Beam diaphragm, EUV light source, and method for operating an EUV light source

Abstract

The invention relates to a beam diaphragm (10) comprising: a diaphragm opening (12) for allowing the passage of a laser beam (14); a deflection unit (16) for deflecting a portion of the laser beam (14) not allowed to pass through the diaphragm opening (12); a reflection unit (18) for reflecting the deflected portions of the laser beam (14); and a sensor unit (20) for detecting the reflex (21) of the deflected portions of the laser beam (14). The invention also relates to an EUV light source (39) having such a beam diaphragm (10), and to a method for operating such an EUV light source (39).

Description

[0001] Beam aperture, EUV light source and method for operating an EUV light source

[0002] The present invention relates to a beam stop with a diaphragm opening for passing a laser beam and a sensor unit with which a misalignment of the laser beam can be detected. The invention further relates to an EUV light source with such a beam stop and a method for operating an EUV light source.

[0003] Beam apertures, which have an opening for passing a laser beam and a sensor unit, are known. Such beam apertures are used in EUV light sources to detect laser beam misalignment.

[0004] Such a device for monitoring the alignment of a laser beam is shown, for example, in WO2015172816A by the applicant. This device comprises a detector with an opening for the passage of the laser beam, at least two temperature sensors attached to the detector, and a temperature monitoring device connected to the at least two temperature sensors to monitor the alignment of the laser beam relative to the opening. The at least two temperature sensors have either a temperature-dependent resistance that increases with increasing temperature or a temperature-dependent resistance that decreases with increasing temperature, and the at least two temperature sensors are connected to the temperature monitoring device in a series circuit. Also disclosed is an EUV radiation generation device that has at least one device as described above for monitoring the alignment of a laser beam.

[0005] It has been shown that such a detector may react too slowly when using high laser powers and short pulse durations, resulting in damage to the aperture.

[0006] The object of the invention is to provide a beam diaphragm, an EUV light source with such a beam diaphragm and a method for operating such an EUV light source, with which the aforementioned disadvantages are reduced, preferably avoided.

[0007] This object is achieved by providing the present technical teaching, in particular the teaching of the independent claims, as well as the preferred embodiments disclosed in the dependent claims and the description.

[0008] The beam diaphragm according to the invention has a diaphragm opening for passing a laser beam, a deflection unit for deflecting portions of the laser beam not passed through the diaphragm opening, a reflection unit for reflecting the deflected portions of the laser beam and a sensor unit for detecting the reflection of the deflected portions of the laser beam.

[0009] If the laser beam is correctly aligned, i.e. in the desired beam position, it will pass completely through the aperture of the beam stop. If the laser beam is misaligned, the portions of the laser beam that are not allowed to pass through the aperture hit the deflection unit and are deflected by it onto the reflection unit. The portions of the laser beam that hit the beam stop are therefore not absorbed but deflected, so that the beam stop is not heated up in the event of laser beam misalignment. The deflected portions of the laser beam are then reflected at the reflection unit and hit the sensor unit. This detects the reflection of the deflected portions of the laser beam. The alignment of the laser beam is thus monitored independently of the temperature of the beam stop.A misalignment of the laser beam is detected immediately and not only when the beam aperture has reached a certain temperature, thus avoiding a time delay between the misalignment and the detection of the misalignment of the laser beam. Because the beam aperture is not heated in the event of a misalignment of the laser beam, damage due to an excessively high surface temperature of the beam aperture, such as local melting of the beam aperture material, can be avoided. Such local melting of the beam aperture material often produces smoke and metal vapor, which can damage subsequent optical elements in the beam path. If the misalignment of the laser beam is not detected in time, people, such as operators, who are nearby can also be injured.

[0010] According to a further development of the invention, the deflection unit has a deflection surface that is aligned transversely with respect to a desired beam position of the laser beam. The deflection surface is aligned such that those portions of the misaligned laser beam that are not allowed to pass through the aperture are deflected toward the reflection unit. In this way, the portions of the laser beam that impinge on the beam aperture are advantageously deflected away from the deflection unit, preventing it from heating up.

[0011] In the target beam position, the laser beam hits optical elements arranged along its beam path at a predetermined angle and at a predetermined position. If the laser beam is misaligned, i.e. its beam position deviates from the target beam position, it may be that - particularly with long beam paths of several meters - it does not hit the optical elements in its beam path, or does not hit them at the predetermined position or at the predetermined angle. A beam axis of the misaligned laser beam therefore runs parallel to or is tilted to a beam axis of the laser beam that is passed through the beam aperture in the target beam position. In the target beam position, the laser beam is aligned such that no portion of the laser beam hits the beam aperture.

[0012] According to a further development of the invention, the deflection surface forms an angle of 30° to 60° with the target beam position. If the beam axis of the misaligned laser beam runs parallel to the beam axis of the laser beam in the target beam position, the portions of the laser beam that are not allowed to pass through the aperture are deflected accordingly by an angle between 120° and 60°. If the beam axis of the misaligned laser beam is tilted relative to the beam axis of the laser beam in the target beam position, the portions of the laser beam that are not allowed to pass through the aperture may be deflected by an even greater angle, depending on the orientation of the beam axis of the misaligned laser beam.

[0013] An angle of 45° between the deflection surface and the target beam position has proven particularly advantageous. At this angle, if the beam axis of the laser beam in the target beam position and the beam axis of the misaligned laser beam are parallel, the portions of the laser beam that are not allowed to pass through the aperture are deflected by an angle of 90°. Since the deflection surface is positioned relative to the reflection unit so that the deflected portions of the laser beam hit the reflection unit, such an arrangement allows for the reflection unit to be arranged on the beam aperture in a structurally simple manner.

[0014] According to a further development of the invention, the deflection unit delimits the aperture at least in sections. An arrangement in which the deflection unit delimits the aperture at least in sections in a ring shape has proven particularly advantageous. The portions of the laser beam deflected by the deflection unit then form - if the deflection unit completely surrounds the aperture in a ring shape - a virtual intersection point at the center of the aperture. If the deflection unit only delimits the aperture opening in a ring shape in sections, the deflected portions of the laser beam form a virtual intersection point at the center of an imaginary circle, with the ring section extending along a circumferential line of this circle. In this case, the deflected portions of the laser beam form a virtual intersection point at an imaginary center of the aperture.

[0015] According to a further development of the invention, the deflection unit is preferably designed as a conical ring mirror or as an internally reflecting ring prism, or as a section of a conical ring mirror or an internally reflecting ring prism. The section of the conical ring prism or the internally reflecting ring prism can, in particular, be designed as a ring section, so that the conical ring mirror or the internally reflecting ring prism does not completely delimit the aperture. Configuring the deflection unit as a conical ring prism or a reflective ring prism enables a particularly simple design of the beam aperture.

[0016] The conical ring mirror or the reflective ring prism, or their cutouts, have an edge that is as sharp as possible. This ensures that the laser beam impinging on the edge of the conical ring mirror or the reflective ring prism is not deflected, or almost not deflected, in directions that do not point toward the reflection unit.

[0017] To prevent the laser beam from being deflected by an inner surface of the conical ring mirror or the reflective ring prism in directions that do not point toward the reflection unit, this inner surface can also be provided with an undercut. An undercut of up to 5° between the inner surface of the conical ring mirror or the reflective ring prism and the target beam position has proven particularly effective.

[0018] The deflection unit can be made of optical glass, e.g. quartz glass, N-BK7, Zerodur, or crystals (ZnSe, sapphire).

[0019] According to a further development of the invention, the reflection unit has a reflection surface on which the deflected portions of the laser beam are reflected. The reflection surface is arranged such that the reflection of the deflected portions of the laser beam is concentrated in a sensor point, which is preferably arranged between the deflection unit and the reflection surface. In a particularly advantageous embodiment of the invention, a sensor for detecting the radiation concentrated in the sensor point is arranged in the sensor point. By concentrating the deflected portions of the laser beam on the sensor unit, only a small mass is heated compared to beam diaphragms that absorb incoming laser radiation. The beam diaphragm therefore reacts significantly faster and more sensitively to misalignment of the laser beam than an absorbing beam diaphragm. This minimizes switching times and increases the safety of the entire system.

[0020] According to a further development of the invention, the reflective surface is at least partially elliptically shaped. A first focal point and a second focal point are assigned to the at least partially elliptically shaped reflective surface, with the first focal point being located at the sensor point. The second focal point lies on a beam axis of the laser beam transmitted through the aperture in the desired beam position. In the case of a deflection unit that is ring-shaped or partially ring-shaped, the second focal point is also located at the center or imaginary center of the aperture. The at least partially elliptically shaped reflective surfaces reflect and focus the reflection of the deflected portions of the laser beam onto the sensor point.This utilizes a fundamental property of an elliptically shaped mirror, whereby all rays that originate, or appear to originate, at the first focal point of the ellipse are imaged at the second focal point. The ellipse underlying the reflective surface is designed such that the first focal point lies at the virtual intersection point of the deflected portions of the laser beam at the center or imaginary center of the aperture. The second focal point lies at the sensor point, so that all deflected portions of the laser beam are focused on the sensor point. The advantage of this type of beam aperture design is that all deflected portions of the laser beam can be detected.

[0021] The reflection surface can be made of copper, particularly by milling.

[0022] A laser beam with a wavelength of, for example, 10.6 pm is reflected by a copper surface, so a beam stop with a copper reflection surface is particularly advantageous as a beam stop for transmitting a CO2 laser beam. Due to the elliptical shape of the reflection surface, at least in some sections, optical imaging properties play a subordinate role—as long as the concentrating functionality is ensured. Therefore, processes that typically produce surfaces with only low surface roughness, such as finish milling, polishing, laser cutting, or wire EDM, can be used to produce the reflection surface.

[0023] The reflection surfaces can be provided with a reflective coating, e.g. a gold or aluminum layer.

[0024] According to a further development of the invention, a cover unit is arranged on the beam aperture in such a way that the sensor unit is shielded from direct portions of the laser beam. The cover unit is arranged in front of the sensor unit, as seen in the direction of propagation of the laser beam. Only those portions of the laser beam that strike the deflection unit and are deflected by it onto the reflective surfaces strike the sensor unit.

[0025] According to a further development of the invention, the cover unit has a particularly circular recess for passing the laser beam through the aperture. The deflection unit and the cover unit are arranged concentrically to one another, so that the deflection unit is not covered by the cover unit when viewed in the beam propagation direction of the laser beam. The cover unit has a chamfer, in particular on an inner surface facing the recess, to prevent the laser beam from being deflected in directions that do not point towards the reflection unit. The provision of a circular recess in the cover unit and a concentric arrangement of the deflection unit and cover unit enables a structurally particularly simple design of the beam aperture.

[0026] According to a further development of the invention, the sensor unit is designed as a temperature sensor, in particular as a pyrometer or resistance temperature sensor. The sensor unit can be glued or screwed into absorbent-coated copper sleeves. The sensor unit can also be designed as an optical sensor, in particular as a photodiode, photovoltaic diode, or camera. The provision of commercially available sensors as sensor units enables a particularly cost-effective and simple design of the beam diaphragm.

[0027] According to a further development of the invention, the beam diaphragm comprises at least two, preferably six, reflection units, each having the same first focal point, which lies on the beam axis of the laser beam transmitted through the diaphragm opening in the desired beam position. The reflection units are arranged around the diaphragm opening. By providing a plurality of reflection units arranged around the diaphragm opening, it is not only possible to determine that the laser beam is misaligned, but also to detect the position of the misaligned laser beam relative to the desired beam position, as well as the shape and / or size of the laser beam transmitted through the diaphragm opening.

[0028] If the deflection unit completely defines the aperture in a ring shape, for example, in the form of a reflective ring prism or a conical ring mirror, the portions of the laser beam that are not allowed to pass through the aperture are deflected by the deflection unit to one of the reflection units, regardless of their position relative to the aperture. Thus, deviations in the laser beam position from the target beam position can be detected regardless of the position of the misaligned laser beam.

[0029] According to a further development of the invention, each reflection unit is assigned a sensor unit. The sensor unit is connected to at least one readout unit. The individual evaluation of the respective sensor units enables, in addition to a purely safety functionality, an analysis of the beam position, beam size, and / or beam shape, for example, the ellipticity of the laser beam passing through the aperture. The sensor units can also be evaluated integrally. For example, the sensor units can be designed as temperature sensors connected to a common water circuit. A change in the water temperature in the water circuit is then detected, indicating a misalignment of the laser beam.

[0030] Alternatively, instead of individual sensor units, water-cooled bars connected hydraulically in series can be provided. At a given flow rate, the temperature increase of the water passing through the water-cooled bars is proportional to the laser power absorbed by the water-cooled bars.

[0031] According to a further development of the invention, the at least partially elliptically shaped reflection surfaces each have a vertex. The vertices are each arranged on an imaginary circular line, in particular rotationally symmetrically, around the beam axis of the laser beam passing through the aperture in the desired beam position. This arrangement enables a simple, compact, and cost-effective mechanical design of the beam aperture while simultaneously utilizing only reflective optical elements—except for the sensor.

[0032] If the beam diaphragm has multiple reflection units, the reflection surfaces assigned to each reflection unit can be manufactured, in particular milled, from a single component, e.g., made of copper. A concentrator manufactured in this way, which has multiple reflection surfaces that are at least partially elliptically shaped, can be formed in one piece.

[0033] The concentrator can also be composed of multiple reflection units. If the deflection unit is designed as an internally reflecting ring prism and the concentrator is composed of multiple reflection units, this has the advantage that the respective sensor units and the aperture can be mechanically separated from each other, so that the laser beam path can be sealed off from the sensor unit. If the sensor unit is destroyed due to misalignment of the laser beam, contamination of the beam path is prevented.

[0034] The invention also relates to an EUV light source with a beam stop as described above, a seed laser for generating a laser beam, a driver laser device for amplifying the laser beam, a vacuum chamber into which a target material can be introduced into a focusing region, a focusing unit for focusing the laser beam into the focusing region to generate EUV radiation, and a beam guiding device for guiding the laser beam to the focusing unit. In such an EUV light source, the beam stop can be used to monitor the alignment of the laser beam. This prevents damage to the beam stop and / or to other components arranged in the beam path of the laser beam.

[0035] It is understood that the beam stop described above can be advantageously used not only in an EUV light source, but also in a laser processing machine or the like, especially when a high-power pulsed laser beam is used.

[0036] The invention also relates to a method for operating such an EUV light source with the following steps:

[0037] • Generating a laser beam in the seed laser,

[0038] • Amplifying the laser beam in the driver laser device,

[0039] • Passing the laser beam through the beam aperture,

[0040] • in the event that the sensor unit detects radiation with an intensity, power or energy that is above a threshold value:

[0041] Switching off the seed laser and / or the driver laser device and / or interrupting the laser beam by a beam interruption unit,

[0042] • in case the sensor unit detects radiation with an intensity, power or energy below the threshold value, or no radiation:

[0043] Focusing the laser beam in the focusing unit onto the focusing area to generate EUV radiation. To avoid damage to the beam stop and / or another component arranged in the beam path of the laser beam, it is advantageous to switch off the laser beam if the sensor unit detects radiation with an intensity, power, or energy above the threshold value. The laser beam can be interrupted by a beam interruption unit, e.g., a shutter, so that components following the beam stop in the beam path are not damaged in the event of a laser beam misalignment. Alternatively or additionally, the seed laser or the driver laser device can also be switched off if the sensor unit detects radiation with an intensity, power, or energy above the threshold value to prevent damage further downstream of the laser beam.If the sensor unit detects radiation with an intensity, power, or energy below the threshold, or if no radiation is detected, the laser beam is focused in the focusing unit onto the focusing zone. In the focusing zone, the laser beam is focused onto a target material, such as a tin droplet. The target material then emits EUV radiation as a result of the laser beam irradiation.

[0044] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further-described features can be used individually or in any combination. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0045] They show:

[0046] Fig.l an embodiment of the beam diaphragm,

[0047] Fig.2 an illustration of the geometric conditions of the beam aperture,

[0048] Fig. 3a, b, c and d the beam aperture at different beam positions, beam sizes and beam shapes of the laser beam, Fig. 4 another embodiment of the beam aperture,

[0049] Fig. 5 an EUV light source with the beam stop.

[0050] Figure 1 shows a beam stop 10 with a stop opening 12, a deflection unit 16, six reflection units 18, six sensor units 20, and a cover unit 32 having a circular recess 34. The beam stop 10 can have any number of reflection units 18 grouped around the stop opening 12. The deflection unit 16 is designed as a conical ring mirror in Fig. 1. The deflection unit 16 can also be implemented by another reflective optical element, for example, as an internally reflecting ring prism. The conical ring mirror has a deflection surface 22. It can be provided with an undercut of up to 5° on its inner side 17, which is not shown in Fig. 1. The reflection units 18 each comprise a partially elliptically shaped reflection surface 28, with each of the reflection surfaces 28 being assigned a sensor unit 20.

[0051] The deflection unit 16 is mounted on a cover plate 33, to which the sensor units 20 and reflection units 18 are mounted. The circular recess 34 of the cover unit 32 is arranged concentrically to the aperture 12, so that the sensor units 20 and the reflection surfaces 28 are covered by the cover unit 32. For a laser beam 14, which, as shown in Fig. 1, is transmitted through the beam aperture 10 from a side facing the cover unit 32, only the deflection unit 16 is visible. The sensor units 20 are each arranged at a sensor point 30, which lies between the respective reflection surface 28 and the deflection unit 16.

[0052] The sensor units 20 are designed, for example, as thermocouples, e.g. absorbent-coated copper sleeves, which are glued or screwed onto the cover plate 33.

[0053] The sensor units 20 are each signal-connected to a readout unit 36. The readout unit 36 ​​is designed to evaluate a signal transmitted by the respective sensor units 20, so that it can be determined at which of the sensor units 20 radiation was detected.

[0054] Multiple readout units 36 can also be provided. Each sensor unit 20 is then connected to a respective readout unit 36. These then forward the received signals to a central control unit.

[0055] In an alternative embodiment, the sensor units 20 can also be connected in series. One of the sensor units 20 connected in series is then in turn connected to a readout unit 36. In this case, the readout unit 36 ​​or a control unit connected to the readout unit 36 ​​evaluates the signal from the sensor units 20 integrally. The position of the beam position of the laser beam 14 in relation to the desired beam position, the beam shape, and the beam size cannot be determined in this case. However, it can be determined whether the beam position of the laser beam 14 deviates from the desired beam position. If this is the case, the laser beam 14 can be switched off depending on whether the energy, intensity, or power of the laser beam 14 measured at the sensor units 20 is above a threshold value.

[0056] The reflective surfaces 28 are formed on a concentrator 29, which is formed as a milled part, e.g., from copper. The reflective surfaces 28, which are elliptically shaped in sections, are machined to exhibit high reflectivity. Adequate surface roughness can be achieved by processes such as finish milling, polishing, wire EDM, or laser cutting, since these surfaces do not need to be perfectly reflective surfaces due to their ellipticity.

[0057] The laser beam 14 is ideally aligned in a desired beam position. In this beam position, the laser beam 14 is transmitted through the aperture 12 of the beam aperture 10 without any portions of the laser beam 14 impinging on the beam aperture 10. The beam axis of the laser beam 14 in the desired beam position runs at an angle of 90° to a plane in which the cover unit 32 and / or the cover plate 33 is arranged. If the laser beam 14 is misaligned, its beam axis is offset from the beam axis in the desired beam position and / or runs at an angle to the beam axis of the laser beam 14 in the desired beam position. In this case, portions of the laser beam 14 may impinge on the deflection unit 16 and be deflected by it onto one or more of the reflection units 18.

[0058] Even if the diameter of a cross-section of the laser beam 14 is larger than the diameter of the aperture 12 or the laser beam 14 has an elliptical shape, it is possible that portions of the laser beam 14 strike the deflection surface 16 and are deflected by it onto one or more reflection units 18. The reflection surfaces 28 of the reflection units 18 reflect the reflection 21 of the deflected portions of the laser beam 14 onto the respective sensor units 20. The sensor units 20 finally detect an energy, power, or intensity of the reflection 21 and transmit the detected measured values ​​to one or more readout units 36.

[0059] Fig. 2 illustrates the geometric relationships of the beam diaphragm 10. The reflection surfaces 28 each extend along a partial section of a circumferential line of an imaginary ellipse 11. A first focal point 31 of the respective ellipse 11 lies between the reflection surface 28 assigned to the ellipse 11 and the deflection unit 16, and a second focal point 37 lies at the center of the annular diaphragm opening 12. Those portions of the laser beam 14 that are not transmitted through the diaphragm opening 12 strike the deflection unit 16 and are deflected by it at an angle of 90° as a reflection 21 onto the reflection surfaces 28. The reflection surfaces 28 concentrate the reflection 21 onto the first focal point 31 of the imaginary ellipse, which coincides with a sensor point 30 at which the sensor unit 20 is arranged.If the portions of the laser beam 14 deflected by the deflection unit 16 are extended in the opposite direction to their propagation direction, they form a virtual intersection point that coincides with the second focal point 37 of the imaginary ellipse 11 and the center of the aperture 12. This utilizes the fundamental property of an elliptical mirror, according to which radiation that comes or appears to come from one of the focal points is always imaged onto the other focal point. The imaginary ellipse 11, along which the reflection surfaces 28 extend, is designed such that the portions of the laser beam 14 that are not transmitted through the aperture 12 and consequently hit the deflection unit 16 are concentrated onto the sensor point 30 and thus the sensor unit 20.

[0060] Fig. 3a, b, c and d show the beam aperture 10 in different application situations.

[0061] In Fig. 3a and b, the laser beam is aligned off-center, with a beam axis that is offset from the desired beam position. In this case, only the sensor units 20c, d in Fig. 3a and 20a, b in Fig. 3b respond, to which the portions of the laser beam 14 deflected by the deflection unit 16 are reflected. The respective sensor units 20c, d and 20a, b detect the power, energy, or intensity of the incident radiation and forward this to the readout unit 36. In this way, it can be determined which of the sensor units 20a to f have detected radiation. This allows conclusions to be drawn about the position of the beam axis of the misaligned laser beam 14 in relation to the desired beam position.

[0062] Fig. 3c shows a laser beam 14 whose cross-section is larger than the target beam cross-section. If this laser beam 14 is passed through the aperture 12, all sensor units 20a to f respond.

[0063] Finally, Fig. 3d shows a laser beam 14 with an elliptical cross-section. When this laser beam 14 is passed through the aperture 12, opposing sensor units—in the case shown in Fig. 3d, sensor units 20a and d—are activated.

[0064] In Fig. 3a to d, the beam diaphragm 10 is shown without the cover unit 32 for reasons of clarity.

[0065] Fig. 4 shows an embodiment of the beam diaphragm 10 in which the concentrator 29 is composed of several segments. In Fig. 4, the deflection unit 16 is designed as an internally reflecting ring prism. The individual segments of the concentrator 29 are sealed from the diaphragm opening 12 by webs 23, so that if the sensor units 20 are damaged or destroyed, the optical elements arranged in the beam path of the laser beam 14 are not damaged.

[0066] Fig. 5 shows an EUV light source 39 with a seed laser 38, a driver laser device 40, a vacuum chamber 42, a beam guiding device 52, and a focusing unit 48. The laser beam 14 is generated by the seed laser 38 and amplified in the driver laser device 40. The amplified laser beam 14 is guided by the beam guiding device 52 to the focusing unit 48, where it is focused onto the focusing region 46. A target material 47 can be introduced into the focusing region 46, which material emits radiation, in particular EUV radiation, upon irradiation with the laser beam 14. The beam diaphragm 10 is arranged in the beam guiding device 52 in Fig. 5. It is understood that the beam diaphragm 10 can also be arranged in another part of the EUV light source, for example between two amplifiers 41a, 41b of the driver laser device 40 or between the seed laser 38 and the driver laser device 40.

[0067] If, during operation of the EUV light source 39, one or more of the sensor units 20 detects a measured value that lies above a threshold value, the readout unit 36 ​​or a control unit 44 connected to the readout unit 36 ​​sends the signal to the seed laser 38, the driver laser device 40, and / or the beam interruption unit 54 to switch off the laser beam 14. For this purpose, the readout unit 36 ​​or the control unit 44 is signal-connected to the seed laser 38, the driver laser device 40, and / or a beam interruption unit 54. In this way, the beam path of the laser beam is protected from the consequences of misalignment of the laser beam 14.

Claims

Patent claims 1. Beam aperture (10) with • an aperture (12) for passing a laser beam (14), • a deflection unit (16) for deflecting a portion of the laser beam (14) not allowed to pass through the aperture (12), • a reflection unit (18) for reflecting the deflected portions of the laser beam (14) • a sensor unit (20) for detecting the reflection (21) of the deflected portions of the laser beam (14).

2. Beam diaphragm (10) according to claim 1, characterized in that the deflection unit (16) has a deflection surface (22) which is aligned transversely with respect to a desired beam position of the laser beam (14), so that the portions of the laser beam (14) striking the deflection unit (16) can be deflected onto the reflection unit (18).

3. Beam diaphragm (10) according to claim 2, characterized in that the deflection surface (22) encloses an angle of 30° to 60° with the desired beam position of the laser beam (14).

4. Beam diaphragm (10) according to one of the preceding claims, characterized in that the deflection unit (16) limits the diaphragm opening (12) at least in sections, preferably in an annular manner.

5. Beam diaphragm (10) according to one of the preceding claims, characterized in that the deflection unit (16) is designed as a conical ring mirror or as an internally reflecting ring prism.

6. Beam diaphragm (10) according to one of the preceding claims, characterized in that the reflection unit (18) has a reflection surface (28) so that the reflection (21) of the deflected portions of the laser beam (14) can be concentrated in a sensor point (30) of the reflection surface (28). wherein the sensor point (30) is preferably arranged between the deflection unit (16) and the reflection surface (28) associated with the sensor point (30).

7. Beam diaphragm (10) according to one of the preceding claims, characterized in that the reflection surface (28) is at least partially elliptically shaped, wherein a first focal point (31) of the reflection surface (28) lies on the sensor point (30) and a second focal point (37) of the reflection surface (28) lies on a beam axis of a laser beam (14) transmitted through the diaphragm opening (12) in the desired beam position.

8. Beam diaphragm (10) according to one of the preceding claims, characterized in that a cover unit (32) is arranged in front of the sensor unit (20) as seen in a beam propagation direction of the laser beam (14), so that the sensor unit (20) is shielded from direct components of the laser beam (14).

9. Beam diaphragm (1) according to claim 8, characterized in that the cover unit (32) has a particularly circular recess (34) for passing the laser beam (14), and the deflection unit (16) and the cover unit (32) are arranged concentrically to one another, so that the deflection unit (16) is not covered by the cover unit (32) when viewed in the beam propagation direction of the laser beam (14).

10. Beam diaphragm (1) according to one of the preceding claims, characterized in that the sensor unit (20) is designed as a temperature sensor, in particular as a pyrometer, or as an optical sensor, in particular as a photodiode or camera.

11. Beam diaphragm (10) according to one of claims 7 to 10, characterized in that the beam diaphragm (10) has at least two, preferably six, reflection units (18), each having the same second focal point (37) which lies on the beam axis of the laser beam (14) transmitted through the diaphragm opening (12) in the desired beam position.

12. Beam diaphragm (10) according to claim 11, characterized in that each reflection unit (18) is assigned a sensor unit (20), wherein the sensor unit (20) is connected to at least one readout unit (36).

13. Beam diaphragm (10) according to claim 11 or 12, characterized in that the at least partially elliptically shaped reflection surfaces (28) each have a vertex (35), wherein the vertices (35) are each arranged on an imaginary circular line, in particular rotationally symmetrical, around the beam axis of the laser beam (14) transmitted through the diaphragm opening (12) in the desired beam position. 14.EUV light source (39) with • a beam diaphragm (10) according to one of the preceding claims, • a seed laser (38) for generating a laser beam (14), • a driver laser device (40) for amplifying the laser beam (14), • a vacuum chamber (42) into which a target material (47) can be introduced into a focusing area (46), • a focusing unit (48) for focusing the laser beam (14) into the focusing area (46) for generating EUV radiation, • a beam guiding device (52) for guiding the laser beam (14) to the focusing unit (48). experienced for operating an EUV light source (39) according to claim 14, comprising the following steps: • Generating the laser beam (14) in the seed laser (38), • Amplifying the laser beam (14) in the driver laser device (40), • Passing the laser beam (14) through the beam aperture (10), • in the event that the sensor unit (20) detects radiation with an intensity, power or energy that is above a threshold value: Switching off the seed laser (38) and / or the driver laser device (40) and / or interrupting the laser beam (14) by a beam interruption unit (54), • in the event that the sensor unit (20) detects radiation with an intensity, power or energy below the threshold value, or no radiation: Focusing the laser beam (14) in the focusing unit (48) onto the focusing area (46) to generate EUV radiation.

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