EUV radiation generation after laser beam rotation

Abstract

The invention relates to a device (10) and a method (12) for generating EUV radiation (14) by irradiating a target material (15) with at least one laser beam (18). The at least one laser beam (18) is shaped by a beam shaping device (20) having a focusing unit (22). A beam rotator (28) is arranged in front of the focusing unit (22) in order to compensate for different image field rotations of different types of beam shaping devices (20). Thus, the same optical component can be located upstream of the various beam shaping devices (20), in particular upstream of the beam rotator (28).

Description

Technical Field

[0001] The invention relates to a device for generating EUV radiation. The device has an optical beam shaping device with a focusing unit for shaping the laser beam. In addition, the device has a target material, in particular in the form of tin droplets, which can be irradiated with the laser beam to emit EUV radiation. The invention also relates to a method for generating EUV radiation using such a device. Background Art

[0002] The general apparatus and the general method are known to the applicant, but they are not necessarily common general knowledge.

[0003] In this respect, it is known that the applicant uses an optical beam shaping device with a focusing unit in which the laser beam is focused onto the target material. The focusing unit has optical elements which are arranged in particular in a vacuum chamber and are suitable for focusing the laser beam onto the target material. Here, the focal position of the laser beam must be adjustable in order to, among other things, adjust the focal position to the position of the target material and thus achieve the maximum possible EUV power. Here, the lateral focal position of the laser beam is adjusted outside the beam shaping device by tilting and / or shifting the laser beam entering the beam shaping device. By adjusting the divergence of the laser beam, the focal position of the laser beam in the beam direction is also controlled outside the beam shaping device. The beam shaping device has one or more optical elements by means of which the laser beam is deflected and / or shaped, i.e. the laser beam entering the beam shaping device and the laser beam focused onto the target material are not colinear with each other. This beam deflection by means of one or more optical elements produces an image field rotation, i.e., a horizontal tilting of the input beam entering the beam shaping device, for example, does not result in a horizontal shift of the focal position, but, for example, in a shift along an axis rotated relative to the horizontal. In order to be able to adjust the focus position, the input and output behavior of the laser beams and thus the image field rotation must be known so that a corresponding transfer function can be defined in the control system. For example, if a movement of the focus, for example along the horizontal axis, is then desired, the control system must issue commands to tilt the laser beam entering the beam shaping device, for example, in two axes. In beam shaping devices in which multiple laser beams, for example a pre-pulse laser beam and a main pulse laser beam or two pre-pulse laser beams and a main pulse laser beam, are focused onto a target material, sometimes the same beam path is provided for the different laser beams, i.e. the laser beams are guided to the target material via the same optical elements within the beam shaping device. This is particularly the case when the laser beams have the same wavelength. In this case, an angular offset is provided between the laser beams, which can be, for example, two pre-pulse laser beams with the same wavelength, which results in a defined local offset between the two laser beams in the focal plane of the focusing unit of the beam shaping device. This angular offset must also be adjusted by the optical elements upstream of the beam shaping device. Therefore, the orientation of the local offset between the two laser beams in the focal plane of the focusing unit also depends on the image field rotation.

[0004] The arrangement and type of optical elements in the beam shaping device differs depending on the type of beam shaping device. Different types of beam shaping devices usually differ in the orientation of the laser beam focused by the focusing unit of the beam shaping device with respect to the orientation of the input beam entering the beam shaping device. Therefore, each type of beam shaping device requires a different control system or other optical elements upstream of the beam shaping device in order to be able to focus the laser beam in the same way. Furthermore, it is more difficult to replace a beam shaping device with another type of beam shaping device having a different input behavior and output behavior. Summary of the invention

[0005] Therefore, the object of the present invention is to further develop a universal device so that the same control system of the beam shaping device can be used for different types of beam shaping devices and to facilitate the replacement of the beam shaping device with another type of beam shaping device. In addition, the object of the present invention is to provide a method for operating such a device.

[0006] This object is achieved according to the invention by a device according to claim 1 and a method according to claim 11. The dependent claims present preferred developments.

[0007] The object according to the invention is therefore achieved by the device mentioned in the introduction, wherein the beam shaping device has a beam rotator for rotating the image field of the laser beam.

[0008] The beam rotator allows a simplified control system and an easy replacement of the type of beam shaping device. When replacing the beam shaping device, it is not necessary to intervene in the control system of the beam shaping device, in particular it is not necessary to adjust the transfer function defined in the control system of the beam shaping device. Furthermore, adjustment of optics upstream of the beam shaping device is avoided.

[0009] The beam shaping device preferably has a plurality of optical elements which can deflect and shape the laser beam multiple times.

[0010] For example, the beam rotator can be designed as transmissive and have a dove prism. However, if a high-power laser beam is used, this can lead to severe heating of the beam rotator and thus damage to the beam rotator. Therefore, the beam rotator is preferably designed as reflective and has at least one mirror, in particular a plurality of mirrors, for guiding the laser beam.

[0011] The beam rotator preferably has an odd number of mirrors for directing the laser beam.

[0012] Particularly preferably, the beam rotator has three mirrors or five mirrors for guiding the laser beam. When three mirrors are used, the design of the beam rotator is simplified in terms of construction, while when five mirrors are used, flat angles of incidence of the laser beam on the mirrors can be avoided. In this respect, in the reference position of the beam rotator, the laser beam is preferably reflected in the beam rotator in such a way that the laser beam entering the beam rotator is collinear with the laser beam leaving the beam rotator. If the beam rotator is now rotated by a given angle about the common beam axis of the incoming and outgoing laser beam, the outgoing laser beam is rotated by twice the angle.

[0013] If the beam rotator is arranged in a section of the beam path of the beam shaping device in which the laser beam is collimated, the construction design and the control system of the beam shaping device are further simplified.

[0014] The beam shaping device can be configured for guiding one laser beam and / or multiple laser beams. In particular, the beam shaping device can be configured for guiding one or more pre-pulse laser beams and a main pulse laser beam so that the target material is continuously irradiated by the one or more pre-pulses before being irradiated by the main pulse. If two or more laser beams with the same or similar wavelength (for example, two pre-pulse laser beams with the same or similar wavelength) are directed to the target material, these laser beams pass through the same optical element within the beam shaping device. A defined local offset in the focal plane of the focusing unit of the beam shaping device is required between these laser beams in order to irradiate the target material at the intended position respectively. The local offset is caused by an angular offset between the laser beams, which is arranged in an optical element upstream of the beam shaping device. The orientation of the local offset between the laser beams depends on the image field rotation in the beam shaping device. Therefore, a beam shaping device in which two or more laser beams are directed to the target material via the same optical element and has a beam shaping device suitable for adjusting the orientation of the laser beams relative to each other in a defined manner is particularly advantageous, because the same control system can be used for different types of such beam shaping devices.

[0015] In this respect, the beam shaping device can have a beam combiner arranged in front of the beam rotator. A beam combiner arranged upstream of the beam rotator can also be arranged in front of the beam shaping device. Laser beams with similar or identical wavelengths can be combined at this beam combiner and guided to the target material via the same optical element. This significantly simplifies the construction design of the device.

[0016] The beam combiner can be constructed in the form of a dichroic mirror.

[0017] In a particularly preferred embodiment of the invention, the device has a vacuum chamber in which the target material can be irradiated. In this respect, it is further preferred that the optical elements of the focusing unit are arranged inside the vacuum chamber and the beam rotator is arranged outside the vacuum chamber in order to optimally utilize the installation space available in the vacuum chamber.

[0018] The object according to the invention is also achieved by a method for generating EUV radiation using a device as described herein. In this respect, the method comprises at least: guiding at least one laser beam through a beam shaping device, in particular through a beam rotator and a focusing unit; and irradiating a target material and generating EUV radiation.

[0019] Features and advantages described with respect to the device also apply to the method, and vice versa.

[0020] At least one laser beam used is preferably pulsed. This is particularly advantageous when the target material is provided as droplets, for example tin droplets. In this case, the frequency at which the laser beam strikes the droplets corresponds to the frequency at which the droplets are emitted from the droplet source.

[0021] The focus position of the at least one laser beam used on the target material in the beam direction is preferably adjusted by adjusting the divergence of the laser beam external to the beam shaping device. This further simplifies the control system of the beam shaping device.

[0022] Multiple laser beams can be directed through a beam shaping device for irradiating a target material. The target material can be irradiated successively with one or more pre-pulse laser beams and then with a main pulse laser beam. In this regard, the focus position of the pre-pulse laser beams can be adjusted outside the beam shaping device, and the focus position of the main pulse laser beam can be adjusted inside the beam shaping device. In this regard, an actuated mirror can be used to adjust the focus position of the main pulse laser beam.

[0023] Further advantages of the present invention are derived from the description and the drawings. Similarly, the features mentioned above and the features still to be described can each be used alone or together in any desired combination according to the present invention. The embodiments shown and described should not be understood as an exhaustive list, but should be understood as having exemplary properties for describing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The device according to the invention and the method according to the invention for generating EUV radiation are schematically shown, wherein the laser beam passes through a beam rotator.

[0025] Figure 2 The image field rotation achieved by means of a beam rotator is schematically shown.

[0026] Figure 3 A beam rotator with three mirrors is shown schematically.

[0027] Figure 4 Another embodiment of a beam rotator with five mirrors is schematically shown. DETAILED DESCRIPTION

[0028] Figure 1An apparatus 10 and a method 12 for generating EUV radiation 14 on a target material 16, here shown in the form of a plurality of droplets, in particular in the form of tin droplets, are shown. In this respect, the target material 16 is irradiated by at least one laser beam 18, which passes through a beam shaping device 20 having a focusing unit 22. The focusing unit 22 has a plurality of optical elements arranged in a vacuum chamber 26. The target material 16 dispensed by the target material dispenser 24 and the optical elements of the focusing unit 22 are preferably located in the vacuum chamber 26 of the apparatus 10.

[0029] The lateral (X / Y) focal position of the laser beam 18 is adjusted external to the beam shaping device 20 by tilting and / or shifting the laser beam 18 entering the beam shaping device 20; the focal position of the laser beam 18 in the beam direction (Z) is also controlled external to the beam shaping device 20 by adjusting the divergence of the laser beam 18 entering the beam shaping device 20. The beam shaping device 20 has a plurality of optical elements that cause an image field rotation of the laser beam 18. For example, a horizontal tilt of the laser beam 18 does not result in a horizontal shift of the focal point, but rather a shift along an axis of rotation relative to the horizontal. Since the focal position is controlled external to the beam shaping device 20, the input / output behavior of the beam path internal to the beam shaping device 20 must be well known.

[0030] In this regard, the beam shaping device 20 can be constructed as a modular assembly that can be easily installed in the device 10 and removed from the device. Figure 1 In an embodiment of the invention, the beam shaping device 20 comprises lenses 31 and 32 as downstream optical elements. The input laser beam entering the beam shaping device 20 is formed by the laser beam 18, which has passed through the two lenses 31, 32 and has not yet passed through the first deflection optical element 33. It should be understood that different arrangements of the optical elements are also possible.

[0031] Different focusing unit types may have different image field rotations. In order to be able to use the same upstream beam shaping and control system for different types of beam shaping devices 20, the image field rotation of the respective type of beam shaping device 20 has to be taken into account in the transfer function of the control system, which means that the same control system cannot be used for different types of beam shaping devices 20. On the other hand, according to the invention, a beam rotator 28 is provided, which enables different image field rotations of different types of beam shaping devices 20 to be adjusted. This enables the same control system to be used for different types of beam shaping devices 20.

[0032] Figure 2 It is shown that when the beam rotator 28 (see Figure 1 ) is an example of a rotation of 45° when the image field plane (shown below) is rotated 22.5°.

[0033] Figure 3 An embodiment of a beam rotator 28 having three mirrors 30a, 30b, 30c is shown.

[0034] Figure 4 An alternative embodiment of a beam rotator 28 with five mirrors 30a, 30b, 30c, 30d, 30e is shown, wherein flat angles of incidence on the mirrors 30a to 30e are avoided.

[0035] In an overview of all the figures of the drawings, the invention generally relates to an apparatus 10 and a method 12 for generating EUV radiation 14 by irradiating a target material 16 with at least one laser beam 18. The at least one laser beam 18 is shaped by a beam shaping device 20 having a focusing unit 22. A beam rotator 28 is arranged upstream of the focusing unit 22 so that different image field rotations of different types of beam shaping devices 20 can be compensated. Thus, the same optical components can be located upstream of different types of beam shaping devices 20, in particular upstream of the beam rotator 28.

[0036] Reference numerals list

[0037] 10. Equipment

[0038] 12 Methods

[0039] 14 EUV Radiation

[0040] 16 Target material

[0041] 18 Laser Beam

[0042] 20 Beam shaping device

[0043] 22 Focusing Unit

[0044] 24 Target material dispenser

[0045] 26 Vacuum chamber

[0046] 28 Beam Rotator

[0047] Mirror 30a to 30e

[0048] 31 Lens

[0049] 32 Lens

[0050] 33. First deflection optical element

Claims

1. A device (10) for generating EUV radiation (14), wherein: The device (10) has the following: a) an optical beam shaping device (20) having a focusing unit (22) for shaping the laser beam (18); b) a target material (16) which can be irradiated by means of the laser beam (18) to emit EUV radiation (14); The invention is characterized in that the beam shaping device (20) has a beam rotator (28) for rotating the image field of the laser beam (18).

2. The device according to claim 1, wherein The beam shaping device (20) has one or more optical elements, by means of which the laser beam (18) is deflected and / or shaped multiple times.

3. The device according to any one of the preceding claims, wherein: The beam path of the beam rotator (28) is constructed in a reflective manner by a plurality of mirrors (30a to 30e).

4. The device according to claim 3, wherein: The beam rotator (28) has an odd number of mirrors (30a to 30e) in the beam path.

5. The device according to claim 4, wherein: The beam rotator (28) has three mirrors (30a to 30e) or five mirrors (30a to 30e) in the beam path.

6. Apparatus according to any one of the preceding claims, wherein: The beam rotator (28) is arranged in the section of the beam path of the beam shaping device (20) in which the laser beam (18) is collimated.

7. Apparatus according to any one of the preceding claims, wherein: The beam shaping device (20) is configured to direct a plurality of laser beams (18).

8. The device according to claim 7, wherein: The device (10) has a beam combiner arranged in front of the beam rotator (28).

9. The device according to claim 8, wherein: The beam combiner is designed in the form of a dichroic mirror.

10. Apparatus according to any one of the preceding claims, wherein: The device (10) has a vacuum chamber (26) in which the target material (16) can be irradiated, wherein the focusing unit (22) is arranged inside the vacuum chamber (26) and the beam rotator (28) is arranged outside the vacuum chamber (26).

11. A method (12) for generating EUV radiation (14) with a device (10) according to any one of the preceding claims, wherein: The method (12) comprises the following method steps: A) directing the laser beam (18) through the beam shaping device (20), wherein the laser beam (18) passes through the beam rotator (28) and the focusing unit (22); B) irradiating the target material (16) and generating EUV radiation (14).

12. The method according to claim 11, wherein: The laser beam (18) is pulsed.

13. The method according to claim 11 or 12, wherein: The focal position of the laser beam (18) on the target material (16) is adjusted by adjusting the divergence of the laser beam (18).

14. The method according to any one of claims 11 to 14, wherein: A plurality of laser beams (18) are directed through the beam shaping device (20) to irradiate the target material (16).

15. The method according to claim 12 in combination with claim 14, wherein: The plurality of laser beams (18) used are each pulsed.

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