Measuring device for adjusting the position of a laser beam

Abstract

The present invention relates to a measuring device (30), in particular to an optical device (10) for generating EUV radiation (12). The present invention further relates to the use of the measuring device (30) in an optical device (10) for generating EUV radiation (12). The measuring device (30) has at least two optical elements (36, 38), which separate a near-field beam path from a far-field beam path and image both the near-field plane and the far-field plane onto a target (34). In this case, the far-field beam path is preferably formed without reflection, and the near-field beam path is preferably formed by multiple reflections, in particular in only one of the optical elements (36, 38).

Description

Technical Field

[0001] Background of the Invention The present invention relates to an optical device for guiding a laser beam in a controlled state. The present invention further relates to the use of a measuring device.

[0002] In an EUV light source, a laser beam is generated by a seed laser and amplified by one or more amplifiers. The amplified laser beam is focused by a focusing unit onto a target that emits EUV radiation. However, the laser beam is reflected at the target and then passes through the amplifier chain and returns to the seed laser for the second time. In particular, when the amplifier in the laser active medium is still in a population inversion state, the reflected laser beam may be amplified in the path passing through the amplifier chain, and the optical system designed for a relatively low-power laser beam may be damaged. In order to block the laser beam traveling in the reflected reverse direction, an acousto-optic modulator (AOM) is used in particular. This acousto-optic modulator (AOM) guides the reflected beam to a beam trap and is switched to allow the laser beam traveling in the forward direction to pass through.

[0003] Ideally, the laser beam preferably exists as a Gaussian beam on the path from the seed laser to the target. However, since the acousto-optic modulator changes the beam shape of the laser beam, after passing through the acousto-optic modulator, the laser beam no longer exists as a Gaussian beam. Therefore, after passing through the acousto-optic modulator, the laser beam is guided through a spatial filter, and this spatial filter filters out the beam components that travel in the transverse direction with respect to the desired beam direction of the laser beam. After passing through the spatial filter, the laser beam becomes (approximately) Gaussian again. To avoid output loss, it is desirable that the main part of the laser beam be guided through the spatial filter. For this purpose, precise positioning of the laser beam is required, and in particular, adjustment of the direction and position of the laser beam before passing through the spatial filter. Such positioning can also be automatically performed, for example, by adjusting the deflection mirror. At the same time, based on the existence of a number of optical elements required to guide the laser beam in a controlled manner in the forward direction over a longer beam path, there is only a small structural space.

[0004] Prior Art The EUV light source described at the beginning is known to the applicant, but is not necessarily known to the public.

[0005] Problems to be Solved by the Invention In particular, accurately positioning the laser beam in the EUV light source described at the beginning is extremely laborious in practice or requires the use of a large measuring device. This problem generally relates to the optical devices that guide the laser beam passing through the acousto-optic modulator and the spatial filter.

[0006] Therefore, an object of the present invention is to enable accurate positioning of the laser beam passing through the acousto-optic modulator and the spatial filter.

[0007] Description of the Invention The above-mentioned problem is solved according to the invention by means of the device according to claim 1 and the use of the measuring device according to claim 14. Preferred developments are indicated in the respective dependent claims.

[0008] Accordingly, the problem of the present invention is solved by an optical device for guiding a laser beam, which has at least one acousto-optic modulator and at least one spatial filter arranged behind this acousto-optic modulator. The optical device further has a measuring device, in particular between the acousto-optic modulator and the spatial filter. The measuring device has at least one first optical element and a second optical element. The two optical elements together are configured to image the near-field plane and the far-field plane of the laser beam onto a target. For this purpose, at least one of the optical elements is configured to split the beam path of the laser beam into a near-field beam path and a far-field beam path, and both of these beam paths are oriented towards the target.

[0009] Thus, in order to guide the laser beam with as little output loss as possible through the spatial filter, the laser beam can be measured using the measuring device before passing through the spatial filter, and the position of the spatial filter can be adapted accordingly. In particular, the position and the pointing (direction) of the laser beam traveling in the forward direction in the measuring device can be determined and this information can be used during the position adjustment of the device.

[0010] The first optical element may be part of a first group of optical elements and / or the second optical element may be part of a second group of optical elements. By using a plurality of optical elements, the optical aberration can be significantly reduced.

[0011] In a further preferred embodiment of the device, the first optical element has a positive refractive power. Instead of or in addition to this, the second optical element may have a negative refractive power. Thereby, the measuring device can be configured particularly space-saving.

[0012] If the first optical element is formed in the form of a lens and / or if the second optical element is formed in the form of a lens, the measuring device can be formed particularly simply structurally.

[0013] The near-field beam path is preferably formed by the laser beam passing directly through the second optical element. The far-field beam path is preferably formed by the laser beam being reflected at least twice on the surface of the second optical element.

[0014] In order to hold the first optical element with at least substantially no reflection, the first optical element can preferably have an anti-reflection coating on two surfaces facing each other. The second optical element may not be coated or may be coated to have partial reflectivity.

[0015] The second optical element is preferably arranged between the target and the first optical element.

[0016] In order to facilitate the adjustment of the position of the laser beam, the target can be configured in the form of a camera, in particular in the form of a camera with a camera sensor.

[0017] More preferably, the device has a beam splitter that outputs a part of the laser beam, in particular a small part, to the measuring device. The beam splitter can be configured in the form of a semi-transparent mirror.

[0018] If the spatial filter is configured in the form of a pinhole aperture, the spatial filter can be realized particularly simply structurally.

[0019] The device can have a beam trap, and the acousto-optic modulator can guide the reflected laser beam to the beam trap.

[0020] In a particularly preferred configuration of the present invention, the device has a seed laser and / or at least one amplifier, in particular a plurality of amplifiers. One of the amplifiers can be a pre-amplifier arranged in front of the acousto-optic modulator with reference to the laser beam traveling in the forward direction. With such an arrangement, since the laser beam traveling in the reverse direction is prevented from reaching the pre-amplifier, the laser beam traveling in the reverse direction is not amplified further in the pre-amplifier and is incident on the acousto-optic modulator with a relatively small output.

[0021] The device can further be configured to generate EUV radiation. In this case, the device can have a target that can be irradiated by the laser beam, in particular a droplet-shaped target made of tin. The device can have a focusing unit that focuses the laser beam onto the target.

[0022] The present invention further relates to the use of a measuring device in a device for generating EUV radiation. The device A) a seed laser for generating a laser beam and at least one amplifier; B) a target that can be irradiated by the laser beam and generates EUV radiation; C) a spatial filter arranged in front of the target; D) an acousto-optic modulator arranged behind the amplifier and in front of the spatial filter and has. Here, the measuring device is used for measuring and positioning the laser beam. The measuring device has at least one first optical element and a second optical element. The two optical elements are both configured to image the near-field plane and the far-field plane of the laser beam onto the target. For this purpose, at least one of the optical elements divides the beam path of the laser beam into a near-field beam path and a far-field beam path, and both of these beam paths are configured to be oriented towards the target.

[0023] In particular, the position and pointing (direction) of the laser beam traveling in the forward direction in the measuring device are determined, and this information is used during the position adjustment of the device.

[0024] All the features described above for the device are also applicable when the measuring device is used.

[0025] Another advantage of the present invention is obtained from the description and the drawings. Similarly, the features described above and below can be used according to the present invention, either individually or in any plurality of combinations. Each of the illustrated and described embodiments is not to be understood as a restrictive listing, but rather has the character of an example for the description of the present invention.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

[0027] Detailed Description of the Invention and Drawings FIG. 1 shows an optical device 10 that generates EUV radiation 12 by irradiating a target 14 in the form of a tin droplet here with a laser beam 16 traveling in the forward direction. The laser beam 16 traveling in the forward direction is generated at a laser source 18 in the form of a seed laser and amplified at at least one amplifier 20. Preferably, a plurality of amplifiers 20 are provided.

[0028] The laser beam 16 traveling in the forward direction may be reflected at the target 14 and damage the laser source 18. In order to guide such a laser beam 22 traveling in the reverse direction generated by the reflection to the beam trap 24, an acousto-optic modulator 26 is provided. In this case, the laser beam 16 traveling in the forward direction is pulsed. Since the deflection angle of the acousto-optic modulator 26 has a time dependence in the case of the corresponding acoustic excitation, the pulses of the laser beam 16 traveling in the forward direction are temporally shifted with respect to the pulses of the laser beam 22 traveling in the reverse direction, and the pulses of the laser beam 22 traveling in the reverse direction receive a different deflection angle from the pulses of the laser beam 16 traveling in the forward direction.

[0029] However, the acousto-optic modulator 26 changes the beam shape of the laser beam 16 traveling in the forward direction. Therefore, a spatial filter 28 is provided, whereby the laser beam 16 traveling in the forward direction is limited to at least approximately Gaussian-shaped portions. The spatial filter 28 is preferably formed in the form of a pinhole aperture.

[0030] One or more amplifiers 20 can be arranged behind or in front of the acousto-optic modulator 26 with reference to the laser beam 16 traveling in the forward direction. In particular, one amplifier 20 can be arranged in front of the acousto-optic modulator 26, while another amplifier is arranged behind the acousto-optic modulator 26 and the spatial filter 28.

[0031] The laser beam 16 traveling in the forward direction can be optimally positioned with respect to the spatial filter 28 using the measuring device 30. In this case, a beam splitter 32 can be provided to guide a small portion of the laser beam 16 traveling in the forward direction to the measuring device 30. The beam splitter 32 is arranged between the acousto-optic modulator 26 and the spatial filter 28.

[0032] The measuring device 30 has, here, a target 34 in the form of a camera, a first optical element 36, and a second optical element 38. The second optical element 38 is arranged between the first optical element 36 and the target 34.

[0033] FIG. 2 shows a measuring device 30 comprising a first optical element 36, a second optical element 38, and a target 34. The first optical element 36 is preferably configured in the form of a transparent lens having a positive refractive power, and the second optical element 38 is preferably configured in the form of a transparent lens having a negative refractive power. The first optical element 36 can have an anti-reflection coating 40, and the second optical element 38 is preferably either not provided with an anti-reflection coating or is coated to have partial reflectivity.

[0034] The second optical element 38 has a first surface 42 and a second surface 44, and the first surface 42 is arranged behind the second surface 44 with reference to the laser beam 16 traveling in the forward direction. The second optical element 38 forms a near-field beam path 46 by the direct transmission of the laser beam 16 traveling in the forward direction. Further, the optical element 38 forms a far-field beam path 48 by reflection at the first surface 42 and the second surface 44.

[0035] The measuring device 30 has an optical axis 50. The optical axis 50 can extend centrally through the first optical element 36. The laser beam 16 traveling in the forward direction can be guided through the measuring device 30 in an offset state with respect to the optical axis 50. Instead of or in addition to this, the second optical element 38 is preferably arranged in an offset state or an inclined state with respect to the optical axis 50.

[0036] The measuring device 30 provides precise yet structurally simple and space-saving means for adjusting the position of the laser beam 16 traveling in the forward direction, particularly with respect to the spatial filter 28 and / or the acousto-optic modulator 26. In particular, due to the partially reflective surface, a plurality of images corresponding to different imaging planes passing through different optical paths are formed. Therefore, not only the beam position at the beam splitter 32 but also the angle of the laser beam 16 traveling in the forward direction (and thus the beam position at other locations) can be determined.

[0037] Viewed together, the two drawings summarize that, in particular, the present invention relates to an optical device 10 for generating EUV radiation 12 provided with a measuring device 30. The present invention further relates to the use of the measuring device 30 in the optical device 10 for generating EUV radiation 12. The measuring device 30 has at least two optical elements 36, 38, and these optical elements 36, 38 separate the near-field beam path 46 from the far-field beam path 48 and image both the near-field plane and the far-field plane onto the target 34. In this case, the far-field beam path 48 is preferably formed without reflection, and the near-field beam path is preferably formed by multiple reflections, particularly in only one of the optical elements 36, 38.

Explanation of Reference Numerals

[0038] 10 Optical device 12 EUV radiation 14 Target 16 Laser beam traveling in the forward direction 18 Laser source 20 Amplifier 22 Laser beam traveling in the reverse direction 24 Beam trap 26 Acousto-optic modulator 28 Spatial filter 30 Measuring device 32 Beam splitter 34 Target 36 First optical element 38 Second optical element 40 Anti-reflection coating 42 The first surface of the second optical element 38 44 The second surface of the second optical element 38 46 The near-field beam path of the laser beam 16 traveling in the forward direction 48 The far-field beam path of the laser beam 16 traveling in the forward direction 50 The optical axis of the measuring device 30

Claims

1. An optical device (10) for guiding a laser beam (16) in a controlled manner in a forward direction, comprising: a) an acousto-optic modulator (26) that transmits the laser beam (16) traveling in the forward direction and deflects the laser beam (22) traveling in the reverse direction; b) a spatial filter (28) for the laser beam (16) traveling in the forward direction, disposed behind the acousto-optic modulator (26) with respect to the laser beam (16) traveling in the forward direction; in the device (10), a measuring device (30) is disposed in front of the spatial filter (28) with respect to the laser beam (16) traveling in the forward direction; the measuring device (30) is configured to image the near-field plane and the far-field plane of the laser beam (16) traveling in the forward direction onto a common single target (34); the measuring device (30) has a first optical element (36) and a second optical element (38); one of the optical elements (36, 38) is arranged to split the beam path of the laser beam (16) traveling in the forward direction into a near-field beam path (46) and a far-field beam path (48) and to direct both of these beam paths towards the target (34). Device (10), characterized in that.

2. The device (10) has a first group of optical elements, and the first optical element (36) is part of the first group of optical elements, and / or The device has a second group of optical elements, and the second optical element (38) is part of the second group of optical elements. The device according to claim 1.

3. The first optical element (36) has a positive refractive power, and / or the second optical element (38) has a negative refractive power. The device according to claim 1 or 2.

4. The first optical element (36) and / or the second optical element (38) is formed in the form of a lens. The device according to any one of claims 1 to 3.

5. The second optical element (38) is light-transmissive, The near-field beam path (46) can be formed by the laser beam (16) traveling in the forward direction directly passing through the second optical element (38). The far-field beam path (48) can be formed by a first reflection at the first surface (42) of the second optical element (38) and a second reflection at the second surface (44) of the second optical element (38). The device according to any one of claims 1 to 4.

6. The first optical element (36) is provided with an antireflection coating and / or the second optical element (38) is uncoated or is coated to have partial reflectivity. The device according to any one of claims 1 to 5.

7. The second optical element (38) is arranged behind the first optical element (36) with reference to the laser beam (16) traveling in the forward direction. The device according to any one of claims 1 to 6.

8. The target (34) is configured in the form of a camera. The device according to any one of claims 1 to 7.

9. The device (10) has a beam splitter (32) that outputs a part of the laser beam (16) traveling in the forward direction to the measuring device (30). The device according to any one of claims 1 to 8.

10. The spatial filter (28) is formed in the form of a pinhole aperture. The device according to any one of claims 1 to 9.

11. The device (10) has a beam trap (24), and the acousto-optic modulator (26) is configured to deflect the laser beam (22) traveling in the reverse direction to the beam trap (24). The device according to any one of claims 1 to 10.

12. The device (10) has a seed laser and an amplifier (20) for generating the laser beam (16) traveling in the forward direction. The device according to any one of claims 1 to 11.

13. The device (10) has a target (14) for generating EUV radiation (12), and the target (14) can be irradiated by the laser beam (16) traveling in the forward direction. The device according to any one of claims 1 to 12.

14. Use of a measuring device (30) in a device (10) for generating EUV radiation (12), wherein the device (10) is A) A seed laser and an amplifier (20) that generate a laser beam (16) traveling in the forward direction; B) A target (14) that can be irradiated by the laser beam (16) traveling in the forward direction and generates the EUV radiation (12); C) A spatial filter (28) disposed in front of the target (14) with respect to the laser beam (16) traveling in the forward direction; D) An acousto-optic modulator (26) disposed behind the amplifier (20) and in front of the spatial filter (28) with respect to the laser beam (16) traveling in the forward direction, which transmits the laser beam (16) traveling in the forward direction and deflects the laser beam (22) traveling in the reverse direction; and has; The measuring device (30) is used to position the device (10) with respect to the spatial filter (28) with reference to the laser beam (16) traveling in the forward direction; The measuring device (30) is configured to image the near-field plane and the far-field plane of the laser beam (16) traveling in the forward direction onto a common target (34); The measuring device (30) has a first optical element (36) and a second optical element (38); One of the optical elements (36, 38) is arranged to split the beam path of the laser beam (16) traveling in the forward direction into a near-field beam path (46) and a far-field beam path (48) and orient both of these beam paths toward the target (34); Use.

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