Projection system with minimised thermally induced, oscillating aberrations

Abstract

The present invention relates to a projection system for a projection exposure apparatus for micro-lithography, in particular for EUV lithography, comprising an optical element. The problem of providing a projection system for a projection exposure apparatus for micro-lithography, in particular for EUV lithography, in which thermally induced, oscillating aberrations are minimised is solved in that the projection system comprises a radiation-absorbing element which is configured to temporarily interrupt the beam path of the projection system behind the optical element.

Description

[0001] Projection system with minimized thermally induced oscillating aberrations

[0002] The present invention relates to a projection system for a projection exposure apparatus for microlithography, in particular for EUV lithography, comprising an optical element. Furthermore, the invention relates to a projection exposure apparatus for microlithography and a method for producing integrated circuits using microlithography.

[0003] The subject matter of German patent application 102023210859.3 is hereby incorporated by reference.

[0004] According to the current state of the art, projection systems for microlithography are subject to periodically changing thermal stress caused by the microlithography work cycle. During the exposure of a semiconductor wafer, the optical elements of the projection system heat up due to the comparatively high light output of the exposure light. This is due to the fact that light absorption by the optical elements, although largely reduced, cannot be completely suppressed due to physical limitations. However, to ensure that no light reaches the wafer area during a wafer change, measures are usually taken to prevent the exposure light from entering the projection system during this time. Consequently, the optical elements cool down again during the wafer change.Within a microlithographic work cycle, which includes both a wafer exposure phase and a wafer change phase, periodic, thermally induced changes in size and / or deformation of the optical elements occur, also known as thermal oscillations. These thermal oscillations can lead to oscillating optical aberrations of the wavefront emerging from the projection system, which in turn negatively impact the optical performance and thus the lithographic yield and throughput during wafer exposure. This is a particularly critical problem in the field of EUV lithography, since higher optical precision is generally required here, and the EUV projection systems used can also suffer particularly severely from thermally induced, oscillating aberrations.However, the problem also generally occurs in projection systems that are not used in microlithography and always occurs when no light enters the projection system during a temporary dead time.

[0005] Against this background, the present invention is based on the object of providing a projection system for a projection exposure system for microlithography, in particular for EUV lithography, in which thermally induced, oscillating aberrations are minimized. Furthermore, the invention aims to provide a corresponding projection exposure system for microlithography and a corresponding method for producing integrated circuits using microlithography.

[0006] According to a first teaching of the present invention, the above-mentioned object for a projection system for a projection exposure apparatus for microlithography, in particular for EUV lithography, comprising an optical element is achieved in that the projection system comprises a radiation-absorbing element which is configured to temporarily interrupt the beam path of the projection system behind the optical element.

[0007] In the context of the present invention, a projection system is understood to mean an arrangement comprising at least one optical element and imaging a light beam emanating from a radiation source from an object plane into an image plane. The projection system is a projection system for a projection exposure system for microlithography. In particular, the projection system is a projection system for a projection exposure system for EUV lithography. For example, the projection system is or comprises a projection lens. Furthermore, in this context, an optical element is understood to mean, in particular, an imaging optical element, such as a lens, a mirror, a prism, a plane plate, or the like.

[0008] In the context of the present invention, the term 'light' is understood to mean electromagnetic radiation in general, without implying a restriction to the spectral range of visible light.

[0009] In the context of the present invention, interrupting the beam path behind the optical element means that the beam path is interrupted at a point that is hit or traversed by a light beam at a later time than the point at which the optical element is located, depending on the propagation speed of the light. In other words, the point at which the beam path is interrupted is located in the beam path behind the point at which the optical element is located.

[0010] As recognized by the inventors, the measures for preventing light from entering the projection system, which are otherwise usually necessary during a downtime of the projection system, such as during a wafer change, can be omitted if a radiation-absorbing element according to the invention is present, which is configured to temporarily interrupt the beam path of the projection system behind the optical element. From the perspective of the projection system, therefore, no input-side measures are taken during a downtime that would already prevent light from entering the projection system. Instead, the beam path is interrupted at the output side or within the projection system.This results in an optical element of the projection system, which is arranged in the beam path upstream of the radiation-absorbing element, being permanently exposed to the light beam emanating from the radiation source and thus absorbing light. Due to this permanent light absorption, a steady thermal state can be established for the optical element instead of thermal oscillations, as the optical element assumes a temperature corresponding to thermal equilibrium. Consequently, in a projection system according to the invention, the oscillating aberrations for the optical element caused by the thermal oscillations can be minimized.Since the temperature of thermal equilibrium can be higher than the ambient temperature, and since this temperature increase can in turn lead to a change in the beam path at the optical element due to deformation of the optical element, the occurrence of temporally constant optical aberrations cannot be ruled out in a projection system according to the invention. However, such temporally constant aberrations can be corrected much more easily than aberrations that oscillate over time. As described above, oscillating optical aberrations caused by thermal vibrations represent a problem in microlithography, which is particularly critical in the field of EUV lithography. In these areas, the use of a projection system according to the invention is therefore particularly advantageous in order to minimize the thermally induced, oscillating aberrations.

[0011] In addition to the minimization of thermally induced oscillating aberrations just described, the radiation-absorbing element, which is designed to temporarily interrupt the beam path of the projection system behind the optical element, can also ensure that no light escapes from the projection system during a dead time, i.e., that no light reaches the area of ​​the wafer, for example, during a wafer change.

[0012] In one embodiment of the invention, the radiation-absorbing element is a beam dump. A beam dump is a radiation-absorbing element that is introduced into the beam path to interrupt the beam path and that must be completely removed from the beam path to release the beam path again. For example, the beam dump can have a sliding mechanism, a pivoting mechanism, or the like. In this way, the beam dump can be configured to temporarily interrupt the beam path of the projection system.

[0013] In an alternative embodiment of the invention, the radiation-absorbing element is a beam shutter. A beam shutter is a radiation-absorbing element that is permanently located in the beam path and has a diaphragm mechanism to temporarily interrupt the beam path and then release it again. In this way, the beam shutter can also be configured to temporarily interrupt the beam path of the projection system. The diaphragm mechanism can have a circular opening, a substantially circular polygonal opening, or a slit-shaped opening.

[0014] In a further alternative embodiment of the invention, the radiation-absorbing element is a combination of a movable mirror and a stationary beam trap. In this embodiment, the movable mirror can be inserted into the beam path to temporarily direct the beam path onto the stationary beam trap, which then absorbs the light radiation. In this way, the combination of movable mirror and stationary beam trap can also be configured to temporarily interrupt the beam path of the projection system.

[0015] In a preferred embodiment of the invention, the projection system comprises at least one further optical element. In this embodiment, the radiation-absorbing element is configured to interrupt the beam path of the projection system behind the at least one further optical element. In principle, any optical element of the projection system that is arranged in the beam path upstream of the radiation-absorbing element can be permanently exposed to the light beam emanating from the radiation source and can absorb light accordingly. Thus, a steady thermal state can be established for each corresponding optical element instead of thermal oscillations.As a result, in this embodiment of the projection system according to the invention, thermally induced, oscillating aberrations can be minimized for each optical element arranged in the beam path in front of the radiation-absorbing element, which overall leads to a projection system with particularly low aberrations.

[0016] Notwithstanding this, certain optical elements of the projection system can also be arranged in the beam path behind the radiation-absorbing element. While such optical elements are exposed to periodically changing thermal stress, this may not be harmful or even desirable for certain optical elements.

[0017] In a further preferred embodiment of the invention, the radiation-absorbing element is designed to interrupt the beam path of the projection system behind the last, second-to-last, or third-to-last optical element of the projection system. In the context of the present invention, the last optical element of the projection system is the optical element through which a light beam strikes or passes last, in particular at the latest point in time, in accordance with the speed of propagation of the light. Accordingly, the second-to-last optical element of the projection system is the optical element through which a light beam strikes or passes last, in particular at the latest point in time, in accordance with the speed of propagation of the light, at the second-to-last position, i.e., last before the last optical element.Furthermore, the third-to-last optical element of the projection system is the optical element which is hit or passed through by a light beam in the third-to-last place, i.e. last before the second-to-last optical element, according to the speed of propagation of the light.

[0018] In order to interrupt the beam path of the projection system behind an optical element of the projection system, the radiation-absorbing element can be temporarily introduced into the beam path of the projection system behind the optical element for a desired duration of the interruption. Particularly for reasons of space, it can be advantageous for the radiation-absorbing element to be configured to interrupt the beam path of the projection system behind the second-to-last or third-to-last optical element of the projection system. Typically, more installation space is available behind the third-to-last optical element than, for example, behind the second-to-last optical element and especially behind the last optical element, which is generally arranged close to the wafer.Furthermore, thermal vibrations occur less severely at optical elements located further back in the projection system, especially the last or second-to-last optical elements. Optical elements that are hit or passed through by a light beam later than those located further forward in the projection system, depending on the light's propagation speed, heat up comparatively less and, accordingly, also cool down less when the beam path is interrupted before these elements.

[0019] In a further preferred embodiment of the invention, a surface of the radiation-absorbing element has an absorption coefficient of at least 0.9, preferably at least 0.95, particularly preferably at least 0.98. For example, the surface can have an absorption coefficient of 0.99 or more. In this context, the absorption coefficient used is, in particular, the directed spectral absorption coefficient for any wavelength when light is incident perpendicular to the surface. This means that the surface of the radiation-absorbing element has a spectral directed absorption coefficient of at least 0.9, preferably at least 0.95, particularly preferably at least 0.98, for example 0.99 or more, for at least one wavelength when light is incident perpendicularly.The at least one wavelength can, in particular, be a wavelength contained in the wavelength spectrum of a light beam that passes through the projection system during normal operation. Furthermore, the surface of the radiation-absorbing element can, in particular, be a surface designed to be introduced into the beam path of the projection system in order to interrupt the beam path. With higher absorption coefficients of the surface, higher light absorption by the surface can generally be achieved, so that thermal oscillations and consequently the oscillating optical aberrations induced thereby can be more effectively minimized.

[0020] In a further preferred embodiment of the invention, a surface of the radiation-absorbing element has a reflectance of at most 0.1, preferably at most 0.05, particularly preferably at most 0.02. For example, the surface can have a reflectance of 0.01 or less. In this context, the reflectance used is, in particular, the directed spectral reflectance for any wavelength when light is incident perpendicular to the surface. This means that, when light is incident perpendicularly, the surface of the radiation-absorbing element has a spectral directed reflectance of at most 0.1, preferably at most 0.05, particularly preferably at most 0.02, for example 0.01 or less, for at least one wavelength.The at least one wavelength can, in particular, be a wavelength contained in the wavelength spectrum of a light beam that passes through the projection system during normal operation. Furthermore, the surface of the radiation-absorbing element can, in particular, be a surface designed to be introduced into the beam path of the projection system in order to interrupt the beam path. With higher reflectances of the surface, a reduction in the light reflection from the surface of the radiation-absorbing element back toward the optical element or elements can be achieved, so that thermal oscillations and consequently also the oscillating optical aberrations induced thereby can be more effectively minimized.

[0021] In a further preferred embodiment of the invention, the radiation-absorbing element comprises a body made of a metal or a metal alloy. Metallic materials are well suited in this context because they generally exhibit high light absorption, which, as described above, has a beneficial effect on minimizing thermally induced, oscillating aberrations. Furthermore, metallic materials also offer the advantages of high mechanical stability as well as sufficiently high temperature resistance and thermal shock resistance.

[0022] In a further preferred embodiment of the invention, the radiation-absorbing element has an anti-reflection coating. The anti-reflection coating can be made of, for example, acrylic paint, carbon nanotubes, anodized aluminum, and / or a chemically etched nickel-phosphorus alloy. Anti-reflection coatings allow particularly low reflectances to be achieved, which, as described above, has an advantageous effect on minimizing thermally induced, oscillating aberrations.

[0023] In a further preferred embodiment of the invention, the radiation-absorbing element has means for active and / or passive cooling. Examples of means for active and / or passive cooling are cooling fins, one or more fans, or a water cooling system. In certain areas of application of the projection system according to the invention, for example in microlithography, but also in laser technology, high light outputs may have to be absorbed by the radiation-absorbing element. Depending on the application, the light output can be, for example, several watts, but in extreme cases even up to several kilowatts. This can lead to the radiation-absorbing element heating up considerably, for example to temperatures above 100°C, which can reduce the durability of the radiation-absorbing element and, in extreme cases, can even damage the radiation-absorbing element.Furthermore, excessive heating of the radiation-absorbing element is detrimental to system safety. Active and / or passive cooling systems can safely dissipate the radiation absorbed as heat, thus eliminating these disadvantages.

[0024] According to a second teaching of the present invention, the above-mentioned object is achieved for a projection exposure system for microlithography in that the projection exposure system comprises a radiation source and a projection system according to the first teaching. In particular, the projection exposure system can be a projection exposure system for EUV lithography. With a projection exposure system according to the second teaching, the oscillating optical aberrations caused by thermal vibrations can be effectively minimized. Reference is made to the explanations in connection with the first teaching.

[0025] According to a third teaching of the present invention, the above-mentioned object is achieved for a method for producing integrated circuits by means of microlithography, in which semiconductor wafers coated with photoresist are exposed using a projection exposure apparatus, in that the projection exposure apparatus comprises a radiation source and a projection system according to the first teaching, wherein the radiation-absorbing element interrupts the beam path of the projection system at least for the duration of a dead time, in particular a wafer change. In the context of the present invention, the duration of a dead time can be understood as, for example, the duration of a wafer change, the duration of a wafer lot change, the duration of a die change, or the duration of a reticle change. A wafer lot can be understood as a batch or lot of wafers that are processed at the same time.A die can be understood as an individual section of a wafer. A reticle is understood as a photomask. At least during a reticle change, a reflective optical element can be introduced into the beam path of the projection exposure system. This reflective optical element is designed to continue to guide light into the projection system instead of the reticle during the reticle change. In this way, light also reaches the projection system during the reticle change, and unwanted cooling of the optical elements of the projection system can be prevented. The reflective optical element can serve as a dummy reticle. This is particularly advantageous since the duration of a reticle change is usually longer than the duration of a wafer change.

[0026] The method can, in particular, be a method for producing integrated circuits using EUV lithography. Because, in such a method according to the invention, the radiation-absorbing element interrupts the beam path of the projection system at least for the duration of a dead time, in particular a wafer change, the measures for preventing light from penetrating the projection system, which are otherwise usually necessary during the dead time, can be omitted. In this way, an optical element of the projection system, which is arranged in the beam path upstream of the radiation-absorbing element, can be permanently exposed to the light beam emanating from the radiation source. This allows the oscillating optical aberrations caused by thermal vibrations to be effectively minimized, as already explained in connection with the first teaching.Nevertheless, the radiation-absorbing element, which interrupts the beam path of the projection system at least for the duration of a dead time, in particular a wafer change, can ensure that no light reaches the area of ​​the wafer during the dead time, in particular a wafer change.

[0027] Further embodiments and advantages of the invention will become apparent from the following detailed description of some exemplary embodiments of the present invention, particularly in conjunction with the drawing. The drawing shows, in Figure 1, a schematic view of a first embodiment of a projection system for a projection exposure apparatus for microlithography according to the first teaching of the invention;

[0028] Fig. 2 is a schematic view of a second embodiment of a projection system for a projection exposure apparatus for microlithography according to the first teaching of the invention; and

[0029] Fig. 3 is a schematic view of a third embodiment of a projection system for a projection exposure apparatus for microlithography according to the first teaching of the invention.

[0030] Fig. 1 shows a schematic view of a first embodiment of a projection system 100 for a projection exposure system for microlithography according to the first teaching of the invention. The projection system 100 comprises an optical element 110, which in this example is a lens 110. The beam path 130, which originates, for example, from a light source (not shown), and runs from left to right in the figure, is indicated by the dashed lines.

[0031] As Fig. 1 also shows, the projection system 100 further comprises a radiation-absorbing element 120. For example, this is a beam trap 120. The beam trap 120 is arranged along the beam path 130 behind the lens 110. Furthermore, the beam trap 120 has a sliding mechanism (not shown) and can thus be introduced into the beam path 130, as indicated by the arrow 140, and subsequently removed from the beam path 130 again. In this way, the beam trap 120 is configured to temporarily interrupt the beam path 130 of the projection system 100 behind the lens 110. As an alternative to the described sliding mechanism, other mechanisms are also conceivable, such as a pivoting mechanism.

[0032] Since the beam path 130 can be interrupted by the beam trap 120 using the sliding mechanism behind the lens 110, measures to prevent light from entering the projection system 100, which are otherwise typically necessary during a downtime of the projection system 100, such as during a wafer change, can be eliminated. In this way, the lens 110 can be permanently exposed to the light beam 130 emanating from the radiation source (not shown) and absorbs light accordingly. This allows the lens 110 to maintain a steady thermal state instead of thermal oscillations, thus minimizing oscillating optical aberrations for the lens 110.Nevertheless, by temporarily interrupting the beam path 130 by the beam trap 120, it can be ensured that no light exits the projection system 100 during the dead time, so that, for example, in microlithographic applications, no light reaches the area of ​​the wafer during a wafer change.

[0033] Fig. 2 shows a schematic view of a second embodiment of a projection system 200 for a projection exposure system for microlithography according to the first teaching of the invention. The projection system 200 comprises a first optical element 210a and a second optical element 210b, which again are lenses 210a, 210b. The beam path 230, which originates, for example, from a light source (not shown), and which again runs from left to right in the figure, is indicated by the dashed lines, as already in Fig. 1.

[0034] As Fig. 2 also shows, the projection system 200 again comprises a radiation-absorbing element 220, here again exemplary in the form of a beam trap 220. The beam trap 220 is arranged along the beam path 230 both behind the first lens 210a and behind the second lens 210b. The beam trap 220 also has a sliding mechanism (not shown) and can thus, as indicated by the arrow 240, be introduced into the beam path 230 and subsequently removed from the beam path 230 again. In this way, the beam trap 220 is configured to temporarily interrupt the beam path 230 of the projection system 200 behind the first lens 210a and behind the second lens 210b. As an alternative to the sliding mechanism described, other mechanisms are also conceivable here, such as a pivoting mechanism.

[0035] Since the beam path 230 can be interrupted by the beam trap 220 using the sliding mechanism behind the first lens 210a and behind the second lens 210b, a stationary thermal state can be established for both the first lens 210a and the second lens 210b instead of thermal oscillations, analogous to the above explanations in connection with Fig. 1, so that oscillating optical aberrations for both lenses 210a, 210b are minimized accordingly. Overall, this leads to a particularly low-aberration projection system.

[0036] Fig. 3 shows a schematic view of a third embodiment of a projection system 300 for a projection exposure apparatus for microlithography according to the first teaching of the invention. The projection system 300 shown can be used in particular in EUV lithography. The projection system 300 comprises a total of six optical elements 310a, 310b, 310c, 310d, 310e, 310f, which are mirrors 310a, 310b, 310c, 310d, 310e, 310f. The beam path 330, which runs from top to bottom in the figure, is again indicated by the dashed lines. In this exemplary embodiment, the beam path 330 shown originates from a reflective mask (not shown), which is located in the beam path emanating from an EUV light source (not shown). As Fig. 3 also shows, the projection system 300 also comprises a radiation-absorbing element 320, here again exemplarily in the form of a beam trap 320.The beam trap 320 is arranged along the beam path 330 both behind the first mirror 310a and behind the additional mirrors 310b, 310c, 310d, 310e, 310f. The beam trap 320 also has a sliding mechanism (not shown) and can thus be introduced into the beam path 330, as indicated by the arrow 340, and subsequently removed from the beam path 330. In this way, the beam trap 320 is configured to temporarily interrupt the beam path 330 of the projection system 300 behind the first mirror 310a and behind the additional mirrors 310b, 310c, 310d, 310e, 310f. As an alternative to the described sliding mechanism, other mechanisms are also conceivable, such as a pivoting mechanism.

[0037] Since the beam path 330 can be interrupted by the beam trap 320 using the sliding mechanism behind the first mirror 310a and behind the further mirrors 310b, 310c, 310d, 310e, 310f, analogous to the above explanations in connection with Fig. 1 and Fig. 2, a stationary thermal state can be established for both the first mirror 310a and the further mirrors 310b, 310c, 310d, 310e, 310f instead of thermal oscillations, so that oscillating optical aberrations for all mirrors 310a, 310b, 310c, 310d, 310e, 310f are minimized accordingly, which overall leads to a particularly low-aberration projection system.

[0038] The beam traps 120, 220, 320 shown in Figs. 1, 2, and 3 have in common that the surfaces 121, 221, 321 of the beam traps 120, 220, 320 have an absorption coefficient of more than 0.99 and a reflection coefficient of less than 0.01. This not only ensures that the surfaces 121, 221, 321 absorb light particularly well, but also that they reflect particularly little light back toward the optical elements 110, 210a, 210b, 310a, 310b, 310c, 310d, 310e, 310f. Both the high absorption coefficient and the low reflection coefficient allow thermal oscillations and consequently the oscillating optical aberrations induced thereby to be minimized particularly effectively.

[0039] Furthermore, the beam traps 120, 220, and 320 shown in Figs. 1, 2, and 3 have in common that they have a metallic body and an anti-reflection coating. While the use of a metallic material for the body offers the advantages of high light absorption, high mechanical stability, sufficiently high temperature resistance, and sufficiently high thermal shock resistance, the anti-reflection coating allows particularly low reflection levels to be achieved.

[0040] Furthermore, the beam traps 120, 220, 320 shown in Figs. 1, 2 and 3 each have means for active and / or passive cooling (not shown). This allows even high light outputs in the range of several watts up to several kilowatts to be absorbed by the beam traps 120, 220, 320 without the beam traps 120, 220, 320 heating up excessively. For light outputs of a few watts at most, purely passive cooling fins are generally sufficient for this purpose. Light outputs in the range of several hundred watts, on the other hand, usually require one or more active fans, possibly in combination with passive cooling fins. For even higher light outputs of several kilowatts, air-based cooling is often no longer sufficient, so that an equally active water cooling system must be used.For applications in EUV lithography, it should also be noted that the projection systems are usually located in a vacuum, so fans are not suitable as a means of active cooling.

[0041] As an alternative to the beam traps 120, 220, 320 shown in Figs. 1, 2, and 3, other radiation-absorbing elements are also conceivable in all three embodiments. For example, a radiation-absorbing element in the form of a beam shutter could also be used in each case, which is permanently located in the beam path 130, 230, 330 and has a diaphragm mechanism to temporarily interrupt the beam path 130, 230, 330 and then release it again. As a further alternative, a radiation-absorbing element in the form of a combination of a movable mirror and a stationary beam trap could also be used in each case. In such a combination, the movable mirror can be introduced into the beam path 130, 230, 330 in order to temporarily direct the beam path 130, 230, 330 onto the stationary beam trap, where the light radiation is absorbed.

[0042] To implement a projection exposure system according to the second teaching, any of the embodiments of a projection system 100, 200, 300 according to the invention shown in Figs. 1, 2, and 3 can be combined with a suitable light source. In microlithography, for example, mercury vapor lamps or excimer lasers are used as light sources. In EUV lithography, for example, light sources are used in which tin droplets are converted into a plasma by laser pulses, which then emits EUV light with a wavelength of, for example, 13.5 nm.

[0043] A projection exposure system just described, which comprises one of the embodiments of a projection system 100, 200, 300 according to the invention shown in Figs. 1, 2, and 3 as well as a suitable light source, can be advantageously used to implement a method for producing integrated circuits by microlithography, in which semiconductor wafers coated with photoresist are exposed using the projection exposure system. In this case, the radiation-absorbing element 120, 220, 320 is introduced into the beam path 130, 230, 330 of the projection system 100, 200, 300 by means of the described sliding mechanism (not shown) at least for the duration of a dead time, in particular a wafer change or a reticle change, so that the beam path 130, 230, 330 is interrupted.As a result, measures to prevent light from entering the projection system 100, 200, 300, which are otherwise typically necessary during the dead time, in particular during a wafer change, can be eliminated and, as already described above, the oscillating optical aberrations for the optical elements 110, 210a, 210b, 310a, 310b, 310c, 310d, 310e, 310f caused by thermal vibrations can be effectively minimized. Thus, in a corresponding method according to the invention, the optical performance and thus the lithographic yield and throughput can be improved during wafer exposure, while still ensuring that no light reaches the wafer region during the dead time, in particular during a wafer change.

[0044] This disclosure also includes the subject matter of the following clauses:

[0045] 1. Projection system for a projection exposure apparatus for microlithography, in particular for EUV lithography, comprising an optical element, wherein the projection system comprises a radiation-absorbing element which is configured to temporarily interrupt the beam path of the projection system behind the optical element.

[0046] 2. Projection system according to clause 1, wherein the projection system comprises at least one further optical element, wherein the radiation-absorbing element is configured to interrupt the beam path of the projection system behind the at least one further optical element.

[0047] 3. A projection system according to clause 2, wherein the radiation-absorbing element is configured to interrupt the beam path of the projection system behind the third-to-last, the second-to-last, or the last optical element. 4. A projection system according to any one of clauses 1 to 3, wherein a surface of the radiation-absorbing element has an absorption coefficient of at least 0.9, preferably at least 0.95, particularly preferably at least 0.98.

[0048] 5. Projection system according to one of clauses 1 to 4, wherein a surface of the radiation-absorbing element has a reflectance of at most 0.1, preferably at most 0.05, particularly preferably at most 0.02.

[0049] 6. Projection system according to any one of clauses 1 to 5, wherein the radiation-absorbing element comprises a body made of a metal or a metal alloy.

[0050] 7. A projection system according to any one of clauses 1 to 6, wherein the radiation-absorbing element has an anti-reflection coating.

[0051] 8. Projection system according to one of clauses 1 to 7, wherein the radiation-absorbing element has means for active and / or passive cooling.

[0052] 9. Projection exposure system for microlithography, in particular for EUV lithography, wherein the projection exposure system comprises a radiation source and a projection system according to one of clauses 1 to 8.

[0053] 10. A method for producing integrated circuits by means of microlithography, in particular by means of EUV lithography, in which semiconductor wafers coated with photoresist are exposed using a projection exposure apparatus, wherein the projection exposure apparatus comprises a radiation source and a projection system according to one of clauses 1 to 8, wherein the radiation-absorbing element interrupts the beam path of the projection system at least for the duration of a dead time, in particular a wafer change.

Claims

Patent claims 1. Projection system (100, 200, 300) for a projection exposure apparatus for EUV lithography, comprising an optical element (110, 210a, 310a), characterized in that the projection system comprises a radiation-absorbing element (120, 220, 320) which is configured to temporarily interrupt the beam path (130, 230, 330) of the projection system behind the optical element (110, 210a, 310a).

2. Projection system according to claim 1, wherein the projection system comprises at least one further optical element (210b, 310b, 310c, 310d, 310e, 310f), wherein the radiation-absorbing element (220, 320) is configured to interrupt the beam path (230, 330) of the projection system behind the at least one further optical element (210b, 310b, 310c, 310d, 310e, 310f).

3. Projection system according to claim 2, wherein the radiation-absorbing element (220, 320) is configured to interrupt the beam path (230, 330) of the projection system behind the third-to-last, the second-to-last or the last optical element (210b, 310b, 310c, 310d, 310e, 310f).

4. Projection system according to one of claims 1 to 3, wherein a surface (121, 221, 321) of the radiation-absorbing element has an absorption coefficient of at least 0.9, preferably at least 0.95, particularly preferably at least 0.

98.

5. Projection system according to one of claims 1 to 4, wherein a surface (121, 221, 321) of the radiation-absorbing element has a reflectance of at most 0.1, preferably at most 0.05, particularly preferably at most 0.

02.

6. Projection system according to one of claims 1 to 5, wherein the radiation-absorbing element (120, 220, 320) comprises a body made of a metal or a metal alloy.

7. Projection system according to one of claims 1 to 6, wherein the radiation-absorbing element (120, 220, 320) has an anti-reflection coating.

8. Projection system according to one of claims 1 to 7, wherein the radiation-absorbing element has means for active and / or passive cooling.

9. Projection system (100, 200, 300) for a projection exposure apparatus for microlithography, in particular for EUV lithography, comprising an optical element (110, 210a, 310a), characterized in that the projection system comprises a radiation-absorbing element (120, 220, 320) which is configured to temporarily interrupt the beam path (130, 230, 330) of the projection system behind the optical element (110, 210a, 310a), wherein a surface (121, 221, 321) of the radiation-absorbing element has an absorption coefficient of at least 0.9, preferably at least 0.95, particularly preferably at least 0.

98.

10. Projection exposure system for microlithography, in particular for EUV lithography, characterized in that the projection exposure system comprises a radiation source and a projection system (100, 200, 300) according to one of claims 1 to 9.

11. A method for producing integrated circuits by means of microlithography, in particular by means of EUV lithography, in which semiconductor wafers coated with photoresist are exposed using a projection exposure apparatus, characterized in that the projection exposure apparatus comprises a radiation source and a projection system (100, 200, 300) according to one of claims 1 to 9, wherein the radiation-absorbing element (120, 220, 320) interrupts the beam path (130, 230, 330) of the projection system at least for the duration of a dead time, in particular a wafer change.

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