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

Abstract

The present invention relates to a method for processing a body (20), in particular an EUV mirror body, by directing an ion beam (18) at a surface (21) of the body (20) to remove material from the surface (21) to be processed. The ion beam (18) is guided along trajectories (22, 23, 24, 25) over the surface (21), the trajectories (22, 23, 24, 25) including a first partial trajectory (22) and a second partial trajectory (23) that is temporally later than the first partial trajectory (22), the ion beam (18) sweeping across the surface (21) during the first partial trajectory (22) and sweeping across the surface (21) during the second partial trajectory (23). The present invention also relates to an apparatus and a computer program product for processing a body.

Description

[Technical Field]

[0001] This application claims priority from German Patent Application No. 10 2022 210 262.2, filed September 28, 2022, the contents of which are incorporated herein by reference in their entirety ("incorporation by reference").

[0002] The present invention relates to a method for processing a body, in particular a mirror body of an EUV mirror, in which an ion beam is directed at a surface of the body in order to remove material from the surface to be processed of the body. The ion beam is guided along a trajectory over the surface. The invention also relates to an apparatus and a computer program product for processing such a body. [Background technology]

[0003] Integrated circuits, especially those with small structures, are manufactured using microlithographic projection apparatus: a mask (reticle) illuminated with extremely short-wavelength deep ultraviolet or extreme ultraviolet radiation (DUV or EUV radiation) is imaged onto the lithography object to transfer the mask structure onto the lithography object.

[0004] Projection exposure apparatus comprise a number of mirrors that reflect radiation, the mirrors having a precisely defined shape and a correct orientation so that the imaging of the mask onto the lithography object is of sufficient quality. Summary of the Invention [Problem to be solved by the invention]

[0005] Large mirrors, which can be hundreds of millimeters wide, are used to ensure that a sufficient amount of EUV or DUV radiation can be directed to the lithography target. In some cases, the manufacturing process for the mirror includes treating the mirror body with an ion beam to remove material from its surface. The dislodged particles receive such high kinetic energy from the ion beam that they detach from the surface of the mirror body. A problem that arises with large mirror body dimensions is that the dislodged particles can settle elsewhere on the surface and form a layer there with components of the ionized process gas coming from the ion beam source. This is undesirable as it compromises the quality of the surface. [Means for solving the problem]

[0006] The object of the present invention is to provide a method, an apparatus and a computer program product which avoid these drawbacks. This object is achieved by the features of the independent claims. Advantageous embodiments are set forth in the dependent claims.

[0007] In the method according to the present invention, the trajectory of the ion beam on the surface to be processed of the body includes a first partial trajectory and a second partial trajectory that is temporally subsequent to the first partial trajectory, the ion beam sweeps across the surface during the first partial trajectory, and the ion beam also sweeps across the surface during the second partial trajectory.

[0008] By sweeping the ion beam across the surface being processed multiple times during the processing of a body, particles can be removed from the surface before they form a layer of deposited particles that is difficult to remove. The present invention recognizes that when the surface being processed is relatively large, the conventional procedure of sweeping the ion beam across the surface only once is disadvantageous. The layer formed by the dislodged particles and components of the process gas forms away from the area of ​​the surface being processed by the ion beam, and for relatively large surfaces, this layer is merely a nuisance. In accordance with the present invention, even if particles adhere to the surface being processed, the method can be utilized because the particles can be repeatedly removed during the course of the method and therefore cannot adversely affect the processing results.

[0009] The method can be performed such that the duration of a single partial orbit is substantially shorter than the total processing time. For example, the duration of a partial orbit can be less than 10%, preferably less than 5%, and more preferably less than 1% of the total processing time. The total processing time varies depending on the amount of material to be removed. In some applications, processing can last 5 hours or more, preferably 10 hours or more, and more preferably 20 hours or more. For example, the duration of a single partial orbit can be 2 minutes to 20 minutes, preferably 5 minutes to 10 minutes. In other applications where only a small amount of material is to be removed, processing times can be shorter, for example, 0.5 hours to 5 hours.

[0010] It is often desirable to process a surface substantially uniformly. This can be achieved by keeping the ion beam parameters constant and directing the ion beam at a substantially constant velocity across the surface to be processed. A velocity is said to be substantially constant if the minimum velocity between partial trajectories does not deviate from the maximum velocity between partial trajectories by more than 10%. In this sense, the velocity can be kept substantially constant across different partial trajectories. Individual partial trajectories can be designed so that they do not include trajectory portions that intersect with each other. Different partial trajectories can be adapted to each other so that they do not intersect with each other. This preferably applies to all partial trajectories according to the present invention.

[0011] In one embodiment, the trajectory is configured on the surface such that the ion beam does not leave the surface during the first and / or second partial trajectory. If the surface to be processed has a round circumferential line, for example, if the surface is circular or elliptical, the ion beam may be directed along a spiral partial trajectory on the surface. The spiral partial trajectory may start from the periphery of the surface and go to the center, or vice versa.

[0012] The partial trajectories are preferably designed so that the ion beam is guided over the surface to be processed without any abrupt changes in direction. Within the meaning of the present invention, an abrupt change in direction is considered to be a change in the speed at which the ion beam is guided over the surface. To avoid abrupt changes in direction within the surface, it may be advantageous to guide the ion beam to an area outside the surface to be processed. Upon leaving the surface to be processed, the ion beam's trajectory can make the desired changes in direction without adversely affecting the uniform processing of the surface. For example, the ion beam can cross the surface to be processed along a first linear trajectory portion, change its direction outside the surface to be processed, and then cross the surface again along a second linear trajectory portion parallel to the first linear trajectory portion. Multiple linear trajectory portions allow the surface to be swept in this way without any abrupt changes in direction over the surface.

[0013] The body can be designed so that the ion beam does not impinge on the body outside the surface to be machined, and the ion beam can impinge on an outer surface area of ​​the body that is outside the surface to be machined and is not the target of machining.

[0014] It may be advantageous to direct the ion beam to a region outside the work surface between the first and second partial trajectories. In one embodiment, the work surface has a central notch. The ion beam may be directed to the region of the central notch during the transition between the first and second partial trajectories, where the desired change in direction occurs.

[0015] For example, the cross-sectional extent of the ion beam transverse to the path direction (transverse cross-sectional extent), expressed as FWHM (Full Width at Half Maximum), may be 30 mm to 150 mm, preferably 50 mm to 100 mm. References to the trajectory along which the ion beam is directed refer to the central ray of the distribution. In other applications, the FWHM of the ion beam may be smaller, for example 0.5 mm to 30 mm.

[0016] The method can be performed such that the central ray between sub-trajectories maintains a constant lateral distance relative to the central ray of the previous trajectory portion of the same sub-trajectory. This lateral distance can be smaller than the lateral cross-sectional area of ​​the ion beam, so that the ion beam overlaps with the previous trajectory portion. The overlap can be 10% or more of the cross-sectional area, preferably 20% or more, and more preferably 30% or more. In other words, the sub-trajectories along which the ion beam is directed can include adjacent trajectory portions, and the distance between the trajectory portions is selected to achieve the desired overlap. For example, the distance between adjacent trajectory portions can be 20 mm to 100 mm. All statements regarding lateral distance refer to the central ray of the ion beam. This can apply to any of the sub-trajectories.

[0017] The second partial trajectory can extend parallel to the first partial trajectory. That is, the central ray of the ion beam during the second partial trajectory follows a path that is a constant lateral distance from the path of the central ray during the first partial trajectory. The second partial trajectory can be directed exactly midway between two trajectory portions of the first partial trajectory. Additional partial trajectories can fill the free space left by the first partial trajectory at equally spaced lateral distances. The method can be performed with 50 or more partial trajectories, preferably 100 or more partial trajectories, and even more preferably 200 or more partial trajectories.

[0018] The process parameters may be kept constant between the partial trajectories. In particular, the ion beam properties may be kept constant, and the ion beam may be moved at a constant velocity along the partial trajectories. Each partial trajectory may be linear or may have a continuous curvature, as in the case of a spiral. The ion beam parameters may also be kept constant when switching between two partial trajectories. The ion beam velocity and trajectory shape are not subject to any particular restrictions in the intermediate phase between two partial trajectories. In a typical use case, there is no intersection between the partial trajectories. The invention also encompasses the possibility of passing through one or more trajectories multiple times in exactly the same way. This may apply to any of the partial trajectories.

[0019] The requirement that the partial tracks not intersect each other primarily serves the purpose of enabling uniform processing of the surface, in particular so that a layer of a constant thickness can be removed from the body. Intersection of the partial tracks can be advantageous if more material is to be removed from certain locations on the surface to be processed than from other locations.

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

[0021] The problem of unwanted deposition of dislodged particles arises particularly when the work surface is large, for example the maximum extent of the work surface may be 300 mm or more, preferably 500 mm or more.

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

[0023] In one embodiment, the mirror body has the shape of a concave mirror. The workpiece surface may correspond to the reflective surface of the concave mirror. The first partial track may be spirally guided from the outer periphery of the reflective surface of the concave mirror to the center of the reflective surface of the concave mirror, or conversely, from the center to the outer periphery of the reflective surface of the concave mirror. The second partial track may extend along the spiral intermediate space between the orbital portions of the first partial track, i.e., may rotate together with the first partial track. All further partial tracks may also extend along the spiral intermediate space of the first partial track.

[0024] The mirror body of the concave mirror may include a central region located outside the work surface. The central region may be concentric with the axis of the concave mirror. In one embodiment, the mirror body of the concave mirror has a central notch that forms a through hole in the mirror body of the concave mirror.

[0025] If the mirror body of the concave mirror has a central region located outside the work surface, the first partial trajectory can extend between the outer periphery and the central edge of the work surface. When the edge of the work surface is reached at the end of the partial trajectory, the ion beam can be directed to a region outside the work surface, where it can be deflected or moved to a position where the second partial trajectory can begin. Thus, all subsequent partial trajectories can be subjected to the same effect.

[0026] The ion beam can be generated using an ion beam source that ionizes a process gas with RF (radio frequency) radiation, and a voltage can be applied to the ion beam source to shape and direct the ion beam toward the surface to be processed.

[0027] The present invention also relates to an apparatus for processing a body, in particular a mirror body of an EUV mirror. The apparatus includes an ion beam source and a positioning system for directing an ion beam emitted from the ion beam source toward a surface to be processed of the body so as to remove material from the surface. The apparatus further includes a control unit for controlling the positioning system so that the ion beam is guided along a trajectory on the surface. The trajectory includes a first partial trajectory and a second partial trajectory that is temporally subsequent to the first partial trajectory. The ion beam sweeps across the surface during the first partial trajectory and sweeps across the surface during the second partial trajectory.

[0028] The positioning system can be designed so that the body is held in a fixed position and the ion beam source moves relative to the body, or vice versa. Positioning systems in which both the ion beam source and the body are moved are also possible. If the body is a mirror body in the form of a concave mirror, the mirror body can rotate about its optical axis. The ion beam source can be appropriately displaced and rotated relative to the mirror body to direct the ion beam to different meridian cross sections of the concave mirror, i.e., to different sections along the meridian of the concave mirror. In doing so, the ion beam source can in each case be aligned so that the ion beam is incident perpendicularly on the work surface of the concave mirror.

[0029] The present disclosure encompasses developments of the method having the features described in relation to the device according to the invention.The present disclosure encompasses developments of the device described in relation to the method according to the invention.

[0030] The invention also relates to a computer program product or a series of computer program products with program parts designed to carry out the method according to the invention when loaded into a computer or a computer on a network connected to a device according to the invention.

[0031] The invention will now be described by way of example only with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0032] [Figure 1] 1 shows an embodiment of the device according to the invention. [Figure 2] 1 illustrates an exemplary procedure for processing a body. [Figure 3] 1 shows a schematic diagram of a partial trajectory according to the invention; [Figure 4] 1 shows a profile formed by an ion beam. [Figure 5] A combination of multiple partial orbitals is shown. [Figure 6] 1 shows a mirror body having a textured surface. [Figure 7] 3 shows an alternative embodiment of the device according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0033] In Figure 1, a body in the form of a mirror body 20 is placed on a support surface of a processing apparatus 15 according to the invention. The processing apparatus 15 comprises a positioning system in the form of an XY positioner 16 carrying an ion beam source 17. The ion beam source 17 generates an ion beam 18 that is perpendicularly incident on a surface 21 to be processed of the mirror body 20. The ion beam source 17 is moved using the XY positioner 16, thereby moving the ion beam 18 across the surface 21 (Figure 2) of the mirror body 20. The processing apparatus 15 comprises a control unit 14 that controls the XY positioner 16 so that the ion beam 18 follows a predetermined trajectory on the surface 21 to be processed.

[0034] 2, the work surface 21 is rectangular, with the longer side of the rectangle being approximately 70 cm. The ion beam sweeps across the work surface 21 in multiple partial trajectories 22, 23, 24, and 25. The first partial trajectory 22 begins with the ion beam 18 crossing the shorter side of the rectangular surface 21 once along a straight trajectory portion 19. Outside the work surface 21, the trajectory of the ion beam 18 is deflected along a semicircular arc so that the ion beam 18 can sweep across the work surface 21 in the opposite direction. The first partial trajectory 22 continues in this manner until it reaches the opposite end of the work surface 21 relative to the longer side of the rectangle.

[0035] The ion beam source 17 is then returned to its initial end outside the workpiece surface 21, allowing the ion beam 18 to be guided over the surface 21 along a second partial trajectory 23. The second partial trajectory 23 has the same path as the first partial trajectory 22, but is displaced relative to the first partial trajectory 22 so that the linear trajectory portions 19 are parallel to one another. This process continues with additional partial trajectories until the intermediate spaces between the linear portions 19 of the first partial trajectory 22 are uniformly covered with the linear portions 19 of the other partial trajectories. This is shown in the simplified diagram of FIG. 2 for four partial trajectories 22, 23, 24, and 25. In practice, this process is regularly performed with many more partial trajectories, e.g., 100 to 200 partial trajectories. The movement speed of the partial trajectories is the same for all partial trajectories. For example, the total processing time may be 20 hours. For example, the duration of a single partial trajectory 22, 23, 24, or 25 may be 5 to 10 minutes.

[0036] 2, 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, and so on. Other orderings of the partial trajectories are possible, for example, such that each current partial trajectory is positioned as centrally as possible between the existing partial trajectories.

[0037] The ion beam source 17 remains on throughout the process, delivering a constant ion beam 18. Referring to FIG. 3, the ion beam 18 is not very tightly focused, but rather has a distinct extent transverse to the direction of the first partial trajectory 22. The full width at half maximum (FWHM) of the ion beam 18 is approximately 70 mm. The transverse cross-sectional extent 26 of the ion beam 18 is therefore large enough that there is an overlap of the areas machined by the ion beam 18 as it is directed along adjacent linear trajectory segments 19 of a single partial trajectory 22. The distance between adjacent linear partial trajectories 19 is approximately 100 mm. This results in the entire surface 21 being machined by each of the partial trajectories 22, 23, 24, and 25.

[0038] Figure 4 shows the profile formed by machining with an ion beam 18. The ion beam 18 penetrates the material of the mirror body 20 by knocking particles off the surface. A groove 29 is formed, the maximum depth of which is formed by the central ray 27 of the ion beam 18, and which flattens out with increasing distance from the central ray 27. The scale of the vertical axis of Figure 4 is in the nanometer range.

[0039] The work surface 21 of the mirror body 20 has an area 30 of 700 mm. Particles ejected from the grooves 29 and components of the ionization process are deposited at a distance of approximately 300 mm from the central beam 27 and accumulate there to form a layer 28. According to the invention, the entire work surface 21 is processed with each partial orbit, so that the layer 28 is removed again in each case after a short time, and the deposited particles do not adversely affect the overall processing result.

[0040] 5 shows a combination of four partial trajectories 22, 23, 24, and 25 suitable for machining a circular surface 21. Each of the partial trajectories 22, 23, 24, and 25 forms a spiral path that begins at the outer edge of the circular surface 21 and continues to the center of the circular surface 21. Each of the partial trajectories 22, 23, 24, and 25 extends within the spiral free space remaining between two adjacent partial trajectories, so that the partial trajectories rotate together. At the end of each partial trajectory, the ion beam source 17 is stopped, and the ion beam source 17 is subsequently moved back out using the XY positioner 16. The ion beam source 17 is then reactivated, and the method continues with the next partial trajectory.

[0041] While the method shown in Figure 5 is based on four partial orbits 22, 23, 24, and 25, it can actually be performed with many more partial orbits. The total processing time can range from 10 to 20 hours. For example, a single partial orbit can take 5 or 10 minutes.

[0042] 6 shows a mirror body 20 having a circular perimeter and a central notch 32. With such a mirror body 20, the partial trajectory pattern from FIG. 5 can be applied without turning off the ion beam source 17 at the end of the partial trajectory. The ion beam 18 can be directed within the notch 32 to a region located outside the work surface 21. There, the trajectory of the ion beam 18 can be changed and deflected as desired without adversely affecting the uniform processing of the surface 21. Upon re-reaching the work surface 21, the ion beam 18 can be redirected at a constant velocity along the next spiral partial path.

[0043] 7 shows yet another embodiment of the apparatus according to the invention. The ion beam source 17 is held on a slider 35 which can be moved in the X direction by means of a linear drive. An articulation drive 36, the articulation axis of which is aligned perpendicular to the image plane, allows the orientation of the ion beam source 17 relative to the slider 35 to be changed.

[0044] A mirror body 20 in the form of a concave mirror with a central notch 32 is attached to a mount 33. A positioning drive 34 can be used to displace the mirror body 20 in the Z direction and rotate it about the Z axis. This four-axis positioning system can be used to align the ion beam source 17 and the mirror body 20 relative to one another so that the ion beam 18 can be directed vertically to any location on the surface 21 of the mirror body 20.

[0045] Using the control unit 14, the slider 35, articulation drive 36 and positioning drive 34 are controlled to cause the ion beam 18 to travel a first spiral partial trajectory 22 on the surface 21, which partial trajectory extends at a substantially uniform speed from the outer periphery of the surface 21 to the central notch 32. Within the central notch 32, the direction of movement is deflected so that the ion beam 18 can travel a further spiral partial trajectory on the surface 21. This is repeated for multiple spiral partial trajectories, each partial trajectory extending into the spiral free space between two adjacent partial trajectories.

Claims

1. 1. A method for processing a body (20), in particular the body of an EUV mirror, comprising: directing an ion beam (18) at a surface (21) of the body (20) to be processed; and guiding the ion beam (18) along trajectories (22, 23, 24, 25) on the surface (21) to remove material from the surface (21), the trajectories (22, 23, 24, 25) including a first partial trajectory (22) and a second partial trajectory (23) that is later in time than the first partial trajectory, the ion beam (18) sweeping across the surface (21) during the first partial trajectory (22) and the ion beam (18) sweeping across the surface (21) during the second partial trajectory (23).

2. 2. The method according to claim 1, wherein the duration of a partial trajectory is less than 10%, preferably less than 5%, more preferably less than 1% of the total duration of the machining.

3. 3. The method according to claim 1 or 2, wherein the total processing time is at least 5 hours, preferably at least 10 hours, more preferably at least 20 hours.

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

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

6. 6. The method according to claim 1, wherein between the first partial trajectory (22) and the second partial trajectory (23), the ion beam (18) is directed to a region outside the surface (21) to be processed.

7. 7. The method according to any one of claims 1 to 6, wherein the first partial track (22) and the second partial track (23) have a spiral shape, and the first partial track (22) is convoluted.

8. 8. The method of claim 7, wherein the work surface (21) has a central notch (32), and the ion beam is directed to the region of the central notch (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 full width at half maximum (FWHM) of the ion beam is between 30 mm and 150 mm, preferably between 50 mm and 100 mm.

10. A method according to any one of the preceding claims, wherein the first partial track (22) comprises adjacent track sections (19), the distance between said track sections being between 50mm and 150mm.

11. 11. The method according to any one of claims 1 to 10, wherein the ion beam (18) is guided along 50 or more sub-trajectories, preferably 100 or more sub-trajectories, more preferably 200 or more sub-trajectories.

12. The method according to any one of the preceding claims, wherein the surface (21) to be worked has a maximum extent of at least 300 mm, preferably at least 500 mm.

13. The method according to any one of the preceding claims, wherein the body is a mirror body (20) having the shape of a concave mirror.

14. An apparatus for processing a body (20), in particular a mirror body of an EUV mirror, comprising an ion beam source (17) and a positioning system (16, 34, 35, 36) for directing an ion beam (18) emitted from the ion beam source (17) to a surface (21) to be processed of the body (20) so as to remove material from the surface (21), and for directing the ion beam (18) along a trajectory (22, 23, 24, 25) on the surface (21). the trajectories (22, 23, 24, 25) include a first partial trajectory (22) and a second partial trajectory (23) that is temporally subsequent to the first partial trajectory (22), and the ion beam (18) sweeps across the entire work surface (21) during the first partial trajectory (22) and sweeps across the entire work surface (21) during the second partial trajectory (23).

15. A computer program product or a series of computer program products comprising program parts designed to carry out the method of any one of claims 1 to 13 when loaded into a computer connected to the apparatus of claim 14 or into a computer on a network.

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