state into a deformed or deflected state by applying a force. If this force no longer acts on the spring sections, they deform independently or automatically from the deformed state back to the undeflected state. The spring sections are in particular leaf spring sections and can also be referred to as such. The shielding element is preferably a one-piece component, in particular a one-piece material component. In the present case, “one-piece” or “one-piece” is to be understood in particular to mean that the base section, the coupling section and the spring sections are not composed of different sub-components, but form a common component, namely the shielding element. In this case, “integral material” means in particular that the shielding element is made entirely of the same material. Suitable materials include metals, for example.

According to a further embodiment, a cover section is arranged between the spring sections.

The cover section is separated from the spring sections by means of gaps. The cover section covers an opening present between the spring sections, so that the cover section prevents larger openings in the shielding element. This improves the shielding effect of the shielding element.

According to a further embodiment, each degree of freedom is assigned a first end stop and a second end stop.

Preferably, two end stops are provided for each degree of freedom. This enables in particular a negative and a positive movement to avoid overloading the spring sections. This means in particular that with three degrees of freedom, six end stops can be provided. In particular, a first end stop and a second end stop are assigned to the coupling section, with the coupling section being arranged between the first end stop and the second end stop. As previously mentioned, the coupling section can perform a translational movement relative to the base section. The end stops limit this translational movement. This can prevent mechanical overloading of the spring sections. Furthermore, end positions of the coupling section are precisely defined using the end stops.

According to a further embodiment, the spring sections merge into the base section by means of continuous curvatures.

In particular, sharp edges and abrupt transitions are to be avoided at a transition between the spring sections and the base section. The curvatures can be radii. The curvatures are in particular adapted to be bionic. In particular, the curvatures can be bionic radii. With the help of the curvatures, mechanical overloading of the spring sections at the transition of the spring sections to the base section can be prevented. The aim of the curvatures is to avoid stress concentrations. The curvatures can be simple radii, bionic radii or second or third degree polynomials.

According to a further embodiment, the shielding element has one fastening point with exactly one degree of freedom, one fastening point with exactly two degrees of freedom and two fastening points with exactly three degrees of freedom.

For example, the exact one degree of freedom of the aforementioned attachment point is a rotational degree of freedom. The attachment point with exactly two degrees of freedom has, for example, one rotational and one translational degree of freedom. The two attachment points, each with exactly three degrees of freedom, each have, for example, one rotational and two translational degrees of freedom, which are oriented perpendicular to each other.

According to a further embodiment, when connecting the shielding element to the support structure, first the fastening point can be connected to the support structure with exactly one degree of freedom, then the fastening point can be connected to the support structure with exactly two degrees of freedom, and finally the two attachment points, each with exactly three degrees of freedom, can be connected to the supporting structure.

By mounting the fastening points step by step, a kinematic assembly process can be implemented. To do this, the shielding element is first connected to the supporting structure using the fastening point that has the fewest degrees of freedom. The other fastening points are then connected to the supporting structure with increasing numbers of degrees of freedom.

According to a further embodiment, the shielding element is a bent sheet metal component.

This allows the shielding element to be manufactured cost-effectively. Furthermore, the shielding element has a small installation space due to its low wall thickness.

Furthermore, an optical system for a projection exposure system is proposed. The optical system comprises a shielding element as explained above and a support structure to which the shielding element is connected.

The optical system can be part of a projection optics. However, the optical system can also be part of an illumination optics. The optical system can be suitable for both EUV lithography and DUV lithography. The optical system can have several components, for example in the form of optical elements, which are shielded using the shielding element. The optical system can have any number of shielding elements. The shielding elements together form a shield which encloses or encloses the components to be protected. As previously mentioned, the support structure can be a support frame. The shielding element can be screwed to the support structure. This means that the shielding element can be mounted and dismantled as often as required.

According to one embodiment, the optical system further comprises fastening elements for connecting the shielding element to the support structure.

The number of fastening elements is arbitrary. In particular, the number of fastening elements corresponds to the number of fastening points. This means that exactly one fastening element can be assigned to each fastening point. The fastening elements can be removed and reconnected to the supporting structure as often as required. Screws are particularly preferred as fastening elements.

According to a further embodiment, the fastening elements are countersunk head screws.

Such a fastening element in the form of a countersunk head screw comprises a head section, which is received, for example, in a countersunk hole in a fastening point as mentioned above, and a shaft section which is guided through a hole in the respective fastening point. A thread can be provided on the shaft section. By using countersunk head screws as fastening elements, the shielding element can be installed in a particularly space-saving manner. If there is sufficient installation space, cylinder head screws, for example, can also be used as fastening elements. In this case, each cylinder head screw can be assigned a washer which rests on the shielding element.

Furthermore, a projection exposure system with such a shielding element and/or such an optical system is proposed.

The optical system is preferably a projection optics of the projection exposure system. However, the optical system can also be an illumination system. The projection exposure system can be an EUV lithography system. EUV stands for "Extreme Ultraviolet" and refers to a wavelength of the working light between 0.1 nm and 30 nm. The projection exposure system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and refers to a wavelength of the working light between 30 nm and 250 nm.

In this case, "one" is not necessarily to be understood as being limited to just one element. Rather, several elements, such as two, three or more, can also be provided. Any other counting word used here is also not to be understood as meaning that there is a limitation to the exact number of elements mentioned. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

The embodiments and features described for the shielding element apply accordingly to the proposed optical system and/or 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 embodiments that are not explicitly mentioned. The person skilled in the art will also recognize individual aspects as improvements or add additions to the respective basic form of the invention.

• 1 zeigt einen schematischen Meridionalschnitt einer Projektionsbelichtungsanlage für die EUV-Projektionslithographie;
• 2 zeigt eine schematische Ansicht einer Ausführungsform eines optischen Systems für die Projektionsbelichtungsanlage gemäß 1;
• 3 zeigt eine schematische Aufsicht einer Ausführungsform eines Abschirmungselements für das optische System gemäß 2;
• 4 zeigt eine schematische Aufsicht einer weiteren Ausführungsform eines Abschirmungselements für das optische System gemäß 2;
• 5 zeigt eine schematische Schnittansicht des Abschirmungselements gemäß 3;
• 6 zeigt eine schematische Aufsicht einer weiteren Ausführungsform eines Abschirmungselements für das optische System gemäß 2;
• 7 zeigt eine schematische perspektivische Ansicht einer weiteren Ausführungsform eines Abschirmungselements für das optische System gemäß 2; und
• 8 zeigt eine schematische Aufsicht einer Ausführungsform eines Befestigungspunkts für das Abschirmungselement gemäß 3, 4, 6 and 7.

Further advantageous embodiments and aspects of the invention are the subject of the subclaims and the embodiments of the invention described below. The invention is explained in more detail below using preferred embodiments with reference to the attached figures.

• 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography;
• 2 shows a schematic view of an embodiment of an optical system for the projection exposure apparatus according to 1 ;
• 3 shows a schematic plan view of an embodiment of a shielding element for the optical system according to 2 ;
• 4 shows a schematic plan view of another embodiment of a shielding element for the optical system according to 2 ;
• 5 shows a schematic sectional view of the shielding element according to 3 ;
• 6 shows a schematic plan view of another embodiment of a shielding element for the optical system according to 2 ;
• 7 shows a schematic perspective view of another embodiment of a shielding element for the optical system according to 2 ; and
• 8 shows a schematic plan view of an embodiment of a fastening point for the shielding element according to 3 , 4 , 6 and 7.

In the figures, identical or functionally equivalent elements have been given the same reference symbols unless otherwise stated. It should also be noted that the representations in the figures are not necessarily to scale.

1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. An 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 rest of the illumination system 2. In this case, the illumination system 2 does not comprise 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.

In the 1 For explanation purposes, a Cartesian coordinate system with an x-direction x, a y-direction y and a z-direction z is shown. The x-direction x runs perpendicularly into the plane of the drawing. The y-direction y runs horizontally and the z-direction z runs vertically. The scanning direction runs in the 1 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 area 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 via a wafer displacement drive 15, in particular along the y-direction y. The displacement of the reticle 7 on the one hand via the reticle displacement drive 9 and the wafer 13 on the other hand via the wafer displacement drive 15 can be synchronized with one another.

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 means of 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 bundled 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 in grazing incidence (GI), i.e. with angles of incidence greater than 45°, or in normal incidence (NI), i.e. with 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 comprise a deflection mirror 19 and a first facet mirror 20 arranged downstream of this in the beam path. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter which separates a useful light wavelength of the illumination radiation 16 from false light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 which is optically conjugated 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 plurality of individual first facets 21, which can also be referred to as field facets. Of these first facets 21, only one is shown in the 1 only a few examples are shown.

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 convex or concave curved facets.

As for example from the DE 10 2008 009 600 A1 As is known, 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, see the DE 10 2008 009 600 A1 referred to.

Between the collector 17 and the deflection 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 the US 2006/0132747 A1 , the EP 1 614 008 B1 and the US 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 be round, rectangular or hexagonal, for example, or alternatively facets composed of micromirrors. In this regard, reference is also made to the DE 10 2008 009 600 A1 referred to.

The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

The illumination optics 4 thus forms a double-faceted system. This basic principle is also known as a fly's eye integrator.

It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugated 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 is the case, for example, in the DE 10 2017 220 586 A1 described.

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

In a further embodiment of the illumination optics 4 (not shown), the beam path between the second facet mirror 22 and the object field 5, a transmission optics can be arranged, which contributes in particular to the imaging of the first facets 21 in 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 (GI mirrors, grazing incidence mirrors).

The lighting optics 4 have in the version shown in the 1 As shown, after the collector 17 there are exactly three mirrors, 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 exposure system 1.

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

Reflection surfaces of the mirrors Mi can be designed as free-form 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, just 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 have 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. In particular, it has different image scales Bx, By in the x and y directions x, y. The two image scales Bx, By of the projection optics 10 are preferably (βx, βy) = (+/- 0.25, +/- 0.125). A positive image scale β means an image without image inversion. A negative sign for the image scale β 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 8:1 in the y-direction y, i.e. in the scanning direction.

Other image scales are also possible. Image scales with the same sign and absolutely the same 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 result in particular in illumination according to the Köhler principle. The far field is broken down 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 superimposed by an associated second facet 23 to illuminate the object field 5 imaged onto the reticle 7. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. The 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 defined geometrically. 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 set. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

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 a redistribution of the illumination channels.

In the following, 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.

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 illuminated precisely with the second facet mirror 22. When the projection optics 10 images the center of the second facet mirror 22 telecentrically 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 distance of the aperture rays is minimal. This surface represents the entrance pupil or a surface conjugated to it in spatial space. In particular, this surface shows a finite curvature.

It is possible that the projection optics 10 have different positions of the entrance pupil for the tangential and the sagittal beam path. 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 1 In the arrangement of the components of the illumination optics 4 shown, the second facet mirror 22 is arranged in a surface conjugated to the entrance pupil of the projection optics 10. The first facet mirror 20 is arranged tilted to the object plane 6. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the second facet mirror 22.

2 shows a schematic view of an embodiment of an optical system 100 for the projection exposure apparatus 1.

The optical system 100 can be part of a projection optics 10 as explained above. However, the optical system 100 can also be part of an illumination optics 4 as mentioned above. However, it is assumed below that the optical system 100 is part of such a projection optics 10. The optical system 100 is suitable for DUV lithography. However, the optical system 100 can also be suitable for EUV lithography.

The optical system 100 comprises an optical element 102. The optical element 102 can be a mirror. The optical element 102 has an optically effective surface 104. The optically effective surface 104 is a mirror surface. The optically effective surface 104 is suitable for reflecting illumination radiation 16. The optically effective surface 104 can be oriented in the 2 be oriented upwards or downwards.

The optical element 102 or the optically effective surface 104 has six degrees of freedom, namely three translational degrees of freedom along the first spatial direction or x-direction x, the second spatial direction or y-direction y and the third spatial direction or z-direction z as well as three rotational degrees of freedom about the x-direction x, the y-direction y and the z-direction z. 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 tilting with respect to the three 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 includes both its position and its orientation. The term "position" can therefore be replaced by the wording "position and orientation" and vice versa.

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

In order to move the optical element 102 from the actual position IL to the desired position SL, the optical system 100 comprises an adjusting device 106. The adjusting device 106 is designed to adjust the optical element 102. In the present case, “adjusting” or “aligning” is to be understood in particular as 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 with the aid of the adjustment device 106. The adjustment or alignment of the optical element 102 can thus be carried out with the aid of the adjustment device 106 in all six aforementioned degrees of freedom. The adjustment device 106 is a so-called hexapod or can be referred to as such.

The adjustment device 106 comprises several actuators 108, 110, 112, which are arranged in the 2 are only shown very schematically. The actuators 108, 110, 112 can also be referred to as actuators or actuating elements. The actuators 108, 110, 112 can be so-called bipods or can be referred to as such. Preferably, exactly three actuators 108, 110, 112 are provided, which are arranged offset by 120° from one another. The actuators 108, 110, 112 are preferably constructed identically.

The actuators 108, 110, 112 are connected by means of connection points 114, of which 2 only one is provided with a reference symbol, is connected to the optical element 102. For example, an adhesive connection or a screw connection can be provided at each of the connection points 114. Preferably, exactly three connection points 114 are provided, with each connection point 114 being assigned an actuator 108, 110, 112.

Furthermore, each actuator 108, 110, 112 is connected via two connection points 116, 118, of which 2 only two are provided with a reference number, coupled to a support structure 120. The support structure 120 can be a support frame (English: force frame) or another immovable structure. The support structure 120 can also be referred to as a fixed world.

With the help of the actuators 108, 110, 112, the optical element 102 can be moved relative to the support structure 120. Each actuator 108, 110, 112 can be assigned two of the aforementioned degrees of freedom. With the three actuators 108, 110, 112, an adjustment of the optical element 102 in all six degrees of freedom is thus possible.

The actuators 108, 110, 112 can be controlled using a control and regulating unit 122 of the adjustment device 106 in order to adjust the optical element 102. All actuators 108, 110, 112 are operatively connected to the control and regulating unit 122, so that the control and regulating unit 122 can adjust the optical element 102 in all six degrees of freedom using suitable control of the actuators 108, 110, 112. This can be done based on sensor signals from a sensor system (not shown) that can detect the actual position IL and the target position SL of the optical element 102.

The optical system 100 comprises a thermal and/or magnetic shield 124 which surrounds or encloses the optical system 100 at least in sections. The shield 124 particularly preferably surrounds the entire optical system 100. The shield 124 surrounds at least the optical element 102. The shield 124 is made up of several parts. The shield 124 is firmly connected to the support structure 120, for example screwed. The shield 124 is particularly suitable for applications with a small amount of available installation space.

3 shows a schematic plan view of an embodiment of a shielding element 126.

The shielding element 126 is part of the shielding 124. The shielding 124 can have several different or identical shielding elements 126. The number of shielding elements 126 is arbitrary. The shielding element 126 is in the form of a sheet metal. The shielding element 126 can be made of a metallic material, in particular of a nickel-iron alloy, such as FeNi48 or FeNi50. To prevent corrosion, the shielding element 126 can be coated.

The optical system 100 requires a magnetic shield 124 of components arranged within the shield 124. The shield 124 should at least reduce line of sight (LoS) errors caused by magnetism. The shield 124 should have the following properties for this purpose. Thermal expansion of the shield 124 should be possible both during transport and during operation of the optical system 100. The shield 124 must be easy to manufacture and assemble.

In order to allow thermal expansion, the shielding element 126 has several different fastening points 128, 130, 132, 134, with the aid of which the shielding element 126 is connected, in particular screwed, to the support structure 120. The fastening points 128, 130, 132, 134 are constructed differently and each have a different number of degrees of freedom. The fastening points 128, 130, 132, 134 are provided on a plate-shaped or sheet-shaped base section 136 of the shielding element 126.

The fastening point 128 has a bore 138 that penetrates the shielding element 126 or the base section 136, as well as a countersunk hole 140. The bore 138 is circular. A fastening element, in particular a countersunk screw, can be guided through the bore 138. A head section of this fastening element is received in the countersunk hole 140. A diameter of the bore 138 is dimensioned such that a shaft section of the fastening element can be guided through the bore 138 with as little play as possible. The fastening point 128 therefore has exactly one degree of freedom, namely a rotational degree of freedom about the z-direction z.

The fastening point 130 also has a bore 142 which penetrates the shielding element 126 or the base section 136, but which is not circular but rather has the shape of an elongated hole. The bore 142 is assigned a countersink 144 which is designed to accommodate the head section of the fastening element. The fastening point 130 has exactly two degrees of freedom, namely a rotational degree of freedom about the z-direction z and a translational degree of freedom along the x-direction x, along which the bore 142 extends.

The fastening point 132 is a hole that penetrates the shielding element 126 or the base section 136 and has a larger diameter than the hole 138. The fastening element is thus guided through the fastening point 132 with play. The fastening point 132 has exactly three degrees of freedom, namely one rotational degree of freedom about the z-direction z and two translational degrees of freedom along the x-direction x and the y-direction y.

The attachment point 134 has a coupling portion 146 which is connected to the base portion 136 by means of two spring portions 148, 150.

The spring sections 148, 150 are elastically, in particular spring-elastically, deformable. A cover section 152 is placed between the spring sections 148, 150. The coupling section 146 comprises a bore 154 which is designed as an elongated hole. A countersink 156 is provided on the bore 154.

The fastening point 134 also has exactly three degrees of freedom, namely a rotational degree of freedom about the z-direction z, a translational degree of freedom along the x-direction x and a translational degree of freedom along the y-direction y. When the coupling section 146 moves in a translational manner along the y-direction y, the spring sections 148, 150 are elastically deformed.

4 shows a schematic plan view of another embodiment of a shielding element 126.

The shielding element 126 also comprises fastening points 158, 160, 162. The fastening point 158 has a coupling section 164 which is connected to a base section 136 of the shielding element 126 via two spring sections 166, 168. A cover section 170 is arranged between the spring sections 166, 168. A bore 172 is provided on the coupling section 164, through which a fastening element as mentioned above is passed.

The attachment point 158 has two degrees of freedom, namely a rotational degree of freedom degrees around the z-direction z and a translational degree of freedom along the y-direction y. During a translational movement of the coupling section 164 along the y-direction y, the spring sections 166, 168 deform elastically.

The attachment point 160 comprises a triangular coupling portion 174 with a bore 176, at which a counterbore 178 is provided. The coupling portion 174 is connected to the base portion 136 by means of spring portions 180, 182, 184.

The attachment point 160 has four degrees of freedom, namely a rotational degree of freedom about the z-direction z, a translational degree of freedom along the z-direction z, a rotational degree of freedom about the x-direction x and a rotational degree of freedom about the y-direction y.

The attachment point 162 has a coupling portion 186 with a bore 188 and a counterbore 190 provided on the bore 188. The coupling portion 186 is connected to the base portion 136 by means of two spring portions 192, 194. The coupling portion 186 is placed between the spring portions 192, 194.

The attachment point 162 also has four degrees of freedom, namely a rotational degree of freedom about the z-direction z, a translational degree of freedom along the y-direction y, a rotational degree of freedom about the x-direction x and a further rotational degree of freedom about the z-direction, in which the coupling section 186 itself is rotated about the z-direction z.

5 shows a schematic sectional view of the shielding element 126.

In particular, the 5 a sectional view through the fastening point 128. A fastening element 196 as mentioned above is passed through the fastening point 128. The same applies to the fastening points 128, 130, 132, 134, 158, 160, 162.

The fastening element 196 is a countersunk head screw. The fastening element 196 comprises a shaft section 198 which is passed through the bore 138 of the fastening point 128. The shaft section 198 is followed by a frustoconical head section 200 which is received in the countersink 140. The fastening element 196 is constructed rotationally symmetrically to a symmetry or central axis 202.

The base section 136 of the shielding element 126 has a front side 204 and a rear side 206 facing away from the front side 204. The depression 140 is provided on the front side 204. The depression 140 is so deep that the head section 200 is flush with the front side 204 or protrudes behind it.

6 shows a schematic plan view of another embodiment of a shielding element 126.

The shielding element 126 has four fastening points 128, 130, 132, 134 as previously mentioned, which are arranged at four corners of the in this case trapezoidal base section 136 of the shielding element 126. As previously mentioned, the fastening point 128 has one degree of freedom, the fastening point 130 has two degrees of freedom, the fastening point 132 has three degrees of freedom and the fastening point 134 also has three degrees of freedom.

To produce the shielding element 126, the fastening points 128, 130, 132, 134 are first introduced into the base section 136 using laser processing. In the event that the shielding element 126 is not plate-shaped and thus flat, but has a three-dimensional structure, bending processes can be used to reshape the base section 136.

The shielding element 126 is then thermally treated to obtain the desired magnetic properties. The shielding element 126 is then surface treated so that the shielding element 126 is corrosion-resistant. A nickel-phosphorus coating (NiP) can be used for this purpose.

A kinematic assembly method is used to mount the shielding element 126 on the support structure 120. For this purpose, the shielding element 126 is first screwed to the support structure 120 at the fastening point 128, then at the fastening point 130, then at the fastening point 134 and finally at the fastening point 132.

7 shows a schematic perspective view of another embodiment of a shielding element 126.

In this embodiment of the shielding element 126, the base section 136 has a first region 208 and a second region 210 oriented perpendicular to the first region 208. For this purpose, the base section 136 can be subjected to a bending process in which the base section 136 is deformed at a bending edge 212. Several Fastening points 128, 130, 134 with different degrees of freedom are provided. The second region 210 is connected to the support structure 120 by means of a fastening element 214.

The bending edge 212 stiffens the shielding element 126. The shielding element 126 is considered stiff about an axis along the bending edge 212. All other degrees of freedom are determined by the attachment points 128, 130, 134.

8 shows a schematic plan view of another embodiment of a fastening point 216.

The fastening point 216 has the same functionality as the fastening point 134. The fastening point 216 has a coupling section 218 with a slot-shaped bore 220, on which a countersink 222 is provided. The coupling section 218 is connected to the base section 136 by means of two spring sections 224, 226. A cover section 228 is provided between the spring sections 224, 226.

Two end stops 230, 232 are provided on the base section 136, which limit a movement of the coupling section 218 along the y-direction y. With the help of the end stops 230, 232, a mechanical overload of the spring sections 224, 226 can be prevented.

Gaps 234, 236, 238, 240 are provided between the spring sections 224, 226 and the base section 136 and between the cover section 228 and the spring sections 224, 226. Optimized continuous curvatures 242, 244, 246, 248 are provided on the gaps 234, 236, 238, 240 at the transition to the base section 136. The curvatures 242, 244, 246, 248 are optimized to prevent material overloading in their area. The curvatures 242, 244, 246, 248 can be radii, in particular bionic radii.

The shielding element 126 is used on a material with a high magnetic permeability and a high saturation point. This allows the largest possible amount of the magnetic field to be enclosed. Preferably, an iron-nickel alloy, in particular FeNi48 or FeNi50, is used.

With the help of the attachment points 128, 130, 132, 134, 158, 160, 162, 216, internal degrees of freedom can be blocked. This allows a higher natural frequency of the shielding element 126 and leads to less disturbances induced by excitations at lower frequencies.

The shielding element 126 is kinematically completely defined. There is no overdetermination or underdetermination. The curvatures 242, 244, 246, 248 prevent excessive stress buildup in the area thereof. Because the shielding element 126 has no large openings, it is particularly suitable for shielding magnetic fields. This is achieved by providing a cover section 152, 170, 228 as mentioned above between the spring sections 148, 150, 166, 168, 224, 226.

The shielding element 126 can be manufactured using a laser cutting process and a subsequent bending process. Because the shielding element 126 is made of sheet metal, it has a particularly small installation space. A defined end stop position can be achieved using the end stops 230, 232. Furthermore, excessive deflection of the coupling section 218 is prevented.

Because the fastening element 196 is a countersunk screw, the shielding element 126 can be mounted in a space-saving manner. When mounting the shielding element 126 - as shown in the 6 shown - first the fastening point 128 is screwed, whereby all degrees of freedom except for a rotational degree of freedom about the z-direction z are determined. Then the fastening point 130 is screwed in order to also determine the aforementioned rotational degree of freedom.

Additional internal degrees of freedom are defined by the attachment points 132, 134, resulting in improved dynamics and a higher natural frequency of the shielding element 126. This in turn results in critical components of the optical system 100 being less adversely affected at low frequencies.

If there is sufficient installation space, cylinder head screws with washers can also be used as fastening elements 196. In this case, tolerances can be compensated by a larger bore diameter at the fastening points 128, 130, 132, 134, 158, 160, 162, 216. In order to increase the contact surface, a washer can be assigned to each fastening element 196 in this case.

The thickness of the shielding element 126 can be adjusted depending on the available installation space. However, the shielding effect also decreases with decreasing thickness. The shielding element 126 can be mounted and dismantled as often as required. Tolerances and heat-related Expansions can be compensated within the elastoplastic material behavior.

When using the shielding element 126, it is possible to use components with larger magnetic fields and to shield the components. This leads to reduced LoS errors in relevant components, such as the optical element 102. To a limited extent, the shielding element 126 can also be used for heat shielding. Additional heat shielding elements, cooling fins or cooling plates can therefore be dispensed with.

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

REFERENCE SYMBOL LIST

1

projection exposure system

2

lighting system

3

light source

4

lighting optics

5

object field

6

object level

7

reticle

8

reticle holder

9

reticle displacement drive

10

projection optics

11

image field

12

image plane

13

wafer

14

wafer holder

15

wafer relocation drive

16

illumination radiation

17

collector

18

intermediate focal plane

19

deflecting mirror

20

first faceted mirror

21

first facet

22

second facet mirror

23

second facet

100

optical system

102

optical element/component

102'

optical element/component

104

optically effective surface

104'

optically effective surface

106

adjustment device

108

actuator

110

actuator

112

actuator

114

connection point

116

connection point

118

connection point

120

supporting structure

122

control and regulation unit

124

shielding

126

shielding element

128

attachment point

130

attachment point

132

attachment point

134

attachment point

136

base section

138

drilling

140

reduction

142

drilling

144

reduction

146

coupling section

148

spring section

150

spring section

152

cover section

154

drilling

156

reduction

158

attachment point

160

attachment point

162

attachment point

164

coupling section

166

spring section

168

spring section

170

cover section

172

drilling

174

coupling section

176

drilling

178

reduction

180

spring section

182

spring section

184

spring section

186

coupling section

188

drilling

190

reduction

192

spring section

194

spring section

196

fastener

198

shaft section

200

head section

202

central axis

204

front

206

back

208

Area

210

Area

212

bending edge

214

fastener

216

attachment point

218

coupling section

220

drilling

222

reduction

224

spring section

226

spring section

228

cover section

230

end stop

232

end stop

234

gap

236

gap

238

gap

240

gap

242

curvature

244

curvature

246

curvature

248

curvature

M1

Mirror

M2

Mirror

M3

Mirror

M4

Mirror

M5

Mirror

M6

Mirror

x

x-direction

y

y-direction

z

z-direction

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102008009600 A1 [0059, 0063]
• US 20060132747 A1 [0061]
• EP 1614008 B1 [0061]
• US 6573978 [0061]
• DE 102017220586 A1 [0066]
• US 20180074303 A1 [0080]

Claims (15)

Shielding element (126) for shielding components (102, 102') of a projection exposure system (1), comprising a sheet-metal base section (136), and a plurality of fastening points (128, 130, 132, 134, 158, 160, 162, 216) provided on the base section (136) for fastening the shielding element (126) to a support structure (120), wherein the fastening points (128, 130, 132, 134, 158, 160, 162, 216) have different numbers of degrees of freedom. Shielding element according to claim 1 , wherein the base portion (136) has a plurality of regions (208, 210) which are connected to one another at one or more bending edges (212). Shielding element according to claim 1 or 2 , wherein at least one of the fastening points (128, 130, 134, 160, 162, 216) has a bore (138, 142, 154, 176, 188, 220) with a countersink (140, 144, 156, 178, 190, 222). Shielding element according to claim 3 , wherein the bore (142, 154, 220) is an elongated hole, and wherein in particular a countersink (144, 156, 222) is provided on the bore (142, 154, 220). Shielding element according to one of the Claims 1 - 4 , wherein at least one of the fastening points (134, 158, 160, 162, 216) has a coupling section (146, 164, 174, 186, 218), and wherein the coupling section (146, 164, 174, 186, 218) is connected to the base section (136) by means of spring sections (148, 150, 166, 168, 180, 182, 184, 192, 194, 224, 226). Shielding element according to claim 5 , wherein a cover section (152, 170, 228) is arranged between the spring sections (148, 150, 166, 168, 224, 226). Shielding element according to claim 5 or 6 , wherein each degree of freedom is assigned a first end stop (230) and a second end stop (232). Shielding element according to one of the Claims 5 - 7 , wherein the spring sections (148, 150, 166, 168, 224, 226) merge into the base section (136) by means of continuous curvatures (242, 244, 246, 248). Shielding element according to one of the Claims 1 - 8 , wherein the shielding element (126) has one fastening point (128) with exactly one degree of freedom, one fastening point (130) with exactly two degrees of freedom and two fastening points (132, 134) each with exactly three degrees of freedom. Shielding element according to claim 9 , wherein when connecting the shielding element (126) to the support structure (120), first the fastening point (128) can be connected to the support structure (120) with exactly one degree of freedom, then the fastening point (130) can be connected to the support structure (120) with exactly two degrees of freedom, and finally the two fastening points (132, 134) can be connected to the support structure (120) with exactly three degrees of freedom each. Shielding element according to one of the Claims 1 - 10 , wherein the shielding element (126) is a bent sheet metal component. Optical system (100) for a projection exposure system (1), comprising a shielding element (126) according to one of the Claims 1 - 11 , and a support structure (120) to which the shielding element (126) is connected. Optical system according to claim 12 , further comprising fastening elements (196) for connecting the shielding element (126) to the support structure (120). Optical system according to claim 13 , wherein the fastening elements (196) are countersunk head screws. Projection exposure system (1) with a shielding element (126) according to one of the Claims 1 - 11 and/or an optical system (100) according to one of the Claims 12 - 14 .

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