Method, device and computer program product for processing a body, in particular a mirror body of an EUV mirror

Abstract

The invention relates to a method for treating a body (20), in particular a mirror body of an EUV mirror, in which an ion beam (18) is directed to a surface (21) of the body (20) to be treated in order to remove material from the surface (21) of the body (20). The ion beam (18) is guided along a path (22, 23, 24, 25) on the surface (21), where the path (22, 23, 24, 25) comprises a first partial path (22) and a second partial path (23) temporally following the first partial path (22), where the ion beam (18) sweeps over the entire surface (21) during the first partial path (22), and where the ion beam sweeps over the entire surface (21) during the second partial path (23). The invention also relates to an apparatus and a computer program product for processing a subject.

Description

[0001] This patent application claims the priority of German patent application DE 10 2022 210 262.2, filed on September 28, 2022, which is referenced and the contents of which are incorporated herein in their entirety (“incorporated by reference”). Technical Field

[0002] The invention relates to a method for treating a body, in particular a mirror body of an EUV mirror. In the method, an ion beam is directed to the surface of the body to be treated in order to remove material from the surface of the body. The ion beam is directed along a trajectory over the surface. The invention also relates to an apparatus and a computer program product for treating such a body. Background Art

[0003] Integrated circuits with particularly small structures are produced using microlithography projection exposure equipment. A mask (=reticle) irradiated with very short-wave deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) is imaged onto the lithographic object in order to transfer the mask structures to the lithographic object.

[0004] The projection exposure apparatus comprises a plurality of mirrors, off which the radiation is reflected. The mirrors have a precisely defined shape and are precisely oriented so that the imaging of the mask onto the lithographic object is of sufficient quality.

[0005] Large mirrors, which may be of the order of several 100 mm in extent, are used to ensure that a sufficient amount of EUV or DUV radiation can be directed to the lithographic object. In some cases, the production process of the mirrors includes a step of treating the mirror body with an ion beam in order to remove material from the surface of the mirror body. The ejected particles receive so much kinetic energy from the ion beam that they move away from the surface of the mirror body. A problem that arises in the case of mirror bodies with large dimensions is that the ejected particles may settle at another location on the surface and form a layer there together with the components of the ionized process gas emitted from the ion beam source. This is undesirable since this impairs the quality of the surface. Summary of the invention

[0006] The problem addressed by the present invention is to provide a method, an apparatus and a computer program product with which these disadvantages are avoided. This problem is solved by the features of the independent claims. Advantageous embodiments are given in the dependent claims.

[0007] In the method according to the invention, the trajectory of the ion beam on the surface to be processed of the subject comprises a first partial trajectory and a second partial trajectory temporally following the first partial trajectory. The ion beam sweeps over the entire surface on the route of the first partial trajectory. The ion beam also sweeps over the entire surface on the route of the second partial trajectory.

[0008] Since the entire surface to be treated is swept several times by the ion beam during the treatment of the body, the deposited particles can be removed from the surface before the particles form a layer that can only be removed with difficulty. The present invention has recognized that the conventional process in which the ion beam is scanned exactly once over the surface to be treated is disadvantageous if the surface to be treated is relatively large. The layer produced by the ejected particles and the components of the process gas is formed at a certain distance from the area of ​​the surface treated by the ion beam, and this layer is troublesome only in the case of relatively large surfaces. Through the present invention, the method can be used even if particles are deposited on the surface to be treated, because the particles are repeatedly removed during the process of the method and therefore do not adversely affect the result of the treatment.

[0009] The method can be performed in such a way that the duration of a single partial trajectory is substantially shorter than the total duration of the treatment. For example, the duration of a partial trajectory can be less than 10%, preferably less than 5%, and further preferably less than 1% of the total treatment time. The total duration of the treatment depends on how much material should be removed. There are applications in which the treatment lasts at least 5 h, preferably at least 10 h and further preferably at least 20 h. For example, the duration of a single partial trajectory can be between 2 minutes and 20 minutes, preferably between 5 minutes and 10 minutes. In other applications, in which only little material should be removed, the duration of the treatment can be shorter and, for example, between 0.5 h and 5 h.

[0010] In many cases, it is desirable that the surface undergo a substantially uniform treatment. This can be achieved by keeping the parameters of the ion beam constant and by guiding the ion beam at an almost constant speed on the surface to be treated. If the minimum speed on the route of the partial trajectory deviates from the maximum speed on the route of the partial trajectory by no more than 10%, the speed is referred to as almost constant. In this sense, the speed can also be kept almost constant on different partial trajectories. Each individual partial trajectory can be designed so that the partial trajectory does not include any trajectory portions that intersect each other. Different partial trajectories can match each other in a way that the partial trajectories do not intersect each other. This is preferably applied to the overall partial trajectories according to the present invention.

[0011] In one embodiment, the trajectory is arranged on the surface in such a way that on the course of the first partial trajectory and / or the second partial trajectory, the ion beam does not leave the surface to be treated. If the surface to be treated has a circular circumference, such as is the case with a circular or elliptical shape of the surface, the ion beam can be guided on the surface along a spiral partial trajectory. The spiral partial trajectory can start in the peripheral area of ​​the surface and lead to the center, or vice versa.

[0012] The partial trajectory is preferably designed so that the ion beam is guided on the surface to be treated without a sudden change in direction. Within the meaning of the present invention, a sudden change in direction is considered to be a change in the speed at which the ion beam is guided on the surface. It may be advantageous to guide the ion beam to an area outside the surface to be treated in order to avoid a sudden change in direction within the surface. Away from the surface to be treated, the trajectory of the ion beam can undergo any desired change in direction without adversely affecting the uniform treatment of the surface. For example, the ion beam can also cross the surface to be treated along a first straight trajectory portion, reverse direction on the outside of the surface to be treated, and cross the surface to be treated again along a second straight trajectory portion parallel to the first straight trajectory portion. Utilizing multiple straight trajectory portions, the entire surface to be treated can be swept in this way without a sudden change in direction on the surface.

[0013] The body may be designed so that the ion beam no longer impinges on the body outside the surface to be processed. The ion beam may also impinge on a peripheral surface area of ​​the body that is outside the surface to be processed and is not subjected to target processing.

[0014] Between the first partial trajectory and the second partial trajectory, it may be advantageous to direct the ion beam into a region outside the surface to be treated. In one embodiment, the surface to be treated has a central cutout. The ion beam can be directed into the region of the central cutout during the transition between the first partial trajectory and the second partial trajectory and can undergo any desired change of direction there.

[0015] For example, the cross-sectional extent of the ion beam transverse to the path direction (transverse cross-sectional extent), specified as FWHM (full width at half maximum), may be between 30 mm and 150 mm, preferably between 50 mm and 100 mm. Statements about the trajectory along which the ion beam is guided refer to the central ray of the distribution. In other applications, the full width at half maximum of the ion beam may be smaller and, for example, between 0.5 mm and 30 mm.

[0016] The method can be performed in such a way that, over the course of a partial trajectory, the central ray maintains a constant transverse cross-section with the central ray of an earlier trajectory portion of the same partial trajectory. The transverse distance can be less than the transverse cross-sectional range of the ion beam, so that the ion beam overlaps with the previous trajectory portion. The overlap can extend over at least 10% of the cross-sectional range, preferably over at least 20%, and further preferably over at least 30%. In other words, the partial trajectory along which the ion beam is guided may include trajectory portions adjacent to each other, wherein the distance between the trajectory portions is selected so that the desired overlap begins. For example, the distance between trajectory portions adjacent to each other may be between 20 mm and 100 mm. All statements about the transverse distance relate to the central ray of the ion beam. This can apply to any of the partial trajectories.

[0017] The second partial trajectory may extend parallel to the first partial trajectory. This means that the path taken by the central ray of the ion beam on the course of the second partial trajectory has a constant lateral distance from the path of the central ray on the course of the first partial trajectory. The second partial trajectory can be guided exactly centered between the two trajectory parts of the first partial trajectory. Further partial trajectories can fill the free space left by the first partial trajectory with equidistant lateral distances. The method can be performed with at least 50 partial trajectories, preferably with at least 100 partial trajectories, and further preferably with at least 200 partial trajectories.

[0018] The processing parameters can remain constant during the partial trajectory. In particular, the properties of the ion beam can remain constant and the ion beam can move at a constant speed along the partial trajectory. Each partial trajectory can be straight or have a continuous curvature, as in the case of a spiral. When switching between two partial trajectories, the parameters of the ion beam can also remain constant. In the intermediate stages between two partial trajectories, the speed of the ion beam and the shape of the trajectory are not subject to any specific restrictions. In common use cases, there is no intersection between the partial trajectories. The present invention also includes the possibility that one or more partial trajectories are traversed identically multiple times. This can apply to any of the partial trajectories.

[0019] The specification that the partial tracks should not cross each other serves primarily the purpose of allowing uniform treatment of the surface so that a layer of in particular constant thickness can be removed from the body. The crossing of partial tracks may be advantageous in cases where more material should be removed from certain locations on the surface to be treated than from other locations.

[0020] The method can be performed on a body whose surface to be treated is provided with a mask, which separates the surface areas from which material should be removed from the surface areas from which material should not be removed. For example, the mask can consist of a photoresist layer. The structures defined by the mask are usually small, so that the ion beam sweeps over multiple surface areas at the same time. Even in such a use case, it is desirable to uniformly treat the surface to be treated by the ion beam.

[0021] The problem of undesired deposition of the spray particles occurs particularly when the surface to be treated is large. For example, the maximum extent of the surface to be treated may be at least 300 mm, preferably at least 500 mm.

[0022] The body may be a mirror body of an EUV or DUV mirror. In the finished mirror, the mirror body may be provided with a coating that is highly reflective to EUV radiation or DUV radiation. The latter may be a multilayer coating, in particular a multilayer coating with alternating layers of molybdenum and silicon. The treatment according to the invention of the mirror body may be performed before the mirror body is provided with the coating. The term EUV radiation denotes electromagnetic radiation in the extreme ultraviolet spectral range with a wavelength between 5 nm and 100 nm, in particular with a wavelength between 5 nm and 30 nm. DUV radiation is in the deep ultraviolet spectral range and has a wavelength between 100 nm and 300 nm.

[0023] In one embodiment, the reflector body has the shape of a concave mirror. The surface to be processed may correspond to the reflective surface of the concave mirror. The first partial track may be guided spirally from the periphery of the reflective surface of the concave mirror to the center of the reflective surface of the concave mirror, or vice versa, from the center of the reflective surface of the concave mirror to the periphery. The second partial track may extend along the spiral intermediate space between the track parts of the first partial track, i.e., be wound around the first partial track. All other partial tracks may also extend along the spiral intermediate space of the first partial track.

[0024] The reflector body of the concave mirror may include a central area located outside the surface to be processed. The central area may be concentric with the axis of the concave mirror. In one embodiment, the reflector body of the concave mirror has a central cutout that forms a penetration in the reflector body of the concave mirror.

[0025] If the reflector body of the concave mirror has a central area located outside the surface to be treated, the first partial trajectory can extend between the peripheral edge and the central edge of the surface to be treated. If the edge of the surface to be treated reaches the end of the partial trajectory, the ion beam can be directed to an area outside the surface to be treated and there the ion beam can be deflected or moved to a position from which a second partial trajectory can start. Thus, all subsequent partial trajectories can be subjected to the same action.

[0026] The ion beam may be generated using an ion beam source in which a process gas is ionized with RF (radio frequency) radiation. Voltages may be applied in the ion beam source in order to shape and direct the ion beam to the surface to be treated.

[0027] The invention also relates to a device for treating a body, in particular a reflector body of an EUV reflector. The device comprises an ion beam source and a positioning system, the positioning system being used to guide an ion beam emitted by the ion beam source to a surface to be treated of the body, in such a way as to remove material from the surface of the body. The device also comprises a control unit, which controls the positioning system in such a way that the ion beam is guided on the surface along a trajectory. The trajectory comprises a first partial trajectory and a second partial trajectory that follows the first partial trajectory in time. The ion beam sweeps over the entire surface on the route of the first partial trajectory, and sweeps over the entire surface on the route of the second partial trajectory.

[0028] The positioning system can be designed so that the main body remains in a fixed position, and the ion beam source moves relative to the main body, and vice versa. It is also possible that the positioning system in which the ion beam source and the main body are both moved. If the main body is a reflector body in the form of a concave mirror, the reflector body can rotate around its optical axis. In order to be able to guide the ion beam to the different meridian sections of the concave mirror, i.e., the different sections along the meridian of the concave mirror, the ion beam source can be displaced and pivoted in a suitable manner relative to the reflector body. In this process, the ion beam source can be aligned in each case in a manner such that the ion beam is vertically incident on the surface of the concave mirror to be processed.

[0029] The present disclosure includes improvements of the method having features described in the context of the apparatus according to the invention. The present disclosure includes improvements of the apparatus described in the context of the method according to the invention.

[0030] The invention also relates to a computer program product or a set of computer program products comprising program parts designed to carry out the method according to the invention when loaded into a computer or into a networked computer connected to the device according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention is described below by way of example based on advantageous embodiments with reference to the accompanying drawings, in which:

[0032] Figure 1 : shows an embodiment of the device according to the present invention;

[0033] Figure 2 : shows an exemplary procedure when processing a subject;

[0034] Figure 3 : shows a schematic diagram of a portion of a trajectory according to the present invention;

[0035] Figure 4 : shows the profile produced by the ion beam;

[0036] Figure 5 : shows a combination of multiple partial trajectories;

[0037] Figure 6 : shows a reflector body having a surface to be processed;

[0038] Figure 7 : An alternative embodiment of the device according to the invention is shown. DETAILED DESCRIPTION

[0039] exist Figure 1 In the embodiment of the present invention, a body in the form of a mirror body 20 is arranged on a support surface of a processing device 15 according to the present invention. The processing device 15 comprises a positioning system in the form of an XY-positioner 16, which carries an ion beam source 17. The ion beam source 17 generates an ion beam 18, which is incident vertically on a surface 21 to be processed of the mirror body 20. By moving the ion beam source 17 using the XY-positioner 16, the ion beam 18 is moved vertically on the surface 21 ( Figure 2 The processing device 15 comprises a control unit 14, which controls an XY positioner 16 so that the ion beam 18 travels a predetermined trajectory on the surface 21 to be processed.

[0040] according to Figure 2 , the surface to be treated 21 is rectangular, the longer side of the rectangle measuring about 70 cm. The ion beam sweeps over the surface to be treated 21 in a plurality of partial trajectories 22, 23, 24, 25. The first partial trajectory 22 begins with the ion beam 18 passing once through the shorter dimension of the rectangular surface 21 along a straight trajectory portion 19. Outside the surface to be treated 21, the trajectory of the ion beam 18 is deflected along a semicircular arc so that the ion beam 18 can sweep over the surface to be treated 21 in the opposite direction. The first partial trajectory 22 continues in this manner until it reaches the opposite end of the surface to be treated 21 relative to the longer dimension of the rectangle.

[0041] Then, the ion beam source 17 is driven back to the outside of the surface 21 to be treated to the starting end, so that the ion beam 18 can be guided on the surface 21 along the second partial trajectory 23. The second partial trajectory 23 has the same course as the first partial trajectory 22, but is shifted relative to the first partial trajectory 22 so that the straight trajectory portions 19 are parallel to each other. The method is continued with further partial trajectories until the intermediate spaces between the straight portions 19 of the first partial trajectories 22 are uniformly covered by the straight portions 19 of the other partial trajectories. This is done in Figure 2In the simplified sketch of , the method is shown for four partial trajectories 22, 23, 24, 25. In practice, the method is regularly performed with significantly more partial trajectories, for example between 100 and 200 partial trajectories. The speed of traversing the partial trajectories is the same for all partial trajectories. For example, the total duration of the treatment can be 20 h. For example, the duration of a single partial trajectory 22, 23, 24, 25 can be between 5 minutes and 10 minutes.

[0042] In accordance with Figure 2 In the exemplary embodiment of , the second partial trajectory 23 is adjacent to the first partial trajectory 22, the third partial trajectory 24 is adjacent to the second partial trajectory 23, etc. Other sequences of partial trajectories are also possible, in which, for example, the respective current partial trajectory is arranged as centrally as possible between existing partial trajectories.

[0043] The ion beam source 17 remains operational throughout the process and delivers a constant ion beam 18. Figure 3 , the ion beam 18 is not very strongly focused, but has a clear extent transversely to the direction of the first partial trajectory 22. The full width at half maximum (FWHM) of the ion beam 18 is about 70 mm. Therefore, the transverse cross-sectional extent 26 of the ion beam 18 is so large that when the ion beam 18 is guided along adjacent straight trajectory portions 19 of a single partial trajectory 22, there is an overlap of the areas treated by the ion beam 18. The distance between adjacent straight trajectory portions 19 is about 100 mm. It is achieved thereby that the entirety of the surface 21 is treated by each of the partial trajectories 22, 23, 24, 25.

[0044] Figure 4 The profile produced by treatment with an ion beam 18 is shown. The ion beam 18 penetrates into the material of the mirror body 20 by knocking particles out of the surface. A groove 29 is formed, the maximum depth of which is produced by the central ray 27 of the ion beam 18 and which becomes flatter with increasing distance from the central ray 27. Figure 4 The scale on the vertical axis is in nanometers.

[0045] The surface 21 to be treated of the mirror body 20 has an extent 30 of 700 mm. The particles ejected from the grooves 29 and the components of the ionized process gas are deposited at a distance of about 300 mm from the central ray 27 and accumulate there to form a layer 28. Since, according to the invention, the surface 21 to be treated is treated in its entirety by each partial track, the layer 28 is removed again after a short time in each case, so that the deposited particles do not adversely affect the result of the entire treatment.

[0046] exist Figure 5In the figure, a combination of four partial trajectories 22, 23, 24, 25 suitable for processing a circular surface 21 is shown. Each of the partial trajectories 22, 23, 24, 25 forms a spiral path, which starts at the peripheral end of the circular surface 21 and continues to the center of the circular surface 21. Each of the partial trajectories 22, 23, 24, 25 extends in the spiral free space left between two adjacent partial trajectories, and the partial trajectories are therefore wound around each other. At the end of each partial trajectory, the ion beam source 17 is deactivated and then the ion beam source 17 is moved back to the outside using the XY-positioner 16. There, the ion beam source 17 is put back into operation, and the method continues with the next partial trajectory.

[0047] exist Figure 5 The method indicated in FIG. 1 based on four partial trajectories 22 , 23 , 24 , 25 can in practice also be performed with a significantly larger number of partial trajectories. The total processing duration may be between 10 h and 20 h; for example, a single partial trajectory may take 5 minutes or 10 minutes.

[0048] exist Figure 6 In FIG. 3 , a reflector body 20 is shown having a circular circumference and a central cutout 32. In such a reflector body 20, a reflector body 20 from Figure 5 The ion beam 18 can be directed in the cutout 32 to a region outside the surface 21 to be treated. There, the trajectory of the ion beam 18 can be modified and deflected as required without adversely affecting the uniform treatment of the surface 21. Once the surface 21 to be treated is reached again, the ion beam 18 can be directed again at a constant speed along the next spiral partial trajectory.

[0049] Figure 7 Another embodiment of the device according to the invention is shown. The ion beam source 17 is held on a slider 35 which can be moved in the X direction using a linear drive. The orientation of the ion beam source 17 relative to the slider 35 can be changed using an articulated drive 36 whose joint axis is aligned perpendicular to the image plane.

[0050] The mirror body 20 in the shape of a concave mirror with a central cutout 32 is attached to a bracket 33. The mirror body 20 can be displaced in the Z direction and rotated about the Z axis using a positioning drive 34. Using this four-axis positioning system, the ion beam source 17 and the mirror body 20 can be aligned relative to each other so that the ion beam 18 can be directed vertically to any position on the surface 21 of the mirror body 20.

[0051] Using the control unit 14, the slider 35, the articulation drive 36 and the positioning drive 34 are controlled so that the ion beam 18 travels a first spiral partial trajectory 22 on the surface 21, which extends at an almost uniform speed from the outer peripheral end of the surface 21 to the central cutout 32. Within the central cutout 32, the movement direction is deflected so that the ion beam 18 can travel a further spiral partial trajectory on the surface 21. This is repeated with a plurality of spiral partial trajectories, each extending within a spiral free space between two adjacent partial trajectories.

Claims

1. A method for treating a body (20), in particular a mirror body for an EUV mirror, wherein an ion beam (18) is directed to a surface (21) of the body (20) to be treated in order to remove material from the surface (21) of the body (20), and wherein the ion beam (18) is directed on the surface (21) along a trajectory (22, 23, 24, 25), wherein the trajectory (22, 23, 24, 25) comprises a first partial trajectory (22) and a second partial trajectory (23) which temporally follows the first partial trajectory (22), wherein the ion beam (18) sweeps over the entire surface (21) on the course of the first partial trajectory (22), and wherein the ion beam (18) sweeps over the entire surface (21) on the course of the second partial trajectory (23).

2. The method according to claim 1, wherein: The duration of the partial trajectory is less than 10%, preferably less than 5% and further preferably less than 1% of the total duration of the process.

3. The method according to claim 1 or 2, wherein: The total duration of the treatment extends over at least 5 h, preferably at least 10 h and further preferably at least 20 h.

4. The method according to any one of claims 1 to 3, wherein: The duration of a single partial trajectory is between 2 minutes and 20 minutes, preferably between 5 minutes and 10 minutes.

5. The method according to any one of claims 1 to 4, wherein: The ion beam (18) is directed at a nearly constant speed along the first partial trajectory (22) and along the second partial trajectory (23).

6. The method according to any one of claims 1 to 5, wherein: Between the first partial trajectory (22) and the second partial trajectory (23), the ion beam (18) is directed into a region outside the surface (21) to be treated.

7. The method according to any one of claims 1 to 6, wherein: The first partial trajectory (22) and the second partial trajectory (23) have a helical shape, and wherein the first partial trajectory (22) is wound.

8. The method according to claim 7, wherein: The surface to be processed (21) has a central cutout (32), and wherein the ion beam is directed into the region of the central cutout (32) between the first partial trajectory (22) and the second partial trajectory (23).

9. The method according to any one of claims 1 to 8, wherein: The ion beam has a full width at half maximum (FWHM) between 30 mm and 150 mm, preferably between 50 mm and 100 mm.

10. The method according to any one of claims 1 to 9, wherein: The first partial track (22) comprises adjacent track sections (19), wherein the distance between the track sections is between 50 mm and 150 mm.

11. The method according to any one of claims 1 to 10, wherein: The ion beam (18) is directed along at least 50 partial trajectories, preferably along at least 100 partial trajectories, and further preferably along at least 200 partial trajectories.

12. The method according to any one of claims 1 to 11, wherein: The surface to be treated (21) has a maximum extent of at least 300 mm, preferably at least 500 mm.

13. The method according to any one of claims 1 to 12, wherein: The main body is a reflector body (20) having a concave mirror shape.

14. A device for treating a body (20), in particular a mirror body of an EUV mirror, the device comprising an ion beam source (17) and a positioning system (16, 34, 35, 36) for directing an ion beam (18) emitted by the ion beam source (17) onto a surface (21) of the body (20) to be treated, so that material is removed from the surface (21) of the body (20), and a control unit (14) for controlling the positioning system (16, 34, 35, 36) 35, 36), so that the ion beam (18) is guided on the surface (21) along a trajectory (22, 23, 24, 25), wherein the trajectory (22, 23, 24, 25) includes a first partial trajectory (22) and a second partial trajectory (23) that temporally follows the first partial trajectory (22), wherein the ion beam (18) sweeps over the entire surface (21) on the route of the first partial trajectory (22), and wherein the ion beam (18) sweeps over the entire surface (21) on the route of the second partial trajectory (23).

15. A computer program product or a set of computer program products comprising program parts designed to perform the method according to any one of claims 1 to 13 when loaded into a computer or a networked computer connected to a surgical microscope according to claim 14.

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