Device for correcting an astigmatism of a laser beam
Patent Information
- Application Number
- EP2022733460
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-06-17
- Publication Date
- 2025-04-23
AI Technical Summary
Existing devices for correcting astigmatism in laser beams have complex structures and lack precision in correction.
A device with an optical element that can be deformed by external forces, supported by diametrically aligned pairs of supports and acted upon by deformation elements to counteract astigmatism, allowing for precise correction of astigmatic wavefront deviations.
Enables precise correction of astigmatism in laser beams with a simple and stable structure, effectively influencing higher-order wavefronts and improving imaging errors.
Smart Images
Figure 1.1
Abstract
Description
[0001] Device for correcting astigmatism of a laser beam
[0002] Background of the invention
[0003] The invention relates to a device for transmitting and / or reflecting a laser beam for at least partially correcting an astigmatism of the laser beam. The invention also relates to a laser system comprising such a device.
[0004] DE 10 2006 047 666 A1 discloses a projection lens with lenses that can be deformed by actuators. The actuators exert forces on the lenses, with the forces having opposite directions. This deforms the lenses in a manner that counteracts the astigmatism of a laser beam passing through the lenses. The actuators are preferably arranged on the respective periphery of the lenses. DE 10 2017 217 695 A1 relates to a method for modifying the deformation behavior of a mirror in an EUV system using a piezoelectric layer of the mirror and an electrode arrangement on the piezoelectric layer. This can reduce undesirable deformation behavior, for example, due to heating of the mirror.
[0005] WO 2007 / 000171 A1 discloses a mirror assembly in a laser processing machine that includes an adaptive mirror. An electrorheological or magnetorheological fluid is located in the cavity of a mount of the mirror to change the focal length of the mirror by applying pressure to the back of the mirror.
[0006] The devices known from the prior art have a comparatively complex structure.
[0007] Object of the invention
[0008] It is therefore an object of the present invention to provide a device for correcting the astigmatism of a laser beam that has a simple structure yet enables precise correction of the astigmatism. It is also an object of the invention to provide a laser system with such a device.
[0009] Description of the invention
[0010] This object is achieved according to the invention by a device according to claim 1. The features of a laser system according to the invention are specified in claim 15. Advantageous embodiments emerge from the dependent claims.
[0011] The device according to the invention comprises the following elements:
[0012] - an optical element deformable by an external force for transmitting and / or reflecting the laser beam; - at least four supports for the optical element arranged along an imaginary circle, the supports being arranged in pairs diametrically opposite each other;
[0013] - at least two deformation elements for exerting a force on the optical element, wherein the deformation elements are arranged diametrically to one another with respect to the center of the circle through the supports, wherein the deformation elements are each arranged on an angle bisector of an angle defined by two adjacent supports and the center of the circle through the supports.
[0014] The deformation elements are designed to act on the optical element with forces, with the supports developing counterforces, as a result of which the optical element is deformed. The connecting paths between the diametrically arranged supports preferably define tilt axes along which the optical element is not deformed or is only slightly deformed. The deformation of the optical element is particularly greatest along the connecting path of the deformation elements when the deformation elements act on the optical element. As a result, a focal length of the optical element in the plane determined by this connecting path and an optical axis of the optical element, and thus an astigmatism of the laser beam, can be effectively changed, preferably corrected. Advantageously, only comparatively few and simple components are required for this.The deformation elements are designed, in particular, as tension and / or compression elements that exert a tensile and / or compressive force on the optical element. For this purpose, the deformation elements are preferably moved toward the optical element and exert the compressive force on the optical element.
[0015] The device can be used to influence, in particular, astigmatic wavefront deviations of laser beams, especially in CO2 laser beam guides. This preferably relates to a wavefront characterized by a fifth-order (Z5) or higher Zernike polynomial and the imaging errors associated with such a wavefront. The device preferably makes it possible to influence a wavefront exhibiting an astigmatic deviation from a desired wavefront shape as follows: eliminating, creating, reducing, and / or enlarging the astigmatic deviation.
[0016] The supports form a defined bearing for the optical element. The supports are preferably arranged at an edge region of the optical element. The edge region is defined in particular as a section of the optical element that runs along the edge of the optical element and extends up to half the distance between the edge of the optical element and the center of the optical element, preferably up to one third of the distance between the edge of the optical element and the center of the optical element. The external forces are introduced into the optical element by the deformation elements in defined regions at the respective angle bisectors between the supports. The deformation of the optical element is intensified in particular by increasing the acting forces, in particular pressure on the optical element. The optical element is preferably designed to be flat.
[0017] In a preferred embodiment of the device, the imaginary connecting lines between two diametrically opposed supports are perpendicular to each other. Between adjacent supports, a quarter of the imaginary circle runs through the supports in this embodiment, so that the supports are arranged rotationally symmetrically. This provides particularly stable support for the optical element. The forces acting on the optical element are also comparatively easy to determine.
[0018] In a further embodiment, the device comprises compression springs which, together with the supports, form holders for the optical element. The compression springs press the optical element against the supports. This fixes the optical element in its position, particularly when the deformation elements are not acting on the optical element. Preferably, unintentional displacement perpendicular to the desired direction of force with which the deformation elements act on the optical element is also prevented. Such a displacement can be caused, for example, by slight deviations of the device from its intended structure.
[0019] In a further development of this design, the supports are arranged on a front side of the optical element, and the compression springs are arranged on the rear side of the optical element, opposite the front side. The optical element can then be fixed simply by clamping it between the supports and the compression springs.
[0020] The supports are advantageously designed as supports. By placing the optical element on the supports, the optical element can be moved into its operating position particularly easily.
[0021] In a preferred embodiment, the contact areas between the supports and the optical element are each linear. The supports are aligned, in particular, along the connecting lines between the diametrical supports. The connecting lines form tilt axes along which the optical element is not deformed or is only slightly deformed. This property is reinforced by the linear contact areas, where the supports support the optical element and thus prevent deformation. The supports preferably form four linear supports on which the optical element rests.
[0022] The supports are preferably designed as cylindrical rollers. Cylindrical rollers are characterized by stability and durability.
[0023] In an advantageous embodiment, the device comprises a housing and alignment means for uniformly pivoting and fixing the optical element, the supports, and the deformation elements in different rotational positions on the housing. The angular position of the optical element, the supports, and the deformation elements is changed with respect to a reference axis through the housing. The optical element, the supports, and the deformation elements are fixed in the new angular position, with the reference axis serving to measure the angle of rotation. The deformation elements cause the greatest deformation of the optical element along the imaginary connecting path between the deformation elements.In this embodiment, the deformation elements and thus also the imaginary connecting path between the deformation elements can be pivoted relative to the housing, so that the plane through the connecting path and an optical axis of the optical element is also pivoted, in which plane the focal length of the optical element is changed most in order to influence the astigmatism of the laser beam. By appropriately aligning this plane, in particular, an astigmatism of the laser beam that already exists before the laser beam strikes the optical element can be increased or reduced. In this embodiment, it is also possible to realign a wavefront with an astigmatic deviation by pivoting the optical element without the action of force from the deformation elements relative to the housing.This allows the alignment of an astigmatic deviation of the wavefront caused by the optical element to be adjusted with respect to the angular position.
[0024] In a further development of the aforementioned embodiment, the rotational positions relate to an optical axis of the optical element. The pivoting of the optical element occurs, in particular, around the optical axis of the optical element. The optical axis of the optical element runs, in particular, through the center of the optical element and / or the center of the imaginary circle through the supports.
[0025] The distance between the deformation elements is preferably less than or equal to the diameter of the imaginary circle formed by the supports. The deformation elements are arranged, in particular, at a smaller or the same distance from the center of the optical element as the supports. The deformation elements are located, in particular, in the edge region of the optical element. In a further embodiment, the device has exactly two deformation elements. This results in a particularly simple structure of the device.
[0026] A preferred embodiment is characterized in that the device has exactly four supports. This gives the device a simple structure, especially in combination with the aforementioned embodiment.
[0027] The optical element is advantageously elastically deformable. The deformation of the optical element then adapts to different forces exerted by the deformation elements and can thus be flexibly adjusted. By applying a targeted force to the areas of the optical element defined by the deformation elements on the respective angle bisectors between the adjacent supports, a deformation of the optical element is achieved that counteracts the specific astigmatism of a laser beam transmitted and / or reflected by the optical element. By adjusting the force application, different deformations of the optical element can be achieved in order to correct different astigmatic deformations of a wavefront of the laser beam.
[0028] The optical element is preferably designed as a mirror and / or lens.
[0029] Furthermore, the deformation elements are preferably designed as threaded pins, screws, and / or piezoelectric elements. The deformation elements are particularly suitable for exerting a compressive and / or tensile force.
[0030] A laser system comprises a target material irradiable with the laser beam, particularly in the form of tin droplets, for generating EUV radiation (extreme ultraviolet radiation), and a device according to one of the aforementioned embodiments for correcting an astigmatism of the laser beam. With such a laser system, an astigmatism of the laser beam can be corrected in a structurally simple manner, in particular to enable better focusing of the laser beam. Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those further detailed can each be used individually or in combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather are exemplary in nature for describing the invention.
[0031] Detailed description of the invention and drawing
[0032] Fig. 1 shows schematically a plan view of a device for transmitting and / or reflecting a laser beam for at least partially correcting an astigmatism of the laser beam.
[0033] Fig. 2 shows schematically a first cross section along the line AA of Fig. 1 through the device.
[0034] Fig. 3 shows schematically a second cross section along the line BB of Fig. 1 through the device.
[0035] Fig. 4 shows a schematic diagram of a laser system with the device.
[0036] Fig. 1 shows a plan view of a device 10 for transmitting and / or reflecting a laser beam 12 (see Fig. 4) for at least partially correcting an astigmatism of the laser beam 12. The transmission and / or reflection of the laser beam 12 is effected by an optical element 14, the shape of which can be changed by an external force. The optical element 14 is designed here as an elastically deformable mirror that reflects the laser beam 12.
[0037] The optical element 14 rests with a front side 48 (see Fig. 2) on four supports 16a, 16b, 16c, 16d, here in the form of supports 42a, 42b, 42c, 42d, which are designed as cylindrical rollers.
[0038] On a rear side 50 of the optical element 14 (see Fig. 2), which is opposite the front side 48, compression springs 52a, 52b, 52c, 52d are arranged, which press the optical element 14 against the supports 16a-16d and fix it in position. The compression springs 52a-52d, together with the supports 16a-16d, form holders 54a, 54b, 54c, 54d of the optical element 14.
[0039] The supports 16a - 16d are arranged along an imaginary circle 18, with a quarter of the circle 18 extending between each support 16a - 16d (for clarity, circle 18 is drawn with a slightly smaller diameter in Fig. 1). Thus, the supports 16a - 16d are arranged diametrically opposite each other in pairs. The imaginary connecting lines between any two diametrically arranged pairs of supports 16a - 16d are perpendicular to each other.
[0040] In addition, the device 10 has two deformation elements 22a, 22b, wherein the deformation elements 22a, 22b are arranged diametrically opposite one another with respect to the center 24 of the imaginary circle 18 by the supports 16a-16d. The deformation elements 22a, 22b are each located on an angle bisector 26a, 26b of an angle defined by two adjacent supports 16a, 16b or 16c, 16d and the center 24 of the circle 18 by the supports 16a-16d. The angles are opposite one another. Forces, in particular compressive forces, can be introduced into the optical element 14 by the deformation elements 22a, 22b, wherein the supports 16a - 16d exert counterforces on the optical element 14, whereby the optical element 14 changes its shape, in particular along the imaginary connecting path through the deformation elements 22a, 22b.As a result, the focal length of the optical element 14 in the plane determined by the imaginary connecting line between the deformation elements 22a, 22b and the optical axis 30 (see Fig. 2) of the optical element 14 is changed in order to influence the astigmatism of the laser beam 12 (see Fig. 4).
[0041] The imaginary connecting lines between the diametrical supports 16a, 16c and 16b, 16d form tilt axes along which the optical element 14 deforms only slightly or not at all when forces, in particular compressive forces, are exerted on the optical element 14 by the two deformation elements 22a, 22b. Due to the elongated shape of the supports 16a-16d in the form of cylindrical rollers, the contact areas between the supports 16a-16d and the optical element 14 are each linear. The supports 16a-16d, and thus also the contact areas, are aligned in the direction of the connecting lines in order to increase the resistance of the optical element 14 to deformations along the tilt axes by the aforementioned counterforces of the supports 16a-16d.
[0042] Located in a receiving flange 34 are alignment means, one of which is designated by 36, for uniformly pivoting and fixing the optical element 14, the supports 16a-16d, and the deformation elements 22a, 22b in different rotational positions on a housing 38 (see Fig. 2). The alignment means 36 have slots, which, for example, also have screws for fixing the optical element 14 in the respective rotational position. The rotational positions relate to the optical axis 30 of the optical element 14 (see Fig. 2), which runs through the center of the optical element 14 in plan view, which here coincides with the center 24 of the circle 18 through the supports 16a-16d.
[0043] The optical element 14 is protected by a cover 40 (see Fig. 2), wherein the cover 40 is fastened to the receiving flange 34 via first fastening means, one of which is designated by 44 in the drawing as an example. The receiving flange 34 is fastened to the housing 38 via second fastening means, one of which is designated by 46 in the drawing as an example.
[0044] Fig. 2 shows a first cross-section through the device 10 along the section line AA in Fig. 1. In particular, it is shown that the optical element 14 rests with the front side 48 on the supports, with the supports 16b, 16d being shown in Fig. 2. The supports are arranged on the receiving flange 34, which is fastened in the housing 38 via the second fastening elements 46.
[0045] The compression springs which press the optical element 14 against the supports and fix it in its position are arranged on the rear side 50 of the optical element 14, wherein the compression springs 52b, 52d are shown in Fig. 2, which, together with the supports 16b, 16d, form the holders 54b, 54d of the optical element 14.
[0046] It is also shown that the compression springs 52b, 52d are arranged on the cover 40, which is fastened to the receiving flange 34 via the first fastening elements 44. The deformation elements, of which the deformation element 22a is shown in Fig. 2, extend through the cover 40. The deformation elements 22a, 22b (see Fig. 1) can be moved in the direction of the optical element 14 to exert pressure on the optical element 14 and thereby deform the optical element 14. By deforming the optical element 14, an astigmatism of the laser beam 12 (see Fig. 4) can be counteracted. The optical axis 30 of the optical element 14 is also shown.
[0047] Fig. 3 shows a second cross-section through the device 10 along the section line BB in Fig. 1. The optical element 14 is shown resting on the supports, with the support 16a being shown in Fig. 3. The compression springs act on the optical element 14 to hold the optical element in its position, with the compression springs 52a, 52d being shown in Fig. 3. The compression springs 52a, 52d are located between the optical element 14 and the cover 40, which is fastened to the receiving flange 34, with the supports 16a-16d also being positioned on the receiving flange 34. The receiving flange 34 is mounted in the housing 38. On the front side 48 of the optical element 14, there are cavities opposite the deformation elements 22a, 22b, wherein in Fig. 3, a cavity 56 is shown as an example, which is opposite the deformation element 22b shown in Fig. 3. The deformation elements 22a, 22b (see Fig.1) preferably exert a compressive force in order to displace the regions of the optical element 14 that bear against the deformation elements 22a, 22b or lie on the connecting path between the deformation elements 22a, 22b in the direction of the cavities 56. In this way, the astigmatism of the laser beam 12 (see Fig. 4), which interacts with the optical element 14, can be changed, in particular corrected. Fig. 4 schematically shows a laser system 58 for generating EUV radiation 60 using the device 10. The laser beam 12 generated in a laser source 62 is directed by the device 10 onto a target material 64, for example a tin droplet, in order to generate the EUV radiation 60. In this case, an astigmatism of the laser beam 12 is corrected by the device 10 for better focusing of the laser beam 12 onto the target material 64.
[0048] Taking all the figures of the drawing together, the invention relates to a device 10 for correcting the astigmatism of a laser beam 12 interacting with the device 10. The device 10 has an optical element 14 and two deformation elements 22a, 22b, which act on the optical element 14, in particular with a compressive and / or tensile force, in order to deform it. Four supports 16a-16d arranged along an imaginary circle 18 are located on the optical element 14 to prevent displacement of the optical element 14 at least in the direction of the forces acting by the deformation elements 22a, 22b. The supports 16a-16d are arranged in pairs opposite one another with respect to the center 24 of the circle 18 by the supports 16a-16d. The two deformation elements 22a, 22b are also opposite each other with respect to the center 24 of the imaginary circle 18 by the supports 16a - 16d.The deformation elements 22a, 22b are arranged on a straight line through the center 24 of the imaginary circle 18, which bisects opposite angles, wherein the angles are each defined by adjacent supports 16a - 16d and the center 24 of the circle 18 by the supports 16a - 16d.
[0049] List of reference symbols
[0050] 10 Device
[0051] 12 laser beam
[0052] 14 optical element
[0053] 16a-d supports
[0054] 18 Circle
[0055] 22a, b Deformation elements
[0056] 24 Center
[0057] 26a, b angle bisector
[0058] 30 optical axis
[0059] 34 Mounting flange
[0060] 36a-f alignment agents
[0061] 38 housings
[0062] 40 lids
[0063] 42a-d Conditions
[0064] 44 first fasteners
[0065] 46 second fasteners
[0066] 48 Front
[0067] 50 Back
[0068] 52a-d compression spring
[0069] 54a-d brackets
[0070] 56 cavity
[0071] 58 laser system
[0072] 60 EUV radiation
[0073] 62 Laser source
[0074] 64 Target material
Claims
Patent claims 1. Device (10) for transmitting and / or reflecting a laser beam (12) for at least partially correcting astigmatism of the laser beam (12), comprising: - an optical element (14) that can be deformed by an external force for transmitting and / or reflecting the laser beam (12); - at least four supports (16a - 16d) arranged along an imaginary circle (18) for the optical element (14), wherein the supports (16a - 16d) are diametrically aligned in pairs; - at least two deformation elements (22a, 22b) for exerting a force on the optical element (14), wherein the deformation elements (22a, 22b) are arranged diametrically opposite each other with respect to the center (24) of the circle (18) by the supports (16a - 16d), wherein the deformation elements (22a, 22b) are each arranged on an angle bisector (26a, 26b) of an angle defined by two adjacent supports (16a - 16d) and the center (24) of the circle (18) by the supports (16a - 16d).
2. Device according to claim 1, wherein the diametrically aligned supports (16a - 16d) are arranged in pairs along an imaginary connecting line and the imaginary connecting lines are perpendicular to each other.
3. Device according to one of the preceding claims, wherein the device (10) comprises compression springs (52a - 52d) which together with the supports (16a - 16d) form holders (54a - 54d) of the optical element (14). Device according to claim 3, wherein the supports (16a - 16d) are arranged on a front side (48) of the optical element (14) and the compression springs (52a - 52d) are arranged on the rear side (50) of the optical element (14) opposite the front side (48) of the optical element (14). Device according to any one of the preceding claims, wherein the supports (16a - 16d) are configured as bearing surfaces (42a - 42d). Device according to any one of the preceding claims, wherein the contact areas between the supports (16a - 16d) and the optical element (14) are each configured as linear surfaces. Device according to claim 6, wherein the supports (16a - 16d) are each configured as cylindrical rollers.A device according to any one of the preceding claims, comprising a housing (38) and alignment means (36) for uniformly pivoting and fixing the optical element (14), the supports (16a-16d), and the deformation elements (22a, 22b) in different rotational positions on the housing (38). A device according to claim 8, wherein the rotational positions are related to an optical axis (30) of the optical element (14). A device according to any one of the preceding claims, wherein the distance between the deformation elements (22a, 22b) is less than or equal to the diameter of the imaginary circle (18) through the supports (16a-16d). A device according to any one of the preceding claims, comprising exactly two deformation elements (22a, 22b). A device according to any one of the preceding claims, comprising exactly four supports (16a-16d). Device according to one of the preceding claims, wherein the optical element (14) is elastically deformable. Device according to one of the preceding claims, wherein the deformation elements (22a, 22b) are designed as threaded pins, screws and / or piezoelectric elements. Laser system (58), wherein the laser system (58) comprises a target material (64) irradiable with the laser beam (12) for generating EUV radiation (60) and a device (10) according to one of the preceding claims for Correcting astigmatism of the laser beam (12).