EUV radiation generation following laser beam rotation

Abstract

The invention relates to a device (10) and to a method (12) for generating EUV radiation (14) by irradiating target material (15) with at least one laser beam (18). The at least one laser beam (18) is formed by a beam-forming arrangement (20) which has a focusing unit (22). Arranged upstream of the focusing unit (22) is a beam rotator (28) in order for it to be possible to compensate for different image field rotations of different types of beam-forming arrangements (20). As a result, identical optical components can be located upstream of types of beam-forming arrangements (20), in particular upstream of the beam rotator (28).

Description

[0001] EUV radiation generation after laser beam rotation

[0002] Background of the invention

[0003] The invention relates to a device for generating EUV radiation. The device comprises an optical beam-shaping arrangement with a focusing unit for shaping a laser beam. Furthermore, the device comprises a target material, particularly in the form of a tin droplet, that can be irradiated with the laser beam for emitting EUV radiation. The invention further relates to a method for generating EUV radiation using such a device.

[0004] The generic device and the generic method are known to the applicant, but have not necessarily become public knowledge. The applicant is aware of the use of an optical beam shaping arrangement with a focusing unit in which a laser beam is focused onto a target material. The focusing unit has optical elements which are arranged in particular in a vacuum chamber and which are suitable for focusing the laser beam onto the target material. The focus position of the laser beam must be adjustable in order to, for example, match the focus position to the position of the target material and thus, among other things, achieve the maximum possible EUV power. The lateral focus position of the laser beam is adjusted outside the beam shaping arrangement by tilting and / or shifting a laser beam incident on the beam shaping arrangement.The focus position in the beam direction of the laser beam is controlled by adjusting the divergence of the laser beam, also outside the beam-shaping arrangement. The beam-shaping arrangement has one or more optical elements by which the laser beam is deflected and / or shaped, i.e., a laser beam incident on the beam-shaping arrangement and a laser beam focused on the target material are not collinear with each other. Such beam deflection via one or more optical elements produces an image field rotation, i.e., for example, a horizontal tilt of the input beam incident on the beam-shaping arrangement does not lead to a horizontal shift of the focus position, but rather, for example, to 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 beam and thus the image field rotation must be known so that a corresponding transfer function can be stored in the control system. If, for example, a shift in the focus is desired, e.g. along the horizontal axis, the control system must issue the command to tilt the laser beam incident on the beam shaping arrangement accordingly, for example around two axes. In beam shaping arrangements in which several laser beams, e.g. 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 on the target material, the same beam path is sometimes provided for different laser beams, i.e. the laser beams are guided to the target material via the same optical elements within the beam shaping arrangement. This is particularly the case when these laser beams have the same wavelength.In this case, an angular offset is provided between the laser beams, which could be, for example, two pre-pulse laser beams of the same wavelength. This angular offset results in a defined local offset between the two laser beams in a focusing plane of the focusing unit of the beam-shaping arrangement. This angular offset must also be adjusted by optical elements located upstream of the beam-shaping arrangement. The orientation of the local offset between the two laser beams in the focusing plane of the focusing unit is therefore also dependent on the image field rotation.

[0005] The arrangement and type of optical elements in the beam-shaping assembly vary depending on the type of beam-shaping assembly. Different types of beam-shaping assemblies typically differ in the orientation of the laser beam focused by the focusing unit of the beam-shaping assembly relative to the orientation of the input beam into the beam-shaping assembly. Therefore, each type of beam-shaping assembly requires a different controller or different optical elements upstream of the beam-shaping assembly to focus the laser beam in the same way. Furthermore, replacing the beam-shaping assembly with another type of beam-shaping assembly with different input and output behavior is complicated.

[0006] Object of the invention

[0007] It is therefore an object of the invention to further develop the generic device in such a way that the same control of the beam-shaping arrangement can be used for different types of beam-shaping arrangements, and exchanging the beam-shaping arrangement for a different type of beam-shaping arrangement is facilitated. It is also an object of the invention to provide a method for operating such a device.

[0008] Description of the invention

[0009] This object is achieved according to the invention by a device according to claim 1 and a method according to claim 11. The subclaims specify preferred developments. The object of the invention is thus achieved by a device mentioned above, in which the beam shaping arrangement has a beam rotator for rotating the image field of the laser beam.

[0010] The beam rotator enables simplified control and easy switching of the beam shaping assembly type. Interference with the beam shaping assembly control system, in particular, adjusting the transfer function stored in the beam shaping assembly control system, is not necessary when replacing the beam shaping assembly. Furthermore, adjustment of the optics upstream of the beam shaping assembly is avoided.

[0011] The beam shaping arrangement preferably has several optical elements that can deflect and shape the laser beam multiple times.

[0012] The beam rotator can be transmissive and, for example, have a Dove prism. However, if a high-power laser beam is used, this can lead to significant heating of the beam rotator and, as a result, damage to the beam rotator. The beam rotator is therefore preferably reflective and has at least one mirror, in particular several mirrors, for guiding the laser beam.

[0013] The beam rotator preferably has an odd number of mirrors for guiding the laser beam.

[0014] The beam rotator particularly preferably has three or five mirrors for guiding the laser beam. Using three mirrors simplifies the structural design of the beam rotator, whereas using five mirrors avoids shallow angles of incidence of the laser beam onto the mirrors. In a basic position of the beam rotator, the laser beam is preferably reflected in the beam rotator such that a laser beam entering the beam rotator is collinear with a laser beam exiting the beam rotator. If the beam rotator is then rotated by a given angle around a common beam axis of the incoming and outgoing laser beams, the outgoing laser beam rotates by twice the angle.

[0015] The structural design and control of the beam shaping arrangement are further simplified if the beam rotator is arranged in a section of the beam path of the beam shaping arrangement in which the laser beam is collimated.

[0016] The beam-shaping arrangement can be designed to guide a laser beam and / or multiple laser beams. The beam-shaping arrangement can, in particular, be designed to guide one or more pre-pulse laser beams and a main pulse laser beam, so that the target material is irradiated successively by one or more pre-pulses before being irradiated by a main pulse. If two or more laser beams of the same or similar wavelength, e.g., two pre-pulse laser beams of the same or similar wavelength, are directed at the target material, these laser beams pass through the same optical elements within the beam-shaping arrangement. A defined spatial offset in the focusing plane of the focusing unit of the beam-shaping arrangement is necessary between these laser beams in order to irradiate the target material at the respective intended position.This local offset results from an angular offset between the laser beams, which is adjusted in the optical elements upstream of the beam-shaping arrangement. The orientation of the local offset between the laser beams depends on the image field rotation in the beam-shaping arrangement. Beam-shaping arrangements in which two or more laser beams are guided to the target material via the same optical elements and which have a beam rotator capable of precisely adjusting the orientation of the laser beams relative to each other are therefore particularly advantageous, since the same control system can be used for different types of such beam-shaping arrangements.

[0017] The beam-shaping assembly can have a beam combiner located upstream of the beam rotator. The beam combiner located upstream of the beam rotator can also be located upstream of the beam-shaping assembly. At this beam combiner, laser beams of similar or identical wavelengths can be combined and guided to the target material via the same optical elements. This significantly simplifies the design of the device.

[0018] The beam combiner can be designed in the form of a dichroic mirror.

[0019] In a particularly preferred embodiment of the invention, the device comprises a vacuum chamber in which the target material can be irradiated. Further preferably, the optical elements of the focusing unit are arranged within the vacuum chamber, and the beam rotator is arranged outside the vacuum chamber in order to optimally utilize the available space in the vacuum chamber.

[0020] The object of the invention is further achieved by a method for generating EUV radiation using a device described herein. The method comprises at least guiding the at least one laser beam through the beam-shaping arrangement, in particular through the beam rotator and the focusing unit, as well as irradiating the target material and generating EUV radiation.

[0021] The features and advantages described for the device also apply to the method and vice versa.

[0022] The at least one laser beam used is preferably pulsed. This is particularly advantageous when the target material is provided as droplets, e.g., as tin droplets. In this case, the frequency at which the laser beam impinges on the droplet corresponds to the frequency at which droplets are emitted by a droplet source.

[0023] 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 outside the beam-shaping arrangement. This further simplifies the control of the beam-shaping arrangement. To irradiate the target material, multiple laser beams can be guided through the beam-shaping arrangement. The target material can be irradiated successively with a pre-pulse laser beam or multiple pre-pulse laser beams and subsequently with a main pulse laser beam. The focus position of the pre-pulse laser beam(s) can be adjusted outside the beam-shaping arrangement, and the focus position of the main pulse laser beam can be adjusted within the beam-shaping arrangement. The focus position of the main pulse laser beam can be adjusted using an actuated mirror.

[0024] 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 combination in any desired manner. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0025] Detailed description of the invention and drawing

[0026] Fig. 1 shows schematically an apparatus according to the invention and a method according to the invention for generating EUV radiation, wherein a laser beam passes through a beam rotator.

[0027] Fig. 2 schematically shows the image field rotation achieved by the beam rotator. Fig. 3 schematically shows a beam rotator with three mirrors.

[0028] Fig. 4 shows schematically another embodiment of a beam rotator with five mirrors.

[0029] Fig. 1 shows a device 10 and a method 12 for generating EUV radiation 14 on a target material 16 (shown here in the form of several droplets, in particular in the form of tin droplets). The target material 16 is irradiated by at least one laser beam 18, which passes through a beam-shaping arrangement 20 with a focusing unit 22. The focusing unit 22 has several optical elements arranged in a vacuum chamber 26. The target material 16, which is dispensed by a target material dispenser 24, and the optical elements of the focusing unit 22 are preferably located in the vacuum chamber 26 of the device 10.

[0030] The lateral (X / Y) focus position of the laser beam 18 is adjusted outside the beam-shaping arrangement 20 by tilting and / or shifting the laser beam 18 incident on the beam-shaping arrangement 20. The focus position of the laser beam 18 in the beam direction (Z) is also controlled outside the beam-shaping arrangement 20 by adjusting the divergence of the laser beam 18 incident on the beam-shaping arrangement 20. The beam-shaping arrangement 20 comprises several optical elements that result in a rotation of the image field of the laser beam 18. For example, a horizontal tilt of the laser beam 18 does not result in a horizontal shift of the focus, but rather in a shift along an axis rotated relative to the horizontal. Since the focus position is controlled outside the beam-shaping arrangement 20, the input / output behavior of the beam path within the beam-shaping arrangement 20 must be well known.

[0031] The beam shaping arrangement 20 can be designed as a modular assembly that can be easily installed and removed from the device 10. In the embodiment according to Fig.l, the beam shaping arrangement 20 comprises the lenses 31 and

[0032] 32 downstream optical elements. The input laser beam into the beam shaping arrangement 20 is formed by the laser beam 18, which has been passed through the two lenses 31, 32 and a first deflecting optical element

[0033] 33 has not yet happened. It goes without saying that a different arrangement of optical elements is also possible.

[0034] Different focusing unit types can have different image field rotations. In order to be able to use the same upstream beam-shaping and control systems for different types of beam-shaping arrangements 20, the image field rotation of the respective type of beam-shaping arrangement 20 must be taken into account in the transfer function of the control, which means that the same control cannot be used for different types of beam-shaping arrangements 20. According to the invention, however, it is provided to provide a beam rotator 28 that enables adaptation of different image field rotations of different types of beam-shaping arrangements 20. This allows the same control to be used for different types of beam-shaping arrangements 20.

[0035] Fig. 2 shows an example of a rotation of the image field plane (lower illustration) by 45° with a rotation of a beam rotator 28 (see Fig. 1) by 22.5°.

[0036] Fig. 3 shows an embodiment of a beam rotator 28 with three mirrors 30a, 30b, 30c.

[0037] Fig. 4 shows an alternative embodiment of a beam rotator 28 with five mirrors 30a, 30b, 30c, 30d, 30e, in which flat angles of incidence on the mirrors 30a-30e are avoided.

[0038] Taking a summary of all the figures of the drawing, the invention relates in summary to a device 10 and a method 12 for generating EUV radiation 14 by irradiating target material 16 with at least one laser beam 18. The at least one laser beam 18 is shaped by a beam-shaping arrangement 20 having a focusing unit 22. A beam rotator 28 is arranged upstream of the focusing unit 22 in order to compensate for different image field rotations of different types of beam-shaping arrangements 20. This allows identical optical components to be arranged upstream of different types of beam-shaping arrangements 20, in particular upstream of the beam rotator 28.

[0039] List of reference symbols

[0040] 10 Device

[0041] 12 procedures

[0042] 14 EUV radiation 16 Target material

[0043] 18 laser beam

[0044] 20 beam shape arrangement

[0045] 22 Focusing unit

[0046] 24 Target material dispenser 26 Vacuum chamber

[0047] 28 beam rotator

[0048] 30a-e mirror

[0049] 31 lens

[0050] 32 Lens 33 First deflecting optical element

Claims

Patent claims 1. Device (10) for generating EUV radiation (14), wherein the device (10) comprises: a) an optical beam shaping arrangement (20) with a focusing unit (22) for shaping a laser beam (18); b) a target material (16) that can be irradiated with the laser beam (18) for the emission of EUV radiation (14); characterized in that the beam shaping arrangement (20) comprises a beam rotator (28) for rotating the image field of the laser beam (18).

2. Device according to claim 1, wherein the beam shaping arrangement (20) comprises one or more optical elements by which the laser beam (18) is deflected and / or shaped several times.

3. Device according to one of the preceding claims, wherein the beam path of the beam rotator (28) is designed reflectively with several mirrors (30a-e).

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

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

6. Device according to one of the preceding claims, wherein the beam rotator (28) is arranged in a section of the beam path of the beam shaping arrangement (20) in which the laser beam (18) is collimated.

7. Device according to one of the preceding claims, wherein the beam shaping arrangement (20) is designed to guide several laser beams (18).

8. Device according to claim 7, wherein the device (10) has a beam combiner arranged upstream of the beam rotator (28).

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

10. Device according to 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. Method (12) for generating EUV radiation (14) with a device (10) according to one of the preceding claims, wherein the method (12) comprises the following process steps: A) Guiding the laser beam (18) through the beam shaping arrangement (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. Method according to claim 11, wherein the laser beam (18) is pulsed.

13. Method according to claim 11 or 12, wherein setting a focus position of the laser beam (18) on the target material (16) is achieved by adjusting the divergence of the laser beam (18).

14. Method according to one of claims 11 to 14, wherein several laser beams (18) are guided through the beam shaping arrangement (20) to irradiate the target material (16).

15. Method according to claim 14 in conjunction with claim 12, wherein the multiple laser beams (18) used are each pulsed.

Images