Laser-machining device

Abstract

The invention relates to a laser machining device (10), comprising - a laser beam source (12) for generating pulsed laser radiation (14); - a focusing unit (18) for focusing the laser radiation (14) onto a workpiece (22) to be machined; - a flow generator unit (24) for providing a flow on the surface of the workpiece (22), wherein the flow generator unit (24) has an inlet channel (26) and a flow generator for generating a flow and for providing a liquid (23) into the inlet channel (26); and - a holding unit (34) which is designed to receive the workpiece (22) to be machined, and wherein the holding unit (34) - has a first holding element (36) which is designed to receive a workpiece (22); - has a second holding element (38) which is designed to receive an annular fastening element (39), wherein the second holding element (38) annularly surrounds the first holding element (36); - a third holding element (40), which annularly surrounds the second holding element (38), wherein the third holding element (40) has a first end (42) which adjoins the second holding element (38) and has a second, distal end (44), and an outer region (46) which comprises the distal end (44), wherein the third holding element (40) has a greater height at its second end (44) than at its first end (42).

Description

[0001] LASER PROCESSING DEVICE

[0002] The present invention relates to a device for laser processing of workpieces (hereinafter referred to as a laser processing device). In particular, the invention relates to a device for laser processing of wafers.

[0003] Laser processing devices are generally well-known. These devices use a laser beam source to generate laser radiation. The laser radiation is focused onto the surface of a workpiece to be processed using a focusing unit. When ultrashort laser pulses are used, a phase transition occurs, which removes material from the surface of the workpiece. In particular, these devices are used to enable material removal from a workpiece. For example, laser processing devices are used to cut workpieces or to texture a workpiece surface. For particularly sensitive workpieces, processing with laser radiation offers significant advantages compared to mechanical cutting processes. In particular, laser processing places considerably less stress on the sensitive workpieces than, for example, the use of conventional mechanical cutting methods.Therefore, laser processing devices are particularly suitable for cutting wafers, which serve as the basis for the production of integrated circuits.

[0004] In some previously known laser processing devices, it has been proposed to perform the laser material processing in a liquid. This offers the particular advantage that the liquid can cool the surface of the workpiece, thus reducing the thermal effects caused by the laser radiation. In some devices, it has been proposed to generate a liquid flow within the processing zone. An advantage of these devices is that the particles removed from the workpiece during the laser processing are carried away by the liquid, thus significantly reducing the influence of these particles on the interaction between the laser radiation and the workpiece.One problem observed with the laser processing devices described above is that air is drawn into the processing zone at high fluid flow rates, as will be explained in more detail below in conjunction with the figures. However, the use of high fluid flow rates is necessary to ensure sufficiently high processing quality, especially at high processing speeds. Nevertheless, the drawn-in air leads to the formation of air bubbles in the processing zone, and these bubbles negatively affect the interaction between the laser radiation and the workpiece.

[0005] Based on the problem described above, the object of the present invention is to provide a laser processing device in which strong fluid flows can be generated without drawing air into the processing zone, thereby improving the quality of the laser processing.

[0006] To solve the described problem, the present invention proposes a laser processing device comprising a laser beam source for generating pulsed laser radiation; a focusing unit for focusing the laser radiation onto a workpiece to be processed; a flow generator unit for providing a flow on the surface of the workpiece, wherein the flow generator unit has an inlet channel and a flow generator for generating a flow and for providing a liquid into the inlet channel; and a holding unit configured to receive the workpiece to be processed, wherein the holding unit has a first side provided for receiving the workpiece, and wherein the holding unit has a first holding element designed to receive the workpiece;a second retaining element designed to receive an annular retaining element, the second retaining element surrounding the first retaining element; a third retaining element annularly surrounding the second retaining element, the third retaining element having a first end facing the second retaining element and a second distal end, as well as an outer area encompassing the distal end, the height of the third retaining element at its second end being greater than the height at its first end.

[0007] By raising the distal end of the third holding element, a reservoir for the fluid supplied by the flow generator is created. This ensures that the workpiece remains immersed in fluid during the machining process, with the fluid level defined by the height of the third holding element (at its distal end). Once the fluid level reaches the reservoir, it can flow out through the distal end of the third holding element. This creates a self-regulating system that continuously provides a predefined amount of fluid. The fluid flowing out of the distal end of the third holding element can preferably be collected by a reservoir, which may be located below the holding unit.Furthermore, it may be provided that the liquid collected in the receiving container is transported back into the liquid reservoir via a pumping device.

[0008] In particular, in the laser processing device according to the invention, the flow generator unit can be movably arranged, allowing the distance between the flow generator unit and the holding unit to be adjusted. The flow generator unit can be positioned so close to the holding unit that the flow generator unit (or its underside) is also in contact with the fluid. This significantly reduces the risk of air being drawn into the processing zone by the generated fluid flow. Typically, the flow generator unit can be positioned a few millimeters away from the holding unit. For example, the distance between the flow generator unit and the holding unit can be a maximum of 0.5 mm, a maximum of 1 mm, a maximum of 3 mm, a maximum of 5 mm, a maximum of 7 mm, or a maximum of 10 mm.

[0009] The focusing unit can be designed in the form of a focusing lens or a focusing mirror. Furthermore, deflection elements, such as a deflecting mirror, may be used to direct the laser radiation onto the workpiece.

[0010] In some embodiments of the invention, the laser processing device may include a spatial light modulator (also known as SLM) or a diffractive optical element (also known as DOE) positioned between the laser beam source and the workpiece. The use of an SLM or DOE makes it possible to deform the laser radiation and thereby generate multiple laser beams that interact with the surface of the workpiece being processed. This enables parallel processing, significantly increasing the processing speed.

[0011] The flow generator can be in the form of a pump. The workpiece can be designed, in particular, as a (semiconductor) wafer. The flow generator unit can be arranged, in particular, between the holding unit and the focusing unit and be designed to generate a fluid flow in a processing zone above the holding unit.

[0012] The liquid provided on the surface of the workpiece is supplied through the aforementioned inlet channel. Optionally, an outlet channel may also be provided in addition to the inlet channel, designed to drain the supplied liquid. Alternatively, no outlet channel may be provided, in which case the liquid supplied in the reservoir can flow out via the distal end of the third holding element. In the laser processing device according to the invention, the first holding element is designed to receive the workpiece. The first holding element can, in particular, be designed as a vacuum clamping device (also referred to as a vacuum chuck or negative pressure clamping device). It can be designed either to receive the workpiece directly or to receive the workpiece indirectly via a film.

[0013] The second holding element is designed to accommodate an annular fastening element (also referred to within the scope of the present invention as an annular fixing element, a retaining ring, or a holding frame). This fastening element preferably surrounds the workpiece in a ring-like fashion (completely or partially). This makes it possible to position a workpiece on a film on the first holding element, while this film extends to the second holding element and can be clamped there by the annular fixing element. This ensures a particularly stable hold for the workpiece, with the ring-shaped clamping of the film helping to prevent any liquid from reaching the first holding element. Furthermore, the cut parts of the workpiece adhere to the film and are not washed away (which would be undesirable).In some embodiments of the invention, the ring-shaped fixing element is part of the holding unit and can therefore also be referred to as a fourth holding element.

[0014] The third retaining element has an outer area extending from the distal end towards the first end, comprising a % of the distance from the distal end to the first end, where a can be a value from 5 to 100, in particular where a is 5, 10 or 20 or 50.

[0015] The first, second, and third retaining elements can be designed as separate elements. However, in some embodiments of the invention, the first, second, and third retaining elements can also be designed as an integral element. Alternatively, the first and second retaining elements can be designed as an integral element, or the second and third retaining elements can be designed as an integral element.

[0016] Furthermore, the flow generator unit preferably has a process window, wherein the flow generator unit is arranged such that the laser radiation is propagated through the process window and focused onto the workpiece.

[0017] Furthermore, the flow generator unit can be designed to generate a flow that runs parallel to the surface of the holding unit on its first side.

[0018] In some embodiments of the device according to the invention, the third retaining element may have a wall element extending orthogonally to a base surface of the third retaining element in its outer area. The wall element preferably has a height of less than or equal to 3 mm, less than or equal to 5 mm, less than or equal to 8 mm, less than or equal to 10 mm, less than or equal to 20 mm, less than or equal to 30 mm, less than or equal to 40 mm, or less than or equal to 45 mm. Furthermore, in some embodiments of the invention, the wall element may be greater than or equal to 5 mm, greater than or equal to 10 mm, greater than or equal to 20 mm, greater than or equal to 30 mm, or greater than or equal to 40 mm. The wall element may, in particular, be annular and designed to define a liquid reservoir.This creates a liquid pool during laser material processing, which helps to ensure that the entire processing operation is carried out in liquid, thus significantly reducing the risk of drawing air bubbles into the processing zone.

[0019] Furthermore, in some embodiments of the invention, the wall element may be annular and have at least two different heights along its annular structure. For example, the wall element may be largely 5 mm high, while in a partial area (comprising, for example, 5%, 10%, or 15% of the entire wall element) the wall element is only 3 mm high. This provides a liquid reservoir designed to maintain a liquid level of 3 mm, while allowing the liquid to drain away at a predefined point (in the partial area with a wall height of 3 mm). In this embodiment, a receiving basin may be provided below the partial area of ​​the wall element with a height of 3 mm to collect the draining liquid.

[0020] Furthermore, the device according to the invention can be designed so that the third retaining element has a linearly increasing height in its outer area. In the embodiments described above, where the wall element is perpendicular to the base surface of the third retaining element, a disadvantage is that, in particularly strong flows, the liquid is transported against the wall element at high velocity. Consequently, the mechanical forces cause vibrations within the laser processing device, which negatively affect the processing process. For applications involving particularly strong liquid flows, embodiments are therefore advantageous in which the third retaining element has a linearly increasing height in its outer area. In some embodiments, the linear increase in height can extend over the entire third retaining element.In these embodiments, the third retaining element has a ramped profile all around. In some embodiments of the invention, it may also be provided that the increase in height extends only to a portion of the annular third retaining element. Thus, the third retaining element may exhibit a linear (ramped) rise in some areas, while in other areas it merely has a wall element.

[0021] Furthermore, in the device according to the invention, the linearly increasing height of the third retaining element in the outer area can have a first slope in a first sub-area inclined towards the second retaining element, and a second slope in a second sub-area inclined towards the distal end, wherein the first slope is smaller than the second slope. This allows the vibrations generated by particularly high fluid flows to be further reduced, since a reduced slope is provided in the inner area of ​​the third retaining element.

[0022] The device according to the invention can also be provided that the third holding element has a parabolically increasing height in its outer area. This can reduce vibrations within the laser processing device, particularly at very high flow velocities, thereby reducing negative interference and enabling more precise processing of the workpiece overall.

[0023] In some embodiments of the device according to the invention, the flow generator unit may have a process window designed to allow the laser radiation to propagate through the flow generator unit. In other words, the process window may be configured such that a window surface is oriented orthogonally to the direction of beam propagation.

[0024] Preferably, in the device according to the invention, the first retaining element or the second retaining element may have a sealing element. This can significantly reduce the risk of liquid coming into contact with the first retaining element.

[0025] Furthermore, the device according to the invention may feature a first or second holding element having a receiving groove on the first side of the holding unit (facing the flow generator unit), with the sealing element arranged within the receiving groove. In particular, the receiving groove and the sealing element may be annular, with the annular sealing element arranged within the annular receiving groove. In some preferred embodiments of the device according to the invention, the holding unit may also have an inlet and / or outlet channel designed to supply the fluid required during laser material processing and / or to drain the fluid accumulated on the holding unit.The channel can be configured as an inlet channel, an outlet channel, or a combined inlet and outlet channel. By using an inlet channel within the holding unit, the fluid reservoir can be filled before the machining process begins. This ensures that the required amount of fluid is available in the reservoir within a very short time. By using an outlet channel, the fluid supplied for the machining process can be drained away after the machining process is complete, allowing for easier and faster drying of the workpiece. The inlet and / or outlet channel can preferably be located in the third holding element.

[0026] In some embodiments of the invention, the inlet and / or outlet channel may be arranged between the second and third retaining elements. Furthermore, a pump device may be provided, designed to introduce liquid into the inlet channel or to extract the accumulating liquid, preferably transporting it into a separate container. This prevents, for example, large quantities of liquid from entering the outer area of ​​the third retaining element, which could lead to the generation of undesirable mechanical vibrations.

[0027] Furthermore, the device according to the invention can include a positioning system designed to adjust the position of the holding unit or the flow generator unit. The positioning system can be configured to move the holding unit or the flow generator unit in one, two, or three spatial directions. For example, the positioning system can be designed as a positioning table and have one or more linear axes. The holding unit can be arranged on the positioning system, or the flow generator unit can be connected to the positioning system.In these preferred embodiments, the holding unit is particularly advantageous because, in general, vibrations can occur, especially during rapid movements of the holding unit or the flow generator unit, caused by the relative flow of the liquid against the chamber wall, whereby such vibrations are avoided or at least greatly reduced by the device according to the invention and, in particular, by the holding unit according to the invention with an obliquely or parabolically extending outer surface of the third holding unit.

[0028] The present invention will now be explained in more detail with reference to the figures. The figures show

[0029] Fig. 1 shows a laser processing device according to the prior art,

[0030] Fig. 2 shows an embodiment of the laser processing device according to the present invention, and

[0031] Fig. 3 shows several preferred embodiments of the holding unit according to the invention.

[0032] Figure 1 schematically depicts a laser processing device 10 known from the prior art. The laser processing device 10 comprises a laser beam source 12 designed to generate pulsed laser radiation 14. The generated laser radiation 14 is deflected by a beam deflection unit 16 towards a workpiece 22. In the embodiment shown in Figure 1, the beam deflection unit 16 is designed as a deflection mirror. The laser radiation 14 is then focused by the focusing unit 18 onto a first surface 22a of the workpiece 22. The workpiece 22 can, in particular, be a wafer used for the manufacture of electronic components. The laser processing device 10 shown in Figure 1 is designed to carry out the laser processing in a fluid, in particular in a liquid 23.For this purpose, the laser processing device 10 includes a flow generator unit 24 designed to generate a fluid flow on the first surface 22a of the workpiece 22. In the embodiment shown in Fig. 1, the flow generator unit 24 has an inlet channel 26, an outlet channel 28, and a process window 30. The focused laser radiation 20 is directed through the process window 30 onto the first surface 22a of the workpiece. The flow generator unit 24 also includes a flow generator (not shown in Fig. 1) designed to provide a fluid flow through the inlet channel 26, so that the supplied fluid 23 flows along the first surface 22a of the workpiece 22 below the process window 30 and then primarily flows out via the outlet channel 28.Since the flow generator unit 24 and the workpiece 22 are spaced apart during processing in the laser processing device 10, some of the supplied fluid 23 also flows through the space formed between the flow generator unit 24 and the workpiece 22. Simultaneously, in the laser processing device 10 known from the prior art, air is drawn in at the edge of the flow generator unit 24 due to the flow generated by the flow generator unit 24 (especially when high flow velocities are present) and due to the distance between the flow generator unit 24 and the workpiece 22.This air intake 32 leads to the formation of air bubbles in the processing zone (the area below the process window where the focused laser radiation 20 interacts with the workpiece 22), which negatively affect the interaction between the focused laser radiation 20 and the workpiece 22. The present invention therefore aims to solve the problem of air bubbles forming in the processing zone and thereby enable more precise laser processing.

[0033] Figure 2 schematically illustrates an embodiment of the laser processing device 10 according to the invention. The laser processing device 10 shown in Figure 2 also comprises a laser beam device 12, a beam deflection unit 16, a focusing unit 18, and a flow generator unit 24. Furthermore, the laser processing device 10 according to the invention comprises a holding unit 34, which is designed to receive the workpiece 22 to be processed. The holding unit 34 has a first side 34a, which is designed to receive the workpiece 22. The holding unit 34 shown in Figure 2 comprises a first holding element 36, which is designed to receive the workpiece 22 on its first side 36a, and a second holding element 38, which is designed to receive an annular mounting element 39 (also referred to as a mounting frame), wherein the second holding element 38 engages the first holding element 36 as shown in Figure 2.In the embodiment shown in Figure 2, the annular fastening element 39 surrounds the first retaining element 36 and the second retaining element 38. The annular fastening element 39 serves to secure a film 41, which is arranged on the first retaining element 36 and the second retaining element 38. The film 41 can, in particular, be an adhesive film with an adhesive layer on one side. The film can be fixed to the first retaining element 36 by applying a vacuum. The use of the annular second retaining element 38 makes it possible to fix the film 41 in a ring shape, thereby ensuring a very stable hold for the film and reducing the risk of liquid ingress onto the first retaining element (which is often sensitive to liquids).Furthermore, the holding unit 34 has a third holding element 40, which surrounds the second holding element 38 in a ring-like manner. The third holding element 40 has a first end 42 (also referred to as the inner end) facing and adjacent to the second holding element 38, and a second end 44 (also referred to as the distal end or outer end), as well as an outer area 46 encompassing the second end 44. The outer area 46 extends from the second end 44 towards the first end 42 and comprises a % of the distance from the second end 44 to the first end 42, where a can be, for example, 5, 10, 25, 50, or 100. The third holding element 40 has a greater height at its second end 44 than at its first end 42. This ensures that a fluid reservoir is provided, thereby preventing air from entering the machining zone.The provided liquid reservoir ensures that during laser processing, the liquid 23 supplied by the flow generator unit 24 does not completely flow off the edge of the holding unit 34, but instead accumulates on the holding unit 34 up to a predetermined height (depending on the shape and dimensions of the third holding element 40). Consequently, the flow generator unit 24 can be positioned so close to the workpiece 22 or the holding unit 34 that it is at least partially immersed in the liquid 23. This prevents air from being drawn into the processing zone below the process window 30, and instead, liquid 23 is drawn from the provided liquid reservoir. As a result, negative interferences that would otherwise be caused by air bubbles are avoided or at least significantly reduced, thereby significantly increasing the laser processing accuracy.In the embodiment shown in Fig. 2, the third retaining element 40 has a base surface 40a and a wall element 48 extending orthogonally to the base surface 40a. The wall element 48 can, for example, have a height of 3 mm, 5 mm, 8 mm, or 10 mm. This ensures that a liquid reservoir of a corresponding height is provided. The height of the wall element 48 can be designed, in particular, depending on the preferred distance between the flow generator unit 24 and the retaining unit 34 or the workpiece 22.For example, if in a specific application a distance of 2 mm is provided between the flow generator unit 24 and the workpiece 22 in order to machine a particular workpiece 22, the wall element 48 can have a height of 3 mm, so that a liquid reservoir with a height of 3 mm is provided accordingly, with the underside of the flow generator unit 24 being immersed in liquid 23 and any air intake into the machining zone below the process window 30 being prevented.

[0034] Fig. 3 schematically shows several preferred embodiments of the holding unit 34 of the laser processing device 10 according to the invention, which are explained below.

[0035] In the embodiment shown in Fig. 3(a), the third retaining element 40 of the holding unit 34 has a linearly increasing height 50. This makes it possible to provide a fluid reservoir in which a predefined quantity of fluid can accumulate during the processing, thereby significantly reducing the risk of air being drawn into the processing zone. Furthermore, the embodiment of the third retaining element 40 shown in Fig. 3(a) offers a further advantage. In the embodiment shown in Fig. 2, it has been observed in practice that undesirable vibrations occur within the laser processing device 10, particularly at high flow velocities. These vibrations arise because the fluid flows against the wall element 48, and the flow causes mechanical forces acting on the wall element 48.In contrast, the linear increase in the height of the third holding element 40 reduces the mechanical forces described above, thus reducing unwanted vibrations within the laser processing device 10 shown in Fig. 3 (a).

[0036] Figure 3(b) shows a further embodiment of the holding unit 34 of the laser processing device 10 according to the invention, wherein the third holding element 40 of the holding unit 34 has a first sub-region 52 and a second sub-region 54 in its outer area 46. In the embodiment shown, the first sub-region 52 borders the first end 42 of the third holding element 40, while the second sub-region 54 borders the second (distal) end 44 of the third holding element 40. In the first sub-region 52, the third holding element 40 has a first slope 56, while in the second sub-region 54, the third holding element 40 has a second slope 58. The first slope 56 is less than the second slope 58.The initially shallower slope in the inner area of ​​the third retaining element 40 further reduces the undesirable vibrations caused by the fluid flow within the laser processing device 10. Simultaneously, the steeper slope in the outer area 46 of the third retaining element 40 provides a compact fluid reservoir that can still hold a comparatively high fluid level.

[0037] Figure 3(c) shows a further embodiment of the holding unit 34 of the laser processing device 10 according to the invention, in which the third holding element 40 has a parabolically increasing height towards the outside in its outer area 42. This design allows the holding unit 34 to serve as a fluid reservoir, preventing the formation of significant vibrations even at high flow velocities, since the fluid flowing towards the outer area 46 of the third holding element 40 can drain away with low friction over the parabolically increasing height. At the same time, the parabolic rise of the third holding element 40 allows for a compact holding unit 34 that permits a comparatively high fluid level. Overall, the embodiment shown in Figure 3(c) further increases the processing accuracy of the laser processing device 10.

[0038] Figure 3(d) schematically illustrates another embodiment of the holding unit 34 of the laser processing device 10 according to the invention, wherein the holding unit 34 has an outlet channel 66, which in the embodiment shown here is arranged between the second holding element 38 and the third holding element 40. The outlet channel 66 is designed to drain the liquid that accumulates on the holding unit 34. This has the advantage that, particularly at high flow velocities, the supplied liquid can drain away more effectively, thus preventing an excessive accumulation of liquid. This leads to a further reduction in vibrations within the laser processing device 10, thereby further increasing the accuracy of the laser processing. In the embodiment shown in Figure 3(d), the third holding element 40 has a height 50 that increases linearly towards the outside.This allows the liquid accumulating on the holding element 34 to flow off the third holding element 40 due to gravity and be discharged via the outlet channel 66. In addition, a pump unit or a suction unit can be provided (not shown in Fig. 3(d)) designed to draw off the liquid that has entered the outlet channel 66, thereby allowing an increased quantity of liquid to be discharged. This can be particularly advantageous at very high flow velocities and lead to a further reduction in vibrations within the laser processing device 10. Fig. 3(e) schematically illustrates another embodiment of the holding unit 34 according to the invention, wherein the holding unit 34 shown has a second holding element 38, in which a receiving groove 62 is provided on one side (the first side), and a sealing element 64 is arranged within the receiving groove 62.The sealing element 64 can be made of a rubber material and be ring-shaped. The provision of the receiving groove 62 and the sealing element 64 arranged therein ensures that the first retaining element 36 is particularly well protected against liquid ingress. This is especially advantageous when the first retaining element 36 is designed as a chuck used as a holding device for fixing a wafer. Such chucks are typically designed as a round plate with indentations. Most chucks have a vacuum suction designed to securely fix a wafer. However, if liquid comes into contact with the surface of a chuck, this can lead to damage or even destruction of the chuck. The risk of such damage or destruction is minimized by the design of the first retaining element 36.The risk of damage to the first retaining element 36 is significantly reduced by the use of a second retaining element 38, which is ring-shaped and has a ring-shaped receiving groove 62 and a ring-shaped sealing element 64.

[0039] REFERENCE MARK LIST

[0040] Laser processing device

[0041] Laser beam source

[0042] Laser radiation

[0043] Beam deflection unit

[0044] Focusing unit focused laser radiation

[0045] workpiece a first surface of the workpiece

[0046] liquid

[0047] Flow generator unit

[0048] Inlet channel

[0049] outlet channel

[0050] Process window

[0051] Air intake

[0052] Holding unit a first side of the holding unit first holding element second holding element ring-shaped fastening element third holding element a bottom surface of the third holding element foil first end of the third holding element second end of the third holding element outer surface of the third holding element wall element linearly increasing height first sub-area second sub-area first slope second slope parabolically increasing height receiving groove sealing element outlet channel of the holding unit

Claims

REQUIREMENTS 1. Laser processing device (10), comprising a laser beam source (12) for generating pulsed laser radiation (14); a focusing unit (18) for focusing the laser radiation (14) onto a workpiece (22) to be processed; a flow generator unit (24) for providing a flow on a first surface (22a) of the workpiece (22), wherein the flow generator unit (24) has an inlet channel (26) and a flow generator for generating a fluid flow and for providing a fluid (23) into the inlet channel (26); and a holding unit (34) configured to receive the workpiece (22) to be processed, wherein the holding unit (34) has a first side (34a) provided for receiving the workpiece (22), and wherein the holding unit (34) has a first holding element (36) designed to receive the workpiece (22);a second retaining element (38) designed to receive an annular fastening element (39), the second retaining element (38) surrounding the first retaining element (36); a third retaining element (40) annularly surrounding the second retaining element (38), the third retaining element (40) having a first end (42) facing the second retaining element (38) and a second distal end (44) inclined away from the second retaining element (38), and an outer area (46) encompassing the second end (44), the third retaining element (40) having a greater height at its second end (44) than at its first end (42).

2. Device (10) according to claim 1, characterized in that the third retaining element (40) has in its outer area (46) a surface extending orthogonally to a base surface (40a) of the third retaining element (40). wall element (48) wherein the wall element (48) preferably has a height of a maximum of 3 mm, 5 mm, 8 mm, 10 mm, 20 mm, 30 mm, 40 mm or 45 mm.

3. Device (10) according to claim 1 or 2, characterized in that the third retaining element (40) has a height (50) that increases linearly outwards in its outer area (46).

4. Device (10) according to claim 3, characterized in that the linearly increasing height (50) of the third retaining element (40) in the outer area (46) has a first slope (56) in a first partial area (52) which is inclined towards the second retaining element (38), and has a second slope (58) in a second partial area (54) which is inclined towards the distal end, wherein the first slope (56) is smaller than the second slope (58).

5. Device (10) according to one of claims 1 to 4, characterized in that the third retaining element (40) has a height (60) that increases parabolically towards the outside in its outer area (46).

6. Device (10) according to one of claims 1 to 5, characterized in that the flow generator unit (24) has a process window (30) designed to allow the laser radiation (14) to propagate through the flow generator unit (24).

7. Device (10) according to one of claims 1 to 6, characterized in that the first retaining element (38) or the second retaining element (38) has a sealing element (64).

8. Device (10) according to claim 7, characterized in that the first retaining element (36) or the second retaining element (38) has a receiving groove (62) on the first side and that the sealing element (64) is arranged within the receiving groove (62).

9. Device (10) according to one of claims 1 to 8, characterized in that the holding unit (34) has an inlet channel designed to provide liquid (23) on the holding unit (34) and / or an outlet channel designed to discharge liquid (23) accumulated on the holding unit (34).

10. Device (10) according to claim 9, characterized in that the inlet channel and / or the outlet channel is arranged between the second retaining element (38) and the third retaining element (40).

11. Device (10) according to one of claims 1 to 10, characterized in that the device (10) additionally has a positioning system designed to adjust the position of the holding unit (34) or the flow generator unit (24).

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