Beam stop, EUV light source and method for operating EUV light source

Abstract

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

Description

Technical Field

[0001] The invention relates to a beam stop comprising: a stop opening for letting through a laser beam; and a sensor unit with which a misalignment of the laser beam can be detected. The invention also relates to an EUV light source having such a beam stop, and to a method for operating an EUV light source. Background Art

[0002] Beam stops with an opening for letting the laser beam through and a sensor unit are known. Such beam stops are used in EUV light sources to detect misalignment of the laser beam.

[0003] Such a device for monitoring the orientation of a laser beam is described, for example, in the applicant's WO2015172816A. In order to monitor the orientation of the laser beam relative to the opening, the device comprises: a detector having an opening for transmitting 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. At least two temperature sensors have a temperature-dependent resistance that increases with increasing temperature or a temperature-dependent resistance that decreases with increasing temperature, and at least two temperature sensors are connected to the temperature monitoring device in a series circuit. An EUV radiation generating device is also disclosed, which has at least one device for monitoring the orientation of a laser beam as described above.

[0004] It has been shown that when high laser powers and short pulse durations are used, such detectors may react too slowly, resulting in damage to the aperture.

[0005] The object of the present invention is to provide a beam stop, an EUV light source having such a beam stop and a method for operating such an EUV light source, with which the above-mentioned disadvantages are reduced, preferably avoided. Summary of the invention

[0006] This object is achieved by providing the present technical teaching, in particular the teaching of the independent claim and the preferred embodiments disclosed in the dependent claims and the description.

[0007] The beam stop according to the present invention comprises: an aperture opening for transmitting the laser beam; a deflection unit for deflecting a portion of the laser beam that is not guided through the aperture opening; a reflection unit for reflecting the deflected portion of the laser beam; and a sensor unit for detecting reflection of the deflected portion of the laser beam.

[0008] In the case of a correct orientation of the laser beam, i.e. in the target beam position, the laser beam completely penetrates the aperture opening of the beam stop. If the laser beam is not oriented, the part of the laser beam that does not penetrate the aperture opening impinges on the deflection unit and is thereby deflected onto the reflection unit. Therefore, the part of the laser beam impinging on the beam stop is not absorbed but deflected, so that in the case of an unoriented laser beam, the beam stop does not heat up. The deflected part of the laser beam is then reflected as a reflection at the reflection unit, so that it impinges on the sensor unit. The sensor unit detects the reflection of the deflected part of the laser beam. Thus, the orientation of the laser beam is monitored independently of the temperature of the beam stop. The misorientation of the laser beam is detected immediately, not only when the beam stop has reached a certain temperature, thereby avoiding a time delay between the misorientation and the detection of the misorientation of the laser beam. Since the beam stop does not heat up in the case of an unoriented laser beam, damages due to excessively high surface temperatures of the beam stop, such as local melting of the beam stop material, can be avoided. This local melting of the beam stop material usually produces smoke and metal vapors which can damage optical elements downstream in the beam path. If the misalignment of the laser beam is not detected in time, nearby personnel, such as an operator, may also be harmed.

[0009] According to one embodiment of the invention, the deflection unit has a deflection surface which is oriented transversely to the target beam position of the laser beam. The deflection surface is oriented in such a way that those parts of the unoriented laser beam which do not pass through the aperture opening are deflected to the reflection unit. In this way, the parts of the laser beam which impinge on the beam aperture are advantageously deflected away from the deflection unit, so that the beam aperture does not heat up.

[0010] At the target beam position, the laser beam strikes an optical element arranged along its beam path at a predetermined angle and at a predetermined position. If the laser beam is not directed, i.e. its beam position deviates from the target beam position, the laser beam may not strike an optical element in its beam path or may not strike an optical element at a predetermined position or at a predetermined angle - especially in the case of a long beam path of several meters. The beam axis of the undirected laser beam extends parallel to or obliquely to the beam axis of the laser beam passing through the beam stop at the target beam position. At the target beam position, the laser beam is directed such that no part of the laser beam impinges on the beam stop.

[0011] According to an embodiment of the invention, the deflection surface encloses an angle of 30° to 60° with the target beam position. If the beam axis of the undirected laser beam extends parallel to the beam axis of the laser beam in the target beam position, the portion of the laser beam that does not pass through the aperture opening is deflected by an angle of between 120° and 60° accordingly. If the beam axis of the undirected laser beam is tilted relative to the beam axis of the laser beam in the target beam position, the portion of the laser beam that does not pass through the aperture opening can be deflected by an even greater angle, depending on the orientation of the beam axis of the undirected laser beam.

[0012] An angle of 45° between the deflection surface and the target beam position has proven to be particularly advantageous. At this angle - when the beam axis of the laser beam in the target beam position and the beam axis of the undirected laser beam are parallel - the part of the laser beam that does not pass through the aperture opening is deflected by an angle of 90°. Since the deflection surface is arranged relative to the reflection unit in such a way that the deflected part of the laser beam impinges on the reflection unit, such an arrangement enables the reflection unit to be arranged on the beam aperture in a structurally simple manner.

[0013] According to an extension of the invention, the deflection unit delimits the aperture opening at least in sections. An arrangement in which the deflection unit delimits the aperture opening at least in sections in an annular manner has proven to be particularly advantageous. In the case where the deflection unit completely surrounds the aperture opening in an annular manner, the portion of the laser beam deflected by the deflection unit then forms a virtual intersection point in the center of the aperture opening. If the deflection unit delimits the aperture opening only in sections in an annular manner, the deflected portion of the laser beam forms a virtual intersection point in the center of an imaginary circle, wherein the annular portion extends along the circumference of the circle. In this case, the deflected portion of the laser beam forms a virtual intersection point at the imaginary center of the aperture opening.

[0014] According to an extension of the invention, the deflection unit is preferably configured as a conical ring reflector or an internally reflecting ring prism, or as a part of a conical ring reflector or an internally reflecting ring prism. The cutout of the conical ring prism or the internally reflecting ring prism can be designed in particular as an annular part, so that the conical ring reflector or the internally reflecting ring prism does not completely limit the aperture opening. Designing the deflection unit as a conical ring prism or a reflecting ring prism enables a particularly simple structural design of the beam aperture.

[0015] The conical ring reflector or the reflecting ring prism or their cutouts particularly have edges that are as sharp as possible. This ensures that the laser beam irradiated onto the edge of the conical ring reflector or the reflecting ring prism will not or will hardly be deflected in a direction not pointing toward the reflecting unit.

[0016] In order to prevent the laser beam from being deflected by the inner surface of the conical ring reflector or the reflecting ring prism in a direction not pointing to the reflecting unit, the inner surface can also be provided with an undercut. An undercut of up to 5° between the inner surface of the conical ring reflector or the reflecting ring prism and the target beam position has proven to be particularly effective.

[0017] The deflection unit can be made of optical glass, for example quartz glass, N-BK7, Zerodur or crystal (ZnSe, sapphire).

[0018] According to an extension of the invention, the reflection unit has a reflection surface on which the deflected part of the laser beam is reflected. The reflection surface is arranged so that the reflection of the deflected part of the laser beam is concentrated at 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 part of the laser beam on the sensor unit, only a small part of the mass heats up compared to a beam diaphragm that absorbs the incident laser radiation. Therefore, the beam diaphragm reacts faster and more sensitively to the misorientation of the laser beam than an absorbing beam diaphragm. This makes it possible to minimize the switching times and increase the safety of the entire device.

[0019] According to an extension of the invention, the reflective surface is shaped at least in sections as an ellipse. The reflective surface shaped at least in sections as an ellipse is assigned a first focus and a second focus, wherein the first focus is located at the sensor point. The second focus is located on the beam axis of the laser beam that passes through the aperture opening in the target beam position. In the case of a deflection unit of annular shape or annular shape in sections, the second focus is also located at the center or imaginary center of the aperture opening. The reflective surface shaped at least in sections as an ellipse reflects and focuses the reflection of the deflected part of the laser beam onto the sensor point. This utilizes the basic property of an elliptical reflector, according to which all beams whose origin is or appears to be at the first focus of the ellipse are imaged at the second focus. The ellipse below the reflective surface is designed so that the first focus is located at the virtual intersection of the deflected parts of the laser beam at the center or imaginary center of the aperture opening. The second focus is located at the sensor point, so that all deflected parts of the laser beam are focused on the sensor point. The advantage of this design of the beam aperture is that all deflected parts of the laser beam can be detected.

[0020] The reflective surface can be made of copper, in particular by milling. The laser beam is reflected on the copper surface at a wavelength of, for example, 10.6 μm, so that a beam stop with a reflective surface made of copper is particularly advantageous as a beam stop for transmitting a CO2 laser beam. Since the reflective surface is at least partially shaped in an elliptical shape, the optical imaging properties play a secondary role as long as the focusing function is ensured. Therefore, to produce the reflective surface, processes can be used that usually produce a surface with only minimal surface roughness, such as fine milling, polishing, laser cutting or wire cutting.

[0021] The reflective surface may be provided with a reflective coating, for example a gold or aluminum layer.

[0022] According to one embodiment of the invention, a cover unit is arranged on the beam stop so that the sensor unit is shielded from the direct part of the laser beam. The cover unit is arranged in front of the sensor unit, as seen in the beam propagation direction of the laser beam. Only those parts of the laser beam that impinge on the deflection unit and are thereby deflected to the reflection surface impinge on the sensor unit.

[0023] According to a further development of the invention, the cover unit has a particularly circular recess for transmitting the laser beam through the aperture opening. The deflection unit and the cover unit are arranged concentrically with respect 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, particularly on the inner surface facing the recess, in order to prevent the laser beam from being deflected in a direction not directed toward the reflector unit. The provision of the circular recess in the cover unit and the concentric arrangement of the deflection unit with the cover unit enable a particularly simple structural design of the beam aperture.

[0024] According to one embodiment of the invention, the sensor unit is designed as a temperature sensor, in particular a pyrometer or a resistance temperature sensor. The sensor unit can be glued or screwed into the absorbent-coated copper sleeve. The sensor unit can also be designed as an optical sensor, in particular a photodiode, a photovoltaic diode or a camera. Providing a commercially available sensor as the sensor unit allows a particularly cost-effective and simple design of the beam stop.

[0025] According to an embodiment of the invention, the beam diaphragm has at least two, preferably six, reflection units, each of which has the same first focal point, which is located on the beam axis of the laser beam passing through the diaphragm opening in the target beam position. The reflection units are arranged around the diaphragm opening. By providing several reflection units arranged around the diaphragm opening, it is not only possible to determine that the laser beam is misdirected, but also to detect the position of the misdirected laser beam relative to the target beam position and the shape and / or size of the laser beam passing through the diaphragm opening.

[0026] If the deflection unit completely delimits the aperture opening in an annular manner, for example in the form of a reflecting annular prism or a conical annular reflector, the portion of the laser beam that does not pass through the aperture opening is deflected by the deflection unit to one of the reflective units, regardless of the position of said portion relative to the aperture opening. Thus, a deviation of the beam position of the laser beam from the target beam position can be detected independently of the position of the undirected laser beam.

[0027] According to an embodiment of the invention, each reflector unit is assigned a sensor unit. The sensor unit is connected to at least one readout unit. In addition to the pure safety function, the individual evaluation of the respective sensor unit also enables the following analyses: beam position, beam size and / or beam shape, for example the ellipticity of the laser beam passing through the aperture opening.

[0028] The sensor unit can also be evaluated as a whole. For example, the sensor unit can be configured as a temperature sensor connected to a common water circuit. Changes in the water temperature in the water circuit are then detected, indicating a misorientation of the laser beam.

[0029] Alternatively, instead of individual sensor units, hydraulically series-connected water cooling webs can be provided. At a given flow rate, the temperature increase of the water passing through the water cooling web is proportional to the laser power absorbed by the water cooling web.

[0030] According to one embodiment of the invention, the reflective surfaces, which are ellipsoidal in shape at least in sections, 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 opening in the target beam position. This arrangement enables a simple, compact and cost-effective mechanical design of the beam aperture, while at the same time designing it to have only reflective optical elements in addition to the sensor.

[0031] If the beam stop has several reflective units, the reflective surfaces assigned to the reflective units can be produced from a single component, for example made of copper, in particular by milling. A concentrator produced in this way with a plurality of reflective surfaces shaped ellipsoidally at least in sections can be constructed in one piece.

[0032] The concentrator can also include several reflecting units. If the deflection unit is designed as an internally reflecting annular prism and the concentrator includes several reflecting units, this has the advantage that the corresponding sensor unit and the diaphragm opening can be mechanically separated from each other, so that the beam path of the laser can be sealed from the sensor unit. If the sensor unit is destroyed due to misorientation of the laser beam, contamination of the beam path is thus prevented.

[0033] The invention also relates to an EUV light source having: 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 in which a target material can be introduced into a focus region; a focusing unit for focusing the laser beam into the focus 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 orientation of the laser beam. This can prevent damage to the beam stop and / or other components arranged in the beam path of the laser beam.

[0034] It should be understood that the above-described beam stop can be advantageously used not only for EUV light sources but also for laser processing machines and the like, especially when a high-power pulsed laser beam is used.

[0035] The invention also relates to a method for operating such an EUV light source, comprising the following steps:

[0036] ● Generate a laser beam in a seed laser,

[0037] ● Amplifies laser beams in driver laser devices,

[0038] ● The laser beam is passed through the beam stop.

[0039] ● In the event that the sensor unit detects radiation with an intensity, power or energy above the threshold:

[0040] switching off the seed laser and / or the driver laser device and / or interrupting the laser beam by means of a beam interruption unit,

[0041] ● In the event that the sensor unit detects radiation with an intensity, power or energy below the threshold or detects no radiation:

[0042] The laser beam is focused onto a focus area in a focusing unit to generate EUV radiation.

[0043] In order 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 a threshold value. The laser beam can be interrupted by a beam interruption unit, such as a shutter, so that components downstream of the beam stop in the beam path are not damaged in the case of non-orientation of the laser beam. Alternatively or additionally, if the sensor unit detects radiation with an intensity, power or energy above a threshold value, in order to prevent further damage in the beam path of the laser beam, 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 below a threshold value or no radiation is detected, the laser beam in the focusing unit is focused on a focusing area. In the focusing area, the laser beam is focused on a target material, such as a tin droplet. The target material then emits EUV radiation due to the irradiation of the laser beam.

[0044] Further advantages of the invention are derived from the description and the drawings. Likewise, the features mentioned above and those yet to be presented can be used alone or in any desired combination in each case. The embodiments shown and described should not be understood as an exhaustive enumeration, but rather as exemplary characteristics for describing the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In the attached picture:

[0046] Figure 1 shows an embodiment of a beam stop,

[0047] Figure 2 A diagram showing the geometry of the beam stop,

[0048] Figure 3a , Figure 3b , Figure 3c and Figure 3d shows a beam stop with different beam positions, beam sizes and beam shapes of the laser beam,

[0049] Figure 4 Another embodiment of the beam stop is shown,

[0050] Figure 5 An EUV light source with a beam stop is shown. DETAILED DESCRIPTION

[0051] Figure 1 The beam stop 10 is shown, which has an aperture opening 12, a deflection unit 16, six reflection units 18, six sensor units 20 and a cover unit 32 with a circular recess 34. The beam stop 10 can have any number of reflection units 18 grouped around the aperture opening 12. The deflection unit 16 is arranged in a Figure 1The deflection unit 16 can also be configured as another reflective optical element, such as an internally reflecting annular prism. The conical annular reflector has a deflection surface 22. An undercut of up to 5° can be provided on its inner side 17, which is Figure 1 The reflective units 18 each comprise a reflective surface 28 which is shaped ellipsoidally in sections, wherein a sensor unit 20 is associated with each reflective surface 28 .

[0052] The deflection unit 16 is mounted on a cover plate 33, on which the sensor unit 20 and the reflection unit 18 are mounted. The circular recess 34 of the cover unit 32 is arranged concentrically with the aperture opening 12, so that the sensor unit 20 and the reflection surface 28 are covered by the cover unit 32. Only the deflection unit 16 is visible to the laser beam 14, as shown in FIG. Figure 1 As shown, the laser beam is transmitted through the beam stop 10 from the side facing the cover unit 32. The sensor units 20 are each arranged in a sensor point 30, which is located between the corresponding reflection surface 28 and the deflection unit 16.

[0053] The sensor unit 20 is designed, for example, as a thermocouple which is glued or screwed onto the cover plate 33 , for example as an absorbent-coated copper sleeve.

[0054] The sensor units 20 are each connected in terms of signals to a readout unit 36. The readout unit 36 ​​is designed to evaluate the signals transmitted by the respective sensor units 20 in order to determine at which sensor unit 20 radiation was detected.

[0055] It is also possible to provide a plurality of readout units 36. Each sensor unit 20 is then connected to a corresponding readout unit 36. The readout units then transmit the received signals to the central control unit.

[0056] 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 then in turn connected to the readout unit 36. In this case, the readout unit 36 ​​or a control unit connected to the readout unit 36 ​​evaluates the signals of the sensor units 20 as a whole. In this case, the beam position, the beam shape and the beam size of the laser beam 14 relative to the target beam position cannot be determined. However, it can be determined whether the beam position of the laser beam 14 deviates from the target beam position. If this is the case, the beam position of the laser beam deviates from the target beam position, 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 unit 20 is above a threshold value.

[0057] The reflective surface 28 is formed on the concentrator 29, which is formed as a milled part made of copper, for example. The reflective surface 28, which is shaped as an ellipse in sections, is processed to have a high degree of reflection. Sufficient surface roughness can be achieved by processing such as fine milling, polishing, wire cutting or laser cutting, because these surfaces do not have to be perfect mirror surfaces due to their ellipse.

[0058] The laser beam 14 is ideally oriented to a target beam position. In this beam position, the laser beam 14 passes through the aperture opening 12 of the beam stop 10 without any part of the laser beam 14 impinging on the beam stop 10. The beam axis of the laser beam 14 in the target beam position extends at an angle of 90° relative to the plane in which the cover unit 32 and / or the cover plate 33 are arranged.

[0059] If the laser beam 14 is not directional, its beam axis is offset from the beam axis of the target beam position and / or extends at a certain angle relative to the beam axis of the laser beam 14 in the target beam position. In this case, parts of the laser beam 14 can impinge on the deflection unit 16 and thereby be deflected onto one or more of the reflection units 18.

[0060] Even if the diameter of the cross section of the laser beam 14 is greater than the diameter of the aperture opening 12 or the laser beam 14 has an elliptical shape, parts of the laser beam 14 may impinge on the deflection surface 16 and thereby be deflected onto one or more reflection units 18. The reflection surface 28 of the reflection unit 18 reflects the reflection 21 of the deflected part of the laser beam 14 onto the corresponding sensor unit 20. Finally, the sensor unit 20 detects the energy, power or intensity of the reflection 21 and sends the detected measured values ​​to one or more readout units 36.

[0061] The geometrical conditions of the beam stop 10 are as follows: Figure 2As shown. The reflection surfaces 28 each extend along a partial segment of the circumference of the imaginary ellipse 11. The first focus 31 of each ellipse 11 is located between the reflection surface 28 assigned to the ellipse 11 and the deflection unit 16, while the second focus 37 is located in the center of the annular aperture opening 12. Those parts of the laser beam 14 that do not pass through the aperture opening 12 impinge on the deflection unit 16 and are thereby deflected as reflections 21 at an angle of 90° onto the reflection surface 28. The reflection surface 28 concentrates the reflections 21 onto the first focus 31 of the imaginary ellipse, which coincides with the sensor point 30 in which the sensor unit 20 is arranged. If the part of the laser beam 14 deflected by the deflection unit 16 extends in the direction opposite to its propagation, it forms a virtual intersection point that coincides with the second focus 37 of the imaginary ellipse 11 and the center of the aperture opening 12. This utilizes the basic property of an elliptical reflector, according to which radiation coming from or appearing to come from one of the focal points is always reflected to the other focal point. The imaginary ellipse 11 along which the reflection surface 28 extends is designed such that the portion of the laser beam 14 which does not pass through the aperture opening 12 and thus impinges on the deflection unit 16 is concentrated onto the sensor point 30 and thus onto the sensor unit 20 .

[0062] Figure 3a , Figure 3b , Figure 3c and Figure 3d The beam stop 10 is shown in different application cases.

[0063] exist Figure 3a and Figure 3b In this case, the laser beam is directed in an off-center manner, with the beam axis offset from the target beam position. Figure 3a The sensor unit 20c, 20d or Figure 3b In response to the 20a, 20b of the undirected laser beam 14, the part of the laser beam 14 deflected by the steering unit 16 is reflected to the sensor unit. The corresponding sensor unit 20c, 20d and 20a, 20b detects the power, energy or intensity of the incident radiation and forwards it to the readout unit 36. In this way, it can be determined which sensor unit of the sensor units 20a to 20f detected the radiation. Thereby, the position of the beam axis of the undirected laser beam 14 relative to the target beam position can be determined.

[0064] Figure 3c A laser beam 14 is shown, the cross section of which is larger than the cross section of the target beam. If this laser beam 14 is caused to pass through the aperture opening 12, all sensor units 20a to 20f respond.

[0065] at last, Figure 3dThe laser beam 14 is shown, the cross section of which is shaped as an ellipse. If the laser beam 14 is allowed to pass through the aperture opening 12, the relative sensor unit - Figure 3d In the illustrated case, sensor units 20a and 20d respond.

[0066] exist Figures 3a to 3d In FIG. 1 , for reasons of clarity, the beam stop 10 is shown without the cover unit 32 .

[0067] Figure 4 An embodiment of a beam stop 10 is shown in which the concentrator 29 consists of multiple parts. Figure 4 In the embodiment, the deflection unit 16 is designed as an internally reflecting annular prism. The individual parts of the concentrator 29 are sealed to the aperture opening 12 via the connecting piece 23, so that if the sensor unit 20 is damaged or destroyed, the optical elements arranged in the beam path of the laser beam 14 are not damaged.

[0068] Figure 5 An EUV light source 39 is shown, which has a seed laser 38, a driver laser device 40, a vacuum chamber 42, a beam guide 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 guide 52 to the focusing unit 48, where it is focused on a focal region 46. A target material 47 can be introduced into the focal region 46, which emits radiation, in particular EUV radiation, due to the irradiation of the laser beam 14. Figure 5 In the embodiment, the beam stop 10 is arranged in the beam guiding device 52. It should be understood that the beam stop 10 can also be arranged in another part of the EUV light source, for example, between the two amplifiers 41a, 41b of the driver laser device 40 or between the seed laser 38 and the driver laser device 40.

[0069] If during operation of the EUV light source 39 one or more of the sensor units 20 detects a measured value above a threshold value, the readout unit 36 ​​or a control unit 44 connected to the readout unit 36 ​​sends a 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 the beam interruption unit 54. In this way, the beam path of the laser beam is protected from the influence of a misdirection of the laser beam 14.

Claims

1. A beam stop (10), comprising: an aperture opening (12) for allowing the laser beam (14) to pass through, a deflection unit (16) for deflecting the portion of the laser beam (14) that does not pass through the aperture opening (12), A reflection unit (18) for reflecting the deflected portion of the laser beam (14), and a sensor unit (20) for detecting a reflection (21) of the deflected portion of the laser beam (14).

2. The beam stop (10) according to claim 1, characterized in that The deflection unit (16) has a deflection surface (22) which is oriented transversely to a target beam position of the laser beam (14) so ​​that a portion of the laser beam (14) impinging on the deflection unit (16) can be deflected onto the reflection unit (18).

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

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

5. The beam stop (10) according to any one of the preceding claims, characterized in that The deflection unit (16) is constructed as a conical ring reflector or as an internally reflecting ring prism.

6. The beam stop (10) according to any 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 part of the laser beam (14) can be concentrated at 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) assigned to the sensor point (30).

7. The beam stop (10) according to any one of the preceding claims, characterized in that The reflection surface (28) is shaped at least in sections as an ellipse, wherein a first focus (31) of the reflection surface (28) is located on the sensor point (30) and a second focus (37) of the reflection surface (28) is located on the beam axis of a laser beam (14) that passes through the aperture opening (12) in the target beam position.

8. The beam stop (10) according to any one of the preceding claims, characterized in that A cover unit (32) is arranged in front of the sensor unit (20) as viewed in the beam propagation direction of the laser beam (14), so that the sensor unit (20) is shielded from the direct part of the laser beam (14).

9. The beam stop (1) according to claim 8, characterized in that The cover unit (32) has a particularly circular recess (34) for transmitting the laser beam (14), and the deflection unit (16) and the cover unit (32) are arranged concentrically with respect 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. The beam stop (1) according to any one of the preceding claims, characterized in that The sensor unit (20) is designed as a temperature sensor, in particular a pyrometer, or as an optical sensor, in particular a photodiode or a camera.

11. The beam stop (10) according to any one of claims 7 to 10, characterized in that The beam diaphragm (10) has at least two, preferably six, reflector units (18), each of which has an identical second focal point (37) which is located on the beam axis of a laser beam (14) which passes through the diaphragm opening (12) in the target beam position.

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

13. The beam stop (10) according to claim 11 or 12, characterized in that The reflection surfaces (28) which are elliptically shaped at least in sections each have a vertex (35), wherein the vertices (35) are each arranged on an imaginary circular line, in particular rotationally symmetrically around a beam axis of a laser beam (14) which passes through the aperture opening (12) in the target beam position.

14. An EUV light source (39) comprising: The beam stop (10) according to any 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) in which a target material (47) can be introduced into the focal region (46), a focusing unit (48) for focusing the laser beam (14) into the focusing region (46) to generate EUV radiation, and A beam guiding device (52) is used to guide the laser beam (14) to the focusing unit (48).

15. A method 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), allowing the laser beam (14) to pass through the beam stop (10), In the event that the sensor unit (20) detects radiation with an intensity, power or energy above a threshold value: the seed laser (38) is switched off, and / or the driver laser device (40) is switched off, and / or the laser beam (14) is interrupted by a beam interruption unit (54), In case the sensor unit (20) detects radiation having an intensity, power or energy below the threshold value or detects no radiation: focusing the laser beam (14) onto the focus area (46) in the focusing unit (48) to generate EUV radiation.

Images